DIYstompboxes.com

Welcome.

I'm designing & building an amplifier. This thread is going to document the process.

This is my first amplifier and I'm self-taught, so I'm treating it as a learning process - hopefully it might be of some interest.

I've made a couple of threads previously, asking about specific elements relating to the power supply, but rather than bits and pieces floating around I thought it'd be nice to amalgamate the information under the one subject heading. It might also help to keep things concise if I need assistance with anything further.

So here goes...

(https://i.imgur.com/fBfZ9Uql.jpg)


Electronic engineering eluded my interest at school (I'm nearly 30 now) but I am an engineer at heart and I've always played guitar. A few years ago I started building fuzz pedals using reclaimed components in an effort to expand my tone a little. Naturally, and with little else taking up my time, things have progressed since then. I've dabbled in tiny speaker cabinets and dreamt about one day partnering them with a separate head of a similar design but the concept of actually designing a functioning amplifier had seemed a distant prospect - That was until I discovered you can get a power amplifier on a chip, capable of driving an actual guitar speaker with nothing more than a power supply and a few supporting components. This was quite a revelation.

The amp I'm building here is of solid-state topology based on the simple LM386 chip; there are a few LM386 amplifiers out there already using a minimum parts count, similar to what is outlined in the LM386 datasheet (check out the Ruby & Little Gem amplifiers for an idea) - but unlike these afternoon projects, I plan to build something that resembles a real amplifier on a miniature scale. As I will come to realise, there is a lot more involved in the process if one is to do it properly - and do it properly I shall.


Concept.

As I understand it, an amplifier can be split into 3 main sections:

    - The power supply, to convert the power source (230v AC here) into a suitable DC supply of the correct voltage for each part of the amp.
    - The pre-amp, responsible for signal processing and tone shaping.
    - The power amp, to amplify the processed signal and drive the speakers attached to its output.


In this case the pre-amp is responsible for shaping the tonal character/colour of the sound, rather like a pedal (boost, overdrive, whatever flavour you like), and the power amp (the LM386) simply makes that sound louder and adds power; imparting no particular colour of its own.
By applying this approach, it seems possible to make a very good sounding amp from even a basic LM386 power chip as long as you work within its limitations.

I'd been designing a pedal for a friend for quite some time whilst I learned the basics of electronics, first exploring Bazz Fuss topology and then the LBP and Electra type distortion - very simple - I'm using 2 BJT gain stages in my latest iteration, diode clipping and I've added a tone stack. You can see how this ticks the criteria for the pre-amp section above. By following it with an LM386 power stage to amplify that signal and drive a speaker, suddenly I've gone from something resembling a basic effects pedal to a functioning amplifier. Et voila! Amplifiers don't have to be as complicated as they first seem.

(https://i.imgur.com/eZpB2RDl.jpg)
2 x 4" in series, 12ohm. 25w combined.


This particular amplifier has separate gain and volume controls. The tone is pre-set to match the voicing of the miniature cabinet it's being paired with. I'm employing two LM386N-4's in a bridged configuration (space permitting) for the maximum possible output whilst leaving them set to the internally limited 20x gain - I don't find op-amp distortion pleasant (read: working within limitations) so this should help retain the tone and detail coming from the pre-amp as it's intended to be heard.

In keeping with the miniature design, I'm using an external supply with 18v DC input to the amp. I can't be sure what the recipient of this amp (or anyone else) is going to plug into it so with that in mind I'm including an onboard reservoir capacitor and LM317 regulator to supply a clean 15v to both the BJT pre-amp and LM386 power amp(s). I've spent a lot of time studying hifi applications of this regulator and came across a wealth of information about its implementation, the key aspect (outwith the datasheet) being that it doesn't like low impedance caps on its output.

Here are a few things I brought back from my travels:
http://www.tnt-audio.com/clinica/regulators_noise1_e.html
http://www.tnt-audio.com/clinica/regulators2_impedance1_e.html
http://www.acoustica.org.uk/t/3pin_reg_notes1.html


Provisional regulated supply:
(https://i.imgur.com/neGbyVDl.jpg)


As you cans see the enclosure is built and there are considerations to be made for EMI suppression (it's a wooden box), heat management and how the amplifier is laid out in regards to supply/signal/ground wiring so these things don't start to wreak havoc on each other ...A lot to think about.

The first breadboarded amp worked well and sounded great (I did post a clip on another thread but at midnight volume levels, it wasn't very flattering).
I'm in the process of breadboarding the amp a second time to better resemble the layout of the finished thing, including a bridged pair of 386's so I can tweak the supply to suit.
A big part of this process is how to route the signal wires separate from the supply and output whilst squeezing it onto the board I've chosen to fit the enclosure.

There's a decent page here which goes some way in explaining how to lay out the supporting components for an IC amplifier, most of it can be extrapolated: https://www.edn.com/circuit-board-layout-guidelines-for-class-d-amplifiers/

I'll admit that using protoboard for the base isn't ideal but this is how I'm thinking of setting out each LM386 (hiding under the heatsink):

(https://i.imgur.com/sqBv9TJl.jpg)
(https://i.imgur.com/diHsvMwl.jpg)

There's a 100nf decoupler right on the supply leg & the FG cap behind it is a 10uf bypass on pin 7 - I'll ground these on Row 23 and join that to the ground rail at the back. There I have another 10u decoupler across the rails. The big cap is the 220u output. The second (inverting) LM386 will go next to that one in the same layout, copy/pasted to rows 23-17. All the input signal and reference grounds are going to be kept separate on the near side of the board.
The pre-amp section is going far left, top and bottom banks probably with stage coupling caps bridging across the centre. Tone stack will end up in the middle somewhere. Control panel is located to the front of the board on the signal side of the power amps.

I was reluctant to use both adjacent +ve and -ve (ground) rails on each side (prefered to have one side dedicated to supply and one side to ground) but I think that would mean running flying leads all over, crossing over the signal path and such so it's maybe best just to join the rails at the bridging points and be mindful of where, on each 'U' rail, I connect the B+ supply from the regulator and the chassis ground. More on that later.


A few resources I've come across so far and thoroughly recommend absorbing as a pre-face to designing an amplifier (or a pedal):

www.valvewizard.co.uk - Just a big old tutorial on everything about designing an amp, it's great. The grounding and supply info is useful in this case.

www.electrosmash.com - Breakdown and analysis of all historically significant pedals, as well as the LM386 and assoiated amps. This site is A+ material - I'm really grateful to whoever is involved!

(More to be added)


I can't promise comprehensive updates as I go along but I'll at least try and talk to myself, noting anything particularly interesting or insightful.

The circuit design for the audio shaping part of the amplifier (ie. the pre-amp) is pretty much complete so this will be more of a 'bringing together' of concepts as a functioning amp. There is still much to do.


Cheers

I don't think I've ever seen such a pristine looking board.

I love pre-patterned boards like this and yours seems to be easy to lay out with the row and column numbers printed on the board.  The five rows of holes on each side of centre is a luxury I haven't had yet.  The proximity of supply rails makes it easy to get good decoupling.  This looks interesting - I will be following your progress as you continue your design and build.

you can also use the LM386 as a class D power amp. and use another opamp as the modulator, a simple triangle wave oscillator and a comparator that compares the triangle with the audio signal. the comparator directly drives the 386.
you are still limited to 1W, and some voltage limiting should be applied to keep the chip from dying through over current, but it keeps the chip from getting hot, and it consumes less current overall. (no quiescent current anymore.)

i'd been looking at similar boards, and also different pasterns, but i am already committed to single hole per pad, since i accidentally bought 100 boards instead of 10... they were only 4 euro tho, so no big deal.

cheers, Iain

Quote from: Rob Strand on February 21, 2021, 03:17:45 AM
I don't think I've ever seen such a pristine looking board.

Quote from: iainpunk on February 21, 2021, 09:32:04 AM
i'd been looking at similar boards, and also different pasterns, but i am already committed to single hole per pad, since i accidentally bought 100 boards instead of 10... they were only 4 euro tho, so no big deal.

Quote from: amptramp on February 21, 2021, 09:07:16 AM
I love pre-patterned boards like this and yours seems to be easy to lay out with the row and column numbers printed on the board.  The five rows of holes on each side of centre is a luxury I haven't had yet.  The proximity of supply rails makes it easy to get good decoupling.

You should feel the weight in them!
The company is based in Seoul but I can only find them selling through amazon; £12 for a pack of 5 plus a mini board that I'm using as a base for the regulator assembly. I've contacted them to see if they'd consider selling the mini boards in black seperately as they're ideal for small pedals. The quality is so good. I have no complaints about using them for small scale production.

(https://i.imgur.com/GMmju1Fl.jpg)
(https://i.imgur.com/0drGQfJl.jpg)

The trial-and-error prototyping I do on that solderless board, which saves me a lot in toasted components and is useful for hot-swapping components in A-B listening testing.


As for decoupling, I was worried about the proximity of the rails interfering with each other at first but maybe this isn't so much of an issue at 15v.

The +ve supply will be fed into that top corner of the board serving the power amps first, with the pre-amp BJTs drawing from further along the rail on the bottom side using their own decoupling caps. Similar to how a traditional guitar amp supply is set out, as can be seen on page 7 of this great resource: http://www.valvewizard.co.uk/Grounding.pdf

The ground will be taken from the opposite corner so the pre-amps are closest to the central ground point at the input jack.
The ground traces on the top side of the power section are for bypassing/filtering supply pins 6 & 7, the traces on the lower side are the unused input and reference ground pins 2/3 & 4. This should hopefully keep the more sensitive stuff grounded on the cleaner side of the board and the supply to the the pre-amp the most filtered, with the shortest supply distance to the heaviest current draw of the power amp section.

(https://i.imgur.com/8oQnaZdh.jpg)

Quotewhich saves me a lot in toasted components and is useful for hot-swapping components in A-B listening testing.

i don't like hot swapping, and don't recommend doing it, but i do it all the time. i try to swap luke-warm, (effect in bypass but power still connected) but i often forget to switch the bypass.

cheers, Iain

Quote from: iainpunk on February 21, 2021, 12:22:32 PM

Quotewhich saves me a lot in toasted components and is useful for hot-swapping components in A-B listening testing.

i don't like hot swapping, and don't recommend doing it, but i do it all the time. i try to swap luke-warm, (effect in bypass but power still connected) but i often forget to switch the bypass.

cheers, Iain

Ah yes the perilous excitement of introducing a discharged reservoir capacitor to a live circuit  :icon_twisted:

Hot swapping is a bit of a necessary evil at times..
The immediate auditory information that your brain processes (useful for making direct comparisons) has a risidual effect lasting about 10 or 20 seconds at best, after which you're only recalling a memory of the sound you heard - and that's about as good as guessing. It's a bit like having a small amount of RAM in front of a selective HDD; the RAM is the only true representation of the information going in but it's being constantly overwritten, especially by any unrelated sound or transient that ocurrs in the 20 second window between A and B.

- Just something I like to remind myself of any time I intend to do comparitive listening tests.

IC a potential issue here... (you see what I did there?)
It comes in the form of supply decoupling on the power amps.

The idea of decoupling is to provide a short reserve of energy for fast transients where the the rails can't keep up with the sudden change of current due to unavoidable impedance over the length of wire from the regulator.

As it is, the 100nf decoupling cap right on the supply pin is going to do a great job at providing a low impedance path for the positive side, but the negative side is routed to the power amp's ground right around the rail on outside of the board, incurring its own impedance along the way - as far as the chip is concerned this is like having series resistance in line with the decoupling cap, which defeats the purpose. However bad it is for the amp closest to the side of the board, it's even worse for the one in the middle as this ground path is twice the length

(https://i.imgur.com/9m9Cbcml.jpg)


What I need to do to improve transient response and solve potential instability issues before they arise is ground the 100nf decoupling cap more like the drawing below; this makes for the least impedance possible as far as the chip is concerned. The 10uf decoupler across the rail I think will be fine where it is given that it's slower to react anyway (I guess that's why the 100nf is used too) and the relative impedance of the rail isn't going to affect it the same.


(https://i.imgur.com/NDHAWXkl.jpg)


The 10uf pin 7 bypass cap (not shown here) I believe can stay where it is, grounded to that upper rail, as it's there simply to filter AC noise from the +ve supply as opposed to providing a short reserve of energy.

That's the difference between decoupling caps and bypass caps in a nutshell  :icon_cool:


PS. Where's RG and PRR - This is what you guys were eluding to in my audio cap esr thread isn't it? Thanks, I got there eventually :)

Yep, that's one way to describe what Paul and I were talking about.

When power amps (and all electronics, really) need power, they need it QUICKLY. wire and PCB traces have resistance and inductance, so the only way to get fast pulses of power to the chips is to have a "bucket" of charge right next to them - a capacitor across their power pins as close as possible. Big value capacitors have bigger ESL than smaller ones, so you often need a combination of high-value electrolytics and small, low-ESL capacitors to ensure read power when the chips need it.

Good work, and good self teaching!

So, I'm not really sure how densely I can populate the board before it turns into a noise generator   :-\

Any advice on this?

This is how I have the inverting and non-inverting bridge amplifiers placed side by side. The small caps are all decoupling/bypass, the big caps are the 220u blocking/filtering caps on each output.


(https://i.imgur.com/YLOOUPbh.jpg)

that looks allright, but i recommend sockets, in case you accidentally blow one of the IC's (i did that on my first IC amp build, oops)

cheers

Thanks.

We'll see about sockets; having it attached directly to the board should help to dissipate the heat better and it's one less mechanical interface in the the ground and signal paths.
I'm going to re-assemble it on the solderless board anyhow, so hopefully we can rule out the possibility of creating an incendiary device before it gets to this stage  :icon_razz:

> attached directly to the board should help to dissipate the heat better

Audio power amp chips are available from 0.4W to 68W.

"Design" might mean not using 1/16" cable to suspend yourself over the alligator pool. Or not using the lamest chip and over-volting it to ignition.

You mean to tell me Paul that in all your wisdom you don't select components based on how cute they are in principle?  :o

Iain, your suggestion of manhattan style upright components is proving useful!

(https://i.imgur.com/E9MgF2Dl.jpg)


Looking forward to trimming these leads is all I can say..

I've used a few offcuts of old wire insulation to slip over the leads in key places, avoiding the problem of shorting things together before it gets tidied.

Quote from: Bunkey on February 23, 2021, 12:24:46 PM
I've used a few offcuts of old wire insulation to slip over the leads in key places, avoiding the problem of shorting things together before it gets tidied.

Looks tidy enough for me =)

Quote from: iainpunk on February 21, 2021, 09:32:04 AM
you can also use the LM386 as a class D power amp. and use another opamp as the modulator, a simple triangle wave oscillator and a comparator that compares the triangle with the audio signal. the comparator directly drives the 386.
you are still limited to 1W, and some voltage limiting should be applied to keep the chip from dying through over current, but it keeps the chip from getting hot, and it consumes less current overall. (no quiescent current anymore.)

i'd been looking at similar boards, and also different pasterns, but i am already committed to single hole per pad, since i accidentally bought 100 boards instead of 10... they were only 4 euro tho, so no big deal.

cheers, Iain

i just realised that you can't actually use a LM386 as a class D audio amp, since its slew rate is way to low, the time i used the 386 as a pwm driver was when i was driving a motor at 2kHz... ignore my earlier post

that upright breadboarding looks super slick! my BB's generally look like a rats nest,,, haha

cheers

Quote from: iainpunk on February 23, 2021, 04:39:47 PM
that upright breadboarding looks super slick!

And super non-uniform heat dissipation for vertically mounted resistors.. :icon_lol:

Heck! It's an amplifier..

(https://i.imgur.com/t2066AYh.jpg)


I spent a bit of time refining and making a few observations this morning:


First and foremost: The power supply has a huge influence on the sound...

Volume maxed, I still had quite a bit of mains hum even with all the smoothing, decoupling and bypass capacitors; I don't think the ripple rejection of the IC's is really much to go on here.
I've added some series resistance to the transformer side of the regulator just before the reservoir capacitor using a pair of beefy 100ohm 2W metal oxide power resistors; one on the +ve line and one on the -ve (shouldn't have to worry about inrush current with these in place either). This did a lot to fix the hum but it's also brought out so much detail -
I said the same about the series resistance on the regulator output cap: it's as if the guitar isn't getting swallowed up by the supply any more.

The sound was quite a bit darker before, very focused around the mids, limited almost; I thought this was a trait of the diodes used in the pre-amp and quite easily could have made the mistake of trying to tweak the EQ to compensate when really the highs (and the lows) were just getting lost in the mud.

Making an effort to clean up the supply before it hits the regulator has resulted in the old 'opening a window' analogy - there's an air and presence about the sound now; the cabinet no longer sounds like a small box; I can almost hear the space around the strings, the plectrum, the resonance in the things I'm not playing; I just touch the thing and it sounds musical  :icon_lol: Even through these 4" speakers it's quite awesome and not something I've had the pleasure of playing before. A good way of describing this, as a guitarist, might be that it makes you want to play less notes and just enjoy the sound between them.

Based on this experimentation, I would say a clean supply is the trick to getting a crisp, clear top end & presence whilst still sounding warm and sweet; it's expanded the perceived bandwidth of the amplifier as a whole and definitely seems like the first thing to address before reaching for the tone control.


Right, waxed lyrical enough about that..


(https://i.imgur.com/EgGcyOgl.jpg)

I've upped the reservoir cap to 4700u to account for the bridged pair of LM386's and parallelled this with a cap of a few hundred uF's. The response of this smaller cap has again brightened things up but I'm going to play around with it as the value affects the frequency it influences - 180u sounds good for now but a 220u or even up to a tenth of the big cap's value might blend a little better here and make the highs less peaky.

I'm going to try setting these LM386's to a slightly higher gain with a resistor & cap across pins 1 & 8 too, if I can avoid distortion.
Bridging them has added a sense of power, the amp handles itself better and it's brought the clean volume level up to something appropriate, but the sound projecting from the cabinet doesn't seem that much louder than it did with a single LM386 - a nice volume but not quite what I imagined it would be. Maybe there's some mechanical dampening at the speaker end which limits the output to an extent, or something, I don't think these are the most efficient speakers, but I'll see if I can squeeze a bit more from this configuration and save the LM380's for a bigger build.

Quote from: Bunkey on February 24, 2021, 10:21:19 AM
I'm going to try setting these LM386's to a slightly higher gain with a resistor & cap across pins 1 & 8 too, if I can avoid distortion.

Nope.

Hmm there's something else going on. A soft fuzz, eminating. Voices. Voices in the distance. Hello?

Hmm.

I've tuned into something, it's all getting a bit... non-linear.. around here.

I think I need another coffee.

I have seen an idea to clean the LM386 boost by adding a resistor and cap in series between pins 5 and 8. I have tried it & it kind of works, but only if the cap between pins 1 & 8 has no resistor in series. With resistance in the boost cap, it oscillates big time!

What Jim said..  :icon_wink:
(red resistor & capacitor..)

(https://i.imgur.com/2lDZAAb.gif)

Quote from: Bunkey on February 24, 2021, 04:00:38 PM
Hmm there's something else going on. A soft fuzz, eminating. Voices. Voices in the distance. Hello?

Hmm.

I've tuned into something, it's all getting a bit... non-linear.. around here.

I think I need another coffee.

i don't know for certain, but it might be corssover distortion. do you have a preamp, what's the schematic and what opamp did you use in the preamp? some opamps like the TL072 don't like capacitive loads, and have some nasty crossover distortion, if you know how it sounds and what to listen for, you can't un-hear it in recordings or even life.
i have done experiments where i have deliberately employed capacitive load to boost this type of crossover distortion, it was meant as the most hideous sounding fuzz ever, i came really close.

cheers, Iain

Hmm that's interesting. Looks like a HPF boost? I'm only guessing, as the datasheet shows a bass boost using pins 1-5...

Well I should note that I deviated from the datasheet slightly with the RC values for the zobel network, without understanding what exactly the function of those components is..
I mistook this for a passive filter of some sort and thought I could tame any shrill transients by reducing the value of R - I've done some googling and realised I was wrong, that this is actually in parallel with the impedance of the speaker and is used to flatten the impedance response, so all I was doing was loading down the power amp.
I've been plugged into the 12ohm cabinet for most of this work with just a slight hint of distortion (discounting what's intended) at the standard 20x gain, which cleaned up below 8 on the guitar and wasn't too unpleasant. I then tried a single 8ohm speaker earlier and that's where the issue became apparent; the distortion was worse and wouldn't clean up. This is what led me to believe it might actually be a product of impedance across the output, or a lack thereof. The gain I tried seperately, it was only 30x and just exaserbated this issue.

I'll have to get some more resistors before I can sort this out.

I've purchased one of those cheap LCR T4 meters to get an ESR reading of the various caps I was auditioning on the regulator output too - I could probably use it to measure the inductance of the speaker coils and work out the actual values required for the zobel  :icon_idea: Just thinking out loud here really.


The pre-amp is a discreet design that I've been working on in some capacity or another for a long frigging time and I'm actually quite proud of it - which is exactly why I haven't posted a full schematic of the amplifier here :icon_razz: Maybe when it's finished and I've got a bigger better amp in the works I'll share it. As I said in the OP it's just a simple design using dual BJT's, diode clipping and a LPF/HPF crossover tone stack. You could build an amplifier just using an off-the-shelf Electra or an LBP1 schematic for the pre-amp if you wanted to, that's kinda the beauty of this project and why I'm trying to keep everything (including the power amp chip selection) inherently simple.


As for the voices possessing the amplifier, well.. I'll light a few candles and say some shit backwards, maybe they'll leave.

Hmm again.

Iain you might actually be onto something with crossover distortion. I'll try and record a clip today and see what you make of it..

There seems to be a low threshold below which the distortion suddenly disappears. I have some Ge diodes clipping the signal to ground (vf ~ 300mV) and I'm wondering if there's some audio present on the ground rail which is leaking back through into the pre-amp. It's very likely that I just couldn't discern it as well through the small speakers as I can through the sensitive 8ohm guitar speakers so it kinda got lost in the mix til now.

*Edit: There are a few possibilities including supply instability. I'll demonstrate what it's doing soon - its developed a number of 'features'.


The Zobel theory is a bit of a grey area...

I'm using an 8.2ohm resistor and 47nf capacitor.

Calculating for the 8ohm Jensen speaker using its datasheet would suggest a 7.5ohm resistor with a 3.3uF cap, which means either the LM386 datasheet is acounting for a speaker with a very different inductance, or the zobel network isn't intended to flatten the impedance response at all...

the candles and backwards speaking might help, i guess shielding the circuit is better tho. its probably picking up some AM radio.

the zobel really needs more than 10 ohm, and less than 22, if the resistance is to low, the Capacitance will take over and cause more crossover distortion. also, its quite normal to expect distortion on the 8 ohm, since its bridged, the amp can only "see" 4 ohm, which is to low for the lm386, so distortion is guaranteed! in bridged mode, you NEED atleast 16 ohm.

also, the inductance you measure with and inductance meter isn't there anymore when the coil is actually moving due to the current. it turns in to resistance.

cheers, Iain

It is magic. I conjure the spirits. I have bridged dimensions.



PS. That confirms a lot about the impedance. Thank you.

We'll just gloss over how flawed my understanding of fundamental concepts is huh...


*The inductance, and the parallelled amplifiers.

The shielding I have a handle on. Let me just claw back a modicum of respectability there  :icon_lol:

Another day, another awesome resource: http://philsal.co.uk/wp-content/uploads/2018/12/Analogue-Guitar-Pedal-Design.pdf

I spend so much time at the deep end trawling through numerical equations and scientific publications just trying to understand the simple things I need to know to get the job done. I've said it before but I find the process exhausting, absorbing that sort of material and hoping the answers might appear between the lines. I can do numbers but it's not an intuitive process for me.
That's why I find it so refreshing, like the valvewizard site, when I come across something such as this which explains circuit design concepts in a practical sense relative to what it is I'm actually trying to do. It's easy to get lost on a forum where everyone seems to have a given understanding of electronic theory, it's almost novel to think that we're basically all guitarists here; I mean, how many guitarists do you actually know irl? Yet here we all are in one place, presenting ourselves as engineers and mathematicians instead. You'd be forgiven for forgetting, I find that quite funny.


Anyway, I took a break from building amplifiers to work a little bit on building an amplifier..

This one's my 1982 A&R Cambridge A60 stereo that I found in a skip (along with a Linn turntable - not even kidding) and lovingly rebuilt last year. No thread of mine passes without its mention.
I received a delivery of some nice 20awg cotton/PVC solid core wire for the guitar amp yesterday, so what better way to show it off...

(https://i.imgur.com/YMtfjkFl.jpg)
(https://i.imgur.com/ECMNQN9l.jpg)

Cotton-covered wire is used a lot for the restoration of antique radios.  A number of places cater to those of us who restore radios and this is one of the products they carry.

The boot laces get me  :icon_lol:

I had some all-cloth 22awg in the past that was a pain to strip without fraying. This pvc type with the cloth braid though is the single best wire I've ever worked with.

I'm guessing you're not in the UK, but if you are Home Bargains has a 2 pack of tiny Rolson folding knives in the DIY aisle just now and it's a real dream combination.


There was a good wee place like that in Hexham actually but it seems to have been swallowed up by the rising tide of late.

I had made a rather large oversight on the original supply which was helped picked up by Rob on another thread..

The 100r resistors I had in line with the supply for noise suppression were, at a theoretical 500mA load from the bridged LM386's, trying to drop 50v across themselves and thus limiting the supply to 180mA at 18v; preventing the op amps drawing the current they need and causing all sorts of mess above 1/3rd or so volume.

I've removed them and replaced with 1ohm 2W resistors I had spare (also tried without). I've also swapped the zobel resistors for 15ohm which had much less to do with anything.
We are on the right track but at full whack I'm getting some crazy distortion which also sounds supply related...

It's prominent when there's a tiny signal input (almost like a gated sputteriness), playing loud is raucous but more like the real tone when the amp is quiet, likely the electronic sounding distortion is just getting swallowed up in the mix.
It is loud now.


So, Pop Quiz time:

What exactly is causing this crazy distortion when the volume is way up near the top?



Makes for some cool AF phasery vibes but heck it's not intentional.
Bridged LM386's. Wall supply is rated 600mA @18v. Everything as above. Wild plectrum scrape to keep you on your toes.

Am I just trying to draw too much current from the wall or is this what op-amp clipping sounds like when there's no current limiting on the supply? It sounds like a flat battery to me :P

Onset is much sooner into an 8ohm load than it was with the 12ohm.

I guess that's to be expected with a supply induced 'feature'.

*Creative Possibility*


This one is called: 'Even a Stopped Clock Tells the Right Time Twice a Day'




Seriously though I need to fix this.

Onset @ 8ohm (Bridged = 4ohm) is about 9am (shown here)
Onset @ 12ohm (Bridged = 6ohm) was about 3pm (shown previously)

...I think I'm literally just below the threshold of what what of impedance the bridged LM386's can handle at full volume (though the datasheet says 4ohm).

I also think a little bit of current limiting on the supply was no bad thing so that might be something to experiment with...
5.6ohm is as big as I can go without dropping more than the required headroom for the regulator.
30ohm would limit an 18v supply to the rated 600mA of the wall transformer but it would also drop 18v across itself at full load so I'm not sure how the finer points of that work...  ???

that phasery clipping reminds me of moving bias. if you add an LFO to a guitar signal, which is then clipped, you have some moving asymmetry, which gives such a phaser-like sound, but its generally less pronounced, and overwhelming.

i'm not saying its that, but it might be.

cheers, Iain

edit:
the LM386 can handle 4 ohm at 4v Vcc, and only the version with the N-4 suffix, check your chips for the suffix!
if it doesn't have that suffix, it can't handle the 18v, just 12... and 8 ohm, not 4
also, it can only reach the full 1W of power at 32ohm!!!

i think another power chip would give you more of everything, power, headroom, less distortion, better sound quality etc..
i recommend the TDA2040, it can run from 9v to 40v

you make me want to give my old DIY amp another shot, inductor loaded class A amp.

cheers, again

Cheers Iain, yeah these are the N4's.

I have asymmetrical clipping in the preamp so based on what you're saying it could just be that running into the available headroom of the chips.

I've tried a single LM380 and it is better quality and little more well-behaved but it was a very hard sound into the tiny cab.. The LM386's are a little more compressed and rounded.
I'll have to audition that again now that I've lifted the current limiting off the supply, maybe it'll sound nicer.

Will try pairing a couple speakers for 16ohm too and see what happens.

The bridged configuration seems to impart more of an interesting and open character than a single chip, which is very much focused and dare I say boring to listen to..
I'm inclined to make this work with a 16ohm load but hmm we'll see.

Where are you getting the minimum impedance for a given Vcc btw?
The TI sheet seems to imply that anything from 4ohm is acceptable @ any supply 5-18v.
Not saying that's wrong - I'm just curious to save myself a bit of trial-and-error.

QuoteWhere are you getting the minimum impedance for a given Vcc btw?
The TI sheet seems to imply that anything from 4ohm is acceptable @ any supply 5-18v.
Not saying that's wrong - I'm just curious to save myself a bit of trial-and-error.

the data sheet tells you that the minimum impedance should be 4 ohms, but not what the power is which it can actually supply to that load.

when there is a Sinus wave of 2v RMS (2.83v 0-to-peak 5.66 peak-to-peak), there will be 1W on a 4 ohm load, that means that everything more than 5.66v peak-to-peak will distort and heat the chip and cause trouble. to keep the trouble from happening, you should use higher impedance, like 8 ohm, which will reach 1 watt with a sinus wave of 2.8v rms, (4v pk or 8v pk-pk)

cheers

Woohoo! A slightly clearer shade of mud :D

So into my bridged config with the 12ohm load, where each chip sees 6ohm:,
The limit for one chip would be 6.9Vpp @ 1W and looking at the datasheet the Vcc to achieve that would be.. gawd the best I can do into a 6ohm load is about 5Vpp with a 9V supply for 0.5W power, after which there's no increase in output no matter what the Vcc.

Right I'm starting to see the problem here. Starting to realise that 'overvolting the chip' as Paul said ageees ago doesn't actually mean exceeding the maximum rating either but rather there's no frigging point to it unless the load is adequate, it's just generating heat and causing problems like you say.

ffs


*Closes LM386 datasheet*
*Opens LM380 datasheet...*

Enter stage left: Another coffee.

It looks like the LM380 is going to be reasonably happy. Looks like about 11-12Vpp with the 15Vcc is ballpark and the output into an 8 or 12ohm load will be 2.25W and 1.5W respectively; which is within device limits as long as I fit a heatsink that brings the 107C/W down to <75C/W (JC=37C/W) and my 70C/W hedgehog sinks should just about do that, assuming this works on a parallel resistance basis.

The Vrms @ 12Vpp is 4.242v, which would make the chip's current draw at full whack:
8ohm = 530mA and 12ohm = 353mA;    *No it wouldn't, see newer posts*

The pre-amp section is drawing <10mA, power indicator LEDs etc. say <20mA

So again this is within the 600mA limit of the transformer...


This is looking good and I certainly don't need much more than 1.5W of output given the size of the cabinet & amp combo. I think more would be too much.


Looks like it's the single LM380 from here on then...

So long bridged 386's, you taught me lots!

(https://i.imgur.com/QDcVtVRl.jpg)

i''m getting quite curious about the preamp you employ, do you have a schematic?

cheers, Iain

If it's peaked your curiosity that probably means I've done something wrong with the calculation  :icon_lol:

Quote from: Bunkey on February 24, 2021, 09:11:49 PM
The pre-amp is a discreet design that I've been working on in some capacity or another for a long frigging time and I'm actually quite proud of it - which is exactly why I haven't posted a full schematic of the amplifier here :icon_razz: Maybe when it's finished and I've got a bigger better amp in the works I'll share it. As I said in the OP it's just a simple design using dual BJT's, diode clipping and a LPF/HPF crossover tone stack.

It's really nothing special, I just like the sound at the edge of breakup and spent a while tweaking values to taste. Bit of an Electra style distortion, the tone stack was heavily influenced by the Big Muff Pi. A couple other additions to make it all work.

Of course, when it's slamming against the low ceiling of a massively compromised power amp it sounds a bit.. different.

> Vrms @ 12Vpp is 4.242v, which would make the chip's current draw at full whack: 8ohm = 530mA

Can't be right? 4Vrms in 8 ohms is 2 Watts. 12VDC at 0.5A DC is 6 Watts. Terrible efficiency. And the apparent 6W-2W= 4 Watts of loss would cook the chip.

Quote from: PRR on March 01, 2021, 10:14:48 PM
> Vrms @ 12Vpp is 4.242v, which would make the chip's current draw at full whack: 8ohm = 530mA

Can't be right? 4Vrms in 8 ohms is 2 Watts. 12VDC at 0.5A DC is 6 Watts. Terrible efficiency. And the apparent 6W-2W= 4 Watts of loss would cook the chip.

Ah I hadn't thought about it like that.

No of course it's not right because the 8ohm load of the speaker and 4.2Vrms AC signal that I was using to calculate this has no connection with the DC component  :icon_lol:

The device dissipation table shows about a max of 1.5W dissipated for the 15v supply with an 8ohm load, so that would suggest 100mA instead?

I'm curious why the dissipation curves the way it does - peaking at around 1.6W output power (extrapolated) - Does this mean it becomes more efficient at higher outputs?

(https://i.imgur.com/7Sb3CPel.jpg)

100mA seems too low...

The output power must be added to this right? (It has to come from somewhere)

So 2.25w is audio dissipation (represented here as output power) and ~1.5W is heat dissipation (represented here as device dissipation), so it's actually 3.75W total consumption = 250mA or thereabouts @ 15v supply.  :icon_idea:


This way everything outputted is accounted for at the input :icon_exclaim: :icon_idea:

Efficiency is always zero at zero output. So it tends to rise when it does real work.

Yes, 1/4A is what my thumbs say too.

Just a wee update.

It's sounding pretty good into an 8ohm speaker with the LM380; a bit more lively than it is at 12ohm so I'm trying the 5" Jensen in the cab again with a slightly thicker 6mm BB baffle.

I'm gonna need a bigger sink for the chip though, the little 70C/W thing is hot to touch at half volume so the junction temps must be way up there.
Using protoboard as a base isn't ideal when it comes to finding a solution to this - I think the best option for the space might be to fit a TO-220 sink like this:

(https://i.imgur.com/uPSo5Lll.jpg)

I've a handful on the way rated at 18C/W. It lines up quite conveniently with the 3mm mounting hole in the board; some sort of spring arrangement to apply pressure directly above the chip would work well.

And this is how I left it all this evening:

(https://i.imgur.com/wRbyy6ul.jpg)


The new baffle has indeed sorted the problem of bloom in the mids. I still think the cab is a bit too small for the 5 inch speaker though.. We'll see tomorrow when it gets turned up.

do you use thermal paste? in my experience, a tiny bit makes a huge difference in chip temp!!! you don't need the expensive computer stuff, just the cheap grey stuff, or you can make it yourself from petroleum jelly and super fine silica sand.

cheers, Iain

Quote from: iainpunk on March 03, 2021, 09:31:48 PM
do you use thermal paste? in my experience, a tiny bit makes a huge difference in chip temp!!! you don't need the expensive computer stuff, just the cheap grey stuff, or you can make it yourself from petroleum jelly and super fine silica sand.

cheers, Iain

Yeah man of course.

The standard 70C/W CA needs derating to at least 35C/W CA according to the datasheet (@1.67W device dissipation).

Most of the standard heat dissipation is going to happen at the top of the chip; once I stick a heatsink there and cover it, the effective device thermal resistance is going to increase dramatically as the device itself is now only dissipating from its tiny sides..

So instead of being 70 case || 70 sink = 35C/W it's going to be more like >140 case || 70 sink = >46C/W which puts it right on, if not over, the 150degC limit at room temp using the tiny sinks I had for the LM386's and dissipating 1.5W as estimated for the 15v supply.

...That's how I'm looking at it anyway and it makes a bit more sense since the device no longer has that top surface area in addition to the heatsink.


I plugged everything into a calculator which is suggesting 12C/W for the sink in 50deg air to keep the Jt <125degC.
18C/W sink = 104C & 135C @20 & 50C repectively but it's the best I can do here.

...That's using some cheap cpu paste I had lying around, C/W = 0.12 per square inch so I've adjusted that to R = 1.2C/W for the 0.6cm^3 area of the chip.

Thought I'd check in with post #50 and a wee game of spot the difference...

(https://i.imgur.com/78pLfMPh.jpg)

Maybe this marks the half way point.


I don't really write much about what I'm doing when I'm actually doing something so yeah it's been a busy few weeks..

The pre-amp has been overhauled somewhat; still the same just different. I went through just about every type of transistor in my possession in every configuration on the board, it was quite remarkable what a difference they make even down to the individual gain of each transistor, regardless of the supporting components.

I won't talk about the cab just yet but obviously there's a lot of work been done, and to be done, there too.

I've since built a DSO138 ocilloscope which is proving really useful - Things started to change for the worse, I think as all the fresh capacitors and bits loosened up, the nice tube-like spongy attack I was getting turned into a hard harshness. From what I gather the LM380 is happy with a few hundred mV of input. My LP outputs peaks upward of 500mV (!), the pre-amp clips to ~300mV then has a make-up stage after the tone stack with about 5x gain, maybe, so I must have been hammering the chip's input at higher volumes and that's exactly what it sounds like. It had a bit of 'give' in the sound at first which was really nice but now it's determined to produce those edges so I need to tame that and maybe try to reproduce the spongy behaviour it was exibiting before, somehow. An LDR compressor might fake it but I don't want to complicate the thing (besides that kinda belongs in a pedal, not an amp) - I think this is more a supply factor with maybe some soft-clip limiting at the power-amp input or something, we'll see.

I had to build a power supply for the scope so I've implemented the same style as the amp to get a feel for the protoboard base and how everything is going to fit together..

(https://i.imgur.com/WWQRfC2l.jpg)

I spent an entire day just laying this out on the board. It's quite a head scratcher condensing full-sized components into a tiny footprint but I think the results are going to be pretty cool. I've still gotta fit screw terminals and things to this supply hence the space at the top.
The amp itself will have neater design elements; hopefully a bit of symmetry and pattern to the layout as well as a more full use of the space (board for the amp's supply is half this size!).

Just do not test the amp while vertical drill and washing machine working..  :icon_wink:

QuoteMy LP outputs peaks upward of 500mV (!),

that's not that much, my epiphone explorer has 600mv on its sustain, and over 1.3v on its attack (passive red led clippers are audibly distorting the attack)

just some food for thought:

an input volume control is nice if you have high-ish gain and low headroom.

if you want to soften the clipping of the power amp, you might want to make the power filtering worse, with a higher resistor and smaller cap, it gives the voltage some sag.
you can also decide to have the pre-amp clip and have a passive attenuator so the power-amp doesn't clip when the pre-amp is totally overloaded.

cheers, Iain

Quote from: iainpunk on March 18, 2021, 09:06:59 AM

QuoteMy LP outputs peaks upward of 500mV (!),

that's not that much, my epiphone explorer has 600mv on its sustain, and over 1.3v on its attack (passive red led clippers are audibly distorting the attack)

Heheh... puny guitar pickups... According to G&L, my L2500 outputs 3V+ in passive mode. They clip the input of almost everything I plug it into.

Also, awesome thread. You motivated me to post the progress on my bass amp. I expect to finish it (as power amp only) in the next couple weeks. Then I'll design an internal preamp.

EDIT: typo

Quote from: iainpunk on March 18, 2021, 09:06:59 AM
if you want to soften the clipping of the power amp, you might want to make the power filtering worse, with a higher resistor and smaller cap, it gives the voltage some sag.

cheers, Iain

Yeah this absolutely does seem to have come about from cleaning up the ground routing and adding a bypass cap to the inverting input of the amp (I was getting sick of listening to all the bullshit on the radio  :icon_biggrin: )

I'd tuned in the sag really nicely with a 100mOhm series resistor on the output of the regulator but I think the caps have broken in a bit and aren't as stiff as they were then so I intend to play around with this some.
Having excess noise taking up the bandwidth does take the edge off really well when it's in the right zone but it's getting fairly inconsistent as the amp settles in and I imagine it'll sound entirely different again in a shielded enclosure, so I need to come up with a more predictable solution to this..
I've a few ideas to try - increasing the supply sag is absolutely one of them. Thanks

Quote from: marcelomd on March 18, 2021, 09:37:45 AM

Quote from: iainpunk on March 18, 2021, 09:06:59 AM

QuoteMy LP outputs peaks upward of 500mV (!),

that's not that much, my epiphone explorer has 600mv on its sustain, and over 1.3v on its attack (passive red led clippers are audibly distorting the attack)

Heheh... puny guitar pickups... According to G&L, my L2500 output 3V+ in passive mode. They clip the input of almost everything I plug it into.

Also, awesome thread. You motivated me to post the progress on my bass amp. I expect to finish it (as power amp only) in the next couple weeks. Then I'll design an internal preamp.

I'd love to see this!
Juicy threads are great - I try my best  :icon_smile:

The pre-amp should be happy enough handling 6-7v peaks at its input. I might think about attenuation since your guitars are so brutal  :icon_lol:
The 'gain' is supposed to be more of a 'clean breakup' control so this area might need some consideration..

(https://i.imgur.com/k7GZtj7l.jpg)
(https://i.imgur.com/P3O6hMil.jpg)

8)

Quotehat's not that much, my epiphone explorer has 600mv on its sustain, and over 1.3v on its attack (passive red led clippers are audibly distorting the attack)

It's usually fair safe to allow for 1.2V to 1.5V peak.

The pics of the supply were terrible yesterday. Here's a better one..

(https://i.imgur.com/9xe7O4mh.jpg)

As a proof of concept for the build style, I think this is looking pretty good.


..More importantly, I got the scope up and running along with a signal generator.
Wow these things are friggin awesome!

So bloody useful - pretty much the difference of being able to build a proper amp instead of just winging it...

So there's nothing wrong with the signal amplitude at the power amp input; about 150mV peak.
I can see where the harshness is though and it's more to do with the tone shaping, which frequencies are being attenuated and how the waveform and amplitude changes with frequency and gain setting.

(https://i.imgur.com/znp6vEyl.jpg)

Rolling the gain right back balances the attack & sustain of the waveform (which sounds really round, warm and nice); high frequencies accentuate that sharp peak where low frequencies do the opposite and make the waveform more rounded; right now this balance point occurs at the start of the gain control so I need to play around with the tone stack to bring this middle point further into the sweep of the control instead. I can see this on the scope and I think it'll make all the difference between having the amp properly dialled in or not.

Also, the clipping that accompanies this harshness is happening at the first gain stage in the pre-amp with amp input signals above 1.5V - it's great being able to see exactly where the ceiling is!

(https://i.imgur.com/aPzSeRtl.jpg)

I'm getting this clipping with the guitar volume cranked above 8 so I'd hazard a guess that this LP with its oddball 700-and-something-kOhm pots is putting out similar peaks to those mentioned above.


Very happy that I can see which bits need attending to now  :icon_mrgreen:
I really recommend the DSO138 if you don't have an oscilloscope. £25 Amazon

With the ESP M-50.

cool dude! really like its off-clean sounds! very natural sounding!

do you have a drawn schematic of the full citcuit? i might learn something

cheers
edit: i generally don't have drawn circuits, its all in my head

I don't think there's much you could learn from me tbh Iain, even less I haven't already posted here.

I'm glad you like it.

I've no frame of reference by which to compare so I don't know what good is. I'm pretty sure it's not finished though.

Oh hello... me again... Seeking some advice...


I feel an update is overdue on this but I've just been playing around with different ideas really and not much has changed; the search for better tends to loop back to where I started more often than not.
Still, the amp is progressing and I'm ever closer to committing it to a 'finished' form.

There are some problems which need to be solved first-


I'm having a bit of an issue with grounding/oscillations and unwanted global feedback. I've pondered this for a few weeks now and wanted to put it out here to see if anyone can offer some input or identify a problem/solution.

This is directly related to master volume. The amp sounds killer at low levels but the higher the output the more signal seems to be finding its way back into the pre-amp, either affecting the tone & sustain of the signal as negative feedback, or at times becoming additive and causing an almighty shriek depending on the fundamental frequency of the noise floor and oscillation.

It was first apparent as NFB - I'd lose sustain, fuzz and the harmonic content the higher the output volume - but the amp was quite useable at low levels, such as my previous video. The bass has always been quite ragged - It produces the low frequencies but distorts unpleasantly with any significant gain.

Most recently I've experimented with adding a dual triode tube stage between the original pre-amp and power amp, to bring some second-order harmonic warmth to the otherwise mid-scooped and slightly thin sound from the preceding stages.
There are a few other issues with this tube stage (such as the separate SMPS heater hum), that I'll ignore for the time being - What it has done is highlight the NFB and oscillation problems at a level and frequency that's useful to demonstrate. The prominent hum has become the fundamental frequency of the oscillation, which is much more palatable than the piercing shrill of additive BJT noise!




Some key points/observations:

The zobel network on the LM380 output; I'm using a 10uF cap with a 4.2 ohm resistor. This combination sounds good and balanced but is obviously letting a lot of audible frequencies to ground. Increasing the value of R to 10 ohm increases the signal at the speaker and reduces slightly the NFB acting on the preamp, but sounds harder so isn't favourable. It doesn't do much to curb the spontaneous oscillation either.

I was measuring a pretty significant audio signal on pre-amp ground a while ago, likely coming from this zobel. I've since separated the pre-amp & power-amp grounds to star at the regulator (reference) ground - this reduced the AC component in the pre-amp ground <10x, however it's obviously still present to some degree.

The intermediate tube stage is fed and grounded pre-regulator to make use of the full 25v (18v loaded) supply.

All stages have 10uf local decoupling (LM380 additional 100nf across supply pins)

The pre-amp features a pair of Ge clipping diodes to ground, preceding an emitter follower, so this is a likely candidate for where the feedback signal is coupling.

The supply itself is a double insulated 18v DC wall wart, so there is no solid earth reference in the amplifier (no chassis ground) - just the +ve and -ve input from the DC supply.

This issue persists after removing the 10r dropping resistors between reservoir and amplifier ground.

See below for a block diagram of the layout. I'm afraid I don't want to publish the full schematic online at this point but I've tried to be as informative as necessary - it's all very simple.

(https://i.imgur.com/879fLERh.jpg)

Hypothesis:

Assuming there is nothing wrong with the ground scheme, I'm wondering if these problems could be due to a lack of reservoir capacitance. Given there is no true earth anchoring the amplifier ground at a fixed point and less capacitance soaks up less AC component; the signal being dumped to ground from the power amp output zobel remains in part on the -ve rail (acting ground in this case) as AC ripple and gets coupled back into the pre-amp via the conducting clipping diodes causing the NFB..? A lack of reservoir capacitance might also account for the bass distortion and hard clipping of large input transients too, if my experience with leaky HiFi electrolytics is anything to go by.

This is speculation. I require some asstance.

The thing sounds quite good otherwise, honest!



PS: I should point out, the amp sounds far more 'passable' without the dual triode - as in the video clip at the bottom of the previous page - It still has the same issues though, they just appear later in the volume travel as there isn't the additional gain on the pre-amp signal. NFB killing the tone/sustain is the main offender here. I'll maybe get another clip of this comparing low & high volumes without the tube stage, if need be.

sounds to me like power line wiggle or ground resistance/ground differentials.
three quick fixes that might be easy to try is splitting the power supply lines like you did with the grounds,
adding bigger reservoir caps,
adding a decoupling cap at every gain stage, just to keep it stable.
another possible but controversial thing to try is coupling the power amp and pre-amp grounds like one continuous ground path. it might case ground loops tho, so that's a possible negative side effect.

[OT]

i really like your cabinet by the way, it looks really nice, my small diy guitar amp looks a lot more janky, being a cigar box with a big black heat sink sporting a good loking TO-3 transistor, a huge DC choke and a modern industrial looking switching power supply mounted on top. it really looks quite dangerous, and i'd advice everyone to not touch the choke's exposed contacts when sound is comming out of the speakers, it kind of zaps you like one of those zapping toys on steroids. it doesn't really hurt, but it does zap.
mine is almost infinitely less complex than yours, having only 3 discrete transistors, of which one is a Bazz Fuss circuit, acting like the pre-amp. fuzz all the time baby!
the other two are that DTS-410 and a luxury BD139 ** in a darlington configuration.
> that;s not really true, i have no idea what electronics are in the power supply, i bought a affordable 60w 12v DC supply block. its way less whiny than i anticipated, i originally put in 10.000uF 25v caps, and there is no power supply whine at all, when running the amp's 4.5A of quiescent current, it doesn't get hot at all!

[/OT]

cheers

* i chose it for its looks, its a DELCO DTS-410, and the red lettering and the font and the shiny case, i really like its looks.
(https://i.ebayimg.com/thumbs/images/g/jMMAAOSw7qFe1b1u/s-l225.jpg)
** its gangster looking. gold plated legs and heat-sink plate in a grey plastic body.

Try connecting the ground side of the cap on the - input of the LM380 to the quite ground (light Blue).   However it is very wise to place a 1k resistor from the ground side of that cap to the noisy blue line to prevent the amp going nuts when you disconnect the "new" wire that goes to the quite ground.

Actually might not need that 1k the LM380's internal resistors might be enough to handle the disconnection case.

Quote from: Rob Strand on April 17, 2021, 10:25:05 PM
Try connecting the ground side of the cap on the - input of the LM380 to the quite ground (light Blue).   However it is very wise to place a 1k resistor from the ground side of that cap to the noisy blue line to prevent the amp going nuts when you disconnect the "new" wire that goes to the quite ground.

Actually might not need that 1k the LM380's internal resistors might be enough to handle the disconnection case.

Well spotted!

Definitely performing better. It didn't solve the oscillation but it has improved the bandwidth/clarity significantly - I have pinch harmonics again! Man I thought I'd just got sloppy  :icon_lol:
Thanks that's a great quality improvement.

AFAIK the unused input on the LM380 can be left open if you like to add a bit of radio broadcast to your tone; or straight grounded but doing so causes it to clip asymmetrically with the slight bias offset, so capacitively coupling allows a little more headroom. Could be a useful characteristic to know if one ever felt compelled to overdrive the chip!

Quote from: iainpunk on April 17, 2021, 07:18:59 PM
my small diy guitar amp looks a lot more janky, being a cigar box with a big black heat sink sporting a good loking TO-3 transistor, a huge DC choke and a modern industrial looking switching power supply mounted on top. it really looks quite dangerous

* i chose it for its looks, its a DELCO DTS-410, and the red lettering and the font and the shiny case, i really like its looks.
(https://i.imgur.com/5LigWd0.jpg)
** its gangster looking. gold plated legs and heat-sink plate in a grey plastic body.

Thanks Iain. I love the idea of this thing. 4.5A is pretty nuts though  :icon_lol:
The ebay img seemed to get nerfed on my browser btw so I've redone the link

I actually managed to salvage a big old 10,000uF LCR elecrolytic from the A60 (the other had spilled its contents across the board); I'll dig this out and and give it a try if it tests good.

Do you post any of your builds?

QuoteI love the sound of this thing.

that's great to hear!

Quote4.5A is pretty nuts though

yes, it is, but its class A, and provides 12-ish watts into 16 ohm, before break-up
EDIT: it should have been 1.5A, the 4.5A quiescent current was with another inductor, which only had 1.25 Ohm, but only 2H, this one has 30H and 3.8 Ohm. i was a bit troubled with the temps the choke reached, burning almost 30W of heat... with the new choke, i have higher efficiency and more volume level with my 16 ohm cabinet, but a lower volume from my 4 ohm cabinet, so its a bit of a trade off.

QuoteDo you post any of your builds?

rarely, i rather focus on new and unfinished ideas when it comes to posts rather than things from the (recent) past.
the rest is helping people here.
another reason is that my taste in circuit design and guitar tones is quite... extravagant. i love lofi sounds and "trick-based" circuit design. most people seem to like more conventional circuit design and sounds.
EDIT: i love the designs i'm working on as long as i am in the process, i keep about 1 in 20 designs in the box they are in, the rest goes on to the ''i dont like it anymore'' pile and i re-use the box

cheers

QuoteDefinitely performing better. It didn't solve the oscillation but it has improved the bandwidth/clarity significantly

Maybe you should add the Zobel Network recommended in the datasheet in parallel with the network you have.   Worth a try.

Something to try, at least temporarily, is a 100uF cap soldered right on the power pins of the LM380.   A few years back Paul Marossy had no end of problems with modern LM386's (not LM380) oscillating  and that solved it.   The design worked fine without the caps on older chips.

i believe he already has Zobel-Network on there, looking at his earlier schematic.
i do echo your suggestion of the Zobel-network to anyone else reading this and planning on building an amp in the future!
it did solve some ringing-when-clipping problems in my sketchy DIY amp.

i think i want to build a configurable-zobel-box. basically a 12 position switch for capacitors and a vintage ''notched'' rheostat. would be a nice tool to try out zobel network values on future diy amp builds. if you want to build multiple amps.

cheers

Quotei believe he already has Zobel-Network on there, looking at his earlier schematic.

Yes, but he's got a large-ish cap which was chosen based on the sound.  Maybe the large cap isn't working so well at high frequencies. That's why I suggested putting the network from the datasheet in parallel.   Really, I'm not expecting it to fix it but when things act weird is pays to try the "right" things.

Quote from: Rob Strand on April 18, 2021, 06:39:40 PM

QuoteDefinitely performing better. It didn't solve the oscillation but it has improved the bandwidth/clarity significantly

Maybe you should add the Zobel Network recommended in the datasheet in parallel with the network you have.   Worth a try.

Something to try, at least temporarily, is a 100uF cap soldered right on the power pins of the LM380.   A few years back Paul Marossy had no end of problems with modern LM386's (not LM380) oscillating  and that solved it.   The design worked fine without the caps on older chips.

Ah yes I'm familiar with the thread. Well I have a 100nF 'right across the pins' with a 10uF in very close proximity - a few mm's - swapping this to a 100uF has no useful effect other than changing the tonal emphasis of the amp.

This is very much an 'additive feedback being coupled into the pre-amp' issue, as opposed to instability of the LM380 itself.

Likewise changing the zobel for the recommended value (2.7ohm / 0.1uf) doesn't fix this. I've tried a lot of values here, again more for their tone shaping, and arrived at the 10uF based on calculations for what actually gives the flattest impedance curve with the speaker I'm using.


With the better grounding on the -Ve input and the 10,000uF reservoir things are moving in the right direction anyway. Maybe a 22,000uf would be an improvement still.

These values look huge compared to whats generally accepted in terms of filtering though - Why the supply & AC signal ground ripple has to be so miniscule I think is a product of the less-than-ideal DC power source with the floating ground.
The solution right now seems to be to limit the pre-amp gain so that risidual ripple isn't amplified beyond the threshold that's going to couple back into the early stages. With the inclusion of that tube stage before the power amp, the total gain far exceeds the threshold; so a tiny bit of risidual audio ripple at the pre-amp ground (caused by the constant heater hum) is turning into the additive feedback you can hear in that clip.

I feel if there were a way to better isolate the audio clipping ground in the pre-amp from the output stage and supply grounds then I might be able to get away with more gain, which it kind of needs.

Quote from: iainpunk on April 18, 2021, 03:21:30 PM
i love the designs i'm working on as long as i am in the process, i keep about 1 in 20 designs in the box they are in, the rest goes on to the ''i dont like it anymore'' pile and i re-use the box

'Perfectionism' This is exactly why I still haven't boxed this thing up!

I'll not bother with the firewood permit this year - Just employ one of your amp circuits instead and it can heat my house  :icon_lol:

QuoteI feel if there were a way to better isolate the audio clipping ground in the pre-amp from the output stage and supply grounds then I might be able to get away with more gain, which it kind of needs.

One possibility is the preamp is oscillating or interacting with power amp to cause oscillation.   A few possibilities:
- Interaction through the power rail: An RC filter on the power to the preamp.    Something like 100 ohms and 100uF.
- If the preamp is interacting with the power due to wiring then adding cap to roll-off frequencies outside of audio is helpful. 
   Such caps can help grounding related oscillations as well.
- If the preamp alone is oscillating then that's a whole different story.   That's a design issue.  Normally fixed by careful placement
  and choice of cap values on the preamp.  However,  you would only expect this if the preamp has a feedback loop.

Quote from: Rob Strand on April 18, 2021, 09:17:10 PM
One possibility is the preamp is oscillating or interacting with power amp to cause oscillation.   A few possibilities:
- Interaction through the power rail: An RC filter on the power to the preamp.    Something like 100 ohms and 100uF.
- If the preamp is interacting with the power due to wiring then adding cap to roll-off frequencies outside of audio is helpful. 
   Such caps can help grounding related oscillations as well.
- If the preamp alone is oscillating then that's a whole different story.   That's a design issue.  Normally fixed by careful placement
  and choice of cap values on the preamp.  However,  you would only expect this if the preamp has a feedback loop.

Every gain stage has its own 10uF decoupling cap (4 in the pre-amp) and there's a 100nf wima to ground located between pre and power for RF filtering (not sure how effective this is). I did audition an RC filter between stages at one point but it didn't sound good. There's every possibility that actually some of the interaction is softening things up and benefitting the sound but there comes a point where it's doing more harm than good.

I'll put together another clip just now without the tube stage comparing low and high volumes so you can hear what I mean with the NFB issue. I don't really get oscillation without that extra stage - just NFB - It's like the ground is acting as that global feedback loop.

Actually it's 3am and I just realised how frigging loud I'm being  ::)

I'm probably asking a bit too much for you to listen to a clip and troubleshoot my amp based on the sound you hear too - this is wishful thinking bordering on procrastination tbh.

I need to set it all out on a fresh breadboard as I intend to build it, using shorter runs of better jumper wire, and take it from there.

I really appreciate your help though Rob, thank you.

Quote from: Bunkey

Quote from: iainpunk on April 18, 2021, 03:21:30 PM
i love the designs i'm working on as long as i am in the process, i keep about 1 in 20 designs in the box they are in, the rest goes on to the ''i dont like it anymore'' pile and i re-use the box

'Perfectionism' This is exactly why I still haven't boxed this thing up!

I'll not bother with the firewood permit this year - Just employ one of your amp circuits instead and it can heat my house  :icon_lol:

its not perfectionism, its more the effect of a short 'attention interest span'.
i might be designing a 100W amp soon, with about 10 to 15% efficiency, basically a room heater with speaker driving capabilities. ill send you the design files when im done drawing them!

have you tried isolating you pre amp like a pedal, and send it to a amp you know works?
this demonstrates if the "feedback" is in the pre amp or between the pre and power amp.

cheers, Iain

Quote from: iainpunk on April 19, 2021, 04:15:12 PM
have you tried isolating you pre amp like a pedal, and send it to a amp you know works?
this demonstrates if the "feedback" is in the pre amp or between the pre and power amp.

Yeah the pre-amp doesn't oscillate plugged direct into the usb interface with headphone monitoring.
This is litereally just the power amplifier output coupling back into the pre-amp in a feedback loop, likely via ground.
This loop is quite stable too, seems to have a ceiling probably at the clipping diodes, so the volume doesn't run away on itself...

I just replaced the tube stage with a single fetzer of low gain and got an entirely different flavour of feedback, based on the harmonic spectrum generated by the fetzer valve. I can see the spectrum in ableton's EQ display, which is probably entirely useless information but pretty cool anyway.

(https://i.imgur.com/919ddat.jpg)

Quote from: Bunkey on April 19, 2021, 04:44:21 PM

that oscillation sounds freaggin amazing in that context, now i want a oscillating fuzz too!!

That was actually two completely unrelated tracks I accidentally triggered together then mixed to taste  :icon_lol:

The non-oscillating rhythm part (if you can call it that) is an example of the amp loud without the extra stage - you can hear it's got some pretty hard clipping going on, not very smooth at all - a bit broken tbh - I can't accept that, so that's what I'm trying to problem solve here.

The oscillating with the extra stage is just... yeah  :icon_razz: it's a bit nuts. Could definitely use the added wamth and body from either JFETS or tubes though so I guess I've got some head scratching to do here.

Are the sockets for the input jack and the speaker jack (I'm assuming you have one) attached to the same metal plate so the grounds are looping back the through the sockets?    That could cause problems.  From your pics it looks like the speaker is connected directly to the power amp.

On a different line of thinking you could be getting some sort of motorboating.   When the amp is driven hard it pulls the supply rail down due to the regulator current limit.   That then upsets the power to the preamp and it starts motorboating.

A test would be to put a diode in the positive rail between the regulator and the preamp.   You might need to put a 100uF cap on the preamp power rails as well - that's on the preamp side of the diode.   The existing 10uF's might work they might not.

Quote from: Bunkey on April 19, 2021, 04:44:21 PM

That actually sounds great. Would be right at home in an indie record, or movie soundtrack, with a bit of production.

Quote from: marcelomd on April 19, 2021, 08:39:27 PM
That actually sounds great. Would be right at home in an indie record, or movie soundtrack, with a bit of production.

Heatstroked descent into delirious jazz abstractation; the sound of extracurricular brain melt, with fuzz
- I'm not sure the genre is widely recognised.

Quote from: Rob Strand on April 19, 2021, 07:16:41 PM
A test would be to put a diode in the positive rail between the regulator and the preamp.   You might need to put a 100uF cap on the preamp power rails as well - that's on the preamp side of the diode.   The existing 10uF's might work they might not.

What would you expect this to do Rob?

I imagined nothing (all things being well) besides dropping the diode fv from the pre-amp supply but adding it as shown caused the amp to oscillate independent of the volume control and made an almighty racket until the power was cut.

(https://i.imgur.com/fyySvlEl.jpg)

split power lines like ground, and add some extra filtering to the pre amp's Vcc
(https://i.postimg.cc/yDxBDtDH/fyySvlEl.jpg) (https://postimg.cc/yDxBDtDH)

hope this helps a bit,
cheers.

edit/ot:

Quotei might be designing a 100W amp soon, with about 10 to 15% efficiency, basically a room heater with speaker driving capabilities. ill send you the design files when im done drawing them!

the 100 W class A transistor amp is going to be a bridged configuration.
(https://sound-au.com/articles/amp-class-f10.gif)

cheers

QuoteWhat would you expect this to do Rob?

I imagined nothing (all things being well) besides dropping the diode fv from the pre-amp supply but adding it as shown caused the amp to oscillate independent of the volume control and made an almighty racket until the power was cut.

You might need to add the 100uF across the power rail on the preamp side.   You can also change the diode to a 100ohm resistor (no diode at all).   The resistor is better as you can keep increasing the value to reduce the preamp supply changes.

The idea is to prevent or at least reduce motorboating.

Suppose you have a preamp with a 12V supply and the transistor collectors a biased mid-supply to 6V.  Now you change the supply to 10V.   The collectors will bias to a lower voltage say 5V (just for arguments sake).  Now imagine continually and rapidly adjusting the power back and forth between 10V and 12V  the change in the bias point on the transistor collectors looks like signal.   That signal will be amplified by the power amp.

When the power amp clips the regulator current-limits and that causes the output voltage of the regulator to drop.    The drop in supply changes the biasing of the transistor preamp.   That drop in supply looks like a signal.  The power amp amplifies the signal but the signal causes the supply to drop or rises.   So you end up with a feedback loop where the power amp feeds back signal to the preamp via the power supply and it oscillates.

By putting a diode and cap, or a resistor and cap on the power supply the power supply changes are reduced.  Hopefully to the point where it cannot sustain oscillations.

The ultimate decoupling of the power supplies is to have a separate regulator for the preamp.    *But*  that's only true if the input supply voltage does not drop too low when the power amp clips.   If the input power rail drops too much the preamp regulator will not regulate.   You will get back the same problem you had before where the preamp power rail is dropping because of what is happening at the power amp.

Anyway, the fact you are seeing a change in behaviour is a good indication we are on the right track.

Quote from: Rob Strand on April 20, 2021, 06:56:50 PM
Suppose you have a preamp with a 12V supply...

Thank you, this is immensely helpful.

Google images was far less adept at helping me visualise the concept...

It makes a bunch of sense and goes some way to explain how the amp sounds the way it does - When it's in the right window it has this really nice juicy spongy quality that I never imagined getting from a solid state amp; I'm gonna have to see about introducing this back in a little more intentionally once I've stabilised the supply.

I guess the sag got a bit too baggy in this case.

Quote from: iainpunk on April 20, 2021, 04:47:36 PM
the 100 W class A transistor amp is going to be a bridged configuration.
(https://sound-au.com/articles/amp-class-f10.gif)

Love the idea Iain. Some good articles on that site too.
I'd like to partner this pre-amp with a discreet power amp at some point - maybe about 1/10th of the power! - Have some TIP3055's here but not quite sure how to use them yet. Keep me posted.

QuoteThank you, this is immensely helpful.

Google images was far less adept at helping me visualise the concept...

It makes a bunch of sense and goes some way to explain how the amp sounds the way it does - When it's in the right window it has this really nice juicy spongy quality that I never imagined getting from a solid state amp; I'm gonna have to see about introducing this back in a little more intentionally once I've stabilised the supply.

I guess the sag got a bit too baggy in this case.

I guess the risk is fixing the motorboating may affect the sound.

A nasty trick occurred to me.     The LM380 has a + input and a - input.   You are currently grounding the - input and putting the signal on the + input.   That's the common method.   So the trick is to drive the - input with the signal and ground the + input (via the input) cap.   Basically swapping the roles of the + and - inputs.    The idea is it reverses the phase relationship between the feedback on the power supply and the preamp.  Maybe just maybe the reversal will turn the positive feedback into a negative feedback.   It might just be enough.     I'm not 100% in favour of doing this.    It would be *much* better to clean-up the supply to the preamp.    However, it might be something which can be used to *if* fixing the preamp supply affects the tone.  See how you go with the supply first.

Something else I noticed is the LM380 has a quiet ground pin which is separate from the noisy ground pin(s) that are used for the output stage.   Technically the LM380 quiet ground should connect to you light-blue quiet ground.   The quiet ground pin number depends on which  LM380 package you have.    If you split the grounds you have to be careful that both grounds are connecting at all times.   If one is disconnected and the other powered is could blow up the chip.  A safety precaution on the breadboard might be to add a 10 ohm resistor between the noisy and quiet grounds near the LM380.

Quote from: Rob Strand on April 21, 2021, 03:02:22 AM
I guess the risk is fixing the motorboating may affect the sound.

A nasty trick occurred to me.     The LM380 has a + input and a - input.   You are currently grounding the - input and putting the signal on the + input.   That's the common method.   So the trick is to drive the - input with the signal and ground the + input (via the input) cap.   Basically swapping the roles of the + and - inputs.

Most certainly! At least now we know how it's interacting, I can figure out how to recreate that in a controlled way - well, attempt to anyway. I have a few ideas so I'm gonna try and muddle through this one myself. No spoilers please  :icon_lol:

I wondered about phase inversion at the opamp input too but the single inverting fetzer stage and the tube stage (using both inverting triodes) both induced feedback at the same sort of volume with their opposite outputs, albeit at different frequenies and slightly different in behaviour. There are two inverting stages in the pre-amp doing different things so I guess these are both reacting in opposite phase to each other and combining in their own way - swapping the phase of the oscillation would be like reversing the order of two pedals in series for a slightly different effect, perhaps.

I will take you up on the quiet ground pin as I had it grounded like that originally then changed it to the drawn schematic to totally distance the chip from pre and rule out possibilities. I shall change that back. All the quiet pins are arranged on one side of the 8-DIP; with the power, bypass and output stage on the other - which is quite handy.

It's funny looking back through this thread. A lot of energy, limited knowledge. A little embarrassing at times.
I've learned a lot just over the course of this project and the amp has come a long way since the beginning of the year - It's been more or less a full time endeavour.
Ironically, the more it grows the less detail I want to publish online - I have stabilised the amplifier though; I actually used zeners to decouple the preamp and then incorporated an element of feedback to get a similar effect. Thanks again Rob for explaining what was happening,

The clip above still uses the LM380 power stage and I'm pleased to say the amplifier as a whole is stable and relatively consistent through the volume range now.


Since the amp has come this far, and actually sounds good, I've been inspired to build a discrete power amp section instead of the chip before I begin working on the enclosure - thank you Iain.

I've been doing a lot of studying over the past month to this end and have a basic topology in mind using a CFB input stage and quasi-complementary output.
All the reference material approaches the design process with an output in mind, works out the power requirements and then builds a supply around that..

I need to do things the other way round

I'm limited to the power supply I'm already using, partly because it's all that's readily available and partly after picking up a few pearls of R.G. wisdom from the infamous Banana Amp thread..
The max voltage is 25v which drops to 18v at full load, unfortunately the max current of these wall-warts is a less-than-ideal 600mA but I've thus far not found a higher-rated alternative.

...This means I need to design my discrete power amplifier around the limitations of this 'safe' power supply and include some sort of current limiting in the design - I've not yet worked out how to do this. I guess 5W output would be achievable in class B though and tbh I'd be fine with anything around there down the 2W the LM380 is currently putting out.
I've found this to be a great output level for recording paired with this 6" speaker cabinet and hopefully the sample above demonstrates that.

Anyway, that's where we're at. I'll get a power amp knocked up on the breadboard once I've figured out some suitable component values.
Any word on current limiting the output stage would be appreciated  :)

Thanks

The fuzzy sound reminds me of Sungrazer, which is no bad thing to my ears. It's also woolly, like a low gain fuzz face, also nice. Good work.

that sounds great so far! i love the resonant character of the light crunch.

QuoteIronically, the more it grows the less detail I want to publish online

i know that feeling.

QuoteI've been inspired to build a discrete power amp section instead of the chip before I begin working on the enclosure - thank you Iain.

you're welcome!

Quotehave a basic topology in mind using a CFB input stage and quasi-complementary output.

nice, you made me really curious now, do i have to think 'zen amp' or 'death of zen' style?

QuoteI'm limited to the power supply I'm already using, partly because it's all that's readily available and partly after picking up a few pearls of R.G. wisdom from the infamous Banana Amp thread..
The max voltage is 25v which drops to 18v at full load, unfortunately the max current of these wall-warts is a less-than-ideal 600mA but I've thus far not found a higher-rated alternative.

have you looked in to laptop power supplies/chargers? they are often 19v and 2 or more ampere.

QuoteAnyway, that's where we're at. I'll get a power amp knocked up on the breadboard once I've figured out some suitable component values.
Any word on current limiting the output stage would be appreciated

LM317 based current limiter.
> page 11 Figure 9
https://www.st.com/resource/en/datasheet/lm317.pdf (https://www.st.com/resource/en/datasheet/lm317.pdf)
the formula for the current limiter is 1.25/R_set=I_max
1.25 ohm give you a 1A current limiter.
keep in mind the Power rating of that resistor!

cheers

Quote from: kaycee on May 15, 2021, 04:26:15 PM
The fuzzy sound reminds me of Sungrazer, which is no bad thing to my ears. It's also woolly, like a low gain fuzz face, also nice. Good work.

Hey thanks and thanks again for the new music. Enjoying their self-titled album right now. I love that acid-tinged Kyuss sound.

The goal is sparkly warm clean that breaks into a pretty crunch; somewhere between reedy jazz, desert rock and 60's psychadelic; this is at the upper end of the amp's gain. I love electronic too so there's an element of that; the harmonic percolator thing can be quite synthy.
If you put a boost in front of this you get a similar thick fuzz - The idea is that kinda 'not high gain but still heavy sounding' textured thing that can be layered onto with pedals. The low-end to the eq is probably responsible for the wool and heft. A bigger speaker might be an interesting proposition.

Quote from: iainpunk on May 15, 2021, 04:39:57 PM

nice, you made me really curious now, do i have to think 'zen amp' or 'death of zen' style?

have you looked in to laptop power supplies/chargers? they are often 19v and 2 or more ampere.

cheers

Very similar yes but the drivers are an NPN & PNP baxandall compensated pair, with a preceding VAS - so one extra BJT.

That Death of Zen might be a good starting point just to get my eye in actually.

I've a few printer supplies here from 15v to 25v but they all tend to be switch-mode, which is a big nope from my experimentation. I'd use an on-board toroidal if I could - and do have one lined up - but after reading about the stringent regulations for anything carrying more than 30v, I'm inclined to get the most out of a low-power linear wall wart; at least for this design concept which will make sense when you see it.

I'll test that regulator setup in the supply line first. The other route is just emitter resistance on the output trannies but apparently that causes all sorts of distortion. I did come across a topology that combines these two ideas though; some external current regulator clamping the lower output transistor with no effect on THD. I think it was a Douglas Self proposal - will see if I can find it again..

(https://i.imgur.com/ZMSBXKkh.jpg)

...I mean, I might just ditch the TIP3055's and use the BD139/140 complementary pair driven by the VAS but idk.

It's gonna be <5W output so...


With 10W total dissipation from the supply I think class A is out of the question whatever I do.

It's early days.

Quote from: Bunkey on May 16, 2021, 03:21:13 AM

Quote from: kaycee on May 15, 2021, 04:26:15 PM
The fuzzy sound reminds me of Sungrazer, which is no bad thing to my ears. It's also woolly, like a low gain fuzz face, also nice. Good work.

Hey thanks and thanks again for the new music. Enjoying their self-titled album right now. I love that acid-tinged Kyuss sound.

The goal is sparkly warm clean that breaks into a pretty crunch; somewhere between reedy jazz, desert rock and 60's psychadelic;

Enjoyed your playing, that's where it took me.if you want Jazz in the mix,try Causa Sui, Mythic Sunship and  Papir all current Euro bands and label mates to each other.

Quote from: kaycee on May 16, 2021, 08:00:36 AM

Quote from: Bunkey on May 16, 2021, 03:21:13 AM

Quote from: kaycee on May 15, 2021, 04:26:15 PM
The fuzzy sound reminds me of Sungrazer, which is no bad thing to my ears. It's also woolly, like a low gain fuzz face, also nice. Good work.

Hey thanks and thanks again for the new music. Enjoying their self-titled album right now. I love that acid-tinged Kyuss sound.

The goal is sparkly warm clean that breaks into a pretty crunch; somewhere between reedy jazz, desert rock and 60's psychadelic;

Enjoyed your playing, that's where it took me.if you want Jazz in the mix,try Causa Sui, Mythic Sunship and  Papir all current Euro bands and label mates to each other.

Excellent :)

Allow me to return the favour...

Quote from: Bunkey on May 16, 2021, 04:52:07 AM
...I mean, I might just ditch the TIP3055's and use the BD139/140 complementary pair driven by the VAS but idk.

It's gonna be <5W output so...


With 10W total dissipation from the supply I think class A is out of the question whatever I do.

It's early days.

yeah, if your power supply is limited in the output power, a Class A amp would be extremely impractical. the only reason i chose a Class A power amp is that my supply could put out 5A. if my supply was limited at a lower current, i'd go directly for a class D design.

cheers

Quote from: iainpunk on May 16, 2021, 08:59:02 AM

Quote from: Bunkey on May 16, 2021, 04:52:07 AM
With 10W total dissipation from the supply I think class A is out of the question whatever I do.

It's early days.

a Class A amp would be extremely impractical.

if my supply was limited at a lower current, i'd go directly for a class D design.

cheers

It would be nice though. I've decided this AB LM380 sounds pretty bad once it's in full B territory. Sounds awesome at low volumes and then... yeah... small and mid-band restricted and a bit naff.
I'm hoping the straight class B discrete will outperform it in that regard.

I think you're just partial to a bit of cerebral peac0cking Iain  :icon_lol:
Would you really design a class D amplifier for guitar, over class B?
I can imagine it appealling to robe-clad Sunn worshipers somewhat.. (not sure about much else!).

Quote from: Bunkey on May 16, 2021, 12:04:41 PM

Quote from: iainpunk on May 16, 2021, 08:59:02 AM

Quote from: Bunkey on May 16, 2021, 04:52:07 AM
With 10W total dissipation from the supply I think class A is out of the question whatever I do.

It's early days.

a Class A amp would be extremely impractical.

if my supply was limited at a lower current, i'd go directly for a class D design.

cheers

It would be nice though. I've decided this AB LM380 sounds pretty bad once it's in full B territory. Sounds awesome at low volumes and then... yeah... small and mid-band restricted and a bit naff.
I'm hoping the straight class B discrete will outperform it in that regard.

that could be the small speaker, they tend to lose more low end the higher the volume goes, basically the bass stays the same volume while the rest gets louder

Quote

I think you're just partial to a bit of cerebral peac0cking Iain  :icon_lol:

yes, i am, but its always 60% serious and 40% ''just because its cool''

Quote
Would you really design a class D amplifier for guitar, over class B?

any day of the week, pure class B is kinda shitty, class AB is a lot better, class A is amazing, class C is just silly (or its an over driven class A amp) and class D is exactly mediocre, but has efficiency on its side, plus you can impart non-linear behavior in the modulator to recreate a more ''analog'' (read non-linear) sound, which can elevate it to super amazing!

Quote
I can imagine it appealling to robe-clad Sunn worshipers somewhat.. (not sure about much else!).

i'm 66% bass player and 33% guitar player, class D is already something im used to for gigging.
small form factor, low in weight, barely gets hot, doesn't waste much power at all.
the only real downside of class D is the output filtering required to not use the speaker wire and voice-coil as a radio transmitter.

cheers

The speaker is mighty capable. The amp just sounds much harder at higher volumes.  The eq did open up a bit after cranking it just then (I hadn't played the speaker loud much from new) but yeah I'm hoping the CFB input and a bit of control over biasing will have a slightly softer feel than the chip.

I'm sure I'll be able to settle on some grossly underperforming topology with obscene THD figures that sounds wonderful in this application..