Hi mates,
I originally posted this in the Schematics/Layouts section of this forum but thought it may get more attention here.
I have a habit of sporadically searching this forum for a vero layout for the Intersound IVP. If any of you have tried the same then you'll know that there's nothing of that kind, just schematics left over from abandoned projects.
Finally had some spare time and I decided to start designing a layout myself. I've split it up into sections and so far have made a layout for the PS, preamp stages (inc decoupling supply) and the bass + treble controls.
If anyone would like to help/check what I've done so far or give any advice then please feel free to do so. I've attached what I've got plus the schematic I'm working from below.
(https://i.postimg.cc/5H985ms9/intersound-schematic.png) (https://postimg.cc/5H985ms9)
(https://i.postimg.cc/9RBJ3D6v/Intersound-IVP-power-supply-layout.png) (https://postimg.cc/9RBJ3D6v)
(https://i.postimg.cc/SX6G8XxJ/Intersound-IVP-input-preamp-stage.png) (https://postimg.cc/SX6G8XxJ)
(https://i.postimg.cc/pmN8Z278/Intersound-IVP-Treble-Bass.png) (https://postimg.cc/pmN8Z278)
FWIW, the 43 ohm resistor on the emitter of the tube-sound current source is actually 430 ohm.
https://www.diystompboxes.com/smfforum/index.php?topic=119132.msg
In another thread, I found a clear picture showing the 430 ohm on the PCB.
https://www.diystompboxes.com/smfforum/index.php?topic=121884.msg
There was also this stuff on the transformer,
https://www.diystompboxes.com/smfforum/index.php?topic=119131.msg
Thanks v much! I imagine i will factor in the transformer to be honest. Do you think there would be any benefit apart from saving space in doing it the way suggested on that thread?
transformer ''abuse'' gives a completely unique response, both in saturation, saturation dependent bass cut, hysteresis loss, and a host of other good sounding effects. you can also saturate a transformer asymmetrically by having a small DC run through the transformer. i have a transformer based fuzz somewhere, (broken after a beer spill during a gig), its a shame that transformers are heavy, bulky and expensive, otherwise i'd use them a lot more.
cheers, Iain
Great to know. I will definitely go ahead and use a t-former in that case.
trying out different transformers can be a good idea if you have multiple. if you know what you are doing, you can even mod a transformer to sound the way you desire. when i build the transformer fuzz, i cut a big slot in the core to make it saturate faster, but you have to know what you are doing when changing the transformer, because if you over do it or do it wrong, you might need to get a new one.
cheers, Iain
Most important is that differential voltage amp circuit and extracting its output differentially, whether with transformer or another diff. amp. I doubt there will be significant transformer saturation with associated low signal voltages and guitar's limited bandwidth. (Especially if you don't want a "farting" overdrive tone).
You could always A/B both arrangements, transformer vs. differential and find out yourself. I have a hunch the transformer merely acts as LC filter, if even that.
(http://www.ecircuitcenter.com/Circuits/Function_Generator/Functi4.gif)
Differential provides symmetric soft clip (enough to convert triangle to sine) when no negative feedback is applied and input is constrained to low amplitudes.
Any transformer's effects on this topology are negligible enough to be ignored by likes of Vox (i.e. Valvereactors, VBM1), Hughes&Kettner (i.e. QT600), dozens of signal generator manufacturers and so on.
Hi Teemuk
Thanks for the info. Think I will attempt to find an appropriate transformer as I would like to make as faithful a clone as is possible on a perfboard!
Where does one find the C2M pots for the EQ section?
I thought about tossing this Phil's way for a PCB, but the pots stonewalled that thought. :icon_rolleyes:
I recently built the tube sound section of the IVP with two of the 4 band parametric eq sections as a standalone pedal, to get around the need for the 2MC pots I used dual gang 1MA pots wired with both pot elements in series and wired 'backwards', so that CCW is wired to the op-amp non-inverting input and the CW and centre pins are wired together.
This gives the correct frequency sweep but the downside is that the pot works in reverse, so that the upper frequency is CCW and the lower is CW. That doesn't really bother me though.
Quote from: digi2t on November 16, 2020, 10:13:12 AM
Where does one find the C2M pots for the EQ section?
I thought about tossing this Phil's way for a PCB, but the pots stonewalled that thought. :icon_rolleyes:
There's a different schematic (Electrovoice/Tapco version) at https://projectivp.wordpress.com/ that calls for A2M pots. I've been looking at that one in LTSpice and tried B2M pots, which are readily available, and the frequency spread doesn't look too bad, but I haven't built it yet, so that's a guess. PCB's are available for the input, 2-band and Tube Voice sections, if you just add the 4-band EQ you've got all the important stuff. 2nd input and clean channel could be omitted, along with the send/receive jacks and balanced output.
It is often the case that such semi-parametric EQ sections overlap substantially in their tunable resonant frequencies, and rarely the case that there is NO overlap. I assume this is to allow for maximum flexibility.
But how much flexibility and overlap in resonant frequency between adjacent bands does a musician need? I'm merely asking the question, not concluding they don't need any. For example, the PAiA 4-band semi-parametric EQ, with a very similar design, sweeps its centre frequencies from 35-680hz, 150-3000hz, 450-8500hz, and 750-15000hz. If one were to chop those ranges by half, you'd still have a fair amount of overlap. Maybe not enough to "tune a room" with several distinct resonances, but a more-than-reasonable capacity to re-voice many instruments. The IVP's resonant EQ bands are stated as tunable between 30-240hz, 100-800hz, 450-3600hz, and 1200-9600hz, with bass and treble shelving controls attending to the rest. As in the PAiA instance, a 50% reduction in range for each section still leaves a fair and usable amount of overlap, though I suppose that depends on the weirdness or quirks of the signal source or user's timbral end-goals.
In that spirit, I suggest trying out C1M pots, and seeing if it's something you can easily live with, whether permanently or until a source for C2M pots is found.
Quote from: Mark Hammer on November 18, 2020, 07:19:48 AM
In that spirit, I suggest trying out C1M pots, and seeing if it's something you can easily live with, whether permanently or until a source for C2M pots is found.
+1, I gave this a try in LTSpice and the difference with C2M is minimal. All it does is raise the low-end cutoff on each band a bit, and there's still more than sufficient overlap. Hi-end of each band is not affected. 2MC vs 1MC low end cutoff: Frequency band 1, 30Hz becomes 40 Hz. F2, 100Hz >> 130 Hz. F3, 450Hz >> 620Hz. F4, 1.2kHz >> 1.6k Hz. For reference, the high-end of each band in sequence remained at 240, 800, 3.6k and 9.6k. I'm sold on C1M for this design.
If you really want it, it's possible to maintain the exact same behavior of the 2MC pots using 1MC pots.
All you have to do is halve *all* the resistances in the EQ section and double the caps. The idea is called scaling.
Technically you should change the boost/cut pots to 25k as well.
So I've gotten to the point where the mixer amp and EQ section are laid out and I have some questions:
Could this be run off of a 9v pedal power supply by incorporating a 9v to 16v converter?
The post EQ section based around U8 - what is it's purpose? Is it needed if I decide to leave out the effects loops?
Could I leave out the clean voice section and just include the tube voice section? And what exactly should I eliminate if I choose to do so?
QuoteThe post EQ section based around U8
there is no U8 on the schematic,
if i understand correctly, you want the input mixer, the elaborate EQ and the tube voice, without effects loops?
(https://i.postimg.cc/PvGG3hnt/intersound-schematic.png) (https://postimg.cc/PvGG3hnt)
cheers, Iain
Apologies, I was looking at the Tapco version. This is the part I'm confused about:
(https://i.postimg.cc/9DDp1qRy/20210214-201217.png) (https://postimg.cc/9DDp1qRy)
And yes that's right
Cheers
that's an audio indicator LED, i believe.
it triggers when the level reaches a certain threshold, and lights an LED. the diode with the arrow pointing away, its datasheet tells me its an red diffused led.
cheers
Okay, well I don't think I need that, so will leave out.
Regarding the amended schematic you uploaded (thank you by the way), will I need to incorporate the output amplifier stage or will the 4558, 2n4401 and 2n4403 form what is effectively the same thing? If the latter is the case I presume I just use the "effects send" as the output for the circuit?
Thanks again
Also, I just noticed that before and after the t former there are two separate 4558 ICs, both of which are only having one half used. Would it be possible to use both halves of one 4558?
Thanks
ow, yeah the effects send is the new output, and that is the output amp, since you probably dont want to stack buffers, that's a waste of components, power and board real estate.
i recommend merging halves, independent of the circuit, there are very few cases where you actually need to keep the opamps in their original pairing, most of the time you can get away with shifting that around a bit, in this case you can too.
if you can work out a layout, i recommend using quad opamps, they are generally cheaper per opamp, and it saves a bit of power management since you only have half the amount of chips.
cheers, Iain
Okay got it.
Makes sense about the quad op amps! Wish I'd thought to ask sooner as I've done most of the layout with dual op amps. Chalk it up to experience I guess.
Thanks a bunch for your help. With any luck I will have the full layout ready to post soon.
One more thing I'm curious about is whether I can avoid having to use 240v mains power and just use a 9v to 16v converter?
Cheers
OTOH quad opamps lead to a lot of wiring in a small area and increased leakage between stages. (R.G. may have notes on this.)
Neither way is wrong. Duals are very popular.
Yeah I suppose that also makes sense, thanks.
I'm up to the point in the layout where I need to place the xfrmr. Could anyone tell me which 4 wires to use if I use the following xfrmr?
https://www.mouser.co.uk/ProductDetail/42TM018-RC/
Cheeeeerrs again.
Wait never mind I think I've got it. I'm presuming that wires 2 and 5 are centre taps? So I'm also assuming that I need wires 1, 3, 4 and 6...
i haven't had much experience with chare pumps and changing 9v to higher voltages, but i don't think the circuit will draw a lot of current so that might not be a problem.
something like this could be something to experiment with:
https://www.ebay.co.uk/itm/12V-Dual-Output-DC-DC-Converter-Step-Up-Voltage-3-3V-5V-9V-to-12V-Boost-Module-/253029625315
a nice large capacitor from both the + and - to ground is important to filter the switching noise.
cheers, Iain
Quote from: jimladladlooklike on February 15, 2021, 04:17:47 PM
Okay got it.
Makes sense about the quad op amps! Wish I'd thought to ask sooner as I've done most of the layout with dual op amps. Chalk it up to experience I guess.
Opinions differ, but I prefer duals for layout because then all the op-amps "point in the same direction". This helps signal flow around the board. On a quad package everything points out from the middle, which I find more difficult to lay out. Plus the power pins are reversed with respect to virtually everything else, which makes it awkward to put them on a board with other parts (unless you add them in upside down, which I also don't like).
If you play around with both, you'll find which you prefer. Depends a bit on your design style, I guess.
Quote
One more thing I'm curious about is whether I can avoid having to use 240v mains power and just use a 9v to 16v converter?
How much current does it draw? Usually voltage boosters are ok as long as the current drawn if fairly light. Big loads make that a lot harder. But doesn't this thing have a +/-16V bipolar supply? In which case, you'd be doing a lot of gymnastics to get that from a +9V input...not impossible, just tricky.
You could think about running from an 18V input and then just adding a rail-splitter op-amp to give you a +/-9V supply. That'd let you use the circuit without making any serious modifications, and 9V isn't so massively different from 16V that you'd notice much. At least, not in this circuit for this application. Yes, you lose a bit of headroom (18V vs 32V), but if we're turning it into a pedal, we don't want mixing desk levels anyway.
Quote from: ElectricDruid on February 16, 2021, 02:21:23 PM
How much current does it draw? Usually voltage boosters are ok as long as the current drawn if fairly light. Big loads make that a lot harder. But doesn't this thing have a +/-16V bipolar supply? In which case, you'd be doing a lot of gymnastics to get that from a +9V input...not impossible, just tricky.
You could think about running from an 18V input and then just adding a rail-splitter op-amp to give you a +/-9V supply. That'd let you use the circuit without making any serious modifications, and 9V isn't so massively different from 16V that you'd notice much. At least, not in this circuit for this application. Yes, you lose a bit of headroom (18V vs 32V), but if we're turning it into a pedal, we don't want mixing desk levels anyway.
Oh right, thanks for pointing that out. It hadn't dawned on me that I would need to get both +16v and -16v from +9v... Will do some research on how.
I don't know how much current it draws, honestly. How would I calculate that? Watts/Volts? How do I find out the wattage? Excuse my ignorance.
Thanks
an educated guess: it uses less than 150mA
you might also want to look at the transformer voltage/freq rating. i expect the transformer to be slightly overdriven, but at a lower voltage, you might not get that, so trying lower voltage transformers might be a good idea here.
cheers
Right, so I think it may be best to abandon the idea of powering with a +9v wall wart.
Instead, would I be able to power it with +32v DC and split the voltage somehow?
you can probably get away with only using 18v to 24v, i think 32v might be overkill here, the gain isn't that high, and the circuit will most probably work just fine on + and - 9v or 12v.
i suggest looking in to charge pumps and other boost converters like the Ebay link i posted earlier, this makes 9v in to a higher voltage
cheers, Iain
Okay, thanks again. Still getting to grips with power supplies and what different circuits require/whether they are affected by a differing voltage.
But, I have finished the vast majority of the layout... I think.
A quick note: I like to drill a larger hole through one of the holes in the strip board to create a trace cut which I then tidy up with a tool afterwards. The DIYLC software only allows lines to be drawn between said holes, so each of these lines represents a hole that will be drilled to the RIGHT of it.
Here we have the input preamps. There are two input jacks on the IVP, both with a lo/hi impedance switch on them. I've simplified it slightly so there is one low and one high, neither of which you can change with a switch. (Also, with regards to the PS decoupling network, I'm not sure I will need this if using a charge pump? I'm guessing this is to eliminate DC ripple? I left it in just in case it's necessary.)
(https://i.postimg.cc/zbhDjgnp/Intersound-IVP-input-preamp-stage.png) (https://postimg.cc/zbhDjgnp)
Following that we have the elaborate EQ section:
(https://i.postimg.cc/4HZGQF4N/IVP-Equaliser.png) (https://postimg.cc/4HZGQF4N)
And finally the tube voice part:
(https://i.postimg.cc/fkFpsPQ3/IVP-Tube-Voice-Circuit.png) (https://postimg.cc/fkFpsPQ3)
As you can see, especially with the EQ, it's a lot of strip board -but I want to put this in some kind of big chassis and use it as an "always on" kind of thing as part of my rig (which it's looking like I will never use again at this rate, but whatever).
Any advice whatsoever would be truly appreciated, likewise if anyone has the time to check it over as per the schematic. I've checked it myself but it's late and my eyes hurt!
PS layout to follow, once I manage to get my head around what to do. Every day is a school day!
EDIT: The resistor on from the emitter of the 2N5210 to -16V on the left of the TV circuit layout is meant to be 36K, oops.
Quote from: jimladladlooklike on February 19, 2021, 06:29:11 PM
A quick note: I like to drill a larger hole through one of the holes in the strip board to create a trace cut which I then tidy up with a tool afterwards. The DIYLC software only allows lines to be drawn between said holes, so each of these lines represents a hole that will be drilled to the RIGHT of it.
DIYLC has a "trace cut" option on the "Boards" menu which is the best way to represent a trace cut on veroboard. It looks exactly like drilling a track out with a wide drill bit. Lines don't work well because they're not the way it was designed to be done.
Seems I'm using a very old version... will download the new one now!
2nd draft:
2n4401 + 2n4403 on EQ board swapped positions and diodes changed accordingly.
Pin 2 of the furthest right 4558 on EQ board now connected to lug 3 of all freq level pots.
Traces now cut using proper tool.
xfrmr added for more accurate size.
(https://i.postimg.cc/s1yWDDmh/IVP-input-preamps.png) (https://postimg.cc/s1yWDDmh)
(https://i.postimg.cc/ppLnzGgV/IVP-Equaliser.png) (https://postimg.cc/ppLnzGgV)
(https://i.postimg.cc/BtgK897w/IVP-Tube-Voice-Circuit.png) (https://postimg.cc/BtgK897w)
Hey again,
I've been looking into this power supply situation. I still want as close to the +/-16v bipolar supply as possible, but admittedly don't have the knowledge to get that from and +9v unipolar wall wart. I have come across this schematic for an op amp voltage splitter which utilises an LM741.
(https://i.postimg.cc/1frPgzrP/power-supply-splitter-circuit-min.jpg) (https://postimg.cc/1frPgzrP)
Theoretically, if I found a 32V AC adapter (or an adjustable one that had that setting or, say, +30V) could I use this circuit. The max supply voltage for the LM741 is +/-22V but does that mean it could essentially handle max +44V from a unipolar supply?
Another thing I'm concerned about is the germanium PNP transistor (MJ2555). Could I replace this with a silicon tranny?
that transistor should, most likely, be marked MJ2955, which is the compliment to the 2N3055, both are silicon. the same transistor pair comes in different packages with different prefixes, eg TIP3055 or MJE3055, probably others I can't remember. that transistor pair would have been selected for their MASSIVE-ish current handling, probably way more than you would need here.
QuoteTheoretically, if I found a 32V AC adapter (or an adjustable one that had that setting or, say, +30V) could I use this circuit. The max supply voltage for the LM741 is +/-22V but does that mean it could essentially handle max +44V from a unipolar supply?
Another thing I'm concerned about is the germanium PNP transistor (MJ2555). Could I replace this with a silicon tranny?
The transistor is actually an MJ2955 which is the PNP compliment to the 2N3055.
You don't need such large transistors for that circuit.
[Edit: duck_arse just posted the same]
Perhaps you could consider an AC input with a voltage doubler feeding a voltage regulator,
http://www.electricalbasicprojects.com/voltage-multiplier-circuits-half-wave-voltage-doubler/
For the positive supply you use one doubler,
(http://www.electricalbasicprojects.com/wp-content/uploads/2017/11/Voltage_Multiplier_Circuit-768x409.jpg)
For the negative supply you use another doubler except with the diodes and caps flipped.
Connect the input caps from each doubler together then to the transformer.
Connect the "through rail" on the each double together then to the other side of the transformer.
If you start with a higher AC voltage you can use this type of doubler,
(https://qph.fs.quoracdn.net/main-qimg-a8d8bada57a1b7820b49bf949d06a8e3)
Cool, thanks for the suggestion, but I don't know where I'd get an AC voltage from. Do such wall warts exist? Also I'm not sure which transformer you mean? I'm trying to steer clear of the need for a PT if that's what you were suggesting. Could I use a version of the schematic I posted but with more apt transistors?
Cheers
So I just breadboarded a version of the schematic I posted, except I didn't have an LM741 handy, so opted for an LM386 instead.
It's powered with +9v DC. (The LM386 doesn't can't handle more than 18V, so will have to use a suitable replacement eventually.)
I used two 560r resistors for the voltage divider, hooked up to the two outer pins of a trim pot, the centre pin of which is connected to the non-inverting input of the op amp.
I replaced the transistors with a 2N5088 and a 2N5087.
After measuring, the reading I get are: C1 + terminal = +9v, "ground" terminal = +4.5v and C2 - terminal = 0V. So basically what I have is a voltage divider... I then disconnected the two above capacitor legs and measured there, having noticed that they were connected to +9V and ground, but I don't know what that achieved as the voltages were all over the place. Is there something I'm missing? are the parts I used not the right kind?
EDIT: I was measuring wrong. I was taking the ground reading from the bottom left point of the schematic, not the junction of the two caps.
It works fine! Now I just need to test with an LM741 when I can get some. Thanks for all of your help on this guys, I feel like I'm learning a lot and it's much appreciated.
The LM386 isn't a (normal) opamp, its a power amp, with some odd quirks when it comes to biasing, to make it work with less external parts. try any other real opamp, that would probably work better.
if you want to simplify and use the 386, you can leave out the transistors, and put both inputs to ground, this provides a strong, stable Vbias
cheers
Oh okay, thanks for the pointer. I was planning on using an LM741 because of it's max input voltage anyway, just wanted to make something similar with what I had to hand. Note to self, always read the datasheet.
QuoteNote to self, always read the datasheet.
that shouldn't be just a note, that should be your RULE #4, the other rules will come to you along the way.
cheers
Quote from: Rob Strand on November 24, 2020, 12:02:33 AM
If you really want it, it's possible to maintain the exact same behavior of the 2MC pots using 1MC pots.
All you have to do is halve *all* the resistances in the EQ section and double the caps. The idea is called scaling.
Technically you should change the boost/cut pots to 25k as well.
A couple months late here, but does the scaling also apply to the 20k resistor on the op-amp that comes afterward, and/or the 10k resistors that come before? Or is it just starting with the 50k pots (reduced to 25k) and everything beneath them?
Quote from: aion on May 14, 2021, 09:52:30 PM
Quote from: Rob Strand on November 24, 2020, 12:02:33 AM
If you really want it, it's possible to maintain the exact same behavior of the 2MC pots using 1MC pots.
All you have to do is halve *all* the resistances in the EQ section and double the caps. The idea is called scaling.
Technically you should change the boost/cut pots to 25k as well.
A couple months late here, but does the scaling also apply to the 20k resistor on the op-amp that comes afterward, and/or the 10k resistors that come before? Or is it just starting with the 50k pots (reduced to 25k) and everything beneath them?
this only aplies to the Gyrator circuits themselves, the 50k pots and the 20k resistances stay the same.
you can just use the Gyrator Calculator (http://www.muzique.com/lab/gyrator.htm) to calculate the Q and freq. of the Gyrator.
by the way, note how the circuit resembles a Tube Screamer tone control, but the Capacitor-Resistor combo is replaced with gyrators.
cheers
Hey again guys.
I've finally gotten around to assembling a rough and ready version of this thing. As you can see it's sort of chopped up into sections. I'm hoping this will make the inevitable de-bugging process easier...
(https://i.postimg.cc/Yv8LjD3B/20210602-215002.jpg) (https://postimg.cc/Yv8LjD3B)
I do have another question though: Should I ground the input jacks via the ground lug on the DC input, or should I tap it from somewhere in the circuit post converting the +32VDC into +/-16VDC? Does it matter? The same question applies to the two preamp gain pots.
Thanks
Hi guys,
So I realised I didn't upload the layout I've been working from so here it is:
(https://i.postimg.cc/4YdmWT9Z/Intersound-IVP-layout-1st-version.png) (https://postimg.cc/4YdmWT9Z)
I'm running it at +9v from my normal power supply and have swapped out the LF356 ICs in the preamp section with 2 x TL071 to compensate for this. Did this just for testings sake until I get my hands on a 32V adapter.
However, I'm having a few issues. there's quite a large voltage drop across the power supply decoupling resistors. It goes from approx +/-4.5V to +/-3V. I think for this reason there is no sound. When I jumper across both resistors with crocodile clips I get some sound when plugged into the low impedance input but nothing when plugged into the high impedance one. Along with this, when plugged into the latter and plugged into neither there is a high pitched sound (oscillation???). It's particularly loud on the output pin (#6) of the top preamp IC on the layout.
At the moment I have connected one jack to the ground lug on the DC socket and so all jacks are connected to that via the chassis, but I'm confused about this. In the schematic there is only one symbol for ground or 0V. obviously a bunch of components are connected to 0V in the circuit, including the input and output jacks. However, when I connected the jacks to 0V, there was 4.5V on the chassis in relation to the DC socket ground lug.
How do I connect the jacks and 0V in the circuit without having this 4.5V floating on the chassis?
Okay so I fixed this problem with a simple solution: plastic jacks.
Now I'm still having trouble powering the circuit. I built a charge pump that creates 33V and shows approximately that voltage when measured separate from the effect. However, when it's used to power said load the voltage at the same point in the charge pump circuit drops to around 7V. Is this due to the load current? Like, how much current the effect part of the circuit is drawing? I'm assuming so. When I connected my multimeter in line with the effect and charge pump it drew 150mA of current. Datasheet says max supply current is 160mA so I though this would work.
Basically, I've clearly bitten off more than I can chew here!
I'm sure it's far beyond the point of being at all useful, but if you need to reference anything against an original IVP (voltages etc) I have one here.
the max current of a SMPS / boost converter is what it can deliver before going dead, not what it can deliver at full power.
there are dozens of relatively cheap 30v power supplies on the market, you might want to add some filter caps to those, maybe even a regulator chip, but most work quite alright in my experience.
i honestly doubt that you need that much headroom when working with a guitar signal, i bet this circuit would work on + and - 6v as well.
cheers
Quote from: mdcmdcmdc on June 16, 2021, 09:54:28 AM
I'm sure it's far beyond the point of being at all useful, but if you need to reference anything against an original IVP (voltages etc) I have one here.
That could come in handy, if you have them. Thanks.
So, I think I know where the problem lies. The two preamp chips (tl071) are working fine when I use my 9v wall watt. However the signal cuts out at the junction between the two 20k resistors and pin 2 of the first rc4558. Same thing happens with a tl072 in its place. However, when the chip is removed I get sound at this point. Looking at the schematic shows that pins 3 and 5 are grounded. Is this something that is normal for non-inverting inputs? I've connected them to 0v on the power section of the circuit as pins 8 + 4 are connected to V+ and V-. Have checked and redone some of the solder connections in case of shorts etc. I'm just v confused at this point.
QuoteLooking at the schematic shows that pins 3 and 5 are grounded. Is this something that is normal for non-inverting inputs?
yes, very normal, mundane even.
this is an inverting opamp stage, which means that the inverting pin should be silent too, but the output should have signal again.
what an opamp does is trying to match the voltage at both pins via the negative feedback loop, if the (+) pin is 0v, the opamp will try and keep the (-) pin at 0v as well, keep this in mind.
if we have an inverting opamp like this:
(https://upload.wikimedia.org/wikipedia/commons/thumb/4/41/Op-Amp_Inverting_Amplifier.svg/300px-Op-Amp_Inverting_Amplifier.svg.png)
where both resistors are the same, and we apply 1v to the input, there will be a current flowing through the resistor Rin. to keep the voltage of the (-) pin at 0v the opamp has to take as much current out of that node as the input puts in, to do this it has to generate -1v at the output/the other side of Rf. changing Rf or Rin changes the voltage the opamp needs to generate to keep the (-) input at 0v, this is how the gain is set.
also keep in mind that the inputs of the OpAmp have near-infinite resistance (for all intents and purposes)
cheers
Thanks for explaining that to me, much appreciated. I've obviously seen an inverting op amp stage before but I guess I'm second guessing everything at this point!
I have made some corrections to the layout: changed position of wires connected to the 1k2 - 9k6 filter pot. Also made the connection from pin 4 of the 4th 4558 to -16v which wasn't there before.
(https://i.postimg.cc/nX39wnzq/Intersound-IVP-layout-1st-version-ammended.png) (https://postimg.cc/nX39wnzq)
It seems I've getting signal passing through the circuit now, which is better, but it's strength diminishes at each op amp stage, then at the output it's super weak and fizzy sounding. I'm going to wait and put this to one side until I get paid and can buy a 30v adapter.
Thanks again for all of the help
So an update with this project:
- Bought an adapter with 32VDC output, realised it was centre positive so swapped wires round on DC jack.
- Found a couple of not-quite-cut traces after realising one of the op amps was getting a bit hot and sorted them out accordingly.
Now the circuit is starting to sound like its working, sort of. Signal is passing through and all the controls seem to work. There's one issue; a loud hum, about as loud as the guitar signal. Could this be a DC filtering issue?
When I take a measurement of the DC at the + and - inputs of each of the first two op amps relative to the power supply 0V I get 0V, but when I measure the same two pins of the same two op amps relative to the ground lug on the DC input jack I get around 14V, is this the problem?
A rough schematic should help us to understand the difference between ground lug and PS 0V point..
Quote from: jimladladlooklike on July 02, 2021, 03:08:45 PM.....relative to the ground lug on the DC input jack I get around 14V, is this the problem?
Why are you saying "ground lug"?
Okay, so, a further update. But firstly, thanks again for all of your help folks, I would have lost all hope without your guidance!
I abandoned this for a day or two and when I revisited I decided to try with my 9V Voodoo Labs power supply and wadayaknow? The hum went away. So now I have an almost functioning preamp which works running off of 9V. The EQ section is so fun and versatile, albeit with the wrong taper pots which I can live with. That into the Tube voice section does exactly what I want. (clang clang).
Quote from: PRR on July 02, 2021, 11:24:50 PM
Quote from: jimladladlooklike on July 02, 2021, 03:08:45 PM.....relative to the ground lug on the DC input jack I get around 14V, is this the problem?
Why are you saying "ground lug"?
With regards to your question: I mean the ground connection on the DC input jack
Quote from: antonis on July 02, 2021, 03:41:41 PM
A rough schematic should help us to understand the difference between ground lug and PS 0V point..
I'm planning on redoing the schematic once I work out all of the kinks (there's PS filtering caps which I've overlooked and I think there may be an issue with the PS - input pre decoupling network.) but it turns out these parts of the circuit function as I had them connected originally.
Now there are two main issues (besides correcting which wires go to which solder lug on a pot or two) -
It's quiet and, whilst it will most likely be an always on kind of thing, I'd like to have some more volume on tap to drive whatever amp I'm using if necessary. Might this be solved with a higher voltage? I tried a charge pump (tested when disconnected and worked fine) but the output voltage dropped to below 9V when hooked up to the circuit (load??) I can always try a new wall wart I suppose.
When I turn the "lo level" knob up past about 8 o'clock and I hold a note or chord and let it naturally fade out, the notes will waver and falter in and out. They sort of warble.
Cheers again
Jim
Hey guys,
I tried the preamp with an 18VDC, 500mA power supply (centre negative this time) and I got this repeated beeping... from the actual power supply plug! Quite alarming
Someone on reddit told me I need to "dereference" the power supply to get proper 0V ground? I've made a rough schem to show how things are grounded.
Cheers
(https://i.postimg.cc/DSdK5y6g/intersound-IVP-clone-grounding-scheme.png) (https://postimg.cc/DSdK5y6g)
I switched the DC Jack with a plastic one and it has sorted the weird beeping issue. I'm not sure but I think the previous DC jack was causing a short between the +18v and ground.
However, I'm now getting DC voltages on all 3 1/4' jacks.
Hi again folks.
So turns out my power supply section was not what was required (I'd basically made a fancy voltage divider), but now I've made a bipolar supply which shares ground with the +18vdc in.
I think I'm finally getting somewhere, in that it works quite well. It's loud enough and has a nice amount of headroom. However, it's still noisy. After measuring the negative supply voltage I noticed that it fluctuated between around -14v and -16v. Could this be a filter cap issue?
I've uploaded the schematic I'm using below.
Cheers guys
(https://i.postimg.cc/rKSHmz4p/bipolar-supply-schem-080921.jpg) (https://postimg.cc/rKSHmz4p)
I should have mentioned that the reading I got was when the supply wasn't hooked up to load. I changed the inductor and now the negative voltage is around -15vdc and stable. However, the voltage drops to about -8vdc when loaded. I'm guessing the PS doesn't meet current requirements.
Try replacing the 7809 with a second 7815, and replace the 637 inverter with a Microchip TC962 CPA, it handles +15v nicely and outputs -15v (or darn near) @ up to 80 mA. The pinout is different than the 637 so watch that.
Thanks Mike, will check that out.
So my ammeter reads around 250 mA when hooked up in series with the circuit, so I may need another solution. I have some ideas of what I need to do so will report back when I can.
Cheers
You need to measure the *output* current on the +V and -V rails.
[Probably clearer if I said you want to measure the current on each rail *to* the IVP circuit. For the negative rail that's the output current of the converter.]
I estimate about typical 50mA on *each rail*. Worst case is less than 80mA to 100mA.
The 43 ohm vs 430 ohm tube sound error on the schematic will pull more current.
The original power supply had a current limit of less than 150mA on each rail.
The DC converter is only say 75% efficient so the -V rail will pull about 67mA typ. (150mA max) from the +ve DC in rail.
Add that converter current to the +V current gives a total input current of 120mA typ (250mA max).
If you converter isn't working very efficiently due to an incorrectly chosen inductor then that would show up
as an increase in the DC input current.
As far as your noise issue goes, if you converted +18V to -18V (or above) then used a -15V regulator on the output of the converter it is likely that will reduce noise. Alternatively use a DC converter without and regulator and place an RC filter or active filter on the output of the -15V to remove noise.
Hi Rob, thanks for explaining that to me. Finally got round to taking said measurements.
The current on the +ve rail was 87.3 mA
The current on the -ve rail was 86.9 mA
They did start off much higher however (+ve around 120mA and -ve around 103mA) then reduced rapidly then gradually settling at the above readings)
So that means a total input current of about 180mA, right? Does this mean the 250mA I previously measured at the DC input shows that I've used the wrong inductor?
If it helps then the supply voltages are as follows:
+ve 14.95 VDC
-ve 13.25 VDC
The from the wall wart itself is +17.83 VDC
Cheers
QuoteThe current on the +ve rail was 87.3 mA
The current on the -ve rail was 86.9 mA
Based on the estimates I made those look a little high. Not sure why. I could have screwed up. Nonetheless it might worth checking some stuff. In a few places in the circuit is an opamp feeding two transistors and those transistors have 10 ohm resistors in the emitters. Measure the voltage across each of the 10 ohm resistors. You can then calculate the current through the resistors as I = Vmeasured / 10.
If we take your -ve rail current at 86.9mA and -15V output that's 1.30W. According to the datasheet, and assuming all is well, the converter efficiency is 85%. The converter input power should be 1.3/0.85 = 1.53W. I realized you are feeding the converter from a 9V rail so that means the input current to the converter will be 1.53W / 9V = 170mA. The input current to the 9V linear regulator will be roughly the same current, so 170mA from the +ve rail going into the 9V regulator.
The total current expected from the positive rail is 170mA + 87.3mA = 257mA. Which is in very good agreement with what you measured.
What that concludes is the converter is working correctly.
Having the 9V regulator at the input to the converter is throwing away half of input power because the 9V regulator drops 9V across it and produces 9V out (the 9V drop loses the power as heat). The converter chip can handle 16.5V in but not with -15V out. With -15V out the input voltage needs to be 24V - 15V = 9V. So the chip is already max'd out. In theory you can save power but not with that chip.
At this point it might be worth checking the current into the various sections of the circuit to see if there isn't a problem somewhere.
Apologies, I should have mentioned that I removed the 9V regulator and supplied the converter with the output of the 15v regulator, the same rail as is supplying the rest of the circuit with v+. That's how I got the measurements shown. I did read the table on the datasheet, hence why I originally decided to supply the converter with +9v from the regulator, but I thought it might be worth a try supplying it with +15v. I did some calculations and decided on a 220uH inductor. (I think I did this right, but it took me a while to figure out, so who knows?)
Anyway, if you're saying the chip is maxed out when supplied with +9v, does that mean I could be damaging the chip supplying it with +15v, or that it will just make no difference to the outcome?
Regardless, I will check over the schem/layout/build itself and measure currents at the points you mentioned and report back.
Cheers again
QuoteAnyway, if you're saying the chip is maxed out when supplied with +9v, does that mean I could be damaging the chip supplying it with +15v, or that it will just make no difference to the outcome?
The way I interpret the note in the datasheet it could be damaging the chip. My guess is the voltage limit is due to the MOSFET ratings inside the chip.
It's probably just a fluke +15V current measurements match the calculations for +9V. If the chips isn't doing something weird and just holding onto it's life then the current does seem high for +15V in and then perhaps something isn't quite right with the inductor. (For example if the inductance value is on the small side it could be saturating and that might push-up the input current.)
Hi again!
So I took a break from this project, partly as I needed to build some stuff for friends and partly because I think I destroyed the chip... It got insanely hot then the thing just stopped working.
Anyway, I found a power supply that I thought might work here:
https://www.ebay.co.uk/itm/303536235236?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649
I hooked it up and got the circuit running at +/-15V, no problem. Once again, it sounds good, all controls work well, but there's a different noise this time. A buzzing that starts on power up, decreases in pitch for a few seconds before settling and continuing at an annoyingly loud volume until powered off. It's not like a hum I've ever herd before, it's very buzzy.
I again took current readings again for both +ve and -ve rails, same results as last time give or take a mA or two, and I didn't let them "settle for as long as I did last time.
I also took readings across those two 10ohm resistors on the emitters of the trannies you suggested. both measured 0.007VDC, so 0.007/10 = 0.0007 so the current through the resistors is around 0.7mA. Does this seem good?
Cheers
Switching supplies can pulse under light loads which can cause whining. That power supply is 20W and the chip perhaps can go even higher.
Try putting some dummy loads on the power supply outputs. Start with say 220 ohm. Given the power supply rating you might need to try 100ohm or 47ohm. For the lower values you will need to increase the resistor wattage or use parallel resistors.
Beyond that would be filtering.
I later remembered the details of this thread. The circuit was pulling a reasonable amount of current already. Nonetheless the dummy load is still worth trying.
QuoteI also took readings across those two 10ohm resistors on the emitters of the trannies you suggested. both measured 0.007VDC, so 0.007/10 = 0.0007 so the current through the resistors is around 0.7mA. Does this seem good?
That seems OK.
Okay, so start with 220 ohm 1/4w carbon film resistors? Then maybe 100 ohm 1/2w?
Cheers again
You can work it out from P = V^2 / R.
For 15V,
R P [W] Current [mA]
470 0.5 32mA
220 1.0 68mA
100 2.3 150mA
47 4.8 320mA
If you only have low power resistors you can use a number of higher values in parallel.
From your previous measurements you circuit was pulling about 87mA for each rail.
Typically we might expect a switchmode to work OK at 10% of the rating so 2W which is 68mA per rail. However when it comes to audio that rule of thumb can quickly go out the window. If you put 2x470ohms 1/2W resistors in parallel on each rail it will increase the current draw by 2x32mA = 64mA.
If you hear a change in pitch of the whine then you know you are on the right track. If the 64mA isn't enough to remove the whine you will have to add more resistors. The question is how much load is required to get rid of the whine, and can you get rid of it at all? You can only do this by experiment.
I noticed the advert says:
"I've measured ripple at approximately 200kHz at 200mV peak to peak when driving 12V at 300mA."
So you might need to add some RC filtering on the supply anyway.
So I put 2 x 470ohm 1/2W resistors in parallel from V+ out on the power supply to V+ in on the circuit, the same from V- out on the PS to V+ in on the circuit.
The whine got lower in pitch. I used the trim pot on the PS to reduce the output voltage and after s couple of turns the whine disappeared. If I remember rightly the output voltage on V+ and V- rails sat at around 14.3V and -14.3V. (Ish). The problem now is that the volume has decreased by a significant amount, not reaching unity gain with a signal going direct from guitar to amp.
ALSO, me being the idiot I am, I wanted to see what would happen with just 1 x 470ohm 1/2W resistor on each rail, so I hooked those up and I either shorted something with the crocodile clips or the circuit just didn't like it? There was a high pitched squeal then no sound except a steady regular popping sound.
The voltages were jumping all over the place after this occurred. So I disconnected the PS from the circuit and they're steady, so I guess I've messed up something in the circuit itself. Think I'm going to try and replace every active component when I get chance. Hopefully that will sort said problem out.
Following that, I will try and find a combination of resistors that rid the whine...
Thanks again for your help
QuoteSo I put 2 x 470ohm 1/2W resistors in parallel from V+ out on the power supply to V+ in on the circuit, the same from V- out on the PS to V+ in on the circuit.
The whine got lower in pitch. I used the trim pot on the PS to reduce the output voltage and after s couple of turns the whine disappeared. If I remember rightly the output voltage on V+ and V- rails sat at around 14.3V and -14.3V. (Ish). The problem now is that the volume has decreased by a significant amount, not reaching unity gain with a signal going direct from guitar to amp.
You might be close to the edge of it working. Probably a good idea to add some more load resistors when the thing is on you desired voltage.
QuoteALSO, me being the idiot I am, I wanted to see what would happen with just 1 x 470ohm 1/2W resistor on each rail, so I hooked those up and I either shorted something with the crocodile clips or the circuit just didn't like it? There was a high pitched squeal then no sound except a steady regular popping sound.
These things happen. High pitch-squeal and on/off (which would cause popping) is a sign of a short.
QuoteThe voltages were jumping all over the place after this occurred. So I disconnected the PS from the circuit and they're steady, so I guess I've messed up something in the circuit itself. Think I'm going to try and replace every active component when I get chance. Hopefully that will sort said problem out.
Yes sure sounds like short or fried part on your board. You can narrow it down by remove the power *both* +ve and -ve to sections of the of the board.
Okay so I've got it working great, no whine either. Some relatively quiet hiss, as expected, but it's finally useable.
The problem was a building error, which I will get to.
I narrowed down the problem by audio probing and taking g voltages at various points. Turns out there were 2 x ICs that had been destroyed during the previous incident. Once those were replaced I continued with the audio probe and discovered that the whine was coming from the 1st output (pin 1) of the last 4558 in the signal chain. Also noticed that said IC was running pretty hot. So, looked around for a bit and discovered one of the 13K resistors, specifically the one going from +15v to the base of the 2n4401, was in fact 13ohms. Once I replaced that the preamp worked perfectly.
Finally! Turns out I just needed to check my work more thoroughly. However, I wanna thank you for helping me out. I've learned some skills I've never had to use before, which will surely help me in the future.
there's a trick when using 1% resistors - look for any gold bands, then ask why they are there.
i like this conclusion to a long long thread!
im happy for you it works now
cheers
QuoteOkay so I've got it working great,
Great news. Not giving up paid off in the end.