DIYstompboxes.com

DIY Stompboxes => Building your own stompbox => Topic started by: El Heisenberg on June 09, 2010, 11:07:37 PM

Title: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 09, 2010, 11:07:37 PM
I wanna build this amp from GGG:

http://www.generalguitargadgets.com/pdf/ggg_lm3886_amp.pdf


But it needs an 18v power source. There's this one:

http://www.generalguitargadgets.com/pdf/ggg_bipolar_ps.pdf


But I don't know if 1A from each of the regulators will be enough to get the full power from the amp? Will this power supply do?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 09, 2010, 11:15:33 PM
I'm having a tuff time finding the 10 ohm 2 watt resistor with 10-12 turns of #22 insulated wire. Anyone know how to find these on mouser??
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Nasse on June 09, 2010, 11:28:19 PM
That supply is for low power stuff like pedals and opamp circuits. For such power amp use full wave rectifier
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: PRR on June 09, 2010, 11:39:13 PM
> tuff time finding the 10 ohm 2 watt resistor with 10-12 turns of #22 insulated wire.

For this same +/-18V amp? Power is small. You can use 1 Watt.

Mouser Part #:  294-10-RC  Manufacturer Part #:  294-10-RC  Carbon Film Resistors 10ohms 0.05  

Use #22 or #24 insulated wire. Strip a bit of one end. Solder to the resistor lead very close to the resistor body. Wrap it around the resistor like a coil (what it is). Try to get at least 8 turns (why you may need to go #24 on this smaller resistor). 10 turns is fine. Cut the wire with about 1/2" end, strip, solder to other resistor lead, trim.

If it is easier, wind 10 close turns of #22 on a pencil. Leave short 1/2" ends. Whack excess pencil. Strip wire ends and solder across resistor.

Resistor must be non-inductive. Carbon (comp or film) is fine. Metal-film may be OK but is not the best plan. Wire-wound may not be fine. In normal use the dissipation is negligible, but it must survive occasional bursts of hypersonic frenzy. A 2 Watt part is usually OK on larger amps. 1W should be fine for a 10W-15W amp.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: PRR on June 09, 2010, 11:49:27 PM
POWER amps usually get UN-regulated power.

The difference between a regulator and a power amp is details. A good power amp (the '3886 is very good) can both amplify audio and reject power ripple. You do want to avoid over-volting the power amp, but the '3886 will stand over +/-40V (more than regulators!) so your +/-18V is not even close to trouble.

Transformer, rectifier, caps.

Use a 24V CT transformer, a FWB, and two caps. For 8 ohm load use 1A transformer and 2,200-4,700uFd 25V caps. For 4 ohm load use 2A transformer and 4,700-10,000uFd 25V caps.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 10, 2010, 07:47:35 PM
This particular design says the amp is 68w.


Also, if I have a 24v CT transformer at 3A will that be fine?
 
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 10, 2010, 08:24:30 PM
Paul I was actually going to also use the 12AU7 preamp you whipped up for my last amp with the TDA2003 again on this amp. That amp was 10 watts. For this I was going to use another 12v 1A or 3A transformer in parallel. With 68w I don't mind having two transformers. I'll mount them on top along with the tube.

Still tho, you said a 2 watt part is OK for a larger amp. But 1 watt is ok for 10-15watts. but this is sposed to put out 68w
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 11, 2010, 01:17:33 AM
I'm curious why the resistor has to be wound with insulated wire
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 11, 2010, 07:05:36 AM
I drew this up real quick. This is what I'd be doing:




(http://i633.photobucket.com/albums/uu56/el_heisenberg/LM3886tube.gif)


Will this work? I've never made anything grounded to a metal chassi. I've always worked with wood or plastic.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 11, 2010, 07:11:23 AM
Oh PPR said to use a CT transformer. What do I do with the center tap?? And a full wave bridge rectifier?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Tubebass on June 11, 2010, 08:32:03 AM
Use a 48 volt 2 amp center tapped transformer and a 3 or 5 amp bridge rectifier. Ground the center tap. Then + and - of the bridge go to filter caps then to v+ and v- pins of your 3886.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 11, 2010, 08:41:10 PM
Blah I just got ahold of a 25.2v CT 2A transformer!
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: PRR on June 11, 2010, 09:29:46 PM
> says the amp is 68w.

That's the show-off rating.

The actual power will depend on supply voltage and load. Ues Ohm's Law, account for peak-to-peak versus RMS, and expect loss.

The power supply you pointed to gives +18V and -18V (at not enough current for a Power Amp). Ideally you have 36V peak to peak; in fact probably 31V p-p. This is 11V RMS. 11V in 8 ohms is 15 Watts; in 4 ohms is 30 Watts.

The 3886 will work fine at this power level. While it is a fraction of what LM3886 "can do", there isn't a better/cheaper chip in this power range. 

(http://i45.tinypic.com/sde0ow.jpg)

> Blah I just got ahold of a 25.2v CT 2A transformer!

That's fine for the 15W-30W zone.

> Use a 48 volt 2 amp center tapped

Using Dave's suggestion you could have 60 Watts in 8 ohms. The 4-ohm rating could be over 100 Watts but you will need VERY big heatsinking for long-term high power. (The show-off rating is 68W for good reason: the chip can't handle the heat or current for higher powers.) Also 48V 2A would be very saggy pulling a 4 ohm load; this is probably a recipe for 8 ohm work.

> What do I do with the center tap?? And a full wave bridge rectifier?

Basic power supply for any tranny amp bigger than a Ruby. Study/plagiarize.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 11, 2010, 10:23:55 PM
where the heck am I gunna get a 48v 2 A transformer??
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 12, 2010, 04:13:41 AM
i've been looking everywhere. I can't find a transformer like that
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on June 12, 2010, 09:29:37 AM
The best target transformer for this chip is 42Vct to 44Vct. 48Vct is a little hot, and may kill it on AC power line surges. The reason this is fussy is that there is a hard stop on total DC voltage for the LM3886. I always try to not exceed the "Absolute Maximums" voltages on any part I use, and a 48ct tranny could exceed it occasionally. But you might get away with it. You could also stick more diodes in series with the rectifiers into the filter caps to wipe off a few volts too. That's cheaper than a new LM3886.

48Vct just happens to be a very common value. So does 24Vct. You can use TWO 24Vac transformers in series to get 48Vct. Same issues with voltage. Better would be two 20V or 21/22V transformers.

Where to get them? http://apexjr.com/miscellaneous.html#Toroids (http://apexjr.com/miscellaneous.html#Toroids) The Chia Yu toroid is just about perfect for a single channel, but not too good for two of them. the Avel-Lindberg one is on the hot side, but you could use them.

There are many other places to get 48Vct at an amp or two. ApexJr is just one I'm familiar with.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on June 12, 2010, 09:36:10 AM
Blah I just got ahold of a 25.2v CT 2A transformer!
 This should do it, probably the same thing I have here.
  If you have to, you can whip up a different PS for it anyway.
  Very loud like this too, of course 'loud' has more to do with speaker effeciency.
  It's a bit like shovelling dirt, the perfect shovel load is too heavy, takes too long to load up, is hard to carry, spills. Much better off with a medium shovel load, since you can repeat it neatly..the dirt will get moved just as fast or faster than trying to perfect the shovel load, then having to clean up because it keeps spilling.
  IE...gleaning every last drop of possible juice from the amp...I suppose it's possible, but why when a somewhat more conservative application can be set up much more easily, then simply duplicated.
  
  
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: davidallancole on June 12, 2010, 01:49:52 PM
My feeling when reading this is that your not up to snuff on your power supply knowledge.  It can be dangerous working with this kind of stuff.  I suggest doing some reading.  The following links have some info about designing power supplys for amplifiers:

http://sound.westhost.com/power-supplies.htm
http://sound.westhost.com/psu-wiring.htm

As far as safety, you'll have to do some looking around for that.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 13, 2010, 04:09:24 AM
Chia Yu Co Ltd       
Input: 2 X 120Vac 50-60Hz 3" Dia X 1 1/2" Tall    
Output 42Vct 21V- 0 - 21V 80VA



Really, I should get this one?? Will 80VA work?

Cos i'm about to buy it....I wanna wait for reply but,....



wait nevermind. I can't buy from this guy. You have to mail him a check or something.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: head_spaz on June 13, 2010, 06:07:05 AM
Antec (http://www.antekinc.com/gview.php)
Dual 22V @ 200VA
AN-2222   
$29.00

Check out chipamps.com
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 13, 2010, 08:42:45 AM
Antec (http://www.antekinc.com/gview.php)
Dual 22V @ 200VA
AN-2222  
$29.00

Check out chipamps.com


 thanks!@   Now I just gotta learn to use the toroid transformers. I've never seen em.


The current rating is 4.5A. Is that gunna be a problem???


What about this one?
http://www.antekinc.com/details.php?p=50
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 13, 2010, 08:57:54 AM
I mean, when it says Dual 22v, thats the same as center tap right? These toroid transformers are wired all different.

And I'm thinking I might not wanna try to deal with all the heat. I might wanna use a lower voltage.


Anyway, I had a TDA2030 that I took out of an Epiphone studio10 amp I had. It was broken and I tore it up way before I knew how to fix it and along the way I've been taking parts out. The transformer is nice. I got a schem of the amp. All I needed to see was the bipolar supply in a schematic to understand how to biuld this. The transformer is 20v CT but I dunno the current rating. I'm gunna build this up real quick while waiting for the LM3886 (equivelent) to come.

Now I'm now worried about power. Just heat. But I'm also confused about the 10 ohm resistor with the coil. What's that for? What's it do? Why? And in the schem it looks like it's parallel. And it says 'with' 10-12 rolls of wire. I guess it makes sense it'd be rolled around the resistor. It's sposed to be one of them big fat grey ones? Would it be better to use solid copper wire, or stranded, or prebonded?? does it matter?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: slacker on June 13, 2010, 10:08:59 AM
I mean, when it says Dual 22v, thats the same as center tap right?

Dual 22v mean it's got 2 22v secondaries, so you wire them in series to get a 44v secondary, the middle where the 2 are connected together is the centre tap.

Quote
But I'm also confused about the 10 ohm resistor with the coil. What's that for?

The wire coiled round the resistor makes an inductor. The data sheet explains what it's for.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 14, 2010, 04:58:49 AM
... this TDA2030 is WEAK!! And all that heat I had to get rid of for such a small sound? BAH!
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 14, 2010, 05:00:40 AM
And the freakin tab that connects to the heat sink is connected to V-

So I can't use the chassi for the heat sink cos I want the chassi ground
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: stringsthings on June 14, 2010, 06:03:40 AM
... this TDA2030 is WEAK!! And all that heat I had to get rid of for such a small sound? BAH!

are you becoming angry?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 14, 2010, 07:11:26 AM
no I was just surprised at what I got out of the TDA2030. The TDA2003 builds I've done are all louder. Still haven't done a preamp, but still. Not very loud. I'll try rewiring half of my cab to 4 ohms. But the 20v ct transformer is only 500mA.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on June 14, 2010, 07:48:11 AM
  Jesse, Jessy..that's mighty darn messy, what is up your nose that makes it sound essey ?
  Sorry, couldn't resist...
  This inductor smooths output currents AIUit, "Inductor"...google.
  Chipamp...numerous examples of Chipamp 3886's, various power supply approaches, pretty much everything peripheral/related to the chips [that is possible], there.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 14, 2010, 09:10:20 AM
Well I bought the dual 20v toroid at 200VA.

And that chipamp site had some good info.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Nasse on June 14, 2010, 09:24:20 AM
Good take, 24 nominal is not always 24 in reality but more, so there is some safe margin. You can build stereo amp later with that transformer, but I believe it runs bit cooler and more reliable than smaller transformer. Just find good rectifier and caps, I used 50 volt caps on my amp
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on June 14, 2010, 09:38:18 AM
dual 20v toroid a 200VA.
  Can't go wrong there...should turn out really nice !
  Bascially power supply = big, ugly, expensive parts, whatever it takes/whatever does it and works is good.
  Here's my take: Make it, distribute it [Jesse sees it this way too], the re-distribute it...if there's not enough power, make more...if there's not enough amp..make more...when you run out of room for speaker cabinets to extend 1 wall all the way from ceiling to floor, left to right...start on the next !
  ~8ohms, 20 or so watts, makes my speaker about loud.  I used to have troubles connecting my monster amps to anything that'd fully utilize their monstrous outputs...then I started distributing the power in a more 'localized' fashion.
  That's the way I look at these amps. In addition I find blown car stereo bloofer amps to be fine sources of toasty output transistors and new capacitors.   
  The caps are otherwise kind of expensive, iron from an old anything whatever has a transformer [big reciever for instance] makes a great amplifier...pull the PS. Or Pull the output board and install the chipamp right there.
  "those amps may not be worth debugging-rebuilding when it's easier to get higher performance with one of these little chips"/
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on June 14, 2010, 09:48:58 AM
Well I bought the dual 20v toroid a 200VA.
That'll work fine. In fact, you can run *three* LM3886s from it at full power into 8 ohms. An LM3886 can't drive more than about 50W into 8 ohms. It will do t his at about 79% efficiency maximum;  this is a theoretical limit that comes out of the math of class AB amps. So you need on the order of 70-80W for a single LM3886 at full power with a full-swing sine wave. In reality, we don't play non-varying sine waves. We play music which has a loudness which rises and falls. The crest factor is a term for the ratio of peak to average power levels. The crest factor for most pop music is on the order of 20-30%. Even for heavily compressed musical instruments, it's usually not over 60%. So the average power from the transformer is probably more like 30W. A transformer which has a VA (watts is a simplification) rating of equal to the power rating of the power amp will run the amp at a crest factor in excess of what is actually needed.

I did notice something you said about heat sinks. You absolutely, positively must use a decent heat sink with the LM3886. You probably cannot use the chassis for a heat sink and have good performance. This is for two reasons.
1. The LM3886, like all Class AB linear audio amps, dissipates something like 20-40% of the output power as heat when it's being driven. The LM3886 is internally thermally protected - which just means if you don't have a good enough heat sink, it suddenly shuts down as it gets hot. Get a decent heat sink for it if you're going to use it at nearly full power.
2. The LM3886, like most power chips, has the thermal tab/heatsink terminal tied internally to V-. This is a quirk of the semiconductor process where the substrate has to be the most negative voltage. You can't simply bolt the LM3886 to a chassis if you're using a bipolar power supply for it.

Some other comments.
- A power amp has POWER gain, not necessarily much voltage gain. The voltage gain may be very modest and require a preamp to properly drive a speaker to full output. Low voltage gain does not mean it does not have low power gain. Use a preamp. This can be as simple as one opamp.
- the output inductor is to decouple the amp from capacitive loads at high frequencies. Capacitive loads can make a power amp unstable enough to kill itself and its power supply oscillating.
- We want you to keep making music. Go learn about how to wire AC power stuff safely before you start hooking up transformers.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 14, 2010, 09:59:45 AM
Thanks R.G. Seeing a post from R.G. in your thread is like xmas morning to you when you read em.

I'm not really worried about safety. I  mean I am worried about safety, but that's why I'm not worried. I take it seriously.


I'm just worried about noise. Every amp I build, it's the noise that gets me.



I plan on using the 12AU7 preamp I've had in my TDA2003 amp. I like it enough. PRR just drew it up off the top of his head and it worked.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on June 14, 2010, 11:30:26 AM
Thanks R.G. Seeing a post from R.G. in your thread is like xmas morning to you when you read em.
Awww... you made my day!! Thanks!  :icon_biggrin:

Quote
I'm not really worried about safety. I  mean I am worried about safety, but that's why I'm not worried. I take it seriously.
Good! Electrocution never sleeps.

Quote
I'm just worried about noise. Every amp I build, it's the noise that gets me.
Then let's do some preventive measures. I've just been leading a guy through de-humming his AC30 in another forum. Here's your chance to do it right the first time.
Star ground your amp.  This requires you to decide, ahead of time, the one and only one place which will be the One True Ground. The One True Ground cannot be "the chassis". The chassis is big enough that currents can flow through it to different places. The One True Ground must be so small that there is no measurable distance for currents to flow through and interact. Chassis is a shield which happens to be connected to ground. Use it for a conductor and you get hum and noise.
1. The power transformer primary side doesn't connect to the chassis or signal ground at all. You all know this, I just say it for completeness.
2. AC power line safety ground connects to the chassis as a safety measure. This has no bearing on the signal grounding.
3. The PT internal shield is an AC power line thing, and it connects back to the place where the AC power line safety ground connects to chassis.
4. The PT wires go to the rectifiers and DO NOT CONNECT TO THE CHASSIS AT ALL.
5. The rectifier outputs go to the first filter caps and DO NOT CONNECT TO THE CHASSIS AT ALL.
6. The zero-volts connection on the filter caps goes to the One True Ground point with a single wire. This wire must NOT contact the wires from the rectifiers except a the zero-volts point of the filter caps. Anything else will introduce some degree of hum.
7. The One True Ground point connects to the chassis through ONE AND ONLY ONE WIRE. This can be a separate wire, or the One True Ground can be a single bolt onto the chassis. You should be able to remove the one wire to the chassis and read open circuit with a voltmeter between the One True Ground and the chassis. If you can't, you've done something wrong in the wiring.
8. The bushing of one of the input jacks **can** be used as the one wire to the chassis. If that is so, no other connections of signal ground to chassis can be made.
9. The speaker return must NOT connect to chassis at the speaker output. It must return to the filter cap zero-volts point. This keeps the speaker current from flowing in the other wiring and prevents certain instability modes.
10. In theory, every component that has one terminal connected to ground should have a separate wire to the One True Ground. That's possible, but impractically difficult to wire. So group grounds by circuit. The input preamp circuit, for instance, may have its own local ground, then one wire goes to the One True Ground. The tone controls may group their grounds to a local point, and a wire go from there to the One True Ground. It helps in the wiring.

Done properly, star grounding will produce a non-humming and noise resistant setup.




I plan on using the 12AU7 preamp I've had in my TDA2003 amp. I like it enough. PRR just drew it up off the top of his head and it worked.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 20, 2010, 09:17:45 AM
R.G., if the signal in and/or out jacks shouldn't be grounded to the chassi, should I be using plastic or a captive output cable?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 20, 2010, 11:21:05 AM
Hey, I got that toriodal transformer and couldn't wait to mess with it.


So I had the TDA2030 amp on my breadboard and I was powering it with a 20v CT 450ma transformer. I had the power amp on a VCR chassi to heat sink it. It caused hum but it got rid of the heat. So anyway, I hooked up the Toroid dual 20v 200VA transformer and plugged it in...immediately the TDA2030 BLEW UP.

BAH!

Is that transformer just way way too much for TDA2030??? It's the same voltage as the transformer I was using but at either 4 or 12 times the Amps (I think, it says it puts out 5.6A on the antek site).


I hope I don't blow up my LM3886 when I get it. It's not even a real LM3886, it's some equivilent that mouse suggested.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Nasse on June 20, 2010, 01:21:57 PM
I think you got over absolute maximum ratings of tda2030, says +/- 18 volts max Vs, check the datasheets, it is always good to check real voltages with multimeter or something

rectified and smoothed 20 ac volts is something like 28 volts dc...
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 20, 2010, 01:52:38 PM
Yea i realized what i did. I dunno how i messed that up. What a massive mind fart. And a long one too. What a waste of the tda2030. Stupid long wait for the heatsink from jarcar and lm3886 from mouser
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Nasse on June 20, 2010, 02:02:27 PM
Hope you can fix your tda2030 amp, that good old chip is cheap and available, and you just helped it being wanted stuff...

everybody is a real hero who can made a power amp ready and working, and in reliable and safe form
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 20, 2010, 10:34:00 PM
Heh, nah I can't fix it. It was just on the breadboard. As soon as I applied all that power the thing blew up. Like instantainiously. And I really mean BLEW UP. Half of it is somewhere, prolly in a million peices scattered around my room.

I wanna get to work making stuff, but my multimeter broke last week! I can't beleive how impotent I am without one!
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: stringsthings on June 21, 2010, 05:30:26 PM
I wanna build this amp from GGG:

http://www.generalguitargadgets.com/pdf/ggg_lm3886_amp.pdf

But it needs an 18v power source. There's this one:

http://www.generalguitargadgets.com/pdf/ggg_bipolar_ps.pdf


now, how are you going to go about finishing your amp?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on June 21, 2010, 06:57:24 PM
  suggestions:
  Follow a known working diagram, one with explicit and detailed instructions/photos/schematic, etc., followed to the T.
  This generally produces a hum free amplifier, however node counts and extensive cross-DMM-ing the board while comparing it to the schematic.
  Be certain V+ from PS goes to V+ node and nowhere else, same for all grounds, clamp the black lead to ground, test every shiny surface, be sure the schematic allows Gnd. only where marked.
  Every possible node-count cross-check involves most of the settings on the DMM, first and last is to test for non-short across the PS and circuit rails, center ground.
 
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 22, 2010, 05:51:41 AM
Well great. I got this huge expensice clunkin thick heatsink for my LM3886. I'd be ready to start building but...


The freakin heatsink has no way to mount the chip amp!! No screw hole at all! I gotta like, drill my own or something!! Dammit!
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 22, 2010, 05:53:29 AM
DANGIT DANGIT DANGIT DANGIT! I'm so MAD! I never saw this comming! A heatsink without any means to attatch an IC or something??? GRRRRRRRRRRRRRRRRRRRRRRRRRR


Here's the heatsink I bought:

http://www.jaycar.us/productResults.asp?keywords=HH8555&keyform=KEYWORD&SUBMIT.x=23&SUBMIT.y=7 (http://www.jaycar.us/productResults.asp?keywords=HH8555&keyform=KEYWORD&SUBMIT.x=23&SUBMIT.y=7)


(http://www.jaycar.us/products_uploaded/productLarge_6496.jpg)



Is that was "no flange" means?

Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 22, 2010, 05:59:10 AM
I don't suppose a battery powered hand drill or a dremmill will solve this problem/...
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on June 22, 2010, 06:52:17 AM
  Most of these ''brick walls'' have work-around threads at DIY Audio.
  These methods are boiled down, the recipe's make it quicker, less expensive, more compact, less frustrating...totally worth the hours and hours of observations.
  HS Metal is generally soft as far as drilling goes, through bolt and nut is what I'd choose if using the 'TF' suffix chip[s?...that heat sink looks Huge.
  Since it's tricky to mount the chip/heatsink on the same board when they're not pre-fitted, keeping the stress from the pins/solder joints will take some consideration. I ended up populating the board with the 'lighter' parts and the chip, putting the HS on the chip for a pre-fit, removing HS, drill 'precision' holes for dowel/columns to which the HS is connected. Since the dowels are relatively short, warping/contracting amounts probably won't pull on the solders/pins beyond flexing. This was on the amp without the "TF" suffix [insulated body] chips, dry wood is a fair insulator...
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 22, 2010, 11:20:12 AM
Yea, I was gunna use rubber stuff to prop the heat sink up. The circuit board would be hanging horizontaly from the heatink off the chassi like an inch or something. But whatever. I'm at a brick wall here.


I've been posting at diyaudio.com. That's where I found the heatsink. And it arrived without a hole!

You think a dremel or a hand drill would do the job?


Hey could you direct me to one of those work arund threads if you know or kind find one off the top of your head? heh.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on June 22, 2010, 02:27:25 PM
  They go in depth with layout/schematics/pictures...for various topologies.
  First, find a FWR/capacitor smoothing that fits your needs, then measure the DC voltage that it converts from AC.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on June 22, 2010, 02:43:48 PM
You think a dremel or a hand drill would do the job?
  Dremel's kinda fast, but if the bit's sharp, should go right through, hand-drill too...careful with the smaller bits cause they break easy.
  As far as power supplies, FWR's have arrows, they point 'up' toward + [that's how I remember it, some schematics show them differently]...the secondary connects [AC has no polarity].
 Anyway lets say you get a volt of DC from each FWR/capacitor smoothing...this is still floating voltage, it works like this, and/or can be assigned to a voltage [like Gnd.].
 I think what you want has "Gnd." as a center voltage, between the _ and + power rails. This can be created by connecting the two floating voltages, one providing a + and one providing a - at this connection makes rails twice the voltage, with a center point. Still floating voltages though, none of the nodes have been assigned to a voltage, take the +/- node [the center tap] and assign it to 'Gnd.' or 1/2v or whatever it is they're notating/calling it.
  Get the volt meter out [actually should be testing each and every move like the 12 days of christmas, get the the Partridge in the Pear tree and sign it again !]...volt meter should be finding a _ potential and a + potential from the center tap.
  The data sheet shows these power supply nodes a Vcc+ and Vcc- or V+ and V-, and shows the pin assignments to which these voltages connect to the chip.
  Before you apply the power test for non-shorted conditions everywhere except where there are 'commons'...ie 'they're supposed to be connected'.
  There's a sticky thread IIRC about power supplies, also threading through the Chipamp forum may show additional power supply information, the basic power supply formations don't really change much, but the filtering./voltages and wiring styles may.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on June 22, 2010, 02:50:37 PM
DANGIT DANGIT DANGIT DANGIT! I'm so MAD! I never saw this comming! A heatsink without any means to attatch an IC or something??? GRRRRRRRRRRRRRRRRRRRRRRRRRR
...
Here's the heatsink I bought: Is that was "no flange" means?

Easy, easy. Welcome to home audio building 101.

Of all the heatsink styles, that one is my **preferred** one. If your heatsink has flanges, you're largely stuck with what they wanted you to do.

First off, you'll probably want to put that on the back side of the metal box you'll be putting your amplifier into. So do it the easy way. Figure out where you want the heat sink to go, leaving the fins running vertically, on the back of the box. Leave room to get your speaker jack, AC power cord, fuse holder, etc on the box too. When you figure out where you want it to go, draw the outline of the heat sink on the box. We'll come back to that.

But next, we figure out how the IC will fit on the heat sink. Fortunately the manufacturer has done this for you. The LM3886 mounts with a single screw.

You figure out where you want it to go on that heat sink on the flat side. Then you scribe the inside of the mounting hole with a sharp pencil, remove the IC, and drill a hole where the marks are. Ideally, you will drill a tapping sized hole and tap the hole so the mounting screw will go right into the heat sink's flat back, and no nuts or washers will be needed. If you can't do that, drill a clearance hole for the IC, **being sure that the other side of the hole comes out in the middle between fins**. This lets you get a nut on the back side to hold it.

A tap wrench seems like an advanced technique, but I love them. You have to be careful tapping into aluminum, using oil in the hole and being very careful not to bend the tap, or they will break off. But what you get is a custom mounting.

When you've figured out where the IC bolts to the heat sink, you cut a big opening in the back of the box where the heat sink will attach exposing the heat sink when it's bolted to the box. With the opening in the box in place, drill mounting holes for the heat sink through the back of the box and into the heat sink. Again, either drill them tapping hole sized, or if you drill through-holes, make sure the holes come out between fins so you can get nuts on them.

What's left is mounting the electronics. There are two ways to do this, parallel to the flat back of the heat sink, or perpendicular to it. I personally like to mount the PCB parallel to the heat sink, and put it where the power IC or power transistors can have their leads bent up to come into the PCB from the bottom. This lets me mount the PCB on the heatsink on spacers (again, there's that drill-and-tap thing!)

If you want to mount the PCB perpendicular to the flat back of the heat sink, is there a hardware store near you? Do they stock aluminum "L" angle stock? This is a stick of aluminum with a cross section like an "L" with equal legs. Around here, it's as common as a bin of screws. Get a section of L angle stock, perhaps 18mmx18mm and 3mm thick. This stuff cuts with a hacksaw like butter, so you can make little L brackets with holes which will attach to the back of the heat sink with ... yep, drilled and tapped holes into the heat sink.

Trust me, this is so much better than running wires to a heat sink with other attachment methods that it's not even close.

Questions? I can probably find pictures on the net somewhere.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 23, 2010, 12:21:08 AM
Ah I can see why you like these type of "blank canvas" heat sinks. I really got ripped off. I paid 20 bucks for this thing!  I guess I'll head down to Lowes or Home Depot tomorrow to try and get the tools for this.



Anyways, R.G. I can understand what you're saying, but pictures would be even better if you wouldn't mind. Since the heatsink will cunduct the V-, I gotta insulate it. Or someone suggested I mount the chip amp with a thermal pad. On my old Epiphone S10 amp that I took apart, when i took the TDA2030 off, there was a layer of stuff. I thought it was like thermal paste that had hardened or something. It looked like old duct tape residue. Anyways, I gotta get some sorta thermal pad for this thing too, so it doesn't conduct.

Title: Re: 18V bipolar power supply for LM3886 amp
Post by: stringsthings on June 23, 2010, 01:26:48 AM
.... I really got ripped off. I paid 20 bucks for this thing!  ....

how did you get ripped off?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on June 23, 2010, 07:29:45 AM
cheap heatsinks:

http://www.surplussales.com/Heatsinks/HeatSink6.html
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on June 23, 2010, 10:00:38 AM
http://www.surplussales.com/Heatsinks/HeatSink6.html
Just to help your composure a bit: First of all, the "$20" you mention corresponds to Australian currency, near as I can guess. The Jaycar price in US dollars is $10. The surplus sales heat sinks are all in US$.  That cuts the difference a lot. Correct me if I'm wrong about you paying in AUD$. It's a guess.

Then there's size. Your heat sink is very close to what I'd pick myself. It's a very good heat sink for an amplifier, being 150mm (abt 6") by 75 (abt 3") by 46mm (abt 1.8") and with a thermal resistance of 0.78 C/W.  The closest heat sink in the SSN list is (HSK) HSIFES50295, 4-9/16" x 2-3/8" x 15/16"H. This is notably smaller, and will not be as good thermally. And it costs US$6.00.

You didn't do badly at all on buying the heat sink.

As for insulation, if you can find Kapton polyimide tape in 20mm or wider sizes, that's ideal for an insulating wafer. You'll want to clean off any adhesive and replace it with heat sink goop. Try a motor or alternator rewinding shop. They likely have small scraps of kapton they'll give you. Don't use other kinds of generic tape. If you can find a silicon rubber insulating wafer, that's even better - no goop to mess with. And a shoulder washer in the mounting hole insulates the (single!) screw from the LM3886 metal tab.

I know this looks like a huge hill at the moment, but trust me - it's a small bump in the road.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 11, 2010, 03:57:36 AM
I went ahead and drilled the hole with ym hand rill. It worked great, and I used a bolt and nut insrtead of a screw. No insulating so the heatsink conduct 28- v. But I jsut wanted to build the circuit already and see if it worked. SO I built the amp Point to point cos the chip didn't fit in perf board. It went alright, but I couldn't use the mute switch cos there was no room. Anyway it sounds great but it's too quiet. It's not as loud as my TDA2003 amp running at +12vDC!

I took measurements and the thing is measuring 28-vDC and 28+vDC. But it's almost half as quiet as my TDA2003 amp which is sposed to only be putting out 8-12 watts. The LM3886 sounds like it's only doing like 5. I'm running it through four 4 ohm speakers. Two pairs wired in series then in parallel to get a 4 ohm load. I dunno what's wrong. The chip isn't even getting hot. It's like i did't even need to use the freakin heatsink. I thought this big honking transformer would make the chip go crazy.




Here:

(http://i633.photobucket.com/albums/uu56/el_heisenberg/LM3886tube-1.gif)

I'll post a pic of the circuit tomorrow I guess.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 11, 2010, 05:28:33 AM
I replaced the 10k trimmer with a 100k pot and it's way louder. I think I can get it louder. THe chip is hot too. But with this heatsnk it could handle way way more. I'll see how loud I can get it before it starts sputtering out. Now I gotta get rid of the hum that's in the preamp stage now that I'm amplifying it so much.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: stringsthings on July 11, 2010, 09:02:12 AM
I went ahead and drilled the hole with ym hand rill. It worked great, and I used a bolt and nut insrtead of a screw. No insulating so the heatsink conduct 28- v. But I jsut wanted to build the circuit already and see if it worked. SO I built the amp Point to point cos the chip didn't fit in perf board. It went alright, but I couldn't use the mute switch cos there was no room. Anyway it sounds great but it's too quiet. It's not as loud as my TDA2003 amp running at +12vDC!

I took measurements and the thing is measuring 28-vDC and 28+vDC. But it's almost half as quiet as my TDA2003 amp which is sposed to only be putting out 8-12 watts. The LM3886 sounds like it's only doing like 5. I'm running it through four 4 ohm speakers. Two pairs wired in series then in parallel to get a 4 ohm load. I dunno what's wrong. The chip isn't even getting hot. It's like i did't even need to use the freakin heatsink. I thought this big honking transformer would make the chip go crazy.


I don't mean to offend you ... but do you have trouble spelling words ? .... or are you spelling words wrong for a purpose ?  ???
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on July 11, 2010, 10:13:48 AM
I took measurements and the thing is measuring 28-vDC and 28+vDC. But it's almost half as quiet as my TDA2003 amp which is sposed to only be putting out 8-12 watts. The LM3886 sounds like it's only doing like 5. I'm running it through four 4 ohm speakers. Two pairs wired in series then in parallel to get a 4 ohm load. I dunno what's wrong. The chip isn't even getting hot. It's like i did't even need to use the freakin heatsink. I thought this big honking transformer would make the chip go crazy.
I replaced the 10k trimmer with a 100k pot and it's way louder. I think I can get it louder. THe chip is hot too. But with this heatsnk it could handle way way more. I'll see how loud I can get it before it starts sputtering out. Now I gotta get rid of the hum that's in the preamp stage now that I'm amplifying it so much.
I have a couple of suggestions now that I know where you're going.
 - The only reason to have that 12V regulator there is to keep the 12V supply to the preamp quiet. The original preamp circuit may have used 12V, but the tubes will happily work up to a few hundred. +18Vdc and +28Vdc will work fine for the tubes if you can keep it quiet. To uncomplicate your circuit, you could ditch the 12V reg and put in a stage or two of 1K/100uF RC filtering on the power going to the tubes.

- alternatively, you could  run the tube plates from +28Vdc and some RC filtering sections, leave the 12Vdc regulator, and run the tube filament/heaters from 12Vdc and eliminate a lot of hum (potentially). As the circuit sits, I'm concerned about the hum you're getting from the way the heaters are wired.

- It would be good to use a 1M pot for the volume pot and then buffer this for use in the power amp. The volume was low because the 10K volume pot was loading down the plate of the second tube section, as you found out. This buffer could have a gain of one, or could even add some gain to drive the power amp to full output.

- As it's set up now, the power amp has a nominal gain of 34 (1+33K/1K), and it's going to drive the output pin to maybe 24Vdc before clipping with +/-28V supplies. The nominal output power will be 24V/1.414 = 17Vrms, and the power about P= (17*17)/8 = 36Wrms into eight ohms. That will be loud. To get there you have to drive it with 24Vpk/34 = 0.705V peak or 0.5Vrms of preamp signal. This 0.5Vrms from the preamp must not load the preamp down in getting it.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Brymus on July 11, 2010, 05:27:52 PM
I give you kudos for sticking it out  :icon_cool:
How about some pics when you get a chance ?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 11, 2010, 09:29:37 PM
I went ahead and drilled the hole with ym hand rill. It worked great, and I used a bolt and nut insrtead of a screw. No insulating so the heatsink conduct 28- v. But I jsut wanted to build the circuit already and see if it worked. SO I built the amp Point to point cos the chip didn't fit in perf board. It went alright, but I couldn't use the mute switch cos there was no room. Anyway it sounds great but it's too quiet. It's not as loud as my TDA2003 amp running at +12vDC!

I took measurements and the thing is measuring 28-vDC and 28+vDC. But it's almost half as quiet as my TDA2003 amp which is sposed to only be putting out 8-12 watts. The LM3886 sounds like it's only doing like 5. I'm running it through four 4 ohm speakers. Two pairs wired in series then in parallel to get a 4 ohm load. I dunno what's wrong. The chip isn't even getting hot. It's like i did't even need to use the freakin heatsink. I thought this big honking transformer would make the chip go crazy.


I don't mean to offend you ... but do you have trouble spelling words ? .... or are you spelling words wrong for a purpose ?  ???

What do you mean you're not trying to offend me? You could've just jumped to your own conclusion and let it be. But nah, I just type real fast I guess. It was late, and I was tired, and I do have several chemical vices.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: PRR on July 11, 2010, 09:33:36 PM
Congrats on getting the 3886 working.

What R.G. said. Or IOW....

I do not understand the tube heater wiring.

It looks like you'll have 4V heat on the 6V heater connection. It sure won't be happy that way.

It looks like you have monster common-mode ripple on your heater leads (very close to sensitive audio leads).

I do not see how you can be getting even 10V DC at the input to the "+12V DC" system.

The tube plates sure will love 28V DC.

Tubes do not need regulated power.

The 100K-250K resistors in the tube and tone-stack will NOT drive a 10K pot well.

I do not think you need a volume control between tone-stack and '3886.

The under-volted heaters will reduce tube gain severely. The 10K load throws-away another 10:1 gain. Input sensitivity could be over 140mV; hard work. Between under-heating, likely low B+ (lower even than 12V which is already pathetic), and serious 10K loading, the preamp probably can't hit the '3886 strong enough to make it work hard, even half-hard.

As R.G. said, take 1K and 100uFd from +28 to the tube B+ line.

Throw-away the 6V rectifier and regulator. Take 6VAC direct from transformer, through leads tight-twisted right up to the tube socket. No 8 ohm resistor. (-OR- use a dedicated 9VDC wallwart WITH the 8 ohm resistor.)

Throw-away the 10K pot. Add 470K from '3886 input to '3886 ground (mostly to hold it if you disconnect the preamp). Connect '3886 input to treble pot wiper. There is an issue here: the pot will scratch and there will be part-Volt DC offset through to the speaker. But it will work a whole lot better, maybe no problem.

Input sensitivity in this configuration should be near 4mV, plenty for any non-thrash work.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 11, 2010, 09:35:54 PM
Gunna post a pic later tonight. I had mounted the 100uf cap backwards!!


I didn't want to run the filaments off the 12v regulator cos I wanted the big glow, but if that's what it comes down to i'll do it. I was already planning on fiddling with the anode supply voltages but I was just stumped that the amp was so quiet.


RG...um what kind of a buffer?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 11, 2010, 09:37:41 PM
Ok wutever RG and PRR says I'm doin.  :)
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 11, 2010, 10:08:24 PM
PRR, when I just connect pin 9 and pins 4 and 5 to the ac rails, I measure 13.2v AC when I measure pins 4 and 5 to pin 9. With the resistor it measures 12.6v, or 6.3v depending on how I take the measurement.


Actually, with the transformer I'm using now, it's only 1.2A. And I'm getting different measurements. So instead of the 8 ohm resistor, I'm using a 2.2 ohm resistor, and it gets me 12.1vAC from 4,5 to 9....or was I supposed to get 6.3 from 4,5 to pin 9...I can't remember...maybe that's why I used the 8 ohm. I actually didn't have an 8 ohm resistor, I settles on three 2.2 ohms in series.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: PRR on July 11, 2010, 10:17:50 PM
> I didn't want to run the filaments off the 12v regulator cos I wanted the big glow

The heaters MUST be fed the RIGHT voltage.

A 12AX7 heater can be wired two ways. For 6.3V (5.7V-6.9V) or for 12.6V (11.4V-13.8V). Under-volt a little, the amp sucks. Over-volt a little, and it will work OK for hundreds of hours rather than thousands of hours. Yes, people do go outside the specified ranges. But get it working first, then play games.

> wutever RG and PRR says I'm doin.

There's differences. Pick one.

R.G. suggested changing the 10K to 1Meg followed by a buffer. This is Good Design. Buffer could be TL071 etc.... but there's no elegant way to power it here. A JFET would be dandy, but it needs a resistor and a cap and a resistor and it is way too humid here tonight to be doing drawings.

I say you do not "need" a gain trim here (there's one after the first triode). And that you "can" connect '3886 input to the treble pot wiper.

My plan is cheap-trick. The tone-stack has zero to 510K of DC resistance. The '3886 has 0.2uA-1uA input current. There could be up to a half-Volt of induced DC (but typically 0.1V DC). The '3886 is wired with a cap in the NFB loop, so input DC is passed to the output with unity gain. Half-Volt of DC will not annoy any loudspeaker suitable for 50 Watts of Guitar. It will "work". You will be able to HEAR yourself without arm-sweat, and you will be able to diagnose the hum issues.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 11, 2010, 10:22:03 PM
Yes, I already ditched the volume pot.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 12, 2010, 12:37:53 AM
This helped marginally with the hum::



(http://i633.photobucket.com/albums/uu56/el_heisenberg/LM3886tube-3.gif)



















Maybe I should do two stages of those? Or maybe different values? That's all I had on hand. I can make trips to the shack or go tearing up some VCRs tho... I GOTTA get this thing done!


This amp is loud enough to play with a drummer. I GOTTA finish it!!

Also, it's on the breadboard so that may be causing some hum. The pot shells aren't grounded either. When I touch them I get a big hum.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 12, 2010, 12:57:51 AM
HAHAHAH! This amp is rediculously loud!
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 12, 2010, 07:01:28 AM
Hey, why not run the tube plates with 56v???


The 1k resistor and 2200 uf cap got rid of alot of noise. I think wutever noise I was getting from the plates is taken care of now. But I don't know, maybe different values will get rid of more noise. The amp is usable now at least. But the hum is still really present. I think it's comming from somewhere else. If I turn the volume pot of the first tube stage all the way down, I still get the same amount of noise. If I ground the input of the amp, it's totally totally silent.  ??? ???

I kinda think I might want a second volume control before the power amp cos the tube preamp sounds different with the volume low.



(http://i633.photobucket.com/albums/uu56/el_heisenberg/LM3886tube-5.gif)


any problemos here?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 12, 2010, 11:28:26 AM
nevermind. trying to run the tubes at 56vDC and still have bipolar supply to the amp was a dumb idea.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: PRR on July 12, 2010, 04:26:32 PM
> it's on the breadboard so that may be causing some hum. The pot shells aren't grounded either

A decent gitar amp has enough raw gain to pick up ALL the hum in the room.

You breadboard to get it working. Yes, this should be a LOUD amp.

Ass-ume most hum now is wide-open hay-wiring. When 90% "done", you will move it inside a low-hum room: a metal chassis. With input far from output and farther from power supply. With effective grounding. I suggest you hard-ground the input jack, buss along the stages and pots to the speaker-common isolated from chassis, then on to the power supply which is not tied to chassis. Your wall-cord ground wire does go to chassis.

> 1k resistor and 2200 uf cap

That's the 30-pound hammer. Use a 2-stage filter. The tube stages pull about 0.25mA, it would be reasonable to allow 10% drop in voltage for 99% drop in hum. Rounding, this is two 5K (4K7) resistors and a couple 10uFd-100uFd 35V caps.

Aside from lower cap-cost, the several-stage filter does a far better job of reducing the high harmonics of 120Hz ripple.

> the tube preamp sounds different with the volume low.

Then go back to the level pot shown on '3886 app-sheet but make it 250K or 500K.

Does the treble-pot "scratch"? The DC input current of the '3886 is "poor design", but 1uA bias won't hurt the pot, and any "scratch" may be mild.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 12, 2010, 07:15:55 PM
???? So the only part of the entire circuit that is grounded to the chassi is the input jack????  

Sorry If I'm misreading  or something.

I was going to tie the power supplys ground lead to the chassis earth post along with the power cord ground.  I also heard it was good to attatch the speakers ground close to the bridge rectifier.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on July 12, 2010, 07:36:07 PM
  that site...
  About the grounds...can't beat reads on grounds for ground questions.
  There are so many it gets confusing.
  Speaker AC currents through the ground wire put a signal through the wire [outside it too but don't run the input wire along it and it won't make a 'transformer = inductance of two wires run along each other]...sensative wires get sensative 'real estate', heavy load wires get their own 'sewer pipe' to the 'dump'.
  A star ground system is nice for proto-work, otherwise if you can figure out how to save copper with X Y Q or K layouts [pretty much would have to design the amp with copper savings up on the priority list, knowing how by trying layouts]...or read about what you can ''get away'' with. Usually the input jack and input volume [example] can share the same ground wire...small currents of same source.
  Other shared grounds may or may not introduce noise, Starring them of course is a good starting point since it's generally low noise regardless, there may be caveat/arguements about lowest possible noise.
  I think the best way to figure out the 'trick' grounding is to read and make 1/2 trick, or for full tricking [least copper, quickest const.]:
  Have a control amp handy that is very stable and low noise.
  Try to beat or cheat it.
  Beat: increase of stability or trick a drop in the noise floor.
  Cheat: less copper/wires and still stable/low noise.
  Sometimes it's 'that wierd stuff' [instability] that you don't even really know is there that's hardest to get rid of.
  Sometimes 'mixed sewage' [from star ground..a long wire..ground Y like input common Gnd. to jack and input volume control] or sometimes everyting to do with a tube stage grounding] doesn't send a pulse/signal ''back-up the ground line'', sometimes it does.
 
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 12, 2010, 07:51:25 PM
PRR, just fired it up. The treble pot is not scratchy. The volume pot after the first triode hums and bumps loudy when I use it. Whenever I touch it it goes "WUUUUM". But it doesn't scratch when I turn it. Still got other noise too.

petemoore, the sites pages that you directed me to are where I'm raising my questions from. I read up all I could before I even attatched the chip to the heatsink. I thought I was stuck so I just read up and then sat around for 2 weeks.

I still gotta get a silicon or rubber washer and a thermal pad or something.


(http://i633.photobucket.com/albums/uu56/el_heisenberg/LM3886tube-8.gif)
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 14, 2010, 01:01:44 AM
Ugh drove to 3 radioshacks today looking for a product. Their website says it's stocked in the stores, but they're wrong! Looks like I ain't the only one liftin stuff from the shack.

But I finally found ONE heatsink mounting kit they have for TO-220. So i got a mica washer and a thin little clear slip. The chip is wider than the slip tho, but the metal part runs down the middle and it SORTA lines up. The top could still make contact tho. But I decided to try it anyway cos I have nothing else and it can't hurt. The heatsink measures 0 volts. Tomorrow I'm gunna find a second one. It'll be a long drive in the hot hot sun. I just wanna have a second one and cut it up and stick it there to be safe. I forgot to put thermal paste too. It's not conducting as well. The chip gets hot at full power and doesn't radiate the heat away to the heatsink as well with the insulating slip. Hope that's just cos no paste. Once I get that done I'm gunna bolt the heatsink to the chassi. I dunno what I'm doing. I'm just guna drill pilot holes, then get a screw and hope it goes in. What I REALLY wanna do is just put electrical tape all over the heatsink and use rubber feet and stuff to keep the keatsink from touching the chassi. Seems harder and easier to do at the same time.


(http://i633.photobucket.com/albums/uu56/el_heisenberg/securedownload.jpg)
nice thumb shot
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 15, 2010, 11:53:42 PM
(http://i633.photobucket.com/albums/uu56/el_heisenberg/photo-1.jpg)
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Brymus on July 16, 2010, 01:49:36 AM
Looks cool, how does it sound aside from being loud ?
Thats the preamp PRR designed right ?
Radio Shack has the thermal grease too,kinda pricey but you dont need alot.
I did the same as you at first ,bought two TO220 mounting kits and cut the mica from one to fill in the gap from the first.
I later bought some real mica sheets from All Electronics,as well as getting some what look like vinyl insulators from the supplier I bought my LM3886 chips from,he says they are for insulating them but they look like flat ribbon cable without wire in them.
I didnt get any further as I wanted to perfect my tube preamp, then got caught up in other projects  :icon_rolleyes:
If I were to do it over again I would spend the extra couple of dollars and get the LM3886T which doesnt need insulators.
I have since bought a toriod capable of driving two 3886's in bridge formation to get a true 100 watts but still other stuff keeps taking my time.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 16, 2010, 01:57:28 AM
Welll I have pictures of the enlosure before and after. I was going to come on here and post them all along with a long post on the problems.


There is still hum dammit. I orginally had two plastic jacks. But either the two I was using from an older amp were broken, or they just didn't work....there....I think they were broken. I put in a metal one and the amp worked but there was hum. I covered both sides of the hole with duct tape, making sure to get the inside rim. The hum went down. I can now turn down the preamp volume and get total silence. So the amp section is quiet. There's still hum from the preamp.

Another strange thing. I've tried two different tubes in. One of them would flash really brightly when I flipped the on switch. It was startling.

I'll post pics tonight and everything with the wiring. I star grounded. I used the guidelines from RGs article and his advice in this post. I'm gunna try to switch with the jacks. Put the metal one at the input. I still haven't measured the filaments either.

The chip is insulated tho. It works. But if I woulda known that the LM3886T didn't need that I woulda just gotten that!!

The hum comes when I turn the bass knob up. With the treble all the way up and the mid and bass all the way down there's only slight hum. Also there's hum when you turn the volume down. There's the least hum with the volume all the way up.


Aside from that I really like it. I like the way it sounds with just the treble knob on 10. It'd be nice to be able to use it other ways. But it's just the PERFECT volume to play drums with. I'm so happy with it. If only I can get this hum out. The hum isn't a big issue on the setting I keep it on. But with the mid or bass up it get's bad.

Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 16, 2010, 07:11:24 AM
here. I made the schem show how I grouped the grounds together and head of the ground symbols is a wire to a long screw and a nut I put in. The mains earth wire is at a different point.

I tried to follow everything everyone's said here and everything here::

http://www.geofex.com/Article_Folders/stargnd/stargnd.htm

but I'm still getting hum. The noise is from the tube preamp cos it only happens after the filaments heat up. Originally I had a wire going from the speaker return to the 0v point at the capacitor leads. After putting this wire to the star ground the hum from turning down the volume went away. But I'm still getting hum from bass and mid control. A tiny amount and some other negligable noise with the treb at full.



When I put my hand near the tube or cup it, the noise is totally gone. ???

Oh wait, I see.  I need a tube sheild to stop this don't I??? Oh man. OOOOOOh MAan. Just when I thought I was done! Arrrgh AAAArgh! I was celebrating.




(http://i633.photobucket.com/albums/uu56/el_heisenberg/LM3886tube-12.gif)
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 16, 2010, 08:34:38 AM
The chassis is a VCR/DVD player. The bottom of it anyway. I put wood sides on it. Spray painted it black. Then mounted the transformers and the tube socket. THe transformers were heavy so I put a peice of wood so didn't buckle and look odd. I used those I dunno what you call em. Terminal strips or something. I used some euro style terminals for the captive mains cable cause I didn't want to cut out a hole for an IEC socket. And I didn't wanna find an IEC socket either.

I'm not real big on planning. So all my builds turn out messy. Don't laugh. I'm working with junk! But please point out everything I did wrong!

I couldn't bolt the heatsink to the enclosure. I ended up drilling a hole through one of the fins and putting a screw the the metal lip through the wood and into the fin. It's stuck there. You can see it in one of the pics

the extra pot is for a digital reverb with the belton reverb brick I'm gunna put in.

(http://i633.photobucket.com/albums/uu56/el_heisenberg/DSC00510.jpg)




(http://i633.photobucket.com/albums/uu56/el_heisenberg/DSC00509-1.jpg)





(http://i633.photobucket.com/albums/uu56/el_heisenberg/DSC00513.jpg)



(http://i633.photobucket.com/albums/uu56/el_heisenberg/DSC00522.jpg)



(http://i633.photobucket.com/albums/uu56/el_heisenberg/DSC00520.jpg)



(http://i633.photobucket.com/albums/uu56/el_heisenberg/DSC00523.jpg)




(http://i633.photobucket.com/albums/uu56/el_heisenberg/DSC00515.jpg)



(http://i633.photobucket.com/albums/uu56/el_heisenberg/DSC00519.jpg)




Guess now I gotta find a tube shield. And a label maker. I ain't using my usual white-out pen for this thing.


I hope the tube shield fixes everything. Thanks everyone who helped me and were so patient with me. Thank you. This thing ROCKS, if it were without hum...







UPDATE: I wrapped the tube in tin foil. Ugly. Can't see the glow :(.

Got rid of ALOT of the hum. Still some when I turn the bass up... dunno why.


But it's ALOT better now. ALOT better. Dammit are there tube shields with slits so you can see the glow? And what's the remaining hum comming from?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on July 16, 2010, 09:30:26 AM
  A good preamp has a sensative input, the layout on the breadboard...I'd say there'd have to be a problem somewhere if it didn't hum ;).
  Electronic artwork !
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Brymus on July 16, 2010, 10:01:19 AM
Thats pretty cool looking for what you had to work with.
If I were to guess,I would say your wiring>you have alot of wires running to and fro.
That transformer for your heaters puts out a pretty good flux field,proximity of spkr jack.
Also you could use shielded wire to your input grid.
Search gain clone amps,thats basically what yours is and look at the layouts of others for ideas.
Maybe PRR or someone can give you better detailed advice on your layout.
Congrats its almost done.

I will listen to the sound clips you sent me after the baby wakes up  :icon_cool:
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on July 16, 2010, 10:09:33 AM
@El: Let me interject another calming note.

Tube amps are notorious for having some residual hum. One probably apocryphal tale has it that Bob Carver accepted a challenge to make one  of his power amps sound indistinguishable from a tube power amp, and did it by carefully analyzing and reproducing the frequency response and damping of the comparison tube amp, and then introducing just a touch of residual hum. He supposedly won the bet.

I've just recently spent several weeks in an ongoing advice/debug set of posts with a fellow over the hum in a factory-made AC30 in another forum.

De-humming a tube amp (yours qualifies because most hum comes from power supplies and preamps, not the power amp) is like the old analogy of peeling an onion. You take off a layer or two at a time, go to the next layer, and cry a lot. Don't lose heart because you still have some layers to go.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 16, 2010, 10:51:20 PM
I will try moving the output jack and using shielded wire for the input. As of now, the tin foil tube shield is keeping out a TON of noise. take it off and it goes 'BRMUUUUUUHHHHHHHHHH!".  As for wiring, I did use more than I would normally, but I read to use seperate wires for this and that. If I woulda just done it, I would have tied all grounds right to the capacitor 0v lead. I would have put the capacitors right onto the bridge rectifier instead of using seperate wires. I don't want to know what it'd be like if I'd have done it like that tho.

But all the wires going everywhere are really ground wires. If I had more than one color wire I'd be easier to tell. I thought it wouldn't matter where I put ground wires since they'd be going to the star ground. I tried to keep the other connections short.

The only noise I get is from turning the bass up past 8 o clock. at 9 or 10 o clock it gets big. The md knob doesn't put in too much anymore.


With this noise it's still very usable and cool. But it'd be way way cooler if it were really quiet.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: phector2004 on July 16, 2010, 11:01:27 PM
that's a really cool VCR amp!

just a thought, maybe the gurus can comment on this: I accidentally bought 2-conductor shielded wire. could something like this further reduce hum by shielding the heater wires, wires going to the switch, etc? (any significant amount more than just braiding, at least?)
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 16, 2010, 11:10:20 PM
HEY! Do these spring things act just like tube shields??!?  I think I could just make something sorta like those.

(http://www.beavisaudio.com/techpages/Vox_Night_Train_Disassembly/Misc_1.jpg)
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 16, 2010, 11:12:17 PM

just a thought, maybe the gurus can comment on this: I accidentally bought 2-conductor shielded wire. could something like this further reduce hum by shielding the heater wires, wires going to the switch, etc? (any significant amount more than just braiding, at least?)


Yea and I was kinda wondering if were I put the twisted AC heater wires was ok or not.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 18, 2010, 02:22:27 AM
All the thin red wire you see in the pics is solid copper. Should I have used the braided wire?????

It was all I had on hand and I didn't wanna spend money on wire.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 18, 2010, 10:32:13 AM
I think I'm kicking a dead horse here. Maybe the tube preamp is so sensitive, it's jsut picking up crazy hum when the bass is turned up and especially when the mid is turned up with the bass. Other than that, I'm at full blast and all I have is some weird intermitent hissing. It's surprisingly quiet for how loud it is. This is a nice chip. I wonder if I really shoulda got a hotter transformer to make it really loud. Maybe I'll do that later.

But yea the dead horse...When I turn the volume control down the hum goes away completely (with the tin foil tube shield). I tried shielding every signal wire in that area. And there was no differece. PRR originally gave me his drawing with a 250k volume pot. I put in in a 1 M every time I built it cos I liked the extra volume. It was never an issue until I was amplifying the preamp so much!!! So I'm letting it be. Everyone said hum is just part of a tube amp. And it's not that loud. I'd like to hear the hum on a real tube amp. I just don't feel like going to guitar stored and plugging guitars in and not really playing anything.

I added my digital reverb circuit in all neatly. I did it with another little 12.6v 300mA transformer and a 12v reg. Now the thing sounds amazing. I wanted to use a DPDT switch to change the tonestack to the Umble type that I saw on runoffgroove.com. I thought it should work. I thought I did everything right but I couldn't get it to work. I'm prolly just real tired from messing with it all. Yea see I'm rambling.





Tho, i'd really like to know if those spring thingies pictured above shield the tubes like a normal tube cover or if they're just there cos of just because because.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on July 18, 2010, 12:14:20 PM
I think I'm kicking a dead horse here. Maybe the tube preamp is so sensitive, it's jsut picking up crazy hum when the bass is turned up and especially when the mid is turned up with the bass.
People who have only done solid state are usually astonished at the hum pickup abilities of tube equipment. This is partly because tubes work at (in general) much higher impedances, and are prone to capacitive pickup, and partly because tube circuits come from a time when modern techniques for power supply immunity were not used.  That LM3886 you're using pretty much does not care if there is a few volts of ripple on its power supply as long as its ground is clean.

Quote
Other than that, I'm at full blast and all I have is some weird intermitent hissing.

That would be parasitic oscillation being kicked off. Capacitive feedback is getting something going. An "angry" sounding hiss in audio is often the symptom of RF oscillation back-modulating the audio path. Thermal hiss is more polite sounding.  :icon_biggrin:

Quote
It's surprisingly quiet for how loud it is. This is a nice chip. I wonder if I really shoulda got a hotter transformer to make it really loud. Maybe I'll do that later.
You will be surprised how little going from where you are to the highest power supply voltage you can put on that chip helps with loudness. You're well out of the region where small power increases make the speakers sound much louder. It will, for instance, take ten times the amplifier power to make the perceived volume be twice as loud.

Quote
But yea the dead horse...When I turn the volume control down the hum goes away completely (with the tin foil tube shield).
And this tells us that the hum is being picked up and passed on before the volume control, right?

Quote
I tried shielding every signal wire in that area. And there was no differece. PRR originally gave me his drawing with a 250k volume pot. I put in in a 1 M every time I built it cos I liked the extra volume. It was never an issue until I was amplifying the preamp so much!!! So I'm letting it be. Everyone said hum is just part of a tube amp.

Hum is an ever-present threat. It is possible to get an almost hum-free tube amp. But you have to not only know what you're doing, you have to work hard at it. There are many ways for hum to get in.
Quote
I'd like to hear the hum on a real tube amp. I just don't feel like going to guitar stored and plugging guitars in and not really playing anything.

Why not? I'm sure the store people would love someone who just wants to audition hum and hiss levels instead of yet another rendition of "Stairway to Heaven".

Quote
Tho, i'd really like to know if those spring thingies pictured above shield the tubes like a normal tube cover or if they're just there cos of just because because.
They're there to hold the tubes firmly in place. Retainers. No significant shielding.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 18, 2010, 09:27:42 PM
Ah cool. Thanks, R.G.!

Looks like I'm done!! There's still hum at the input even when nothing is plugged in. I'll try disconnecting stuff and see where it goes. I still don't know enough to get rid of it. I think I'll come back later and be able to fix it.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 19, 2010, 01:18:04 AM
Eh, one more question. Would using a 12.6v 3A transformer for the tube filaments be better than using a 12.6v 1.2A transformer? I have both now and was wondering if it's worth the effort to replace it.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: Brymus on July 19, 2010, 01:57:56 AM
IIRC  the 12**7 series only draws 150 ma at 12V and 300ma at 6.3V,so you have more than enough for one or even two tubes (4 triodes total)
Also solid or stranded wire doesnt make a diff in your application (some would disagree)
You might get less noise running your heaters on DC (again some would disagree) in my own amps I find it to be noticably quieter with DC heaters.
I also use shielded wire for the signal path except for short runs between tubes.
Keep your wires as close to the chassis as possible(you probably did already),and read up at Valve Wizard or any tube site, GEOFX is good too, on what wires dont play well next to each other ,I forget off the top of my head.
Looking at some layouts of tube pre amps might be of some help with that as well.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 20, 2010, 12:57:55 AM
thanks, brymus.


I have one more question because I just popped in a tube that I've never tried in that amp. It's a JJ electronics 12AU7 and there's no need for a tube shield. I took it off and it's totally fine. I don't get it. I need a tube shield for my other two tubes, but not this one.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on July 20, 2010, 11:12:18 AM
The phrase "a rose is a rose is a rose" does not apply to tubes. All tubes are not equal, and there is no valid set of industry standards getting tubes to be, well, standard.

I would be surprised if multiple different tubes from different places - or even the same place from different batches - all sounded and acted the same. There was a massive engineering effort expended to get all tubes of a given type to be the same back in the Golden Age. That effort no longer exists. To the electronics world, tubes are an atavistic curiosity.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 20, 2010, 06:41:03 PM
I knew tubes varied from brand to brand, and since I know it's old tech, I expected differences from peice to peice. But I didn't expect such a drastic change.

I thought I needed the tube shield because the transformers or something were giving off noise that the tube was picking up. When I covered it with tin foil it behaved. Witht his tube, I just pug it in and play. The tin foil does nothing. There's no loud hum without it. Do some tubes have some sort of internal shielding or a better layout or something? All the tubes I have do sound different. This tube is my least favorite sounding, but was most expensive. It's the only one that's totally quiet tho.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: R.G. on July 20, 2010, 06:44:46 PM
More likely the heater is leaking in the one with the bad hum. Just a guess. Mark that one as "Hums a lot" and put it back in the box as a spare if the others all burn out and you don't have any other replacement.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: dschwartz on July 21, 2010, 04:19:51 PM
all this hum subject makes me remember my attempts to build a couple of tube driver clones (years ago)..i just couldnt get rid of the hum....too many sources of noise and limited patience made me stop my attempts..

strangely, my latter 4-triode tube preamp designs were pretty noise-free (but not without extensive learning about grounding, shielding, and layout)

maybe your layout is wrong in some way..if i were you, iŽd discard the tube and have fun designing something SS..for example using joe davison "diode compression opamp" will get you even closer tu a tube amb than an actual triode there
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on July 22, 2010, 09:52:58 AM
Well, I can live with this hum until I build the next amp. Every amp I build sounds better than the last, and this is no different. It's also crazy louder.

I couldn't leave it alone. I tried to add a switch to switch from the fender tone stack to the Umble tone stack on Runoffgroove.com. I thought I had it with a DPDT switch. Maybe my connections were bad or putting a 12k resistor across a 100k pot to make it around 10k doesn't work.


I added a tremolo too. A really really simply one.

(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=40411&g2_GALLERYSID=8352aca76b6778aff60ab3b4ab1ade7c)

The MPF102 is by the input and there's a SPDT switch to lift the depth pot and disengage the tremolo.

I was going to try something like what the vibracaster is, but I didn't want the tremolo after the reverb, which is before the tube preamp.
I wanted to put the reverb after the preamp, but I was afraid there would be problems.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on July 22, 2010, 10:26:15 AM
  The Piaa stereo preamp k100 [on sale ;)] should show up here, hopefull 'build itself' and be ready for the LM3886's application.
  More than happy to describe how it goes..
  Preamp outside the amp area [in separate enclosure].
  The times I've DIY'd preamps:
  Made as easy to be fiddled with, until a replacement is the preamp or performance has been optimized, can't be outclassed [easily.
  Racing preamps is fun business, I have a Presonus TubePre...a 'top racing champ'..nice as a standard [comes in very handy with the Beta58 mic/98% of all other 'patch through / preamp / cable conversion / matching' needs.
  Great preamps are inherently sensative.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on August 02, 2010, 08:23:31 PM
I think i spent so much effort trying to reduce hum that i totally ignired hiss. Never had an amp that could amplify it that much. Weird tjing is is that sometimes i switch it on an play and the hiss is terrible. Other times i have almost no hiss. Its still a great amp. I put a valvecaster eith a 12at7 and the vibracaster mod. That goes through the GGG digital reverb, then throguh the 12au7 preamp and into the lm3886. Wish i had put a JFET buffer and a 1 meg pot in front of the pwer amp. The thing is so loud and all i can control is the gain of the preamp an not the volume. 8 knobs already tho. Not much room for another.
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: petemoore on August 03, 2010, 12:15:32 AM
 So with nothing plugged in to the amplifier it is noisy ?
Title: Re: 18V bipolar power supply for LM3886 amp
Post by: El Heisenberg on August 03, 2010, 01:16:17 AM
Just hissy. Hisses. Like muffled bacon frying