18V bipolar power supply for LM3886 amp

[El Heisenberg]

Antec
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

[El Heisenberg]

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?

[slacker]

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.

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.

[El Heisenberg]

... this TDA2030 is WEAK!! And all that heat I had to get rid of for such a small sound? BAH!

[El Heisenberg]

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

[stringsthings]

... this TDA2030 is WEAK!! And all that heat I had to get rid of for such a small sound? BAH!

are you becoming angry?

[El Heisenberg]

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.

[petemoore]

  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.

[El Heisenberg]

Well I bought the dual 20v toroid at 200VA.

And that chipamp site had some good info.

[Nasse]

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

[petemoore]

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"/

[R.G.]

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.

[El Heisenberg]

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.

[R.G.]

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! 

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.

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.

[El Heisenberg]

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?

[El Heisenberg]

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.

[Nasse]

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...

[El Heisenberg]

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

[Nasse]

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

[El Heisenberg]

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!