Woogie SS power amp troubles

[jmaf]

It's ok to yank transistors off the PCB, especially if your favorite text editor is VI.

[Steve Conner]

Beginner's guide to vi: Press Esc, Q to quit. Try another text editor.

[jmaf]

Beginner's guide to vi: Press Esc, Q to quit. Try another text editor.

LOL Make that :q! to quit.

(PS. I wouldn't completely dismiss VI, in fact, in some places, it's still the preferred developers' editor to this day.)

[Swampy]

Yo. Found it. 100 nf from speaker output to ground was misbehaving. With it lifted the amps DC levels are good.

I got nasty power supply hum and hf at the output though, I guess replacing said bad cap will kill the hf, I guess replacing all the caps on the board is a good idea right, especially the electrolytics that have been reverse polarised.

JM, The relay is operated by the standby switch and is between o/p cap and speaker output jack.

Thanks to you all for your patience and help - it's been a extremely beneficial learning experience for me.

Swamp

[teemuk]

Good to hear you're getting it sorted out.

Is there a chance you could scan and post the schematics for future reference?

[Swampy]

Hey Teemuk,

I don't have any factory schems, that was a miscommunication sorry. I don't know a whole lot about these amps but I believe a relatively small number of them were made, and many are one offs / customs etc.

FYI I replaced the 100 nf and voltage is pulled down again. The scope confirms a parasitic oscillation, it seems counterintuitive that the zobel network is making it more resonate though??

Swamp

Anyway, I'm gonna replace all caps and see what happens.

[J M Fahey]

I think it was unstable from day one, so the designer added (klunky, in my opinion) extra correction patches which didn't fully work.
Personal opinion, I would place the Zobel network from the speaker rail out to ground, add a 100pF capacitor base_to_collector on Q8, and would lift one leg of the 560pF in parallel with R12 (this kind of compensation ofter brings more problems than it solves) and/or lift one leg of C4 (Q8's base_to_emitter).
Try these last two mods one at a time (the B_C 100pF and Zobel stay forever) to see which one restores stability.
In theory those caps cut high frequency gain and *should* help, in practice they add dangerous phase shifts which turn the amp into an oscillator.
Something that scratches me the wrong way is having R17/13/14 plus C3/4 return to the *upper* side of R11 (Q8's emitter), are you sure?
They should return straight to ground.
As shown, you would have some positive feedback there, not a good thing in any case.
*If* the schematic you posted is correct, try shorting R11 with a piece of wire.
I think the Woogie designer was a tube guy, not quite an expert on SS circuits, who found some hard to correct troubles and patched them as well as he could, barely so.
Good luck.
PS: you still owe us some pictures, I think they would help, maybe there is a grounding or layout problem which obviously can't be seen on the schematic.
(Not to mention that we don't find the schematic 100% accurate to begin with)

[Swampy]

Lifting C4 and replacing 100R with a jumper seem to have done the trick, I'll pop a 100 pf base to collector just for safe measures also.

Sorry I don't have a camera for pics.

Churs everyone, looks like a happy ending.

[J M Fahey]

All is well that ends well.
Good luck.

[jmaf]

All is well that ends well.

Such amazing f'n wisdom. I am in awe.

[J M Fahey]

Such amazing f'n wisdom. I am in awe.

You aren't very fluent in English, are you?
It's a "popular wisdom" phrase, and a very common one to boot.
Sorry, I did it again.
Now I'll also have to explain you that "to boot" does not mean "to start a computer's O.S." but "in addition to"
To boot
If proper UK English is too much for you, maybe you can use "Simple English", as in:
Boot - Simple English Wikipedia, the free encyclopedia where they state:

Another term "To boot" is an idiom meaning also. For example, people say "he had a beer, and a whiskey to boot." This means that the person had a beer, and also had a glass of whiskey.

Besides his, did you make *any* useful contribution to this post or to solve this problem?
No counting your absolutely unrelated reference to VI Editor.
May I respectfully ask: do you have a drinking problem?
Something like that seems to show in your posts.
If so, sorry, hope you can solve it.

EDIT: since it looks I did not answer your original doubt, here it is:
It's also a very popular English Proverb, so much so that it was used by a certain William Shakespeare (Google it) as the *title* of one of his plays. (no, "play" in this case is not what kids and pets usually do, but a Theater piece).
http://www.englishproverbs.org/wise-...llendwell.html
It states: "Common Usage: This is a well-known proverb, perhaps more so for being the title of a Shakespeare play, and may be quoted at the completion of a difficult task or journey, accompanied by a sigh of relief."

[jmaf]

You aren't very fluent in English, are you?
It's a "popular wisdom" phrase, and a very common one to boot.
Sorry, I did it again.
Now I'll also have to explain you that "to boot" does not mean "to start a computer's O.S." but "in addition to"
To boot
If proper UK English is too much for you, maybe you can use "Simple English", as in:
Boot - Simple English Wikipedia, the free encyclopedia where they state:


Besides his, did you make *any* useful contribution to this post or to solve this problem?
No counting your absolutely unrelated reference to VI Editor.
May I respectfully ask: do you have a drinking problem?
Something like that seems to show in your posts.
If so, sorry, hope you can solve it.

I've never been to Buenos Aires, UK. I appreciate a beer. Yanking is VI slang. I don't understand the rest of your post.

[J M Fahey]

I don't understand the rest of your post.

Why doesn't it surprise me?

As of your reference to

Buenos Aires, UK

, maybe being raised in a Bilingual family and having right to a British Passport gave me an unfair advantage.
Getting high grades in the British Council (Cambridge) Exams didn't hurt either.
Sorry for that.

[Steve Conner]

Jmaf has a foul temper from constantly struggling with vi. He would be happier if he used WordPerfect for DOS, and saved as plain text. Or Emacs which is the open source equivalent.

[jmaf]

Jmaf has a foul temper from constantly struggling with vi. He would be happier if he used WordPerfect for DOS, and saved as plain text. Or Emacs which is the open source equivalent.

I've got PTSD from constantly using octal dump

Edit: Of course the worst form of punishment would have been working with COBOL, but I got a good deal with the DA and I was given the lighter sentence of disassembling x86 code via od, which was a pleasure in the end.