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-   -   Pioneer VSX1020 like TGM1 ? (http://www.diyaudio.com/forums/solid-state/226482-pioneer-vsx1020-like-tgm1.html)

Bigun 27th December 2012 03:35 AM

Pioneer VSX1020 like TGM1 ?
 
1 Attachment(s)
I pulled a dead Pioneer VSX1020 out of the trash (not dead, but powers on, then waits, then cuts out and powers on again and again and again) and didn't see any easy way to fix it so pulled it apart instead.

I was interested to see that the amplifier design was very simple indeed. But even more surprising was that it appears to use a resistor between the output and the top of the LTP to inject 2nd harmonics !

Eventually I found a free service manual on-line (if I'd found it earlier I might have been able to fix it but now it's trash). The schematic of interest is attached. Look at resistor R1209SBL. If you look at my TGM1 amplifier thread you'll see the same thing was tried out in the initial design phase. Am I reading the schematic right ?

Ian Finch 27th December 2012 04:06 AM

Hi Bigun, 470K is certainly not much coupling but I would suggest this and many related
tweaks have been lurking in "high-end" amps for many decades - toob era even! :wchair:.
The compensation caps C12245,12235,12115 are also odd...Was this a "trim with the
wire cutters" grade amplifier or do you think they ran out of 250 pF caps? :D

Bigun 27th December 2012 03:49 PM

Hard to say what they were thinking here, but I believe it was sold as a fairly expensive unit.

AKSA 28th December 2012 08:22 PM

Interesting, isn't it Bigun? It seems they would not achieving for the lowest THD.

Bigun 28th December 2012 11:02 PM

1 Attachment(s)
Quote:

Originally Posted by Ian Finch (Post 3300328)
The compensation caps C12245,12235,12115 are also odd...

The bulk of the parts are through-hole on the front side, but there are few parts that are surface mounted. These 3 caps are tiny surface mount caps on the backside and all three are populated on the pcb for each channel. In fact I'm not sure there are any other SMD parts on the amplifier pcb.

I see phase lead (33pF) but I don't see any Cdom. The Vas compensation seems to depend on a 47k shunt load on the collector and a kind of zobel between base and -ve rail. The Vas is degenerated with a 47R.

Quote:

Originally Posted by AKSA (Post 3302335)
Interesting, isn't it Bigun? It seems they would not achieving for the lowest THD.

Yes indeed, you are probably more familiar with this design than I ;)

I like that it has no Cdom, a different compensation scheme than I've used on anything I've built.

I'm getting more curious about it.

destroyer X 29th December 2012 05:36 AM

First you build it to make it stable, then you break it to
 
obtain good sonics.

Some of us have learned the lesson.... thanks God by that!

Tune and detune.... in radio frequency the quality goes in tuning... in audio in detuning.

Not only the 470K dear Bigun.... watch it carefully.... we have more tricks there.

I'm doing the lottery federal investment .... 500 bucks per month .... one day i will have Millions of dollars and i will move to the U.S. to start the real Dx Corporation ... you Bigun, Hugh Dean, and some others will be invited .... can you imagine what we gonna achieve together?

We gonna research separatelly..each one of us creating our own secret "pearl" amplifier....the task is:

- Beat me if you can!

The winner amplifier will go into production.

After that we cooperate...tips and tricks gonna be shared in between us...then we gonna start all over again..

- Beat me if you can!

Ahahahahahahah!..... we gonna be the most terrible nightmare to the competition! (Dx, Aksa and Bigun) ... while poor guys will be trying precision on amplifiers..we gonna be searching sonics!

Observe that we gonna use the major powers we have in humans..the instint of competition, also the cooperation and the main one in thousand of years of human culture...the tribe, the clan, the Union (guild).

regards,

Carlos

destroyer X 29th December 2012 06:09 AM

The one that discovered some "special resources" in the first place
 
Was Hugh Dean.... he have switched on a "light" inside me.

You know dear Bigun...you watched the movie 2001, Space Odissey.... do your remember about the monolite that made humans evolute....that resistor is alike a monolite (one of them)... evoluting us a little bit more.... touching the monolite we learn how to use tools...we became better chimps.

Humans are so stubborn that Hugh have explained the stuff many times..also i did that..now your are pointed that dear Bigun...and nobody believe...nobody understand the gift we are giving to them...also they do not believe in extra terrestrians.... and we are here.

There's a say in Brasil that shows the stupidity:

- "Eu não sei, não quero saber e tenho raiva de quem sabe!"

- "I do not know, i do not want to know, and i hate the ones have the knowledge!"

Hugh Dean is the Master.... he sniff good things... detect things, discover things... his car is a Toyota.... the best one!

Our forum is now a days having a lot of propaganda... sadly this is happening.... i see the donate button have not worked... sadly we are entering the market place...also here... a pity.... add block engaged.

regards,

Carlos

Ian Finch 29th December 2012 11:34 AM

Quote:

Originally Posted by Bigun (Post 3302486)
.... These 3 caps are tiny surface mount caps on the backside and all three are populated on the pcb for each channel. In fact I'm not sure there are any other SMD parts on the amplifier pcb.....

Ah....the penny drops. This may have been a cap. grade issue and larger values weren't available in that type. Perhaps the designer was at pains to avoid non-COG, NPO or similar ceramic material for the cap, necessary or not.

Bigun 1st January 2013 04:54 AM

What I can't figure out is why the service manual clearly prescribes that the idle current be set up so that there is only 2mV (+/- 10%) across each output Re resistor. This seems very low to me, as I understand it should be around 26mV for minimal cross-over distortion.

Bigun 18th January 2013 08:07 PM

Quote:

Originally Posted by destroyer X (Post 3302727)
I'm doing the lottery federal investment .... 500 bucks per month .... one day i will have Millions of dollars and i will

I'm waiting for the big win my friend !

But I don't think Class AB is the way of the future. I am sad, but I believe it is a dead technology. It does not mean we can't enjoy making Class AB amplifiers, I enjoy it a lot, but Class D is the proper way, in my view.


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