SVT 7 pro no speaker output

[lowell]

Reposting to this older thread. Can't find any post from me saying that I did fix this thing by replacing that IRS20955.. but also in a hurry here so I may have missed it. FYI that chip is now replaced with the improved IRS20957.

[teemuk]

You know, I had read that page. Very good info.. but it still doesn't explain how the PMW is created. It mentions using a triangle wave generator, but I don't think that the Ampeg uses that topology. Even then, the page doesn't describe the triangle wave generator in great detail.

Thread resurrection, but I just bumped into this thread by Google searching SVT-7Pro schematics and I feel the particular topic was left somewhat unexplained.

This amp uses a so-called "self-oscillating" class-D amp topology, concept that - I think - was pioneered by a Philips designer and is often referred to as "UcD". Basically in such amps there is no dedicated, individual oscillator circuit that would create the high frequency carrier wave, but the wave is created by oscillation tirggered by phase shifts resulting from the propagation delay of the output and a phase lead network from output to comparator. (A network thatby a quick glance basically looks just like a plain feedback path). The amp is bridged so you have two of such feedback paths, combined to a single output by a differential amplifier. The phase shift is designed to turn feedback positive at the switching frequency and it triggers oscillation in the comparator stage, which in turn pulse width modulates the signal as usual.

It's a clever concept, naturally with its own unique drawbacks as well.

[Jazz P Bass]

I had to look that one up.
UCD: Universal Class D
Thanks for the insight Teemuk.
It certainly was left hanging how that works.

[thor69]

Hello everyone.
Sorry for reminding old posts, but really needs these schematics to repair my SVT 7 pro (0032538-XX REVA00 SCH.pdf, 0032540-XX REVB00 SCH.pdf, 0032543-XX REVB00 SCH.pdf) - I can not download from links above...
I'll be very grateful to you for sharing me these schematics (or send via e-mail: thor69@poczta.onet.pl)
Thanks in advance
Regards

[nickstomp]

Me tooooo

[Jazz P Bass]

Reposted the files here: Ampeg SVT7 Pro

[liveservice]

Sorry for reminding old posts, but really needs these schematics to repair my SVT 7 pro (0032538-XX REVA00 SCH.pdf, 0032540-XX REVB00 SCH.pdf, 0032543-XX REVB00 SCH.pdf) - I can not download from links above...
I'll be very grateful to you for sharing me these schematics (or send via e-mail: liveservice@tiscali.it)
Thanks in advance
Regards

[Enzo]

The links in post #96 right above you just worked for me.

[liveservice]

The links in post #96 right above you just worked for me.

enzo hello can you help me? I apologize for writing errors are Italian.

[Enzo]

Each post here has a number. Your most recent post is #99 for example. Go back to post #96, and notice " Ampeg SVT7 Pro" there is a different color. It is a link. CLick on it, and it opens to another page with schematic files. I just again tried to open those files, and they opened for me. They should open for you too.

[Jazz P Bass]

Here is a shortcut: http://music-electronics-forum.com/t...36/#post307936

[liveservice]

Each post here has a number. Your most recent post is #99 for example. Go back to post #96, and notice " Ampeg SVT7 Pro" there is a different color. It is a link. CLick on it, and it opens to another page with schematic files. I just again tried to open those files, and they opened for me. They should open for you too.

enzo excuse I try these files 0032538-XX REVA00 SCH.pdf, 0032540-XX REVB00 SCH.pdf, 0032543-XX REVB00 SCH.pdf ok thanks

[thor69]

Thanks a lot for schematic - I downloaded it - everything OK
Best regards

[mnow]

Here's a funky one!
U3 is pulsating from high/low keeping the amp in the mute state.
TR is constant high at 4.75v.
Checked cap 127 and is OK
Found 85 ohms across R238 and replaced Q31 but is still the same.
Replaced U3 as well but is still shutting down the amp.
Also pin 7 on U3 keeps discharging the cap C127.

One odd note, did find R115 burned up ( the 22ohm on the output) but C161 is OK.

Any idea's on this issue?

[Jazz P Bass]

Check pin 2 (CSD) of the output ic.
If IT is bouncing (because of a faulty output ic), that may translate down to the 555 ic.
Try isolating the pin by lifting R39.

If the 555 ic TR (trigger) pin is held high, there is really no reason for it's output (pin 3) to 'bounce'.