That might have done it/Ok, maybe......

[Bob-I]

EDIT:

Maybe I forgot that these are entire systems. The filters helped, but it was still dull and boomy. I disconnected the reverb and it improved.

So I found that there was too much NFB going to the reverb through the balance resistor. I had 100K in there as per Glassman's orignal schem. I upped it to 220K and not only does the amp sound richer and less boomy, but the reverb sounds better too.

END EDIT:

Solved the boomyness problem in my 3 channel amp.

I just got home from Japan today, went through the drawers and found 3 22uF/450V caps. I replaced the 3 47uF caps with the 22uF caps.

Since my 2 1/2 year old foster daughter is sleeping at the other end of the house I could only play at low volume.

At first I played a bit and was wondering where all the highs went . Then I looked over and noticed I'd put my scope right in front of the speaker . Moved the scope and it seems pretty good. Lots more highs and better definition on the lows. I'll crank it up tomorrow and see what it's like.

[Bob-I]

Nope, still boomy. Better but just not the same as my other amps.

Time to break out the scope and check for oscillations etc causing trouble.

[dogears]

Time for a roadtrip here Bob.....

Nope, still boomy. Better but just not the same as my other amps.

Time to break out the scope and check for oscillations etc causing trouble.

[Bob-I]

Time for a roadtrip here Bob.....

Nope, still boomy. Better but just not the same as my other amps.

Time to break out the scope and check for oscillations etc causing trouble.

Sounds like a plan, Saturday ok?

[keithrick]

EDIT:
So I found that there was too much NFB going to the reverb through the balance resistor. I had 100K in there as per Glassman's orignal schem. I upped it to 220K and not only does the amp sound richer and less boomy, but the reverb sounds better too.

Bob, just curious, is the balance resister you speak of connecting the 470pf cap to the 4.7M resister at the PI entrance on Norm's layout? I am still looking for the last 10% as well. Still toying with the Dumbleator idea too. I really need to get a cab for this amp! [/quote]

[Bob-I]

Bob, just curious, is the balance resister you speak of connecting the 470pf cap to the 4.7M resister at the PI entrance on Norm's layout? I am still looking for the last 10% as well. Still toying with the Dumbleator idea too. I really need to get a cab for this amp!

There's no 4.7M resistor, in fact Norm told me he removed that too. The balance resistor is connecting the in to the out so that some of the dry signal passes.

In the attached it's a 100K labeled R1.

[Darkbluemurder]

By changing the balance resistor from 100k to 220k I would think that the amp loses a tiny bit of highs and gets a slightly stronger reverb. I am not sure how this can help in lessening the boominess.

Good luck!
Stephan

[Bob-I]

By changing the balance resistor from 100k to 220k I would think that the amp loses a tiny bit of highs and gets a slightly stronger reverb. I am not sure how this can help in lessening the boominess.

Good luck!
Stephan

That's what I was thinking too, so I didn't look at this at first. As it turns out, the NFB caused by this low value of the balance resistor caused some lows to be accented, go figure. I also placed a 39pF bypass across the 220K balance to bring out some highs.