Try 250 to 500 ohms on that choke replacement resistor.
Is the clean bright?? OD?
WHat snubbers??? I like 390pf to 420pf depending on amp.
The extra uf will add bass. This could make some high frequency "buzz" in my experience. Not brighter per se, but since there is more bass, it may appear to have more fuzz on top.
What CL2 bypass cap you got??
Chris G wrote:Man.......the amp got bright as hell!!!!!
I had 2 -100uf@350vdc for a sum of 50uf@700volts........I read the post entitled "first stage filltering" and decided to try 2- 220uf@385 volts.
This amp is about 80 watts,(twin trannies) I also uped the choke resistor from 100ohms to 150 ohms. no other changes anybody have any thoughts?
Try 250 to 500 ohms on that choke replacement resistor.
Is the clean bright?? OD?
WHat snubbers??? I like 390pf to 420pf depending on amp.
The extra uf will add bass. This could make some high frequency "buzz" in my experience. Not brighter per se, but since there is more bass, it may appear to have more fuzz on top.
What CL2 bypass cap you got??
Chris G wrote:Man.......the amp got bright as hell!!!!!
I had 2 -100uf@350vdc for a sum of 50uf@700volts........I read the post entitled "first stage filltering" and decided to try 2- 220uf@385 volts.
This amp is about 80 watts,(twin trannies) I also uped the choke resistor from 100ohms to 150 ohms. no other changes anybody have any thoughts?
Thanks
Chris
Hi Scott,
I will try the different resistors for the choke.
The high end on both channels is up........alot
I did lower the bright cap on the master from 51pf to 20pf.
snubbers are 330pf ceramic disk
cl2 was 1uf changed it to 5uf and dropped od2 to 1uf.
The amp had alot more warmth to it before,it was pretty close to what I would call the dumble tone!!!! very warm,very smooth and was so close to that note bloom you hope you wind up with.....................just missed!!!!
Thank-you Scott!!!
Chris
Scott, I would like to talk to you in person about this, I now I missed your call a while back!!
The master bright cap will have a huge effect on things. I run a 12pf on mine.....
For the non HRM, I like about 1.5uf on CL2 and the full 5uf on OD2.
Maybe try raising the snubs to 390pf.
Also, you can reduce the 220k feeding the 100k OD trim to a 180k or so. I like the feel of thi smod. THen the 390pf snubs make even more sense.
Make sure you have around 200v on the V1 and V2 plates. Keep it under 220v.
Put a 500pf ceramic as the CL2 grid bypass cap.
Also, make sure you are not using silver mica in the stack... Ceramic is best.
Lastly, try a fixed treble bleed network on OD2. Put a .001uf on the plate of V2b and connect ot ground with a 150k resistor in series. That will really smooth things.
Report back
Chris G wrote:
dogears wrote:Chris,
Try 250 to 500 ohms on that choke replacement resistor.
Is the clean bright?? OD?
WHat snubbers??? I like 390pf to 420pf depending on amp.
The extra uf will add bass. This could make some high frequency "buzz" in my experience. Not brighter per se, but since there is more bass, it may appear to have more fuzz on top.
What CL2 bypass cap you got??
Chris G wrote:Man.......the amp got bright as hell!!!!!
I had 2 -100uf@350vdc for a sum of 50uf@700volts........I read the post entitled "first stage filltering" and decided to try 2- 220uf@385 volts.
This amp is about 80 watts,(twin trannies) I also uped the choke resistor from 100ohms to 150 ohms. no other changes anybody have any thoughts?
Thanks
Chris
Hi Scott,
I will try the different resistors for the choke.
The high end on both channels is up........alot
I did lower the bright cap on the master from 51pf to 20pf.
snubbers are 330pf ceramic disk
cl2 was 1uf changed it to 5uf and dropped od2 to 1uf.
The amp had alot more warmth to it before,it was pretty close to what I would call the dumble tone!!!! very warm,very smooth and was so close to that note bloom you hope you wind up with.....................just missed!!!!
Thank-you Scott!!!
Chris
Scott, I would like to talk to you in person about this, I now I missed your call a while back!!
I must be missing something here. If the amp sounded better with 50uF filtering, why not just go back to 50uF? I'm convinced that a key aspect of getting these amps to sound their best is tuning them to the iron. (Otherwise, we'd all have amps that sound the same based on the hybrid-A schematic. )
I think a lot of the discussion around first stage filtering was about ghost notes or loose bottom at high volume. If neither of these conditions exist, does it still make sense to go to larger filter caps? That really WAS a question and not a smart-a$$ response.
As for note bloom (and just as importantly, sustain and harmonic feedback), that seems to be the toughest thing for me to nail as well. I'm really tempted to reconnect the choke and try a 100R/10W resistor in series to the OPT. I suspect that there are tricks with the NFB circuit that can improve sustain as well.
It is all a system Norm. If the amp reacted that badly to the larger caps, there must be some other issue IMO. The caps do matter but the symptoms described concern me. Merely, bandaiding it by going back may never unveil the issue. Then, once the issues are addressed, the cap comparison becomes more valid.
Normster wrote:I must be missing something here. If the amp sounded better with 50uF filtering, why not just go back to 50uF? I'm convinced that a key aspect of getting these amps to sound their best is tuning them to the iron. (Otherwise, we'd all have amps that sound the same based on the hybrid-A schematic. )
I think a lot of the discussion around first stage filtering was about ghost notes or loose bottom at high volume. If neither of these conditions exist, does it still make sense to go to larger filter caps? That really WAS a question and not a smart-a$$ response.
As for note bloom (and just as importantly, sustain and harmonic feedback), that seems to be the toughest thing for me to nail as well. I'm really tempted to reconnect the choke and try a 100R/10W resistor in series to the OPT. I suspect that there are tricks with the NFB circuit that can improve sustain as well.
Hi Guy's,
just a quick note,I changed the choke to 300 ohms and the amp is close to where it was before the cap changes.
Scott,I still want to try some of your suggestions(I need some ceramic disk caps to finish ) the plate voltage is right in the park all b+ nodes are under 220vdc.
I will try the rest of the changes tonight and report back.
Thanks
Chris
Hi All,
Here are the changes so far choke:300 ohms/10 watt
cl2 by-pass 2uf@50v
od2 by-pass 5uf @50v
treble cap from 500pf mica to 470pf ceramic
I will try the others as soon as I'm able to get my hands on some ceramic disk caps.........
Thanks
Chris
Chris G wrote:Hi All,
Here are the changes so far choke:300 ohms/10 watt
cl2 by-pass 2uf@50v
od2 by-pass 5uf @50v
treble cap from 500pf mica to 470pf ceramic
I will try the others as soon as I'm able to get my hands on some ceramic disk caps.........
Thanks
Chris
