|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
|
|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
In Reply to: OK, thx, TK. I think the cap removal is the 1st thing I'll try. posted by jeffreybehr on March 13, 2007 at 11:12:21:
It's the easiest way of reducing gain and way better than a pot IMO. It will change the sound a little and you may or may not like it. You should also know that removing the bypass cap will also degrade PSRR by almost 50% and increase the OP impedance by a similar amount but neither should be a factor in your circuit.Actually the first stage is not an SRPP at all since the drive is taken from the plate of the bottom tube. It's more like a symmetrical CCS grounded cathode stage but the 1K plate R provides a very poor load. I'm not a fan of this configuration because it forces the use of the same value plate R as the cathode R and this compromise leads to a quiescent current and a plate R that are both too low for good linearity. It also (normally) forces you to bypass the cathode R for good gain and low OP impedance. It would be simple to improve by adding a few components.
For the solution to the specific problem you seek TK's suggestion is the best. For other benefits with simple mods consider also 1) taking the drive from the cathode of the top triode and 2) increasing the value of all cathode and plate Rs to between 1K5 and 2K2. Here, running the first stage from the same B+ as the driver would help to keep quiescent current up. The HC voltage of most 6sn7s is 200V so should not be a problem. Also, what you'll lose in higher PS noise you'll gain in better rejection. These mods are simple and worthwhile evaluating seperately. I'd be interested in your feedback should you try any of them.FWIW, both stages are not very linear but the driver particularly so due to the high voltages it must swing (which would be helped considerably by mod 2), however distortion will be mostly 2ndH and I've found that this is actually desirable in SE driver stages since it goes a long way towards cancelling some of the distortion generated in the OP stage since it's opposite in phase.
Naz
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- TK is right ... - Naz 18:37:50 03/13/07 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
