What about this 300B schematic..?

RE: What about this 300B schematic..?, posted on October 4, 2014 at 07:34:46
danlaudionut Audiophile Posts: 5480 Location: Schenectady Joined: June 6, 2002	Balle You have way too much gain - 300+. Do you even use the feedback? I would remove the input cap. And change the 6SL7 for another 6SN7. Just plug one in and see if you like it. You can optimize it later. DanL

RE: actual gain is gain is 30x, posted on October 4, 2014 at 08:04:56
Balle Clorin Audiophile Posts: 781 Joined: July 30, 2003	Thanks for your input,. With 2.5 db feedback the overall gain is 30x, I see what a 6SN7 on input gives. Best regsrds Balle

Why so much gain?, posted on October 4, 2014 at 09:36:07

andy evans
Audiophile

Posts: 4382
Joined: October 20, 2000

This is a 4 stage amp. Why not a 2 stage amp? Drive the 300b with a 6E5P or something with more gain and the same high current and low plate resistance. A few options.

Don't see the need for any of this - you are probably using sensitive speakers since this is a 300B SET. If you need more gain use a preamp, but DACs give out 2v or more these days.

Feedback would just ruin a natural sounding amp and tighten up the sound.

RE: actual gain is gain is 30x, posted on October 4, 2014 at 10:53:36
Tre' Industry Professional Posts: 17302 Location: So. Cal. Joined: February 9, 2002	You might want to try getting rid of the 6sl7 stage altogether and re-bias the 6sn7 (change the cathode resistor value) and see what that sounds like. You won't get full power from the 300b but, depending on your speakers, you might not need it. Tre' Have Fun and Enjoy the Music "Still Working the Problem"

RE: What about this 300B schematic..?, posted on October 6, 2014 at 21:18:54

Paul Joppa
Industry Professional

Posts: 7296
Location: Seattle, WA
Joined: April 23, 2001

At present, the SRPP output is from the cathode of the upper tube, which is acting sort of like a cathode follower. If you take that output from the plate of the lower tube, you will get an output with less of the CF sound. It's an easy experiment, and if you hear a difference, that is generally thought to be due to the cathode follower feedback action.

Notice I am not predicting which one you will prefer, or even whether you will have a preference!

This is how it distorts with different 6SN7 tube manufacturers , posted on October 16, 2014 at 09:09:32

Balle Clorin
Audiophile

Posts: 781
Joined: July 30, 2003

Amazing how much the distortion changes between tube manufacturers. All tubes are supposed to be good. No wonder why tubes sounds different. Or maybe not, my listening level corresponds to about 0.3 watt.., so the difference is 0.1 vs 0.22 % THD. Not easy to hear I think

Different 6SN7 gives 1.5/1.1/0.8 % THD at same (5) Watt output!!! The best one is the cheapest by the way..

That's all folks,
Balle

RE: actual gain is gain is 30x, posted on October 17, 2014 at 06:04:28

JoshK
Audiophile

Posts: 820
Location: NJ/NYC
Joined: August 3, 2001

Better yet, take a look at the Aikido schematic. It would be pretty simple to modify this front end to be an Aikido front end instead. That is the direction I would go. In this case the gain would be ~1/2 mu of first tube, so probably stick with 6SL7 for first, eliminates the second gain stage and you don't need the feedback.
----------------
"When Khruschev said "we will bury you" I don't think he meant with surplus parts." zacster

Tube DIY Asylum

What about this 300B schematic..?

84.211.93.117