The Hundred-Buck Amp Challenge - Page 52

quikie22 · 9th July 2011, 06:06 PM

completed my BERSIH2.0 based on 6N2P and 6P1P.. Sounds too clean (Bersih means clean in local dialect)...now to start playing with distortion and overdrive... so far total cost of is around 70USD.

Wavebourn · 9th July 2011, 06:29 PM

Sounds on different levels of gain. Almost the same loudness, different timbres. Is it good, or too much compression?

YouTube - ‪World Champion guitar amp project -- sounds on different levels of gain‬&rlm;

Wavebourn · 9th July 2011, 06:33 PM

Quote:

Originally Posted by costis_n

Can you please explain the power supply and output stage, it it too strange looking for my feeble mind... Pretty please?

Preamp and screen grid are powered from a network that supplies more of voltage on low signals, less voltage on high signals. It increases tone dynamics decreasing SPL dynamic.

TheGimp · 9th July 2011, 06:50 PM

Quote:

Originally Posted by Wavebourn

If you wired ground as drawn on your picture it have to oscillate.

Which wiring? First and second stage B+? They actually have an RC stage between them.

Ground is star connection with common point where B+ enters from HP supply.

Wavebourn · 9th July 2011, 07:10 PM

Quote:

Originally Posted by TheGimp

Which wiring? First and second stage B+? They actually have an RC stage between them.

Ground is star connection with common point where B+ enters from HP supply.

What about input and output jacks?

TheGimp · 9th July 2011, 07:46 PM

Input jack is grounded at the capacitor bank where power comes in.

Output tied to star as well.

All of signal path is single end grounded RG-174/U shielded cable.

Wavebourn · 9th July 2011, 07:48 PM

Quote:

Originally Posted by TheGimp

Input jack is grounded at the capacitor bank where power comes in.

Output tied to star as well.

All of signal path is single end grounded RG-174/U shielded cable.

Are they both isolated from chassis, or form a loop through it?

By the way, I recorded sound on high pitch strings, to show compression of my amp:

http://www.youtube.com/watch?v=pRF05L9btYM

TheGimp · 9th July 2011, 08:17 PM

No chassis. This is on a tube-lab type breadboard.

Since there is no global feedback, I've tried removing the ground to the output and letting it float. No change in the oscillation.

I also considered the possibility of feedback between the triode and pentode in the 6GH8A which were stages 1 and 3 which were in phase, so I changed the position of the triodes so that it is 6GH8A Pentode input driving tonestack, 6GH8A Triode second gain stage after tonestack, 6F4P triode 3rd gain stage, other 6F4P triode as Concertina, then the two output 6F4P Pentodes.

The oscillation breaks out at the peak of the signal and is only seen now on the 3rd gain stage through output.

I switched to a 400Hz test tone.

TheGimp · 9th July 2011, 08:21 PM

At 30 and 31 seconds it sounds like your amp is note switching briefly.

Nice.

Wavebourn · 9th July 2011, 08:22 PM

Did you try 10k grid stopper for the output tube?

9th July 2011, 06:29 PM	#512
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Sounds on different levels of gain. Almost the same loudness, different timbres. Is it good, or too much compression? YouTube - ‪World Champion guitar amp project -- sounds on different levels of gain‬&rlm; __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

9th July 2011, 08:22 PM	#520
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Did you try 10k grid stopper for the output tube? __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

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9th July 2011, 06:06 PM	#511
quikie22 diyAudio Member Join Date: Sep 2009	completed my BERSIH2.0 based on 6N2P and 6P1P.. Sounds too clean (Bersih means clean in local dialect)...now to start playing with distortion and overdrive... so far total cost of is around 70USD.

9th July 2011, 07:46 PM	#516
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	Input jack is grounded at the capacitor bank where power comes in. Output tied to star as well. All of signal path is single end grounded RG-174/U shielded cable.

9th July 2011, 08:21 PM	#519
TheGimp diyAudio Member Join Date: Aug 2009 Location: Johnson City, TN	At 30 and 31 seconds it sounds like your amp is note switching briefly. Nice.