RB 971 MKII with tubes

egnolegno · 17th March 2004, 09:04 PM

Hey guys,
is there anyone that has the RB 971 MKII schematics ?
I would like to tweak it, changing the preamp input witha tubes one (like all hybrid amplifiers).
Bye
Egnolegno

mb · 18th March 2004, 12:33 AM

I've done a bit with my 971 (Mk I) preamp section:
- replaced the opa2604 with op2134
- bias the 2134 to class A
- improved the power supply to the linestage
- improved the dc block caps; bypassed (shorted) the second set of blocking caps

The weak link is probably the volume pot, but I can't get a suitable replacement that will fit.

Having done this, I think that if you want to proceed with a tube linestage, take the signal just after the attenuator, then shunt it back where the 2604 would have fed the signal onwards. Otherwise, just bypass it all, and use the 971 as a power amp. BTW, the mods above work very well.

egnolegno · 18th March 2004, 12:01 PM

Dear MB,
mine is the RB 971 power amplifier, no potentiometer.
I think you have another one.
What about the final stage: is it with the couple 2SD1047-2SB817?
Bye

mb · 19th March 2004, 08:34 AM

Oops. Silly me. Yes, the output devices are identical.

17th March 2004, 09:04 PM	#1
egnolegno diyAudio Member Join Date: Mar 2004 Location: Treviso	RB 971 MKII with tubes Hey guys, is there anyone that has the RB 971 MKII schematics ? I would like to tweak it, changing the preamp input witha tubes one (like all hybrid amplifiers). Bye Egnolegno

18th March 2004, 12:01 PM	#3
egnolegno diyAudio Member Join Date: Mar 2004 Location: Treviso	RB 971 MKII Dear MB, mine is the RB 971 power amplifier, no potentiometer. I think you have another one. What about the final stage: is it with the couple 2SD1047-2SB817? Bye

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18th March 2004, 12:33 AM	#2
mb diyAudio Member Join Date: Dec 2002 Location: Singapore	I've done a bit with my 971 (Mk I) preamp section: - replaced the opa2604 with op2134 - bias the 2134 to class A - improved the power supply to the linestage - improved the dc block caps; bypassed (shorted) the second set of blocking caps The weak link is probably the volume pot, but I can't get a suitable replacement that will fit. Having done this, I think that if you want to proceed with a tube linestage, take the signal just after the attenuator, then shunt it back where the 2604 would have fed the signal onwards. Otherwise, just bypass it all, and use the 971 as a power amp. BTW, the mods above work very well.

19th March 2004, 08:34 AM	#4
mb diyAudio Member Join Date: Dec 2002 Location: Singapore	Oops. Silly me. Yes, the output devices are identical.

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