Hi-end GM70 amplifier with only 2 stages

audiodesign · 21st February 2009, 12:13 PM

As suggested by George in the other forum:

Andrea, you have the irons, you have most of the circuit needs, why don't you try the promising D3a - Gm70 2stage SE solution, D3a can do the trick also with 1:1 interstage...
Regards,
George

I have started the measurements of this configuration using Bartolucci interstage 1:1 48H INT8C and Tango X-10S (soon I will test Bartolucci OPT)

http://www.audiodesignguide.com/Clau..._8ohm_90mA.gif

Very good frequency band 10Hz at -3db and 22KHz at -1db

http://www.audiodesignguide.com/Clau..._8ohm_90mA.gif

Power about 16.5W on 8ohm with only an input of 0.7Vrms

Soon complete schematic.

audiodesign · 21st February 2009, 12:56 PM

This is the schematic.

It is necessary use DC filaments for the GM70 to skip ac noise.

aroS3 · 21st February 2009, 01:43 PM

Quote:

Originally posted by audiodesign
As suggested by George in the other forum:

Andrea, you have the irons, you have most of the circuit needs, why don't you try the promising D3a - Gm70 2stage SE solution, D3a can do the trick also with 1:1 interstage...
Regards,
George

I have started the measurements of this configuration using Bartolucci interstage 1:1 48H INT8C and Tango X-10S (soon I will test Bartolucci OPT)

http://www.audiodesignguide.com/Clau..._8ohm_90mA.gif

Very good frequency band 10Hz at -3db and 22KHz at -1db

http://www.audiodesignguide.com/Clau..._8ohm_90mA.gif

Power about 16.5W on 8ohm with only an input of 0.7Vrms

Soon complete schematic.

Very good results Andrea. I'm glad that worked this way. Looking forward for different OPTs comparison and sonic results also.
Regards,
George

Gluca · 21st February 2009, 05:42 PM

I'd suggest to stack the supplies and direct couple the tubes (getting rid of the interstage). Been there wit GM70, you will be surprised.

Gianluca

aroS3 · 21st February 2009, 05:54 PM

Quote:

Originally posted by Gluca
I'd suggest to stack the supplies and direct couple the tubes (getting rid of the interstage). Been there wit GM70, you will be surprised.

Gianluca

Gianluca tell us some more details about your results, measurements, operating points e.t.c

audiodesign · 21st February 2009, 06:21 PM

Today first comparation test with 4 my friends:

1) 6HV5A+845 with new INT8C + Tango X-10F

2) D3A+GM70 copper with orig. INT8C + Tango X-10F

3 on 4 prefer the second amplifier.

GM70 graphite give a bad result when compared to copper type.

Cobra2 · 21st February 2009, 06:41 PM

Quote:

Originally posted by audiodesign
Today first comparation test with 4 my friends:
---
GM70 graphite give a bad result when compared to copper type.

Then maybe you should do some adjustments...there are no reason that the inferior("copper") tube should do better, just because it's rarer and more expensive...

Arne K

serph1nia · 21st February 2009, 06:44 PM

Do you think an amplifier like this will still be worth it on high sensitivity speakers (97db+)? Or is it power vs. quality?
I'm looking for a SET that can do rock, house and heavy orchestra.

What is the difference between your 845 amplifier and this one, instead of saying gm70 is better. Maybe include a 300b to the comparison.

I enjoy your worjk very much and I'm learning alot!

moray james · 21st February 2009, 07:15 PM

Zero Feedback Impedance Amplifiers

http://www.dddac.de/op06.htm

JoshK · 21st February 2009, 10:53 PM

Quote:

Originally posted by Gluca
I'd suggest to stack the supplies and direct couple the tubes (getting rid of the interstage). Been there wit GM70, you will be surprised.

Gianluca

Surprised good or surprised bad?

21st February 2009, 12:13 PM	#1
audiodesign diyAudio Member Join Date: Sep 2005	Hi-end GM70 amplifier with only 2 stages As suggested by George in the other forum: Andrea, you have the irons, you have most of the circuit needs, why don't you try the promising D3a - Gm70 2stage SE solution, D3a can do the trick also with 1:1 interstage... Regards, George I have started the measurements of this configuration using Bartolucci interstage 1:1 48H INT8C and Tango X-10S (soon I will test Bartolucci OPT) http://www.audiodesignguide.com/Clau..._8ohm_90mA.gif Very good frequency band 10Hz at -3db and 22KHz at -1db http://www.audiodesignguide.com/Clau..._8ohm_90mA.gif Power about 16.5W on 8ohm with only an input of 0.7Vrms Soon complete schematic.

21st February 2009, 07:15 PM	#9
moray james diyAudio Member Join Date: Aug 2003 Location: Calgary on the Bow	Have a look at these..... Zero Feedback Impedance Amplifiers http://www.dddac.de/op06.htm __________________ moray james

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21st February 2009, 05:42 PM	#4
Gluca tarmac ripper diyAudio Member Join Date: Nov 2004 Location: Back to Italy	I'd suggest to stack the supplies and direct couple the tubes (getting rid of the interstage). Been there wit GM70, you will be surprised. Gianluca

21st February 2009, 06:21 PM	#6
audiodesign diyAudio Member Join Date: Sep 2005	Today first comparation test with 4 my friends: 1) 6HV5A+845 with new INT8C + Tango X-10F 2) D3A+GM70 copper with orig. INT8C + Tango X-10F 3 on 4 prefer the second amplifier. GM70 graphite give a bad result when compared to copper type.

21st February 2009, 06:44 PM	#8
serph1nia diyAudio Member Join Date: Feb 2008	Do you think an amplifier like this will still be worth it on high sensitivity speakers (97db+)? Or is it power vs. quality? I'm looking for a SET that can do rock, house and heavy orchestra. What is the difference between your 845 amplifier and this one, instead of saying gm70 is better. Maybe include a 300b to the comparison. I enjoy your worjk very much and I'm learning alot!

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