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Old 21st February 2009, 12:13 PM   #1
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Default 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.
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Old 21st February 2009, 12:56 PM   #2
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This is the schematic.

It is necessary use DC filaments for the GM70 to skip ac noise.
Attached Images
File Type: gif 845claudio_sch_ver2_gm70a.gif (27.3 KB, 3829 views)
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Old 21st February 2009, 01:43 PM   #3
aroS3 is offline aroS3  Greece
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Default Re: Hi-end GM70 amplifier with only 2 stages

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
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Old 21st February 2009, 05:42 PM   #4
Gluca is offline Gluca  Italy
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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
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Old 21st February 2009, 05:54 PM   #5
aroS3 is offline aroS3  Greece
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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
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Old 21st February 2009, 06:21 PM   #6
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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.
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Old 21st February 2009, 06:41 PM   #7
Cobra2 is offline Cobra2  Norway
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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
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Old 21st February 2009, 06:44 PM   #8
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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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Old 21st February 2009, 07:15 PM   #9
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Default Have a look at these.....

Zero Feedback Impedance Amplifiers

http://www.dddac.de/op06.htm
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Old 21st February 2009, 10:53 PM   #10
JoshK is offline JoshK  Canada
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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?
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