The GEM amplifier

hajame · 5th May 2007, 01:24 PM

Has anyone built this GEM amplifier by Graham Maynard?

http://gmweb2.net/Diagrams/GEM/GEM200.gif

I am planning to choose a good circuit for low efficiency and low impedance loudspeakers. I find this design very special and rather complex. Lots of large caps are used. But the designer claims it can deal with the back emf of the loudspeakers to control them very accurately. So I am posting here to seek for builders' comments on the performance of this circuit.

Nordic · 5th May 2007, 02:05 PM

Graham is a very highly esteemed member of this forum, many of the schematics in circulation will not work without modification...

He has a newish circuit I am sure he'd love you to build... you will just need to hang on a few hours for the man himself to do his usual rounds...

Christer · 5th May 2007, 02:13 PM

You are aware of this thread?

Incredible quality amplifier by Graham, prepare your ears for it

destroyer X · 5th May 2007, 03:06 PM

There are many units constructed in Brasil.

People loves GEM amplifiers...they are rigth.

regards,

Carlos

hajame · 6th May 2007, 01:06 AM

Um... Seem that it's really a great amp. I am gonna build it.

And I want to clarify that whether the two 8 ohm resistors at the outputs are necessary. If they and an 8 ohm loudspeaker are connected to the three outputs respectively, the load of the amp will become 2 ohms. So I guess the 8ohms are representing another two loudspeakers to show that this amp can drive 2 ohm load. Is that right?

destroyer X · 6th May 2007, 05:57 AM

As soon as possible.

regards,

Carlos

Graham Maynard · 6th May 2007, 06:50 AM

Hi Hajame,

I have added a link to the thread you link above.

As Carlos clarified above - there is no such thing as a universally 'best' amplifier, so don't assume that it will automatically sound better.

If some component values from the GEM were shifted to the Dx, and the same devices were fitted the Dx would sound more like the GEM (and vice-versa) but that is not what Carlos wanted; Carlos has designed a specific amplifier, so have I, so it must be up to a constructor to decide which they might manage to construct, and then which is the nicest to listen to.

Going to watch MotoGP now,

Cheers ........ Graham.

Graham Maynard · 6th May 2007, 10:35 AM

Hi Hajame,

Carlos is so fast with his constructions he became the first person to build a GEM after me.

He had some genuine bias and stability problems causing output device destruction which were not down to the 'Destroyer' himself; now cured.
Also the first circuit had a fractional mix of class-A and class-AB bias currents at the output stage which were audible; now separated.

Before anyone builds they should read this long page first.

http://gmweb2.net/Documentation/GEM...n%20Maynard.htm

In;-

http://gmweb2.net

The matching Mar07 buffer/pre-amp circuit has also been fully tested.

http://gmweb2.net/Diagrams/BUFFER/buffer8307.gif

Cheers ........ Graham.

nhwadia · 13th December 2010, 06:20 PM

Hi Graham!
I am a new member with some experience in constructing valve amplifiers LONG ago (I am 71 now!). I am intrigued by people's comments on the later version of G.E.M. 100W, and would like to try to build your new GEM.
Are there any other "aids" I can look for or receive from you, that can help me, please?
I mean Power supply suggestions, PCB layouts, any thing that can give me a little more support?
Your reputation is awesome on this forum, and I wish to benefit from your knowledge.
Nariman (nhwadia{at} gmail....com)

5th May 2007, 01:24 PM	#1
hajame diyAudio Member Join Date: Jun 2005 Location: Hong Kong	The GEM amplifier Has anyone built this GEM amplifier by Graham Maynard? http://gmweb2.net/Diagrams/GEM/GEM200.gif I am planning to choose a good circuit for low efficiency and low impedance loudspeakers. I find this design very special and rather complex. Lots of large caps are used. But the designer claims it can deal with the back emf of the loudspeakers to control them very accurately. So I am posting here to seek for builders' comments on the performance of this circuit.

5th May 2007, 03:06 PM	#4
destroyer X diyAudio Member Join Date: Feb 2004 Location: Recife - Brasil Northeast	One of the best 8 amplifiers i had listened. There are many units constructed in Brasil. People loves GEM amplifiers...they are rigth. regards, Carlos __________________ Try to build an amplifier folks ... it is pure adrenaline!

6th May 2007, 05:57 AM	#6
destroyer X diyAudio Member Join Date: Feb 2004 Location: Recife - Brasil Northeast	Your post was sent to Graham Maynard..he will answer you soon As soon as possible. regards, Carlos __________________ Try to build an amplifier folks ... it is pure adrenaline!

6th May 2007, 06:50 AM	#7
Graham Maynard diyAudio Member Join Date: Dec 2003 Location: UK	Hi Hajame, I have added a link to the thread you link above. As Carlos clarified above - there is no such thing as a universally 'best' amplifier, so don't assume that it will automatically sound better. If some component values from the GEM were shifted to the Dx, and the same devices were fitted the Dx would sound more like the GEM (and vice-versa) but that is not what Carlos wanted; Carlos has designed a specific amplifier, so have I, so it must be up to a constructor to decide which they might manage to construct, and then which is the nicest to listen to. Going to watch MotoGP now, Cheers ........ Graham. __________________ http://www.gmweb1.net/ and http://www.gmweb2.net/

6th May 2007, 10:35 AM	#8
Graham Maynard diyAudio Member Join Date: Dec 2003 Location: UK	Hi Hajame, Carlos is so fast with his constructions he became the first person to build a GEM after me. He had some genuine bias and stability problems causing output device destruction which were not down to the 'Destroyer' himself; now cured. Also the first circuit had a fractional mix of class-A and class-AB bias currents at the output stage which were audible; now separated. Before anyone builds they should read this long page first. http://gmweb2.net/Documentation/GEM...n%20Maynard.htm In;- http://gmweb2.net The matching Mar07 buffer/pre-amp circuit has also been fully tested. http://gmweb2.net/Diagrams/BUFFER/buffer8307.gif Cheers ........ Graham. __________________ http://www.gmweb1.net/ and http://www.gmweb2.net/


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5th May 2007, 02:05 PM	#2
Nordic diyAudio Member Join Date: Sep 2005	Graham is a very highly esteemed member of this forum, many of the schematics in circulation will not work without modification... He has a newish circuit I am sure he'd love you to build... you will just need to hang on a few hours for the man himself to do his usual rounds...

5th May 2007, 02:13 PM	#3
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	You are aware of this thread? Incredible quality amplifier by Graham, prepare your ears for it

6th May 2007, 01:06 AM	#5
hajame diyAudio Member Join Date: Jun 2005 Location: Hong Kong	Um... Seem that it's really a great amp. I am gonna build it. And I want to clarify that whether the two 8 ohm resistors at the outputs are necessary. If they and an 8 ohm loudspeaker are connected to the three outputs respectively, the load of the amp will become 2 ohms. So I guess the 8ohms are representing another two loudspeakers to show that this amp can drive 2 ohm load. Is that right?

13th December 2010, 06:20 PM	#9
nhwadia diyAudio Member Join Date: Dec 2010	Hi Graham! I am a new member with some experience in constructing valve amplifiers LONG ago (I am 71 now!). I am intrigued by people's comments on the later version of G.E.M. 100W, and would like to try to build your new GEM. Are there any other "aids" I can look for or receive from you, that can help me, please? I mean Power supply suggestions, PCB layouts, any thing that can give me a little more support? Your reputation is awesome on this forum, and I wish to benefit from your knowledge. Nariman (nhwadia{at} gmail....com)

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