I`ve had this problem since I bouth the amp. Got no help from Graaf as they went out of business short time after. As long as I play my music at low volume its working but as soon as I turn up the volume a bit the relay kicks in. And I have tried several preamps and cd players and its the same. I`ve tried to get in contac with Giovanni Marian and other people from Graaf wihtout any luck. Is there any of you out there that know of any people from Graaf that is stil doing some repair or can help solve this problem.
As with most Italian companies, you will not get support even from this manufacturer if one have technical questions - go to
Graaf GM20 mods - help!
and
Graaf Graafiti WTB One - Schematic needed
the main reason for this is that, in order to long-term reliability, none of the models has performed a good circuit design - so I think.
And the GRAAF developer know this.
That means, that also on this solid state model under
Mono and Stereo High-End Audio Magazine: GRAAF GM 400 power amplifier review
a circuit diagram is to be made with help of the disassembled main boards as first step, and in the second step, a circuit analysis has to be carried out in order to eliminate possible weak points.
Unfortunately I don't see a better way.
Maybe one of the members already do this and can upload the schematic.
Mono and Stereo High-End Audio Magazine: GRAAF GM 400 power amplifier review
Graaf GM20 mods - help!
and
Graaf Graafiti WTB One - Schematic needed
the main reason for this is that, in order to long-term reliability, none of the models has performed a good circuit design - so I think.
And the GRAAF developer know this.
That means, that also on this solid state model under
Mono and Stereo High-End Audio Magazine: GRAAF GM 400 power amplifier review
a circuit diagram is to be made with help of the disassembled main boards as first step, and in the second step, a circuit analysis has to be carried out in order to eliminate possible weak points.
Unfortunately I don't see a better way.
Maybe one of the members already do this and can upload the schematic.
Mono and Stereo High-End Audio Magazine: GRAAF GM 400 power amplifier review
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Sorry to say but I think you hit the nail. But since the amp cost me a shitload of money I have to try to get it fixed, somehow. I`ve already made a new pcb layout with all the components with the right values and was thinking of making a schematic out of that. But my brain thinks its too complicated and will not cooperate. So yes, I hope someone have the schematic at hand.
To be specific, I made an exact copy of the main board in Proteus PCB Design. Next step was to make a schematic out of that. THEN my brain refused to cooperate any further.
Probably protection circuitry kicking in due to the offset then, so the DC offset needs addressing? The offset must be at or before the volume control circuit - perhaps this whole amp is DC-coupled?
The Graaf GM400 is a power amp. The offset is at zero when idleing. And start to rise when signal is increasing.
Ah, I see, its signal specific, not volume specific. Something is asymmetric in the feedback path? Electrolytic gone dry?
Yes,I also had the same unwanted situation.
Nevertheless I have get success someday - go for examples to post #51+52 under
tweaking classic Linn LK1 & LK2 / LK280
or post #12 under
Omtec Mono Power Amplifier "CA 25" (CA25) - Schematic wanted
In case of a circuit topology without negative global feedback check out this URLs:
Power amplifiers without negative feedback
No - feedback amplifier
Thule Audio Vintage Integrated Amplifier IA-120 (IA120) Schematic wanted (post #9)
Maybe this helps a little while creating of schematic diagram.
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My first attempt to make a schematic of the driver board. If you see any logical failure in the schematic, please let me know.
It doesn't look very good. Perhaps it's just the way it is drawn. To begin with you should have the positive PS rail on top.
Ok. Just flipped the drawing if it helps. But what isnt good? The layout of the driver or the way I have made the drawing? I`m not so good at making schematics from looking at a pcb. 😱
