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Old 11th January 2004, 07:34 PM   #1
Ossi is offline Ossi  Germany
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Default Adcom GFP-750

I do not know exactly if this is the right place to post this, but as I know that Mr. Nelson Pass as design this Pre/Amp I thought of asking my questions over here.
First of I do not have this Pre right know, but I was thinking of buying one. However I did read several reviews where one complain was the implementation of the remote functions, expecially the delayed volume reactions.
So I am wonder if someone has a service manual of this pre to look up this problem. I could not find one on the net yet.
Maybe someone knows a way arround or has updated the unit itself already?
Thanks,
Oliver.
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Old 12th January 2004, 04:58 PM   #2
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Hi Ossi,

I've heard great things about this preamp. I've just put together a BOSOZ, and the total cost was about $250 USD for the parts. This was after some shopping around. I will need to invest another $100 USD to get it configured with the right number of connectors and other basic final build items not yet put together.

Right now on eBay there is a 220v GFP-750 for sale in California for a little over $400! No one here can use 220v here and will need they pay extra for a 120v conversion. With the Euro conversion to the dollar, I bet this is a great deal.

At that price, I personally would not be bothered by the issues mentioned if true.

http://cgi.ebay.com/ws/eBayISAPI.dll...category=14974

Good luck,

-David
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Old 12th January 2004, 05:22 PM   #3
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Just for the record, I licensed the circuit to Adcom (before the
ownership change) but am not otherwise involved. I haven't
seen inside the unit, and don't have the schematic, so I can't
be helpful here.
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Old 12th January 2004, 08:43 PM   #4
Ossi is offline Ossi  Germany
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Thanks for the replies. I have checked the one on Ebay and will keep this opportunity in close memory.
However if someone here has a clue where I could get the schematics or order them this would be very welcome. I have so far checked some sites to no avail.
It is kind of problematic to ship a unit around the world in case of problems that one could solve itself with the right papers on hand. Furthermore as the GFP 750 is not available in Germany and I even think it is nowhere in Europe.
I have done some research on basic remote control schematics and I do guess that the delayed reaction of the volume control is related to a capacitor that seems to be needed to deliver the power to overcome rotary start moment of the potentiometer motor. Therefore charging/discharging it could be responsible for the cause as this occurs only after engaging a volume change with the remote command. Obviously this is a cheaper way of realising this function as a "power gate" would imply considerably more parts.
I will go into this once I have a unit.
Thanks,
Oliver
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Old 13th January 2004, 09:16 PM   #5
mlloyd1 is offline mlloyd1  United States
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ossi:

Adcom has never turned me down when I offered to buy a service manual for any of their products including the 750 preamp.

It's been a long time since I ordered anything from them, but a google search may show a link to their service department.

I've heard the 750 in a nice setup - it's a very nice sounding piece (no surprise, I suppose)

mlloyd1
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Old 14th January 2004, 11:35 PM   #6
Ossi is offline Ossi  Germany
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dw8083:

I used my chances and got the one on Ebay (230V).
Now I hope the preamp will find its way to me (hopefully within the next 2 weeks) and that it is in good optical and technical shape. Still looking for a remote ...
Thanks,
Oliver
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Old 15th January 2004, 03:05 AM   #7
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Hi Oliver,

Congraulations! I'm sure everything will work out fine. I've bought several computer and Hifi components on Ebay with good success. In fact I just received an Adcom GDA700 DAC for my Marantz CD63 SE. The unit performs alot better than the on-board Marantz DAC. It also has balanced outs for my BOSOZ. http://cgi.ebay.com/ws/eBayISAPI.dll...category=14980

Keep an eye on Ebay. I've routinely seen the 750 remotes for sale between $20-40USD. Might check with Adcom to see if this one will work: http://cgi.ebay.com/ws/eBayISAPI.dll...category=15065

Comeback to this thread and give us your analysis of the 750 preamp once you've had a chance to listen and check it out.

Take care,

-David
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Old 15th January 2004, 04:57 AM   #8
amt is offline amt  United States
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I have owned my GTF750 for 3 years now and love it. I was upset at the delayed and slow remote volumn function at first, having been used to quicker and faster versions on other equipment. But I later found that the "lethargic" operation made for much more precise volumn control on my high efficiency speakers. My previous preamps took alot of quick up and down button pushing to get it right but the Adcoms' slower creap makes a very precise selection easy. It is more annoying though when I use it with my Magnepans and have to wait to get the wattage ramped up but better this that no finite control on the low power/HE combo.

Ossi, I will see if I can get one of several "universal" remotes I have to operate the Adcom. If a $7 All4One will work, at least you can find a factory one at your leasure. I will post back if I have any luck.

amt
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Old 19th January 2004, 05:44 PM   #9
wayne is online now wayne  United States
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The GFP750 used an NEC transmitter chip when I wrote the original software for it. The reciever feeds into an 87C750 series microcontroller. Most of the speed of the remote is due to software delays used to make precise adjustments. The cap across the Alps Pot has little effect but to smooth response and lower noise.
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Old 4th May 2009, 03:32 AM   #10
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yes just wonder what is the 750 based to? aleph-p? or x ?
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