Adcom GFP-750 just came in, low volume

heiney9

You never answered whether the remote worked, especially the volume control.

H9

chandler9a

sorry, yes the remote works just fine. Everything seems to function the way it should, its just the gain that is off to me. What you explained with your previous post and volume level is what I would expect from this pre but it doesn't seem to be so. Its as if its in passive mode all the time and I have switched that back and forth to check.

heiney9

Not only is the level different in passive mode, but it sounds slightly different as well. In my system it seems a tad drier and a tad less dynamic but it depends heavily on the source material. Also synergy with other gear and especially cables plays a huge role. I run all MIT Shotgun cables and my I/C's have user switchable impedance so maybe that helps a little bit in my case. I don't notice a whole lot of difference when switching the impedance on the I/C's however.

If it helps maybe this weekend I can do what SCompRacer suggested and take some voltage measurements at the output of the pre-amp in both active and passive mode and you can compare to yours.

H9

chandler9a

thanks Brock, that would be great if you are able to check the voltage measurements. No worries if you can't, I just called a shop an hour from me that deals with Adcom gear and they said they could take a look at it for me.

Plus, this place is right near Audio Classics so it will give me an excuse to go check out all the gorgeous Mac gear I can't afford.:cheesygrin:

-Aaron

audiocr381ve

chandler9a wrote: »

thanks Brock, that would be great if you are able to check the voltage measurements. No worries if you can't, I just called a shop an hour from me that deals with Adcom gear and they said they could take a look at it for me.

Plus, this place is right near Audio Classics so it will give me an excuse to go check out all the gorgeous Mac gear I can't afford.:cheesygrin:

-Aaron

Cool dude, glad you're having it looked at. Please keep us posted!

FTGV

heiney9 wrote: »

..... take some voltage measurements at the output of the pre-amp in both active and passive mode and you can compare to yours.

H9

For that to be a valid comparison you'll need to feed each preamp with a sinewave of the same known level and frequency (plus equally accurate meters).

heiney9

FTGV wrote: »

For that to be a valid comparison you'll need to feed each preamp with a sinewave of the same known level and frequency (plus equally accurate meters).

I can't just measure the voltage at the rca output for active and passive and have him do the same? I'm just pyramiding off Rich's suggestion to use a VOM at the output rca's. Atleast that's how I interpreted his comment.

H9

P.s. I guess I forgot it's not a constant voltage coming out of there, duh! And that our VOM's would not be calibarated exactly equal.

FTGV

You'll need a test signal(ie sinewave) that is duplicable on both units.

heiney9

FTGV wrote: »

You'll need a test signal(ie sinewave) that is duplicable on both units.

Can I use my scientific calculator to generate that? It has several sine functions :cheesygrin:

H9

chandler9a

Okay you guys are way beyond me at this point... I got a degree in psychology, not electrical engineering.

audiocr381ve

chandler9a wrote: »

Okay you guys are way beyond me at this point... I got a degree in psychology, not electrical engineering.

lolz

SCompRacer

FTGV wrote: »

You'll need a test signal(ie sinewave) that is duplicable on both units.

I've used test tone CD's to level match output and it seemeed to work OK. IIRC that pre doesn't have as high output as some of the lower in the food chain Adcoms, it is like 5v max on the RCA's? I actually recall that from an old thread at the DIY forum, answered by Nelson Pass. Brock was even in that thread.

A review with specs.

http://www.stereophile.com/content/adcom-gfp-750-preamplifier-measurements-part-2

FTGV

SCompRacer wrote: »

I've used test tone CD's to level match output and it seemeed to work OK.

Yes if they had the same test tone they could compare apples with apples.

A review with specs.

http://www.stereophile.com/content/adcom-gfp-750-preamplifier-measurements-part-2

The measurements state a little above 8db gain unbal which as has been stated on the low side.Most pre's will have atleast 10db of gain somtimes as much 20 db.Volume setting of course will be system dependant ie.source output level ,speaker sensistivity ,amplifier gain,room etc.

chandler9a

Alright, here is the update and I will try to keep it simple.

The good news-My GFP 750 checks out totally fine and in great order.
The bad news, well that' going to take some explaining. I took the Pre to an authorized repair service shop which was about an hour from my house. As soon as the technician hooked it up to his Harman Kardan amp, I noticed the volume was at an appropriate level (6:00-7:00) and the sound was loud, full and clear. NOT what I experienced on my system. So needless to say, he and I both agreed all was good.

I drove home, hooked the GFP-750 back up to my system and there we go again. I had to turn the volume up to 2:00 to reproduce the same amount of gain as I heard at the shop!

I immediately drove to my local hifi shop where I know the guys and told them my problem. They were more than happy to start testing the pre right away on one of their systems to see what the deal was. They hooked it up to their high end Cary gear and some monitor audio speaker. Volume was GREAT! Didn't have to turn it up past 11:00 and it was playing loud and clear...They offered to take it off my hands:rolleyes:

So at this point I am feeling like a crazy person and my friends at the shop are laughing at me. Here's where things start to come together. They happened to have my same amp, GFA-555, at the store and didn't wasted any time hooking the 750 up to it to see what happened. And there we are again, they could literally turn it up all the way without any problems (so now I was not feeling that crazy) and the guys at the shop were scratching their heads. No clipping, no bleeding ears, just kind of loud like I experienced at home. They were surprised at the drastic difference in gain but assured me that it wasn't unheard of and the Preamp was totally fine.

So, I don't understand all of the technical info but it simply looks like input/output of these two pieces of gear together just isn't what you would normally see, I guess. I am planning on keeping the 750 and possibly getting a different amp at some point that works better for me. Also, this might explain why the seller kept his volume at 12:00-1:00, he was using an Adcom 5802 amp.

I'd love to hear your thoughts, I have to admit, I am still VERY surprised in the difference in gains between amps. I would not have believed it if I didn't see it for myself.

FTGV

As I suspected..Are you looking to another amp simply because of the gain issue(which is not indicative of a fault) or are you looking to move up the sonic ladder?I would expect the 5802 to be a move in the more refined sounding direction vs the 555.

chandler9a

I would like an amp that has a better "gain match" I guess, and I may as well find an amp that is a step up sonically as I am sure there are plenty out there. I just have a hard time believing Adcom would design two pieces of gear that didn't seem to match better. It even surprised the technicians.

FTGV

The gain issue really is'nt a fault and doesn't aversely affect the performance of that pairing as long as you can get the level of output you desire.I can only assume the lowish input sensistivy of the 555 relates to the higher gain pre's that Adcom where producing at that time.

chandler9a

Well, there was one concern I had but it might not matter that much. They hooked up some equipment to the pre to determine how much power the amp was producing at full volume and it came to 30 watts. Is that normal? does it even matter? They speakers were full range towers.

You guys would know more than me on this issue but I just couldn't get over the difference in gain. This Pre is high end so I understand the low gain to some extent.

heiney9

It doesn't matter where the volume indicator is on the vol knob as long as you get enough gain to listen at the level you want. Have you maxed it out and still not achieved the volume level you want? It doesn't matter if there is 2 gallons of gas in a 2 gal can or 2 gallons of gas in a 5 gal can, as long as 2 gallons of gas is enough.

H9

chandler9a

Yes, very good point. I have learned a lot with this whole ordeal. For some reason I assumed if the volume HAD to be turned up that much then something could be wrong. It turns out that is not the case. I have not played it at full volume for an extended time nor do I need it to be to enjoy the music. At most probably around 3:00 depending on the song and how it was recorded.

I still want to find a different Amp at some point, something up the latter a bit, but for now I am happy.

Thanks for all the input guys.

audiocr381ve

chandler9a wrote: »

Yes, very good point. I have learned a lot with this whole ordeal. For some reason I assumed if the volume HAD to be turned up that much then something could be wrong. It turns out that is not the case. I have not played it at full volume for an extended time nor do I need it to be to enjoy the music. At most probably around 3:00 depending on the song and how it was recorded.

I still want to find a different Amp at some point, something up the latter a bit, but for now I am happy.

Thanks for all the input guys.

Very interesting. I'm glad to hear the 750 is okay though.

How's it sounding? Is it a massive improvement or something you're getting used to?

FTGV

If your 555 had balanced inputs you would gain another approx. 6-ish db running XLR's from the pre. thus requiring lower VC setting.

chandler9a

audiocr381ve wrote: »

Very interesting. I'm glad to hear the 750 is okay though.

How's it sounding? Is it a massive improvement or something you're getting used to?

I'll have to spend more time with it. From what I've heard so far its just so much smoother than anything I've every had. Bass is great once you turn it up a bit. Tight and pronounced.

I look forward to hearing it on my speakers with another amp however. I have access to an Onkyo Integra M-504 so I might try that on for size.

twochannel

I have had a GFP-750 as my pre for years. I have used this with my 5802,565 monos, and 555mk2 and have noticed very little difference with the gain levels. Most of the time I listen in the 10 to 11 o'clock position active and 1 o'clock passive.

FTGV

A quick check shows that the 555 has a gain of 27 db which is within the range typical of solid state amps,so not unusally low.The 5802's gain is listed a bit higher at 29db.

heiney9

For reference the gain on my Aleph 30 has 26dB of gain and I never turn it up anywhere close to where you do. How big is your room? What speakers and source are you using?

H9

chandler9a

This is why I was confused. I have never turned anything up that high and and would continue to think something was wrong if I did not see the exact same issue at the shop with the same amp I am using (GFA-555). On other amps however, completely different. 11:00 is the most I would have had it at with the other amps we tested.

I Currently have the 750 in my Fathers system and it sounds great, still have to turn it up a bit with his NAD 218 amps but not as much.