Someone wanna trade me their adcom 4 channel for 2 ppi a600.2?

[ppia600]

I probably should just stick to my tried and true ppi's with their headroom and no fan noise but I'd like to try an adcom to see if its worth all the hype. People seem to think they are worth more than their weight in gold for some reason and I'm curious.

So yeah, someone want my two ppi a600.2 amps for their four channel adcom car amp? Also, I don't want to trade for one that's been repaired. The only repair on my amps are the new rca input jacks I installed on one. Both amps work perfectly.



If this thread needs to be moved, please let me know where it goes to, lol.

[1moreamp]

Good luck on your search my friend. I happen to own several GFA series amps, and the matching line driver crossovers. They just don't build things like this anymore ya know...They were a one of kind type amplifier for the car.

I think you will find them very nice to listen to for very long periods of time with out fatigue of your auditory senses. This is why I like mine so much. The rest is just spec's and bolstering.......C

[ppia600]

So which ones are you using in your vehicle?

Originally Posted by 1moreamp

Good luck on your search my friend. I happen to own several GFA series amps, and the matching line driver crossovers. They just don't build things like this anymore ya know...They were a one of kind type amplifier for the car.

I think you will find them very nice to listen to for very long periods of time with out fatigue of your auditory senses. This is why I like mine so much. The rest is just spec's and bolstering.......C

[1moreamp]

None currently, my GFA-5475 is brand new in the box still sealed , and my other two GFA-5275's have been pulled due to security reasons. But they will soon see a new car to play in. I sold two white GFA-5475's over the last few years, and I have not forgiven myself yet...

[ppia600]

That's what I was wondering. You see, I've never actually heard or seen one running in someone's vehicle yet people claim they are great. I've never listened to one in an audio shop and I used to visit tons of them (high end and "high end" lol) in California. I have listened to hafler, soundstream, blade, etc in shops though. What are the most common issues the adcoms have as far as repair? Leaking caps like most amps or are there any other things to look out for?

Also, why would you need the "line driver crossovers" with the high preamp voltage and built in crossovers decks have today? Wouldn't that just add noise and distortion? Couldn't you use the din converters and get great sound?

Originally Posted by 1moreamp

None currently, my GFA-5475 is brand new in the box still sealed , and my other two GFA-5275's have been pulled due to security reasons. But they will soon see a new car to play in. I sold two white GFA-5475's over the last few years, and I have not forgiven myself yet...

[1moreamp]

Originally Posted by ppia600

That's what I was wondering. You see, I've never actually heard or seen one running in someone's vehicle yet people claim they are great. I've never listened to one in an audio shop and I used to visit tons of them (high end and "high end" lol) in California. I have listened to hafler, soundstream, blade, etc in shops though. What are the most common issues the adcoms have as far as repair? Leaking caps like most amps or are there any other things to look out for?

Also, why would you need the "line driver crossovers" with the high preamp voltage and built in crossovers decks have today? Wouldn't that just add noise and distortion? Couldn't you use the din converters and get great sound?

The Adcoms have a balanced input so a balanced line driver is typically used to drive them with up to 8 volts of pretty much noise free signal level. BLD's were top of the line back when these were made and only top end gear had this option back then. Even PG built BLD's in receiver/transmitter pairs to achieve the same thing. Noise free system interconnections like the studios still use today.
Adcom made DIN to RCA adapters for those choosing not to use BLD operation. No biggy, I just think if your going to use one of these for SQ then following Adcom's advice and using their auxiliary components is just second nature. It's pretty good gear so I run with it, and back then its was all top notch gear for what it was. The 90's was a golden era for car audio coming into its own, with all sorts of studio grade options and what not. These things are not so popular nowadays. but then again neither is someone spending 22K on a system either.

I own some unique things from the past Like Carver bass processors, and center channel adapters, and the Very rare Blade bass enhancer. All toys in the attic now but very precious to me as history and keepsakes.

I tested the adcoms for the dealership in San Jose that was considering carrying them. I shorted a Adcom 60 watter out in mono with screw drivers being powered off a Lab grade Harrison type HP power supply rated at 50 amps continuous at 14 volts DC. The amp pulled the HP supply all the way down and never failed even dead shorted at 50 amps draw. NO other car amp ever past this test back then, since most of them barely had any protection circuitry in those days. The Adcoms have no protection circuitry at all, except for their raw design. And it went back to playing music like nothing ever happened to it at all. It did warm up a bit and make it fan run at full speed for 15 minutes like this, but it never shut down and it never failed.
They are a all Mosfet design except for a single Darlington current source for the input pairs. The outputs were all matched 2% or better gain spec at build, so the current shared properly to begin with.
I have often asked those that are in the know of things if the honorable Nelson Pass had anything to do with the designs of these amps. The frontend input and class A driver sections are typical Nelson Pass design configurations, only the output is different IMO, as it appears to be typical somewhat of standard class AB outputs, not class A like Nelson Pass's renowned work is.
It's about as close as to Mr. Pass's Mosfet design work I think you will ever see in a car amp. If your interested in his work please click back to the front page of the forum, as I recall he has his own section on this forum. Yes I am a big fan of his work in the audio industry. All of his gear is unique and very interestingly designed, and most all of it is Class A design work. His work and projects make for very interesting reading. A very smart fellow again IMO.

The amps are very simple inside with a two mosfet input pair and a 4 mosfet class A driver stage and the output stage. Total for a 75 watt amp is 10 mosfets with one Darlington transistor current source for the input stage. The GFA series has a huge heat sink located internally and it was variable speed fan cooled, controlled by temp sensors.
Caps were in huge banks in the supply side which was isolated to the other side of the sink away from the amps side and inputs. The caps were all high grade snap in types arraigned in banks that were the envy of the industry back then. They caps and their numbers were a advertised selling point of these amps. If you look at Amp-guts over on DIYMA you will see the huge banks of internal storage filter caps. I believe as with most amps the power supply was the big design control point that helped make these amps sound the way they did and kept them alive even in the face of utter stupidity, and shear brutal testing even the like that I use to do in my younger years.

Oh the dead shorted output was a old Phase Linear test I robbed to use as to test safety circuitry operations. So absolutely no credit is deserved to me for any of the above.

The Adcom's sound uniquely different. Not like tubes but not like Bi-polar transistors either. Sort of in a class of their own. By the way one of the Adcom's I sold went to the president of XXX Car amps for his own car, so I think you will find yourself in good company if do manage to buy one of these amps. He even said he liked the way they sounded. And I must agree with him myself.....I am also sure I have exceeded my posting limits on the DIY with this post so if you want to just PM me, I'll be glad to share any info I might have.....

[1moreamp]

Oh there are a bunch of Adcoms on sale on that auction site. I cannot recommend doing business with that person. Been there, won't do that again...PM me for the reality check.

[ppia600]

I'll keep looking, might even find a two channel but not sure if I'd be happy running front and rear mids on the same two channel. The way my car is designed its difficult to keep the front stage up, the rears overpower them unless the fronts are at higher volume. I may modify my doors to get a better stage but until then...


And running the phd3 will be wasteful if I dont' have plenty of mids/highs spl to keep up for the fun times

[ppia600]

Well I found a 5450 for $225 shipped, can't wait to see how it sounds. I'll probably replace most of the caps with 105c versions. Looked in good shape. I would have bought a 5475 from him but its huge and I needed room for the phd3 next to it. I may buy 2 ohm components to get more spl or just go ahead and mod the heck out of my doors and rear deck for the kicker cvt65 subs. I'm curious to see how it will sound without the balanced adapters, may have lots of engine noise. Otherwise I might end up looking for a pair of those but we'll see.

So yeah, I'm not looking for one anymore and I guess I'll keep the arts for now.

[1moreamp]

The BLD's that come with it are very basic < the little box's with RCAs on both ends >. I have those and the much larger BLD Crossover modules that allow for crossover modification by SIP modules. The size difference is a lot < a box with 5 pin DIN connectors out and RCAs in.
You could use just about anybodies Balanced line driver as long as you have the pin outs to match up to the RCAs Tip and shield connections correctly.

The big deal about the Adcom and the BLDs is that the Adcoms are No IC's and your plugging directly to the input stage of the main amps after a gain control of course. On 90's era gear 2 volts was just not enough to really drive the Adcom very well, this plus the desire for max SQ lead to the Balanced line driver setups. BLDs were the way to go back in days gone by.

remember that just about anybodies BLD will work if connected properly...