Adcom Gfa-555

Sami

And my apologies if someone took any offense to what I said, it certainly was not meant to be that way.

DarqueKnight

heiney9 wrote:

The original GFA series was in fact designed by Nelson Pass and was pretty much the same as the regular production model of series I amps. Adcom made some cost cutting measures which they felt very minimally affected the performance, but the circuit design was essentially the same.

Email exchanges I have had with Nelson Pass lead me to believe that he was, and still is, a little bit pissed off with Adcom about those "cost cutting measures".

DarqueKnight

heiney9 wrote:

Series II amps are capacitor coupled meaning rather than using a differential pair of tranny's to "couple" the front end (input) to the backend (output) they used capacitors.

Personally I prefer the series I amps because they are direct coupled, with a more simplistic design (less parts).

The GFA-555 Mk II was a direct coupled design (see last paragraph of page 1 of the owner's manual). The GFA-545 Mk II used a servo circuit to minimize DC offset voltage.

heiney9

DarqueKnight wrote:

The GFA-555 Mk II was a direct coupled design (see last paragraph of page 1 of the owner's manual). The GFA-545 Mk II used a servo circuit to minimize DC offset voltage.

Owners manuals are notoriously incorrect. As far as I know (regardless of the owners manual the series II were capacitor coupled). This comes from a tech who is very well versed in Adcom products. And yes, Nelson was a bit dismayed at the final product; but Adcom never mentioned him by name. You have to know the Adcom history to know he was inovolved. Same goes for Nakamichi; he was not thrilled with the way Nak incorporated his Stasis topology. When it was originally concieved, a reciever was not the ultimate end result. The Nak amps are nice sounding amps but the Adcom, IMO, is a much more revealing amplifier.

H9

EDIT: He was thrilled at the money Nak paid him for the rights to use the STASIS trademark.

Systems

Interesting,I was not aware that N Pass was involved in the 545/555 series of amps.I knew he worked on some of the later models.
At least Nak paid him for the use of the Stasis circuit.Most of the big Japaneese manufacturers copied the concept and called it by their own name eg.Technics New Class A,JVC Super A.

univera

What the hell is DC offset? This is a great site, but sometimes, you technically gifted people completely forget that many of us here aren't electrical engineers/techical gurus and don't understand this stuff. Heiney, while I completely appreciate your vast knowledge and helpful persona, your earlier breakdown is great for people who understand that stuff. But with all due respect, you might as well be speaking Chinese. You go into this long, techincal explanation, but you don't bother to explain the significance of of "DC offset" beyond mentioning the design will reduce noise levels caused by such an occurence.

It would be a big help when you give super detailed, techincal explanations, that you explain what something like "DC offset" is and why it is important/relevant to a great sounding system. I understand it has to do with noise, but I don't understand it on a lay level anymore than that. I know good sound and good equipment, but that doesn't mean I understand why it sounds great.

Additionally, there are some people, with all due respect, who don't take the time to type a coherent thread that makes sense. Perhaps grammer and proper sentence structure is completely passe these days....It's just some threads need an interpreter to figure out. Choppy, funky threads. If you want to be understood, take the time to make sense by typing a sentence someone can understand. (Not you Heiney. I'm referring to the incoherent, non-technical attempts at the English language.) I am certain I am not the only one who thinks this way. Write a thread and actually re-read it to make sure it is coherent. I leave out words many times in my haste when typing a thought. It seems some tend to leave out half a sentence...

Cfrizz, thanks for your down to earth talk. I am with you. I don't want to upgrade every other month. I'd rather lay down my money and get the best within reason and be done. I waited until I could buy the best t.v./hi-fi I could afford instead of jumping the gun and getting something of lesser quality/power.


However; I do like the tubes... And yes, I did wake up on the wrong side of the bed this morning. A Gamecock win would have alleviated that...

heiney9

Sorry Uni....sometimes I get carried away and forget many don't share my "geekyness" when it comes to learning about how audio equipment works. I'm by no means a tech when it comes to this stuff, but I do like to understand the principles and how different designs affect things. I gotta run right now but I will post a bit more of a layman's explanation perhaps later tonight when I have time.

If you have some time here is a great link to AudioKarma on a thread started by Echowars a very knowledgable guy. This is a long thread but if you take the time to read it you might begin to understand it a bit.

In a nutshell DC (direct current) in large amounts is bad for speakers. You primarily want AC (alternating current) in the output signal. High DC output usually means you have a problem somewhere. There are many methods to control/reduce DC offset to minimal/insignificant levels which all have pro's/con's and affect performance.

http://www.audiokarma.org/forums/showthread.php?t=5634&page=1&pp=15

heiney9

Ok Univera, I promised a bit more of a layman's explanation of DC offset, so here it is.

When an amplifier delivers DC (direct current) to a speaker, the speaker cannot do anything with that DC but turn it into pure and simple heat. If this DC component of the signal is low, it will be effectively insignificant, of no practical consequence. However, if not so low, it will do two things. One is to produce more and more heat in the speakers, which is bad for the speakers as it heats them up and causes them to change their operating parameters, and the second is to effectively blur the sound you hear, since the speaker cones are busy heating up instead of reproducing sound.-- www.tnt.audio.com/clinica/bias_e.html

Some amps have manual trim pots to adjust DC as parts lose tolerance or if they were a bit lazy and didn't match output tranny's etc. Some amps use capaciter coupling which effectively blocks DC, but can color the sound and can wear out over time. Yet others use a servo which detects and compensates for DC offset. All methods have advantages and disadvantages.

If you read thru a few of the first posts at the audio karma link I provided you will see the importance of checking DC offset if you have an older amplifier/reciever. It's simple, safe and gives a good indication of the condition of the unit so you don't blow up your speakers.

Hope this helps.

H9

heiney9

So Aaron did Doug make it over the other night with the Outlaws? Sorry I couldn't make it just too busy this week.

H9

dkg999

H9 - headed over in a few hours with the Outlaw M200's and a Parasound HCA-1000. Doug.

heiney9

dkg999 wrote:

H9 - headed over in a few hours with the Outlaw M200's and a Parasound HCA-1000. Doug.

Damn, when is a few hours. It would be great to join you guys but I've got to get some things done around here today.

Brock

dkg999

H9 - 1 pm is when I plan to get over to Aaron's.

Lowell_M

heiney9 wrote:

Damn, when is a few hours. It would be great to join you guys but I've got to get some things done around here today.

Brock

Sorry Brock...I didn't see your posts! Come on over. I'll PM my phone number!