Damping factor in DIY amp

[djk]

OK, explain why an Adcom GFA 555 with its high (over 400) DF sounds like a bucket of sludge compared to a McIntosh MC 2120 with its DF of 14?

I should mention the McIntosh also sounded like a bucket of sludge until I added a pair of 47uF bypass caps in parallel with the main filter caps.

 

[TerryO]

Lots of NFB and bring the feedback pick-off point right to the output terminal, assuming no output network. If there's a network between the feedback point and the output terminal, and there usually is, be sure the coil is heavy gage wire, along with the rest of the wiring. Be sure the return wiring is heavy as well. The benefit of very high damping is debatable, since any length of speaker wire quickly destroys it anyway. It's more of a marketing thing.

I think that in the early days of transistors, the enormous amounts of NFB needed to tame the bipolar transistors produced such high numbers (Damping Factor) that it, along with THD, were exploited to delineate the "Advances" in amplifier design that the new devices were ushering in. The numbers took on an importance that the actual results wouldn't have, IMHO.

Best Regards,
TerryO

 

[mhtplsh]

OK, explain why an Adcom GFA 555 with its high (over 400) DF sounds like a bucket of sludge compared to a McIntosh MC 2120 with its DF of 14?

I should mention the McIntosh also sounded like a bucket of sludge until I added a pair of 47uF bypass caps in parallel with the main filter caps.

I hv posted power supply circuit of pro amplifier with modification as
suggested by u.

Pl. see the post :
http://www.diyaudio.com/forums/showthread.php?postid=1617519#post1617519

 

[Wavebourn]

Mechanical resonances should be damped mechanically, right on the place, according to many years of my experience.

 

[traderbam]

Re: sorry a bit long....

just for a moment i would like to revisit the original question.....

Good observations, unclejed.
My experience is that amplifier dc damping factor has a tenuous relationship to how "tight" the sound is and how convincing the sound is, for that matter.
There are amps that sound tight as a nut with damping factors below 50 and there are amps that play tuneful, articulate bass with damping factors below 20.
In my experience, an output resistance of 0.1 ohms is easily low enough for excellent performance, into an 8 ohm speaker.

A simple experiment is to listen to a good bass system and then add increasing series resistance to the speaker cable until you start to notice significant degradation. By the way, with some amplifiers you may find the sound improves with increasing resistance before it gets worse!

 

[unclejed613]

actually how amps sound with large or small damping factors really depends on the speakers and the room. amps with high damping factors can sound great when used at a live venue, such as a PA system outdoors, but sound terrible in a 20X10 room. amps with low damping factors tend to be the opposite. we can pretty much ignore the spec sheet of an amp if it has a damping factor much over 100, since wiring resistances will pretty much limit it to between 20 and 100 anyway (unless the amp is in a powered sub, where you can pretty much do anything you want with the short wires).

the amp with the low damping factor of 14 or less might sound great through one set of speakers, but terrible through another set of speakers. the amp with high damping factor will sound pretty much the same through any decent set of speakers, and this is probably a characteristic a lot of designers are shooting for with high damping factors. room acoustics play a role in speaker resonances as well, and this may also have an effect on the sound of a low DF amp. in fact in some ways a low DF amp "adapts" itself to speaker and room combinations.

i am thinking the idea of using a sense line to a speaker is intriguing, but has to be done right.....