Superphon: DC offset a serious problem?

[kirk57]

I was over at the AudioKarma site and in the 'Vintage Solid State' forum there is a sticky about DC offset in solid state amps.

I measured my 23 year old Superphon DM200 amp and found about 60 mv DC on each channel. Some questions:

1) Is this enough offset to be concerned about?

If yes, then:

2) Can I simply adjust the bias to reduce this offset or is it more involved than that?

3) Does anybody have a schematic for this amp? (hoping beeger sees this....)

Thanks in advance guys.

Kirk

[nigelwright7557]

Originally posted by kirk57
I was over at the AudioKarma site and in the 'Vintage Solid State' forum there is a sticky about DC offset in solid state amps.

I measured my 23 year old Superphon DM200 amp and found about 60 mv DC on each channel. Some questions:

1) Is this enough offset to be concerned about?

If yes, then:

2) Can I simply adjust the bias to reduce this offset or is it more involved than that?

3) Does anybody have a schematic for this amp? (hoping beeger sees this....)

Thanks in advance guys.

Kirk

The offset is not enough to worrry about in my opnion.
Its hardly going to move the speaker if at all.

Many amps have a preset on the pcb to adjust the DC offset.
But be careful coz some amps also have a bias preset as well and adjusting that instead could fry the amp.

[Bigred]

Originally posted by kirk57
[B]I was over at the AudioKarma site and in the 'Vintage Solid State' forum there is a sticky about DC offset in solid state amps.

I measured my 23 year old Superphon DM200 amp and found about 60 mv DC on each channel. Some questions:

1) Is this enough offset to be concerned about?

Not enough that its going to cause any harm but enough IMO to look into it, especially if your amp has provisions for adjustment.

2) Can I simply adjust the bias to reduce this offset or is it more involved than that?

The bias is completely different and I WOULD NOT go messing with it unless you have a clue what your doing. No disrespect but its obvious you don't.

3) Does anybody have a schematic for this amp? (hoping beeger sees this....)

Sorry can't help but I would leave well enough alone until you DO get a schematic and/or SM and then be very clear about what you are doing and adjusting.

[kirk57]

No you're right, I don't have much experience with solid state stuff and haven't messed with it much since engineering college many years ago.

Still hoping to find the schematic, won't touch anything until I do...

[Nelson Pass]

Check it after it's warmed up for an hour or so.

[kirk57]

This amp is always on...when I think about it , it's probably been turned on for a good 20 years of it's life!

[EchoWars]

The 60mV you're measuring is not ideal, but harmless to your speakers, the amp, your cat, and your cholesterol level. If there's an easy way to reduce it, go for it. If not, don't lose too much sleep (but by learning how to reduce it, you might learn something about amps ).

I started the thread at AK about offset years ago, and it was made a sticky by the mods. Don't ask why it is 100 pages long & 2500 posts. Perhaps just the concept that the non-tech types can check and maybe tweak something besides an IC cable strikes a chord with them. Still, I'd like to think that I saved a few speakers from destruction on amps without protection circuitry. Consider that my contribution to the hobby.

[kirk57]

Echowars-

Ah so that was your post over on AudioKarma.

OK, so if my speakers are not in any danger (or my cat)
is there an impact to the sound of the amp by having this much offset?

If so I'd like to see it can be addressed, first step is to find a schematic.

Kirk

[h_a]

Originally posted by kirk57
is there an impact to the sound of the amp by having this much offset?

Nahh, stop worrying about that. Your speakers do not care about some mV of offset. You can adjust it if you find it interesting, informative or you're outrightly bored.

Have fun, Hannes

PS: after 20 years you could change the caps

[AndrewT]

Electrolytics and 200,000hrs of use could be an indicator that cap replacement is due.
I wonder how hot they have been running?