Citation 12 Questions

[audioboy]

Helo everyone,

I've recently completed Nelson Pass's Citation 12 amplifier. Sounds absolutely wonderful! Thank you so much Nelson pass! I have a few questions, however, the voltage of the speaker output is 0.14v on one side and 0.12v on the other. Some people said that it should not exceed 0.1v, is this normal? Also, when I turn the volume up swiftly without any music on, there's a moderate scratchy sound coming form the speakers. The noise doesn't kill your ears, but it would be great if I could eliminate that problem.

Any help would be appreciated.

Allen

[Nelson Pass]

So nice to see older projects still getting built.

The .14V is a bit much, but is not likely to do any damage.
Is it positive or negative?

Is the circuit identical to the published schematic?

As to the scratchy sound, I assume that you are running a
pot right on the input, becuase a scratchy sound during
silence means that their is either some DC on the pot. This is
not much of a problem - if you are directly coupling the input
of the amplifier to the pot, then you are most likely seeing a
smal amount of DC on the input, and this may relate directly
to your offset.

[anatech]

Hi Nelson,

The .14V is a bit much, but is not likely to do any damage.

True. I like to call 50 mV defective though.

As to the scratchy sound, I assume that you are running a

No doubt about that! Is the control after C2?

Hi Allen,
Did you match the input transistors? Q1 and Q2 should be both high gain and the beta should be matched between the to. That is why the original part was a dual part. They should be tied together so they are the same temperature as well. Also check that R1 is the correct value (12K).

-Chris

[audioboy]

Hi,

Maybe it won't do any damage in like ten minutes but long-term-wise, would it have any affect on my speakers? I didn't exactly build this whole project my self. I'm only 16, so, I don't really have the skill to analyse schematics yet. I often find it hard just to build from certain schematics. And since I'm only a kid, it is also better for me to built it from a kit because it saves money and time.

Yes, I am currently using a pot as volume control. Last time I checked the schematic is almost the same with the power supply being the most different. R1 is 18K though.

This is not much of a problem - if you are directly coupling the input of the amplifier to the pot, then you are most likely seeing a smal amount of DC on the input, and this may relate directly to your offset.

Sorry Mr.Pass, I don't quite understand everything you've just said. Do you mean to say that the scratchy noise lead back to the output voltage?

Nope, I did not match the transistors at all and just soldered them on board randomly. Sorry if this is a stupid question but how would I match the input transistors?

The .14V is a bit much, but is not likely to do any damage. Is it positive or negative?

What do you mean by that? I'm so confused

I have attached the schematics that I used to build the amplifier. The Q1, Q2 and Q3 have been changed to MPS8599. Output transistors are replaced by IRFP240.

Sorry if I'm not able to understand all your replies, but help is better than no help so I am very gratefull.
Thanks again!

Allen

[audioboy]

I'm not sure if I attached the file correctly, so I'm gonna try one more time.

[Nelson Pass]

Well, is the DC on the output positive or negative?

[audioboy]

The DC on the output is negative. Why does the output voltage drop from 0.12v to 0.03v when I have the signal cable connected?

Allen

[anatech]

Hi Allen,
Firstly, please use the built in quote function. It's much easier to read. It's the button above that says "Quote" and looks like

[.QUOTE] text[./QUOTE]

. I had to add the periods, they are not normally there.

The DC offset drops because your source is providing a resistance to ground. Can you draw by hand how you added your control please?

-Chris

[audioboy]

Hey Chris & Mr. Pass:

Sorry about the misleading quote thing.

I didn't add a control, my control is the same as a passive preamp so it's in a seperate box. Nothing much to draw about that. I just connect the input of the pot to the input, output to output, and gnd to gnd + box.

Allen

[Nelson Pass]

What about the 10kohm to ground on the original?