[tigger]

When omitting the input caps on a Cmoy, do resistor values change? I know about the risk of leaving out the caps but would like to try it anyway.

 

[tangent]

Quote:

When omitting the input caps on a Cmoy, do resistor values change?

No.

 

[was ist los?]

What advantage does omitting the input caps have?

 

[tangent]

Quote:

What advantage does omitting the input caps have?

It's answered in the META42 docs.

 

[Tomo]

Hello,

Omitting input coupling capacitors will improve accuracy. However, it comes with a grave risk. Incoming DC voltage may kill your headphones. So make sure that your source has absolutely no DC offset. Also, some chips might have input DC offset due to leakage current.

I bypass with 1~2kohm resistors like ppl instructed loooooong ago. I don't remember the reasons. I upgraded these bypass resistors with esoteric carbon resistors later.

Tomo

 

[tigger]

Tomo, So what you are saying is you use resistors in place of input caps, not just jumpers?

 

[Tomo]

Yes,

It has to do with attenuating signals to protect FET inputs. They are very vulnerable. Bypassing caps with a wire is not necessarily good idea since spark may damage your FET inputs.

Although the bypassing resistors will protect the fet inputs, DC offset will get amplified by opamp to create significant offset voltage at the output. This is also a problem. This one will kill your headphones. (potentially)

So skipping coupling cap is like working around a bookbag full of waterballons. It is a matter of time before an accident happens. But then if you will never ever fall, it is ok. ... You get the picture?

Tomo

 

[Tomo]

So,

In another words, this is an upgrade if fail can cause serious damage. So if you are not confident about your electronics expertise, it is simply NOT recommended.

Get a super spec caps. 0.1~1uF super high quality cap cost like 5~10 dollars. If you get lucky, you can get bulk from some dude in Ebay. I got a huge load of Siemen MKP 0.47uF 250V (WIMA-like) for a dollar a pop. They sounded superb in my CMOY amp.

(Or you can get super confident in your understanding in electronics. ... But then that could take many lunch time reading.)

Tomo

 

[tangent]

You don't need an inline resistor in the META42 if you jumper C1, because R1 is already inline with the FET inputs of the op-amp.

 

[tigger]

Getting back to the original Cmoy scenario, what value resistor would one use in place of C1?
As far as amplified DC goes, it is my understanding Meier Audio Corda amps use no input caps without any reported problems.

 

[tangent]

Oh jeez, I guess I've got META42 on the brain....Sorry about that. But the solution is the same: do like the META42 and put a 1K resistor there.

 

[tigger]

Thanks Tangent