Recommend a DC blocking cap?

[tipsy]

My preamp puts out just a tad too much DC and is setting off the DC protection in my amp. Only occasionally. Generally only when inductive or large loads are turned on in the house. Yep, I've tried different outlets and power conditioners, to no avail.

The (tube) preamp maker tells me that I may run into this issue with an amp that is DC-coupled, which mine is.

I've thought about a DC blocking cap on the outputs of the preamp. My worry is transparancy, loss of bass, etc. But, do decent audio caps have to cost $80 each?

I was wondering if anyone can recommend the brand and value of caps to try. Thanks.

 

[belgianbrain]

What voltage are you blocking? I take it your tube preamp doesn't have the signal riding on 200VDC?

I use Duelunds in my tube based DAC. About $400+ for two caps. Unbelievable sound.

But you know what I find comes pretty darned close? Nichicon Muse Bipolar ES. I bypass them with a small Vshay Roderstein MKP 1837. Spend $10 on this and, IMHO, you are not far off of those Duelunds!

This assumes the voltage rating of the electrolytic Muse caps is sufficient for your application.

For a middle of the road approach, I also like Mundorf MCap Supreme. Bypass those by the Vishay and you're spending maybe $40-50 for both channels.

 

[tipsy]

Thanks for the response!
The preamp outputs about 10mV DC, occasionally (a few times per 10 minutes) drifting up to 55mV and back down, and occasionally up to 150mV (once or so every 10 minutes) and back down. This "spike" lasts long enough for my Fluke meter to catch it on peak hold, but not much longer than that. This DC offset doesn't change much as volume is increased, or at 0.

So, I just want to block this small amount of DC, without altering the sound. Ideally, a high-pass filter (FMOD) or similar should work, but that seems like overkill, and the quality of those devices is unknown.

Thanks for the advice on the Nichicon Muse Bipolars.

 

[Lavane]

In some Marantz integrated amps there was some DC build up from the filter board so they put .47uf lytics between the preamp output and input to the amp section. I replaced them with Wima stack films. The Muse Bipolars are good as well. Don't know what value you should use in your case though.

 

[tipsy]

It can't hurt to try 0.47uF. Will the cap, along with the input impedance of my amp, make a high pass filter? If so, it's likely to be a cutoff in the single digit hertz, which is great.

 

[belgianbrain]

I have noticed in my very good sounding Yamaha preamps that they use large values like 10uF for coupling caps. It's easy to go there when you're using an electrolytic.