0.300 VDC (from soundcard) on LM3875 GC input !!!

[danielwritesbac]

Just a question : on your x-fi card ouput, would you please check for me if you have the same DC presence?

Its not exactly the same as yours, but mine does output DC. So does an RCA Pearl. So do many modern digital sources.

If you have the extraneous power supply wire plugged into the back of the X-Fi card, you might try unplugging it.
It powers the front panel expansion pack, or in absence of the front panel expansion pack, it causes trouble. 😉
You might also unplug every wire from the X-Fi and then reconnect only the audio output wire.
The CD cable is unnecessary on systems that do full digital transfers--most do, so you don't need that additional ground loop.

Black Gate N type electrolytics are better for coupling than most film caps; use either 4.7uF or 10uF value.

He mentioned budget. Do you recall which Panasonic is very, very similar to those Black Gates?

I'm curious. Why do electrolytics need to be larger than film caps when used at the input filter? They do, and I've never known why. Do you think that 4.7uf or 3.3uf could be sufficient? Thank you!!

P.S. You did Caddock on your kits? I like!! In Aussie, that would be: "Cool bennies!!" 😉

 

[danielwritesbac]

Peter, I was wrong indeed to suggest that there is a cheaper alternative to the Black Gate.

I've been soldering different options in place for hours and come to find out that the Black Gate is the most economical option, being so much less expensive than purchasing several of the wrong thing first. 😉

What specific models do you recommend?

 

[Leglandu]

I have always considered DC-coupled inputs to be a risky proposition and therefore have never done it in any of my audio amplifier circuit designs, especially when the output is also DC-coupled and doesn't have DC protection circuitry.

I prefer to always stay on the safe side, don't want a faulty source device taking your speakers along the ride of destruction!

Good summary of the situation !
Perhaps the risk is still acceptable after a pre-amp or a DAC with high quality output cap in a permanent installation. Now, if the amp can be lent or sold later, the input cap is a judicious choice to avoid... big troubles 🙂

 

[Leglandu]

danielwritesbac,

My card is a simple Extrememusic, no extra-cable connected and CD/DVD directly managed by windows in "numeric" mode, no humm nor distortion, the sound is perfect for me and I appreciate a lot the numeric EQ, nice for tweaking of fullrange drivers...

Blackgate N is not too much expensive in regard to the cost of the double mono GC I'm assembling :
5.9 € (=8.7 USD, including taxes) for a 4.7uf 50V... although less impressive compared to MKPs :
dimensions = 5 x 11 mm 🙁

 

[Peter Daniel]

Peter, I was wrong indeed to suggest that there is a cheaper alternative to the Black Gate.

What specific models do you recommend?

I most often use BG type N 4.7/50; it is approx $3.50 from either percyaudio or partsconnexion. If you need higher values, 10uF or 47/50 is fine too, but 4.7uF sounds to me a bit better.

Although bipolar, those caps are sensitive to orientation and for coupling I prefer long pin on the output.

 

[danielwritesbac]

I most often use BG type N 4.7/50; it is approx $3.50 from either percyaudio or partsconnexion. If you need higher values, 10uF or 47/50 is fine too, but 4.7uF sounds to me a bit better.

Although bipolar, those caps are sensitive to orientation and for coupling I prefer long pin on the output.

Thanks!

That's an odd thing with most of my bipolar caps, no matter what material, they're all orientied backwards. 😉 Maybe I should use a paint marker?

Have you interviewed their 3.3uf? I frequently need that specific value for ecaps.

Thanks again!

 

[Peter Daniel]

That orientation is valid for BG N caps only, I didn't test any other bipolars. As far as I know, BG N are not available in 3.3uF value.

 

[danielwritesbac]

I most often use BG type N 4.7/50; it is approx $3.50 from either percyaudio or partsconnexion. If you need higher values, 10uF or 47/50 is fine too, but 4.7uF sounds to me a bit better.

Although bipolar, those caps are sensitive to orientation and for coupling I prefer long pin on the output.

I'd like to have your recommend for NFB filter cap too. It seems that its fidelity is even more important than the input filter cap. So, what cap(s) do you like for that job?

Thanks again!

P.S. My preference is a big warm sound with much air and not a forwards midrange. 😉

 

[Leglandu]

Hi, I just found out a site about input capacitors and inter-connexion between amp and preamp. It is in French but Google-translation will handle that…

http://www.sonelec-musique.com/electronique_theorie_condensateur_liaison.html

The author says that where an output caps from a preamp is connected to a input caps, a resistor (100K to 1M) is needed between them (to the ground) to fix the potential and avoid a “floating” polarisation of the common legs of the caps.
In the case the resistor is missing at the output preamp AND at the input amp, it can be added directly in the cable plug. As per the author, this avoid some “plop” and a “soft” and distorted sound.

So, to be tested…

Now, I would like to thank you guys for all your help and advices. I got all the answers I needed (for the moment 🙂) and will report as soon as my CG is ended.