Yaqin and Musical Fidelity Tube Buffer Questions

This post just seemed to end for no apparent reason about 18 months ago, and a few of the questions were left open ended.

For one, clint_e had successfully added an Epcos 33uf/400VDC electrolytic cap to the power supply side of the 2-tube CD-2, and a member with the 1-tube CD-1 version had asked what value might work on the CD-1.

I just purchased a CD-1 and would like to know how to calculate the proper value to use.

Thanks.
gw

This post has been edited by inspired on September 26, 2009 09:41 pm

I came to the conclusion that the best upgrade we can do to this cathode follower or as we call it a buffer, is changing the polyprop caps to better ones and also by-passing the litycs with good polys, too.
I have done this and it sounds fantastic.
Something like this:

Attached Image (Click thumbnail to expand)

I understand a lot more can be done, but that single 33uf/400VDC Epcos electrolytic cap you added to the CD-2 seemed like an extremely easy and cost-effective tweak.

The CD-1 insides (image below) look very similar to the insides of the CD-2, but the main cap values are different so I'm guessing the 33uf value you used on the CD-2 may not be the right value for the CD-1 single tube version.

So in your image all of the RED polypropylene caps were replaced, and the 3 GREEN polypropylene caps were added?

Yes. The red ones are WIMA (MKT) and the by-passing ones (green) on the rectifier bridge and to ground are ERO (MKT). If you're going to do this mod becareful of the residual electric current from the big filtering caps.

Thanks for the help!

My only problem is that I can't find a schematic for the Yaqin CD-1 and I'm sure they are different than the values on the CD-2

It looks like I won't be able to learn any of the polypropylene capacitor values until I de-solder the whole thing, and then I'll be shut down until I can source the parts and get them delivered here.

Replacing the originals (blue color in my photo) is no problem as I will simply be matching value for value, but I am curious how you calculated the values for those used to bypass rectifier bridge electrolytic caps. Again, I believe the electrolytic cap values for the CD-1 are different than the CD-2.

Generally 1uf works very well when by-passing caps. Caps bypassed to rectifiers/diodes are used to smooth the cut off reverse current peak which causes HF distortions. The smaller a cap is, the better it performs in the higher frequency range
The best i ever tried was 0,1UF M-Cap Supreme from Mundorf.

Generally 1uf works very well when by-passing caps. Caps bypassed to rectifiers/diodes are used to smooth the cut off reverse current peak which causes HF distortions. The smaller a cap is, the better it performs in the higher frequency range
The best i ever tried was 0,1UF M-Cap Supreme from Mundorf.

Do you think there would be a noticeable improvement just bypassing the electrolytics with a good quality poly cap, but NOT replacing the other poly caps that came from the factory?

This post has been edited by inspired on September 29, 2009 06:10 pm

Generally 1uf works very well when by-passing caps. Caps bypassed to rectifiers/diodes are used to smooth the cut off reverse current peak which causes HF distortions. The smaller a cap is, the better it performs in the higher frequency range
The best i ever tried was 0,1UF M-Cap Supreme from Mundorf.

Do you think there would be a noticeable improvement just bypassing the electrolytics with a good quality poly cap, but NOT replacing the other poly caps that came from the factory?

Yes, I do.
At least in the high frq range. More definition and accuracy in the upper freq range.

I just want to verify, you used 0.1uf (1 tenth of 1uf), but are also saying anything up to 1uf (One uf) is generally acceptable?

I just want to verify, you used 0.1uf (1 tenth of 1uf), but are also saying anything up to 1uf (One uf) is generally acceptable?

Yes.
Generally, and as a rule of thumb, you can try with 0.5% to 1% of the base cap to improve the effective high frequency performance of the base cap.
Keep us posted.

I've purchased Mundorfs from this company before so I'm going to get an order in the works for a couple of the .1uf Mundorf Supremes today.

http://www.madisound.com/manufacturers/mundorf/cap-ms.php

Awesome! Mundorf are very good.

The bypass caps will be here soon and I'm pre-planning the simple mod ahead of me.

What's the best, safest way to discharge the current from the filtering caps?

The bypass caps will be here soon and I'm pre-planning the simple mod ahead of me.

What's the best, safest way to discharge the current from the filtering caps?

Since they are small caps just touch the two lead terminals with the tip of a screwdriver with insulated handles and thats it. Even tough i advise you to use some gloves and eye protection.
Handling high-voltage capacitors, on the other hand, is a different story.