Coupling cap bypass

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Coupling cap bypass
« on: 24 Dec 2015, 03:56 am »

A few pictures of my first tube amp.  It is a Tubelab SE (TSE) built for 45 tubes. After a few sorting out issues it is playing wonderful music.  Mills  upgraded wirewounds for power supply and Takman Rey for 1/4 watt metal resistors.  From the reports on sound I thought all along that AudioCap Theta would be the ticket for coupling and it is hard to believe 1 1/2 watts can sound this rich.  There is good sense of depth and the recording venue really is portrayed well.  I have around 125 hours on it right now.  I know the theta's take awhile to brake in

I would hate to upset the whole tonal picture but is there anything you would recommend as a bypass for the coupling caps to add a little sparkle?  It is not that anything is missing it is not.   Do I need to give these more play time?

Another question slightly off topic.  This amp has a separate power supply supply for the bias  section.  Fred diodes and a RCRC filter.  The amp I would like to say is dead quiet, have never owned another amp that was so oblivious to lights and appliances being switched on and off.      Are the caps for the bias section important to audio quality?

G Georgopoulos

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Re: Coupling cap bypass
« Reply #1 on: 24 Dec 2015, 04:06 am »
bypass coupling caps, do nothing
filter caps for bias, yes, if you want less hum



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Re: Coupling cap bypass
« Reply #2 on: 13 Jan 2016, 05:23 pm »
Personally, I am against bypassing coupling caps (even power supply caps for that matter).
Long ago I had my Counterpoint SA-5 preamp bypassed not knowing what it does at that time and sold it soon.
I guess my ears didn't like it at that time. The music signal gets altered after bypassing.
If you have to, then Russian Teflon caps are low cost and very effective.


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Re: Coupling cap bypass
« Reply #3 on: 16 Jan 2016, 02:58 am »
Your amp looks beautiful and I am sure it sounds the same too!

David Ellis

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Re: Coupling cap bypass
« Reply #4 on: 19 Feb 2016, 01:56 pm »
I realize this is a slightly old topic, but a I haven't posted in a while and I feel like typing this morning  :) .

Randomly, in my subjective opinion, and experience:

Many years ago, the 1st really good capacitor I used was the Audio Cap Theta.  There was no grit, no noise, and darn good dynamics.  Wahooo  :thumb:  I used it subsequently behind some tweeters in a few projects, and in a coupling circuit (or perhaps two).  Over time I experimented with other capacitors too... Mundorf Gold, Mundorf Silver/oil, Sonicap Gen 1 & 2, Sonicap Platinum, Audio Note (don't recall specifics), a few other "fancy" ones, and obviously, the "normal" Solen, Bennic, Axon variety.  I eventually found the Theta to be slightly "dull" by comparison.  Yes, it was good, but lacked sparkle - the exact sentiment you conveyed.  I suppose that one persons "sparkle" is another person's grit & noise.  Nonetheless, this is my opinion.

I think the Audio Cap Theta would be perfectly implemented behind good aluminum dome tweeter.  I currently use Theta's behind some silk domes and it's almost too much "smooth".

During my initial years in hifi I was not a fan of bypassing, but eventually I did a good experiment with a friend and some good source gear.  It was enlightening and changed my opinion completely. Generally, bypassing has an impact in ALL cases, but capacitor quality, character and implementation location MUST be considered.  I do believe these are important.

Amplifier break-in does happen - especially if Black Gate capacitors are used. In my opinion, Black Gate capacitors are quite dull initially, but after 100 hours they come to life.

So... I do generally agree the Audio Cap Theta capacitor may be at the root of your perceived problem.

Specifically, I recommend replacing the Theta with a Sonic Cap Gen 1 having the same value.  It WILL have more sparkle, but you will lose some of that smooth sound.  If you generally like what you hear, install a 1/10th value SonicCap Platinum (bypass).  If you can't get a Platinum, telephone Jeff/Elliot for their bypass recommendation.  I suspect the answer may be a Mundorf Silver/Oil.

And... Great Project !!!



« Last Edit: 19 Feb 2016, 05:37 pm by David Ellis »