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-   -   Another Zen V2 hum question, yawn... (http://www.diyaudio.com/forums/pass-labs/8937-another-zen-v2-hum-question-yawn.html)

Shoog 22nd December 2002 05:24 PM

Another Zen V2 hum question, yawn...
 
I have just completed my Zen V2 and my Bride of Zen and have been listening to them for about a week now. I have a hum problem which I have managed to deminish by introducing a hand wound inductor in the supply line between a 10,000uf cap and a bank of 2x22,000uf caps. This has helped some, but it has proved physically impossable to get an inductor of a high enough inductance with the materials to hand locally. By the way I am using a single supply transformer.
What I have noticed however is that with no source connected the hum completely disappears. I have used sheilded cable from the input phones to the main boards, but have only connected the shield to the phono earth and hence to the chassic.
Is this hum to be expected and why does it go away if the source is open.

Other than this the amp is very impressive and a big step up from the Leak Stereo 20 I was using before.(though it doesnt have that hang in the air ambience that you get with a valve amp).

Thanks for all the help getting me this far

Shoog.

till 22nd December 2002 05:30 PM

please go to this place:

http://www.passlabs.com/articles.htm

and have a look for the ground loops article.

jh6you 22nd December 2002 07:21 PM

Re: Another Zen V2 hum question, yawn...
 
Quote:

Originally posted by Shoog
... What I have noticed however is that with no source connected the hum completely disappears...
I had exactly the same experience with my ZV2.
I solved the problem by reducing the active current source gain.
Try to increase R15 from 1.5k to about 2.8k. You will see a good result.

Shoog 23rd December 2002 05:11 PM

Wouldnt that kill the Bass
 
I was finding the bass a bit thin so decided to decrease the R15 to 1K. This is in line with the fact that I am using a IRF150 as Q1 which has a higher transconductance, and I am also biasing the whole thing at about 2.6A. Wouldnt your sujestion kill off the gains in bass response for which the Alpha Current source was introduced in the first place.

Shoog

Nelson Pass 23rd December 2002 07:34 PM

When you disconnect the input, the Zen amps go to
very low gain, and the extra feedback reduces the
hum by about 12 dB.

I think filtering the supply is where you want to go.

Shoog 23rd December 2002 08:05 PM

Thanks Mr Pass
 
That is very useful information and answers the logical contradictions.I did have an underrated EI type transformer on the circuit before and it produced negligable hum. I believe it was acting as a self regulating inductor. All I have to find now is an inductor which can cope with 6+ Amps without frying itself. Could I use the secondaries of one of my big EI transformers, would there be less of a load on it than the full transformer role ?

jh6you 24th December 2002 12:19 AM

My experience tells me that the variation of R15 does not affect the amount of bass, but changes bass character in-between looseness and tightness, in combination with the speaker quality. For me, a bit relaxed bass is better than too tight bass. It would be of course depending on personalities of different ears and different perceptions.

I thought about my way of possibility to reduce the hum in case you did not want the inductor-filtering of Nelson Pass.

Using secondaries of EI transformer is a smart idea for me. I hope it will work... :)

Shoog 24th December 2002 06:07 PM

I have just tried the EI as a choke
 
Using the secondaries of a large EI tranformer as a choke, with the primaries connected through a small choke which is known to go down to 50hz has produced satifactory results. The secondaries resistance is 0.9ohm. The transformer filterered out all hum initially, but after about 4hours and a rise in temp to about 40centigrade the hum has crept back a little. It is very low though and is the best result so far.

I am coming round to thinking that a R15 value of 1k is a little bit to low and I will probably bring it back up to 1.3k

Shoog

jh6you 25th December 2002 07:14 AM

The EI as a choke is very impressive and interesting.

My estimation of ac current gain is about 60% with R15 of 1.3k. I hope it will be a solution for the bass sound and the hum level. By the way, I have met my satisfaction with R15 of 2.4k giving about 40% ac current gain, for 4ohm-92dB speakers.

Merry Christmas.

Shoog 26th December 2002 05:09 PM

Status Report
 
I just put the EI Choke in the case and thought I would report back. Firstly it was a tight squeeze, this meant sitting the EI right above the torodial transformer. This seems to produce an unsavoury intereaction. The EI heats up much quicker and to a higher level. This sujest to me that its magnetic field is cutting through the torodial and leading to saturation of the EI. The filtering isnt quite as good either. The windings arent heating any more than before. I dont like having a hot transformer near my big caps so I might have to look at active regulation.

The 1.3K R15 has brought back a bit of tightness to the overall sound.

Shoog


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