Preamp hissing??

210.254.95.193

Posted by JustRelaxin on April 29, 2007 at 06:16:09

I recently purchased a used Meixing MC-7R tube pre-amp (12AX7,12AU7 and 5Z3). Tube rectification and no phono stage. My first tube pre-amp!

Prior to this, I had been using a Marantz PM-17SA integrated(pre-amp section only) into a pair of Audiospace AS-9 monoblocks (6DJ8,6CG7,EL34).
With no music playing this is a very quiet setup. With ear next to speaker, there's a minute bit of hiss that gets louder with volume,
but only when the volume is near the max on the Marantz is it discernible from anywhere beyond a couple feet.

Using the MC-7R as a pre-amp and the Marantz's power amp section only, then with min volume setting and with my ear up close to the
speaker there sounds like hiss and buzz. The hissing increases linearly with volume, the buzz does not seem to increase.
At max volume this hissing is barely audible from 10 feet away. About the same from both channels.

Using the MC-7R with the tube monos is when my issues arise.
Monos amps only switched on, there's very little hiss, very little buzz.
With MC-7R pre-amp on (and min volume) then there is low but audible hiss and buzz detectable from 10 feet away.
With volume up to normal listen levels (dial at 9o'clock position) the hiss is more obvious and buzz probably same as before.
Again about the same from both channels.

With music playing, the hiss and buzz are only noticeable during the most quiet passages.

To remove the hiss and buzz, I have tried the following
1) 2 prong cheater plugs on all amps - no difference
2) replaced 12ax7 in pre-amp with known good 12ax7 - no difference
3) replaced 12ax7 in pre-amp with 5751 - no difference
4) replaced 12au7 in pre-amp with known good 12au7a - no difference
5) tapping the tubes, externally exposed capacitors, transformers, preamp inputs/outputs - no unusually noises/pops from speakers

Is there anything else I can do to quieten this combination?
I'm super thrilled with the sound of this system otherwise, so I could just live with it, but I thought I might ask the experienced people here....

Thanks,
Jeff

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Topic - Preamp hissing?? - JustRelaxin 06:16:09 04/29/07 (3)

Sounds like you have either...... - Chuck Y 13:57:38 04/29/07 (1)

Re: Sounds like you have either...... - JustRelaxin 18:41:26 04/29/07 (0)

Problem fixed! - JustRelaxin 01:53:04 05/03/07 (0)

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