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RE: Re: Joule Electra tube noise w/ Merlins (long question)

Posted by Rich Brkich (D) on April 2, 2009 at 08:16:21

In Reply to: Re: Joule Electra tube noise w/ Merlins (long question) posted by The Groovy Guru on March 30, 2009 at 23:50:26:

Thanks for your post! Some good tips there. Here are some thoughts on your comments:

"1. Provide good isolation for the variac. The variac used to hum quite loudly. I use an Equarack isolation system, which utilizes a combination of viscoelastic and ball bearings. This tweak reduced the noise level to a barely audible level. Also effective for isolation were a 4 inch maple block (good) and a Grand Prix Monaco amp stand (better, but expensive).

2. Place a Walker resonance control disc on top of the knob of the variac. Not quite sure why, but this tweak also reduced the noise quite a bit. There is a steel shaft under the knob. Perhaps the Walker disc helps to prevent the shaft from disturbing the big coil shaped transformer that is inside the case of the variac. I am just speculating. Anyways, the Walker disc fits perfectly on top of the knob. This tweek is very effective.

3. Use a good power conditioner. I use an Audience aR1p (relatively cheap to buy) with the variac. If I unplug it and go directly into the wall, the noise increases."

Ahh, the variac.... its benefits allow the OTL's to be operated at the sweet spot of filament voltage and bias, independent of local line voltage, but yes, they can be noisy. The noise here is MECHANICAL... i.e vibration which is why all the things above can make a difference. This vibration is caused by the nature of the variac's design and also by power line noise (DC offset, power line asymmetry). Mechanical damping devices (like a walker puck) just simply act to damp vibration and can be very effective. Because the variac is a type of toroidal transformer, things like DC noise on the power line or asymmetry can get the coils in the the variac vibrating in which case a good power line conditioner can help if this is the issue. The variac will generally always make some degree of noise if you ear is close to it though. I'm pretty sure Jud Barber started putting the Variacs into wooden cases (like the amps main chassis) in later verions of the OTLs becuase the larger wooden enclosure helps cut down on variac noise (sound) a bunch.

A note about power regenerators.. I have tried a few over the years. Some like the PS audio are very good, but there are others which use DC/AC switching (power converters) ... these latter types will do the job in making up for power losses at current peaks, BUT they are often significant noise generators. I have found them to often make a good sounding system sound worse than bypassing them and going directly into the wall. In general, we (I) like the balanced transformer power conditioner units on the OTLs (made by Equitech, BPT and there may be a few others out there) which have worked very well for us and other Joule OTL customers.

Having set-up many systems with Merlin VSM's with Joule OTLs, I have not run into any issues cable runs being a cause for noise. I'm guessing, you must live in a very heavy RF environment. I am not familiar with the VD cables though and some cables designs are more prone than others to picking up noise.

As to the JPS Analog AC and Digital AC power cords, they reduce noise because the cables are made with filter networks and a cable whose dielectric material absorbs EMI/RFI. This help prevent external noise form getting in or out of the power cord.

I'm curious if you have tried grounding your metal rack? If cables make more noise when touching the metal parts of the rack, it could be that the RFI that the rack is picking up has no place to go (ground). Just a thought! :-)

Again, thanks for your post.. glad you are enjoying your Joule OTLs and Merlin speakers!

Happy Listening,
Rich Brkich
Retailer & Audio Asylum Industry Liaison

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