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Old 7th February 2006, 04:38 PM   #11
KT is offline KT  United States
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Peter,

Thanks for the updated information. Always good to hear about your new discoveries.

I'm enjoying the PEC in my preamp and integrated very much. I can surely see, though, how some folks might not like its particular sound.

I have the Elma switch that's second from the left in your picture. I bought it through a group buy that was going on at Head-fi.org some time back. Shortly afterward, there was some talk of how the gold plated contacts on the Elma corroded over time leading to compromised sound. I don't know if that's the case, but there were a number of folks who wrote to concur.

Just out of curiosity, could tell us the names of the switches you have pictured? I'm also interested in which ones you found to perform particularly well.

Also, where can one purchase the nude Vishays?

Thanks,
KT
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Old 7th February 2006, 04:51 PM   #12
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The biggest switch in a picture is Shallcross, which I think is the same as Shallco. It seems to have silver contacts.

Two other switches are from Elma. I like Elma for a reason of smooth switching action, I can't get used to hard turning of the others, Grayhill is particularly unpleasant.

I can't say how well Elma will perform over the time, but the preamps I sold two years ago still don't produce any switching noises (I'm using a better grade of Elma from Percy). Besides, a stepping motor can be attached to Elma for remote convenience. You can't do that with other, possibly better switches. Another advantage the Elma may have, is very little metal in contact area, and if low mass has some advantage in RCA connectors and binding posts, it may as well be important here.

Regarding nude Vishays, the info was posted here: "Naked" Vishay S102 resistors???

They are cheaper than S102, but also sightly different sounding. I'm not particularly fond of neither of them but couldn't find a better alternative yet. To me S102 is too soft sounding, the nude one is a bit too aggressive. I might try to aplly some silicone damping to nude verision to see if the sound can be adjusted in some way. For shunt application, Caddock is my first choice.
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Old 7th February 2006, 05:02 PM   #13
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As I mentioned, there are at least two grades of switches from Elma, the better ones should not have contact bounce and I did not observe it in last two years I was using them.
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Old 7th February 2006, 05:17 PM   #14
KT is offline KT  United States
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Thanks Peter,

Also, take a look at this assessment from the guy who used to do Counterpoint:

http://www.altavistaaudio.com/resistors.html

Best,
KT
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Old 7th February 2006, 05:26 PM   #15
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Depending on a place in a circuit, there will be different preferences on resistors. So, in a NOS DAC I/V, nude Vishay didn't work well and was bettered by both Riken and Caddock (TF020), MK132 was rather bad.

In GC feedback and input shunt application MK132 was better than both TF020 and nude Vishay, Riken was behind those two.

In Levinson DACs, a nude Vishay is used for I/V.
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Old 7th February 2006, 07:34 PM   #16
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Hi Peter,

Just a thought... why not a small board with all the resistors you need and a row of jumpers?
That way you could just change one jumper per channel for setting the volume.
Silver solder everywhere, more reliable than sockets, although the jumpers need to be decent.
There are lots of gold plated jumpers and connectors on old computer motherboards, you know?
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Old 7th February 2006, 08:17 PM   #17
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I hope nobody took too seriously my implementation of a "perfect" attenuator. Although it's really good, it can only serve as a reference for developing other circuits.

To be more practical, I intend to mount shunt resistors to a rotary switch and have at least 24 settings. The series element is fixed, the shunt is switchable, but a single resistor for each setting (altogether 25 resistors per channel, allowing 24 steps).

I'm also working on a more universal solution, where smaller number of resistors is used to create much more steps. It uses double sided PCB and relays (gold plated, silver clad contacts)
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Old 8th February 2006, 01:31 PM   #18
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Peter,

Will you have a balanced option?

Jam
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Old 8th February 2006, 02:25 PM   #19
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Yes. One board is needed per channel, balanced operation will require two such boards per channel.

The operation of the attenuator is very simple. There are two strings of resistors: one in a series position one in shunt. The resistors are shorted by relays in sequence and that produces 130 steps with average resolution 0.2 dB in most critical range section. There is never more than 7 active resistors (both series and shunt).

The signal path length is defined only by resistors size and relay switches length.

There will be display board available, remote control as well as encoder for manual adjustment.
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Old 8th February 2006, 02:32 PM   #20
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Attached is attenuator calculator. Any resistor values can be used, but it's better to multiply them by two in order to achieve smooth attenuation curve. The input impedance is fixed. There are two additonal resistors (user adjustable) to extend the atenuation range blow 42dB (in two 6dB steps down to 54dB or so).
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