2. amps-preamps
  3. 1301627003

Can I swap a Stepped Attenuator for a Potentiomer?

Hi I have a Motif MC-7 Preamp that I am going to hotrod a little bit. I wasnt thinking of it and dont want to but when you turn the volume control fast it makes a painful squeaking, I dont turn it fast but its not a good sign and cleaning did not address it as its in a sealed case (Very nice pot that I cant find)

Also there is some crosstalk between inputs on the selector switches. DACT Makes a unit that looks like it should fir the bill more than fine. I was thinking of using either Goldpoint or DACT stepped attenuators if possible or using as good if not a better potentiometer.

What hurts is its completely dual mono meaning to volume controls and 2 input switchers.
128x128systembuilder
7 responses Add your response
ngjockey
1,042 posts
 
Tripped over this lately.

http://www.analogmetric.com/category.php?id=29
rodman99999
6,156 posts
 
And, since the subject came up; Percy also offers Shallco selector switches(solid silver contacts), for building either discrete resistor attenuators, or stereo selector switches. See page 13, of the aforementioned catalog. BTW: Should you decide to roll your own attenuator; Use either Vishay nude bulk foil, or Caddock Ultra-Precision resistors. They drive the price up, but will pay for themselves in transparency.
atmasphere's avatar
atmasphere
11,810 posts
 
Switches make a difference in performance. The reason is that not all contacts are created equal- the best will be doubled up to increase contact pressure and area. So yes, the input switches can make a difference.

If you are really considering doing this sort of work you will want to consider that you want to make it worth your time. If I were you I would get an Electroswitch or Shallco part and build the volume control up from fixed resistors. Its harder, but beats the ready-made stuff quite handily. If you go this route, keep in mind that the switch you use should be a make-before-break variety.
systembuilder's avatar
systembuilder OP
111 posts
 
Thanks yall, I really appreciate it. My preamp uses awesome older ALPS Pots. They are encased in a plastic/resin? compound. I am really interested in what I will see in my upgrade especially as it is already two mono preamps.

I really appreciate all the help and now look forward to more homework.

Does anyone know the advantages of going with a higher quality input selector? I am having crosstalk between my inputs and I dont really care but I am sure it has to at least somewhat affect my preamps ability to achieve it full potential
ngjockey
1,042 posts
 
When I did this years ago, the choice was 10Kohm or DIY. Customized my own, soldering each tiny resistor, to replace a 250Kohm pot and what a PITA but what a difference. Did it again for another biamp project because I just wasn't happy with pots. Much more options now. Marchand is another brand.
rodman99999
6,156 posts
 
TKD makes a very good stepped attenuator, with discrete resistors for each position. I've also used a lot of Alps and Noble controls in projects(less salty), but they are getting rare. See pages 13 & 14, of this catalog: (http://www.percyaudio.com/Catalog.pdf) Also- Understand the difference between an, "Audio" or, "Log" taper, and a "Linear" taper, as you may find that knowledge useful.(http://tangentsoft.net/audio/atten.html) (http://www.acoustic-dimension.com/tkd/TKD-main.htm)
systembuilder's avatar
systembuilder OP
111 posts
 
Ok, So I Did a lot of searching and as long as you have the same impedance/resistance? you should be good to go?

Rather amazing to think a machine could go 100% all the time that wasnt origanially designed this way, Is this right?

Also what are the best Stepped attenuators, DACT, Goldpoint, Khozmo or Elma or someone I havent heard of?
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