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Which preamp for Amp Camp?
Which preamp for Amp Camp?
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Old 21st January 2019, 09:24 PM   #81
Dennis Hui is offline Dennis Hui  Canada
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Which preamp for Amp Camp?
Maybe a 4 pole stepped attenuator, something like this:

1pc 4pole 24Step Attenuator Ladder type Control Pot Log 10K Stereo Potentiometer | eBay
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Old 21st January 2019, 11:37 PM   #82
jfuquay is offline jfuquay  United States
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Which preamp for Amp Camp?
Elwood625, you said you are using two four-gang pots for input and two for output. But why two of each? It sounds to me as I’ve been reading that a single four-gang pot is good for a pair of balanced signals. Why not one 4-gang or, for help with balance and to match Nelson’s design, two 2-gang pots on each end?

And thank you, Dennis Hui. I had not seen that product.
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Old 23rd January 2019, 10:26 PM   #83
elwood625 is offline elwood625  United States
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I'm only using one 10K and one 5K.
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Old 23rd January 2019, 11:19 PM   #84
metalman is offline metalman  Canada
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Quote:
Originally Posted by jfuquay View Post
I'm having a very tough time finding four-gang pots in 10K. There is an eBay seller, orexmen, offering an ALPS for $40 each. However, I don't see his part numbers on the ALPS website. Any other suggestions?
You could always use one of these and then build your own at any impedance you desire.

ConneX Rotary Switch 4 Deck 1 Pole/Deck x 24 Position

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Old 24th January 2019, 04:46 AM   #85
jfuquay is offline jfuquay  United States
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Which preamp for Amp Camp?
elwood625: Well, I finally did the simple thing and went back to Digi-Key and entered N.P.’s original part numbers. Both listed as obsolete, but the 10K input and 5K output are single-gang pots; he specs two of them for each value. I don’t see how that would work since the XLR terminals have the two signal posts.

metalman, I’ll pass on that soldering job, thanks. I guess I’ve only got so much DIY in me.
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Old 24th January 2019, 06:47 PM   #86
elwood625 is offline elwood625  United States
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Here is what I'm using, one is 10K and the other is a 5K ohm 24 step pot. The red wires are input, which will connect to the output of the input selector switch. The blue wires are the output which will connect to the PC board L+, L-, R+, R-. The black wires are a shielded ground.
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Old 24th January 2019, 06:48 PM   #87
elwood625 is offline elwood625  United States
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The selector switch is a DACT CT-3/3,4,5 which is adjustable for 3 - 5 positions depending on where the stop pin is placed. I have it at 4 since I only need four inputs. The website has drawings of how to wire the selector switch for balanced and/or single ended. Google DACT, beware these are very pricey, I had one from when I was building a EL-34 tube amp. I ended up using only two inputs so I used a DPDT toggle switch instead.
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Old 24th January 2019, 06:53 PM   #88
elwood625 is offline elwood625  United States
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The one that Dennis Hui sent the link for is half the price of what I paid for each pot. Like I said, the 5K pot was custom made since i couldn't find one anywhere with four poles for balanced mode. I don't care about balance, if you are, then look for 2 10K dual pots, one for each channel. Since the 5K controls "gain" quality(?) I'm using a four gang pot.
Don't forget that no matter which pot you use, there is a resistor in series shown on the schematic that is not on the PC board as they go before P1 - P2 and again on P3 - P4.
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Old 24th January 2019, 07:24 PM   #89
jfuquay is offline jfuquay  United States
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Which preamp for Amp Camp?
Thanks for the info. I haven't bought a switch yet so I'll check out the DACT. I went ahead and ordered two ALPS 10K 2-gang pots and a couple of Parts-Express 5K pots. I don't know if I'll install the 5Ks or not. And yes, I just noticed the two resistors between the 10K and the PCB. I couldn't figure out why I had an R-18 and R19 without a place to stuff them!

I also just ordered the Y23 transformers from Avel Lindberg. Seem like nice folks. When I get all that big stuff I'll figure out what I need for a chassis.
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Old 26th January 2019, 08:47 PM   #90
jfuquay is offline jfuquay  United States
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Which preamp for Amp Camp?
Default Chassis option

So I've got all my major components and now looking for a chassis. I laid the two PCBs for my ZBLS plus the two transformers and here's what it looks like on paper that measures the inside dimensions of diyAudio Store's Galaxy case. (That's not my pot, just a piece i had for scale.) That looks like enough space to me. Is it? I'll be using two input pots on the front, plus a power switch and a select switch.

Also, my tallest component is just under 2 inches. I planned to use 10 mm standoffs, so with the PCB that gets me up to maybe 65mm. The 2U Galaxy is 80 mm inside height. Is that enough clearance? Do steel vs. aluminum covers make any difference? Any advice appreciated. Thanks.

ZBLS layout.jpg
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