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Which preamp for Amp Camp?
Which preamp for Amp Camp?
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Old 28th January 2019, 01:32 AM   #101
elwood625 is offline elwood625  United States
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I want to have RCA and XLR inputs so I can finally A/B the Music Hall 25.3 in balanced out and then the RCA output with the tube. I wonder if I'll hear any difference, balanced seems to reduce noise levels by design, that I'm looking forward to.
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Old 28th January 2019, 01:42 AM   #102
6L6 is offline 6L6  United States
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Which preamp for Amp Camp?
The sound difference of the ACA is noticeably different when driven via XLR vs. using the RCAs in bridge mode. It's not going to be apples to apples if you're trying to listen to the source's differences.
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Old 28th January 2019, 05:45 PM   #103
jfuquay is offline jfuquay  United States
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Which preamp for Amp Camp?
So if I really want to do apples-to-apples, I need to finish this preamp and run the DAC through the two different inputs, XLR and RCA, but stick with the same output. Right? Works for me, I'm planning four inputs (2 XLR/2 RCA) and two outputs (1 XLR/1 RCA). I still need to buy a source select switch. What do I need? 4 decks/4 poles?

BTW, 6L6, another thanks for your build guides. Such a help to the noobs like me.
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Old 28th January 2019, 07:12 PM   #104
elwood625 is offline elwood625  United States
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Correct on the DAC A/B as far as inputs. Yes, 4 position and 4 poles. The type of switch seems to make a difference as far as pops and clicks when selecting a new input, the zener diodes on the Line Stage PC board are supposed to help according to N.Pass.
Can anyone suggest a selector switch?
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Old 28th January 2019, 07:19 PM   #105
chrisb is offline chrisb
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For anyone looking for a simple pre with phono inputs the Elekit TU 8500DX available on the DIY Audio store might be worth a look. Note only single ended outputs, and no DAC.

Elekit TU-8500DX 12AU7 Pre-Amplifier Kit – diyAudio Store
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Last edited by chrisb; 28th January 2019 at 07:22 PM.
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Old 28th January 2019, 07:46 PM   #106
jfuquay is offline jfuquay  United States
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Which preamp for Amp Camp?
The Elekit had caught my eye, but at the time I hadn't even done the ACAs. No way was I going to try something with a power supply, incidentally. So completing the ACAs at least got me past that by using the SMPS. But I'll still be careful.

I thought I wanted a tube preamp, but after hearing the ACAs' clarity I decided to stick with solid state. Maybe another time for tubes. I still need to find a little more guidance on the PCB connections in and out.
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Old 28th January 2019, 09:50 PM   #107
Ben Mah is online now Ben Mah  Canada
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Quote:
Originally Posted by elwood625 View Post
Much better, now with twin power cables for the line stage.
Next, send the front panels out for engraving, and the line stage rear panel for CNC machining.
Looking at your DC chassis connectors, it would be safer if you had female chassis connectors at the DC supply. That way you won't run the possibility of exposed live DC if you have your supply turned on but no cable plugged in.
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Old 28th January 2019, 10:11 PM   #108
elwood625 is offline elwood625  United States
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I have plastic caps that came with the connectors, they thread on.
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Old 4th February 2019, 03:48 PM   #109
jfuquay is offline jfuquay  United States
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Which preamp for Amp Camp?
As eager as I am to get started wiring it up, I thought I'd pause and get some thoughts from more experienced hands. This is a "by the book" ZBLS, so pots on the inputs and outputs as well as trimpots on the circuit PCB. One XRL/one RCA out, two XRLs/two RCAs in, so four inputs total. I've arranged the power supply, including the IEC, fuse, and on/off switch, on one side. The signal inputs will be on the opposite side with the circuit PCB, select switch and input pots. The output pots will go about in the middle in the back.

I was going to run my power wiring along the left chassis wall. What's a good awg for the power switch. How about gauge for the IEC connections and especially chassis ground? Finally, from the power supply PCB to the circuit PCB?

I was going to run the input signal wires along the right side. I thought I'd use 24awg wire from a CAT5 cable for signals, a la 6L6's recommendation. Is that a single 24awg wire or a twisted pair as in the CAT5? Finally, gauge from the circuit PCB to the outputs?

I may be making harder than it is, but I haven't found an overview of preamp wiring anywhere. If you know of what please let me know. Thanks.
Jim
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Old 4th February 2019, 04:18 PM   #110
elwood625 is offline elwood625  United States
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I used 18 AWG for all 110v wiring. I also used the same for the 60vdc rails including two 4 foot umbilical cables which run from the power supply to the Line Stage. I've used the same wire size for tube phono section wiring, once again with a remote power supply and umbilical cable.
Don't forget to find the Hot side of 110v, which is the larger pin on the 110v outlet. The Hot side must go to the fuse and switch for proper protection.
For the RCA inputs, I'm using two wire coax with a shield. The shield and ground wire for the RCA go together at the INPUTS only. The other end the shield is not used. For the RCA's in parallel with the XLR, simple 24 AWG from the XLR to the RCA works fine.
For the XLR inputs I'm using three wire coax with a shield, once again the shield and ground wires go together at the INPUTS only. The other end the shield is not used.
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