Hello. I have a adcom preamp with only a single phono input. I have tube amps and decent speakers. I got an Alexandra 2 and also a homebuilt DIY table. I’d love to have a phono source selector to switch between the two but hear about noise introduced by sloppy switches. Any suggestions for an input or should I get a tube phono preamp? Recommendations.
Thanks.
Thanks.
Find high quality 4-pole switch with gold plated contacts, then each of L and R can use two poles paralleled for better reliability. Many switches are designed for power rather than signal and the contact meterials are chosen for robustness and high current, not low-level signals, and often oxidize over time unless several mA flow through the switch (the arcing blasts through the oxide). Gold doesn't oxidize.
You could use signal relays too, and have a cheap switch to energize the relay...
You could use signal relays too, and have a cheap switch to energize the relay...
Thanks for the info. I can definitely build a box. Then I start to over think wires rca jacks switch and or relays. Do you know of an off the shelf solution that’s good? I saw a rec-o-kut one for $55. But don’t know if it’s good or for double that I can get something nice. I’m on the fence. On the other hand a nice DIY box that matches the style of my DIY table would be fitting. Any recommendations on specific switches and rca connections and internal wire. I’ll also need a central ground point.
Datasheets for switches and relays will explain which part numbers are the gold-plated version - thick gold plate is needed for frequent use, "gold flash" is much thinner and typically used for infrequently plugged connectors. There are literally 100,000's of switches and signal relays out there, but companies like Digi-key and Mouser make parametric search relatively easy these days.
For connectors the same applies, thick gold plate, reputable manufacture, has a datasheet...
For connectors the same applies, thick gold plate, reputable manufacture, has a datasheet...
Another thing you may want to do is remove the caps from the phono input of the adcom and move them to before the switch/relay. That way you can adjust the cap size for different carts. Some cart's like some AT's like very low cap (<150pf) which usually means no cap at all in the phono when you factor in cabling capacitance. Many other cart's want to see around 300pf which means around a 150-200pf cap on the phono in.
You can buy stand alone phono preamp for the second turntable and connect it to some of the line inputs.
DIY-ing a phono stage (maybe Adcom clone) is also an option
DIY-ing a phono stage (maybe Adcom clone) is also an option
Simple option is a 10 pole dip switch - I had a such as MM / MC selector + selection of various resistors for MC input.
Some will say it is not a high quality option but I've seen it done in phono preamps of couple thousand dollars.
Some will say it is not a high quality option but I've seen it done in phono preamps of couple thousand dollars.
Hi - if it's for a record player, you definitely will want a phono preamp. You might also try searching for "audio switcher" or "Headphone Amplifier 4 Channel" or similar on Amazon. They have plenty of options. If you really want to get fancy, you could use an Arduino or Raspberry Pi to switch channels, and control it with your phone over bluetooth? For my purposes, I found using a good quality switch (e.g., 3PDT) in a shielded box sounded fine.
PS if you're the FortyTwo who made this 4 player Pong game in qbasic:
(https://www.tapatalk.com/groups/qbasic/4-player-pong-help-t34438.html)
you might be interested in QB64 and QB64PE, which is updated quickbasic for modern PCs, and this code that lets you use multiple mice plugged into 1 PC to control pong paddles:
https://qb64phoenix.com/forum/showthread.php?tid=2836
cheers!
PS if you're the FortyTwo who made this 4 player Pong game in qbasic:
(https://www.tapatalk.com/groups/qbasic/4-player-pong-help-t34438.html)
you might be interested in QB64 and QB64PE, which is updated quickbasic for modern PCs, and this code that lets you use multiple mice plugged into 1 PC to control pong paddles:
https://qb64phoenix.com/forum/showthread.php?tid=2836
cheers!
You don't want to switch the MM cartridge outputs. The switch contacts, wiring, and pcb traces are all bad for low level voltages.
Some even switch MC outputs - crazy. I use a pcb mounted jack, on the same board as, and mounted immediately adjacent to,
the input circuit of the RIAA stage. I'd rather have a separate phono preamp for each of the cartridges, than switch their outputs.
You should have 2 identical riaa preamps to toggle between turntables .
Noise , distortion and cart loading will affect playback unless preamp is set up for 2 cartridges
Noise , distortion and cart loading will affect playback unless preamp is set up for 2 cartridges
You are allowed to use shielded wiring... Then the main issue is contact resistance and oxidation - a signal-rated switch with gold plated contacts will fix that for MM, as the signal impedances are high. For MC though the variation in switch contact resistance is potentially going to be audible - switches are microphonic at these low impedances (if you've built an MC amp on a breadboard you'll likely have noticed the breadboard contacts become microphonic, same thing). But a good quality switch (once you stop playing with it) should be reasonably quiet - but thick gold plating is rare and expensive and is required for long-term reliable behaviour I think.
I think a practical aim is to make sure the circuit is less microphonic that the input connector - often that's the worst component in the chain - and its worth paying attention to the quality of that and the cable first.