I have three turntables and only one phonostage. I made a source selector using a 4P3T rotary switch connected by shielded wire to four pairs of RCA female terminals. However, there is a humming sound. It's not my turntables since when I connected each to the phonostage, there is no noise. What could the problem be? Thanks.
The phono signals are extremely low and prone to picking up noise. This is especially true with MC cartridges though i suspect you have the higher (but still low) signal MM cartridges.
The shielding and grounding of the switch box is important. Also, do you have the hum if you just run one signal through the switch (unplug the other TT RCAs)?
You could be picking up noise through the 2 unused pairs of RCA cables.
Keep in mind that as you lengthen the TT signal cables the capacitance goes up which will roll off the high frequencies.
The shielding and grounding of the switch box is important. Also, do you have the hum if you just run one signal through the switch (unplug the other TT RCAs)?
You could be picking up noise through the 2 unused pairs of RCA cables.
Keep in mind that as you lengthen the TT signal cables the capacitance goes up which will roll off the high frequencies.
Keep in mind that each cartridge needs its own optimum load set by the phonostage input; unless you have three times the same cartridge, at least 2 of them will work not optimally.
There are a couple of decent opamp based phonostage designs around here, so you could go all the way of building another 2 phonostages for small money
Re: Yamaha PX-3 linear tracking turntable
Re: Technics SL-1400 MK-2 radial tracking turntable
Re: Bang & Olufsen 4004 linear tracking turntable
Re: Sony TA-E2000ESD preamp
I have the same problem. I need to switch these 3 turntables into the 1 phono input on the preamp.
I E-mailed the tech. people at phonopreamps.com about this. They advised that due to the very small voltage output of phono cartridges, any mechanical switch contacts would quickly corrode.
That made me thing about using Mercury Wetted relays to do the switching. That would eliminate the corrosion problem.
I've found lots of SPDT mercury relays on E-bay. 2 E-bay sellers stores also had DPST mercury relays, but they were around $30 each (w/o sockets)!!!
Next problem is the pwr. sup. I think it would be easier to build a divorced power supply, & simply have a DC input to the switcher. That takes care of the whole pwr. sup. hum issue.
With this type of project, you could even include MC step up XMFR's in the design.
Back in the '70's Pioneer made a huge switcher (model U-24) that many high end stereo stores used to switch multiple inputs, to multiple preamps/receivers for testing. The U-24 could switch 3 phono's. It also switched a lot more stuff, that doesn't apply to this thread.
Anybody else have any ideas on building a Phono Switcher?
MLStrand56
Re: Technics SL-1400 MK-2 radial tracking turntable
Re: Bang & Olufsen 4004 linear tracking turntable
Re: Sony TA-E2000ESD preamp
I have the same problem. I need to switch these 3 turntables into the 1 phono input on the preamp.
I E-mailed the tech. people at phonopreamps.com about this. They advised that due to the very small voltage output of phono cartridges, any mechanical switch contacts would quickly corrode.
That made me thing about using Mercury Wetted relays to do the switching. That would eliminate the corrosion problem.
I've found lots of SPDT mercury relays on E-bay. 2 E-bay sellers stores also had DPST mercury relays, but they were around $30 each (w/o sockets)!!!
Next problem is the pwr. sup. I think it would be easier to build a divorced power supply, & simply have a DC input to the switcher. That takes care of the whole pwr. sup. hum issue.
With this type of project, you could even include MC step up XMFR's in the design.
Back in the '70's Pioneer made a huge switcher (model U-24) that many high end stereo stores used to switch multiple inputs, to multiple preamps/receivers for testing. The U-24 could switch 3 phono's. It also switched a lot more stuff, that doesn't apply to this thread.
Anybody else have any ideas on building a Phono Switcher?
MLStrand56
Re: Line Level switching
I could use several straight amps (NO phono EQ), then a regular line level selector, THEN Pad the output back down to the 5mv range. That sounds like a recipe for disaster.
I think it's easier to build a straight switcher & let the preamp phono ckt handle the EQ part.
MLStrand56
That is the easy way & what the tech. guys at phonopreamps.com suggested. But it also precludes using the phono ckt. in the pre-amp.
I could use several straight amps (NO phono EQ), then a regular line level selector, THEN Pad the output back down to the 5mv range. That sounds like a recipe for disaster.
I think it's easier to build a straight switcher & let the preamp phono ckt handle the EQ part.
MLStrand56
"But it also precludes using the phono ckt. in the pre-amp."
no it does not...
if you have three turntables, one can go to the phono input of your preamp, than you actually need only two external phono sections, and plug them into line level of you preamp, easy...
if all your line inputs are occupied, make simple external line switcher, with spare inputs, and output of this box will go to your preamp
boy, why are you trying hard to make this as complicated as possible?
no it does not...
if you have three turntables, one can go to the phono input of your preamp, than you actually need only two external phono sections, and plug them into line level of you preamp, easy...
if all your line inputs are occupied, make simple external line switcher, with spare inputs, and output of this box will go to your preamp
boy, why are you trying hard to make this as complicated as possible?
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