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Old 17th January 2013, 12:46 PM   #1
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Default Phono Switcher

I need to switch 4 turntables into 1 pre-amp @ phono level.

I've already discussed this at length with the technicians at phonopreamps.com, so I know the problems associated with switching Tiny voltages/currents. I believe those problems can be overcome.

I'm NOT interested in using outboard phono amps/EQ's & a line level switcher (mixer Aaaaarrrrggggghhhhh) into an AUX ckt. That's Not acceptible!!!!

I think that using Mercury Wetted Relays, will solve the problem of switching tiny voltages/currents with No added resistance..

The problem then becomes the total switched load to the pre-amp phono ckt. How much will a Zero Resistance (Capacitance?) switcher affect the Phono-pre-amp/EQ?

I really need to hear from Phono guys with more experience than I have.

MLStrand 56
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Old 17th January 2013, 05:56 PM   #2
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I tried switching from a field hydrophone to a gun hydrophone on a geophysical data acquisition system with relays. Even with a relay and a separate timer shorting the switching relay when the points were open, it made a big bang in the data just from the switching.
I would build 4 phono circuits and mix them with a conventional op amp mixer, myself. ST33078's are pretty **** quiet, there are even quieter op amps available. The RIAA stuff on my op amp input (Herald Electronics RA-88a) is about 6 resistors and caps around a 50x op amp. Sounds good to me. I've got 2 RIAA inputs, a radio input and a CD player input all mixed together 17 hours a day, no obnoxious level of noise at the speakers. And I don't have to walk around the piano to change the switch from one to the other when I change from LP to CD, for example.
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Old 17th January 2013, 06:22 PM   #3
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Seems like you already have been answered. You know the problems < what makes you belive they can be overcome. and why are the options you have been given not acceptable...

Best Regards Mark

Quote:
Originally Posted by MLStrand56 View Post
I need to switch 4 turntables into 1 pre-amp @ phono level.

I've already discussed this at length with the technicians at phonopreamps.com, so I know the problems associated with switching Tiny voltages/currents. I believe those problems can be overcome.

I'm NOT interested in using outboard phono amps/EQ's & a line level switcher (mixer Aaaaarrrrggggghhhhh) into an AUX ckt. That's Not acceptible!!!!

I think that using Mercury Wetted Relays, will solve the problem of switching tiny voltages/currents with No added resistance..

The problem then becomes the total switched load to the pre-amp phono ckt. How much will a Zero Resistance (Capacitance?) switcher affect the Phono-pre-amp/EQ?

I really need to hear from Phono guys with more experience than I have.

MLStrand 56
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Old 17th January 2013, 06:56 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

You could build a shunt feedback RIAA stage and use it as a mixer
for the 4 phono inputs. Optionally relays could short unused inputs
to ground but its not necessary, if you use one deck at a time.

The noise "disadvantage" of shunt feedback is not that bad
with typical MM's due to typical MM cartridge inductances.

As it happens, 4 decks wired into a shunt RIAA will be less noisy
than one, being shunt the number of inputs will not affect the
RIAA stages frequency response at all.

rgds, sreten.
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Last edited by sreten; 17th January 2013 at 07:07 PM.
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Old 17th January 2013, 06:57 PM   #5
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Hi,
What about using the NJM2521?
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Old 17th January 2013, 07:41 PM   #6
AuroraB is offline AuroraB  Norway
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Some, but not many, amps have two phono inputs, - and one internal phono pre. Some have cascaded MC and MM inputs, all or most operated by fairly mediocre quality switches, so good quality switches or relays can certainly be used, albeit at the expense of some added loading capacity. This could possibly be remedied by modding the input load capacitor that's probably in there already ..........

I would reverse any relays, so that unused inputs are shorted. Crackle and pops when switching is to be expected and dealt with ( shorting switch or volume control :-) ) Everything in life is a compromise.........

Otherwise, Sretens suggestion looks reasonable.....

BTW - unless you have old stock at hand, I think you'll have problems finding mercury wetted relays these days..........
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Old 19th January 2013, 11:35 AM   #7
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Quote:
Originally Posted by AuroraB View Post
BTW - unless you have old stock at hand, I think you'll have problems finding mercury wetted relays these days..........
Mercury wetted relays are readily avail. on E-bay USA. $8-$20 ea.

MLStrand56
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Old 19th January 2013, 11:37 AM   #8
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Default NJM2521???

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Originally Posted by tauro0221 View Post
Hi,
What about using the NJM2521?
What is a NJM2521?

MLStrand56
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Old 19th January 2013, 11:47 AM   #9
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Quote:
Originally Posted by sreten View Post
Hi,

You could build a shunt feedback RIAA stage and use it as a mixer
for the 4 phono inputs.
So you're talking about using a post RIAA EQ, line level mixer into an AUX pre-amp input.

Not interested in a mixer (I'm not a DJ), BUT it's easy to build a 4:1 line level switcher. Sure there are commercial 4:1 line level switchers avail. (even inexpensively), but they all look like schitt & don't match the style of my other equip. I'd rather spend the money to build something that performs well & looks good.

MLStrand56
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Old 20th January 2013, 01:06 AM   #10
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A few mercury relays from a long time Cleveland shop.

Mercury
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