I want to do listening tests on a mono amp with built-in riaa stage. The amp's input is just the grid of a tube plus 47kOhm.
The cartridge of the turntable however is stereo.
If I just connected both channels in parallel to the riaa, one channel of the cartridge would load the other; doesn't sound right ...
connecting in series is also problematic because again the signal from one channel would flow thru the other and because of the external RCA plugs.
So ... how could this be done correctly ?
The cartridge of the turntable however is stereo.
If I just connected both channels in parallel to the riaa, one channel of the cartridge would load the other; doesn't sound right ...
connecting in series is also problematic because again the signal from one channel would flow thru the other and because of the external RCA plugs.
So ... how could this be done correctly ?
It is not as bad as you fear. The signal in both channels will be largely similar, so it is only stereo information which will be affected and you are throwing that away anyway!
The real issue is that a mono 47k input impedance shared between two MM channels will look to the cartridge like 94k. If you are worried about sound quality then add a 47k resistor in parallel.
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The signal in both channels might be largely >dis-similar< and I don't want to throw them away ...
94kOhm ? really ? ...
the cartridge's left channel sees the 47k of the mono input plus the impedance of the cartridge's right channel in parallel - which is unknown;
the same holds true for the right channel's cartridge.
I can't believe that connecting the real ohms of the right cartridge and it's inductance and it's capacitance in parallel with the 47k of the amp >increases< the load impedance as seen by the left cartridge - it should be lower ... shouldn't it ?
Depending on the magnitude of the source impedance of a cartridge, part (or the better part maybe) of the signal produced by one cartridge will be fed to the other one instead of to the amp and what is worse, the combined load impedance will be frequency dependent.
And just as I write this: wouldn't the signal produced by the left actually >drive< the right cartridge into mechanical motion ? even with poor efficency this might cause any sorts of trouble.
94kOhm ? really ? ...
the cartridge's left channel sees the 47k of the mono input plus the impedance of the cartridge's right channel in parallel - which is unknown;
the same holds true for the right channel's cartridge.
I can't believe that connecting the real ohms of the right cartridge and it's inductance and it's capacitance in parallel with the 47k of the amp >increases< the load impedance as seen by the left cartridge - it should be lower ... shouldn't it ?
Depending on the magnitude of the source impedance of a cartridge, part (or the better part maybe) of the signal produced by one cartridge will be fed to the other one instead of to the amp and what is worse, the combined load impedance will be frequency dependent.
And just as I write this: wouldn't the signal produced by the left actually >drive< the right cartridge into mechanical motion ? even with poor efficency this might cause any sorts of trouble.
The only information that will be thrown away is the out-of-phase (L-R) information.
You always lose this information when listening to a stereo recording in mono.
I'd follow DF96's advice. Just combine the two cartridge channels and (if necessary) add another 47k loading resistor in parallel with the existing resistor.
You always lose this information when listening to a stereo recording in mono.
I'd follow DF96's advice. Just combine the two cartridge channels and (if necessary) add another 47k loading resistor in parallel with the existing resistor.
Hi,
A stereo cartridge is most likely to work best wired in parallel
into a standard 47K whatever pF input. Series will work too,
with higher output, but loading is more complicate, 100K, and
source inductance is twice normal, needing low capacitance.
For parallel its much easier to add capacitance if needed.
Parallel with ideally 22K or 25K loading is the easiest.
rgds, sreten.
A stereo cartridge is most likely to work best wired in parallel
into a standard 47K whatever pF input. Series will work too,
with higher output, but loading is more complicate, 100K, and
source inductance is twice normal, needing low capacitance.
For parallel its much easier to add capacitance if needed.
Parallel with ideally 22K or 25K loading is the easiest.
rgds, sreten.
What I did
This is what I did in same app as yours. I didn't have the values shown and used 680R instead of 470 and 22K instead of 20K.
Instead of using a stereo and mono 1/4" jack as shown in the diagram, I used two female RCA connectors and one male connector to make the wye. It worked well .
This is what I did in same app as yours. I didn't have the values shown and used 680R instead of 470 and 22K instead of 20K.
Instead of using a stereo and mono 1/4" jack as shown in the diagram, I used two female RCA connectors and one male connector to make the wye. It worked well .
Attachments
Thank you for your answers, but for some reason it does not seem to work for me.
First I thought it's the mono amp under test which is not sounding good, but after some experimenting I suspect it's the paralleling of the cartridge.
So I compared a commercial ss pre-amp with 2-ch input but set to mono out ... good.
Same cartridge paralleled, same pre-amp ... sounds worse.
Finally I built a simple cathode follower, dual triode ECCxx, 47k grid leak each, connected stereo to the cartridge, common 1k cathode resistor to do the summing and 10u cap to link to the amp under test. (Finally an application for those computer dual triodes with common cathode
)
I think this is a sound solution and it also sounds much better.
First I thought it's the mono amp under test which is not sounding good, but after some experimenting I suspect it's the paralleling of the cartridge.
So I compared a commercial ss pre-amp with 2-ch input but set to mono out ... good.
Same cartridge paralleled, same pre-amp ... sounds worse.
Finally I built a simple cathode follower, dual triode ECCxx, 47k grid leak each, connected stereo to the cartridge, common 1k cathode resistor to do the summing and 10u cap to link to the amp under test. (Finally an application for those computer dual triodes with common cathode
)I think this is a sound solution and it also sounds much better.
I took a couple of minutes and connected a 'Y' cable on the output of my turntable.
When I listened to the turntable, I really didn't hear a significant difference in audio quality. Certainly, the two channels were combined and I was listening to only one speaker but the fidelity seemed to be about the same. Perhaps a little more highs. I did not hear any distortion.
When I listened to the turntable, I really didn't hear a significant difference in audio quality. Certainly, the two channels were combined and I was listening to only one speaker but the fidelity seemed to be about the same. Perhaps a little more highs. I did not hear any distortion.
As I said, simple paralleling of the cartridge channels into a 47k input presents the wrong impedance. When comparing you have to compare like with like. Adding a 22k resistor (as one person suggested) or omitting the 47k resistor both give the wrong impedance (although in opposite directions). Some cartridges are quite sensitive to impedance.
A MM cartridge has a typical source impedance of 1k. The follower 1/gm approx. 200 ohms. Into 47k this shouldn't make a big difference, I thought ...
Noise, well adds a little, but gain is unity.
Interesting again. You like the sound enough to leave it that way or is it just good enough for the test?
Hi:
In order to get MONO , we have the antibiotics to prevent that , from a STEREO cartridge :
For lateral , that is side to side records , most mono's , jumper the L ground terminal to the R hot terminal then hook the shield to the RG terminal and the hot wire to the L hot terminal.
For vertical , that is hill and dale records , a few early records , jumper the L hot terminal to the R hot terminal and hook the shield to the RG and the hot to the LG terminals.
Make sure you also have a 78 RPM stylus for your cartridge !
Hope this helps
Electrical playback of old records
Try this site if it still works , I got this in 2006
In order to get MONO , we have the antibiotics to prevent that , from a STEREO cartridge :
For lateral , that is side to side records , most mono's , jumper the L ground terminal to the R hot terminal then hook the shield to the RG terminal and the hot wire to the L hot terminal.
For vertical , that is hill and dale records , a few early records , jumper the L hot terminal to the R hot terminal and hook the shield to the RG and the hot to the LG terminals.
Make sure you also have a 78 RPM stylus for your cartridge !
Hope this helps
Electrical playback of old records
Try this site if it still works , I got this in 2006
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