Playing Mono Records Through Cornet 2 - Mono switch not installed

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G E

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Hello,

With the release of "The Beatles Mono Box" there has been lots of discussion on some forums about using "Y" cables on turntable out jacks to sum the signal.  Some have suggested doing this via the Tape circuits of preamps so equipped.
 
The Cornet2 has a Mono switch option, which I did not install.

My questions -

1) If I install the Mono/Stereo switch cartridge loading drops to 23.5K.  I have a Grado Ref Sonata hi output.  How does this affect sound?  I recall reading that Grado is less fussy about loading than other carts. 

2) in one posting here it is suggested that R200 (47K resistors) be changed to 100K values for mono play.  It isn't very practical to switch resistors every time I want to play a mono record.  A switch arrangement raises the spectre of hum and noise injection....  has anyone figured out a way to do this in a practical manner?

3) Is it advisable to add a "Y" adapter at the output of the Cornet2?  I read Jim's comments that tube sections need to be exactly matched.  I have specified tightly matched sections in buying my NOS tubes (as well as lo noise, lo microphonics).  And then there is the matter of adding "crummy wire" into the chain.

4) Or should I just not worry about it?

Any thoughts on best approach?  I don't mind opening up the box and adding the switch if hat is the best way.  Any excuse to fire up the soldering iron.

Thanks in advance for any insights!

Greg

jupiterboy

FWIW, I had the designer of my phono stage add a mono switch to the output by connnecting the two center pins to a switch. He also upped the resistors at the output stage as you mention.

The other way would be to use a Y adapter like this, and rig a small switch between the two open RCA ports. You could use RCA plugs or just solder it in and use some heavy heat shrink to add rigidity.




poty

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using "Y" cables on turntable out jacks to sum the signal.
IMHO there is some sort of looking for problems. Output signal of a turntable is so tiny that adding more contacts is likely the way of deteriorating it. If we agree that our cartridge is good than why we should bother about choosing from the alternatives: playing each channel through the corresponding channel of stereo amplifier-corrector system or summing the signal and play it again through the same stereo system?
1) If I install the Mono/Stereo switch cartridge loading drops to 23.5K.  I have a Grado Ref Sonata hi output.  How does this affect sound?  I recall reading that Grado is less fussy about loading than other carts.
It's normal. Tying the load resistors together you will parallel the sources too, so the resulting currents will be the same (well, not entirely, of course - there will be some "equalizing" currents sourcing from the differences in the output signal from each coil of the cartridge, but they are very small).
2) in one posting here it is suggested that R200 (47K resistors) be changed to 100K values for mono play.  It isn't very practical to switch resistors every time I want to play a mono record.  A switch arrangement raises the spectre of hum and noise injection....  has anyone figured out a way to do this in a practical manner?
In my opinion anything that is put on the way of the tiny signal is bad. So the only "good" way of doing things in that regard is switching the outputs of the first stages of phono-amplifier, each tuned to its own cartridge.
3) Is it advisable to add a "Y" adapter at the output of the Cornet2?  I read Jim's comments that tube sections need to be exactly matched.  I have specified tightly matched sections in buying my NOS tubes (as well as lo noise, lo microphonics).  And then there is the matter of adding "crummy wire" into the chain.
If you still insist on summing the channels - the Y-adapter at the output of the Cornet 2 is less harmful than at the input.
4) Or should I just not worry about it?
IMHO, the only good thing I can think of. :)
Really, you have different cutting in the mono and stereo records, sometimes you have different correction parameters, even in the Cornet 2 channels differ from each other... And you still want to hear the tiny difference in the cartridge channels?
Any thoughts on best approach?  I don't mind opening up the box and adding the switch if hat is the best way.  Any excuse to fire up the soldering iron.
I think the best way is leaving everything "as is".
You can also try to "sum in cartridge" - make an interconnect that disconnects the ground wires from the input of the Cornet 2 (in a balanced sort of interconnecting).
Y-adapter at the output of the Cornet or even further in the amplifying chain is also possible way.

Speedskater

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You should never connect two outputs together! You need to read the Rane Note about summing outputs.

Why Not Wye?
Dennis Bohn, Rane Corporation
RaneNote 109 written 1991; last revised 4/04

    Splitting Signals
    Subwoofing in Mono
    Unbalanced Summing
    Balanced Summing
    Output Impedances


http://www.rane.com/note109.html

poty

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You need to read the Rane Note about summing outputs.
He is wrong. As soon as both outputs are voltage sources they will "block" the inter-sources current. The only current involved will be the difference current. Think of two batteries paralleled and driving one load.

Speedskater

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Think about it this way.
Take a power transformer  with two secondaries. One is a 18V winding and the other is 12V. Connect them in parallel and watch for smoke.

The correct way to Mono a phone cartridge, is to run each channel through it's own pre-amp then use a resistor network to sum them together.

poty

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Think about it this way.
Take a power transformer  with two secondaries. One is a 18V winding and the other is 12V. Connect them in parallel and watch for smoke.
Wrong example. First of all, when you connecting any two secondaries in parallel, even if they are formally equal in spec, they are in practice different and still nothing wrong happens (rather widely used case). The output amplitude of a phono preamp is negligible to cause appreciable current first of all and the difference in the signal is also very small (definitely much smaller than 150% you showed in your example) too. This article is to fright newcomers than to help.
Regarding this precise case. The output impedance of the Cornet 2 is 1k, which is more than two times bigger than the recommended 475+475 mentioned in the article. So this output impedance will act as the summing resistors from the article. Mono signal from the cartridge would have very small differences from channel to channel, so almost no use in the summing resistors anyway.

hagtech

Seems to me everybody is correct, each in their own way...

Poty is right that you don't have to worry about loading, because each of the coils remains loaded in 47k whether you parallel the inputs or not. 

We have the choice of paralleling inputs, outputs, both, or none.  They all work!  My original choice was to strap the cartridge coils together to erase any differential before it got further down the chain.  It also tends to lower noise just a little bit.  Paralleling outputs tends to erase any difference in equalization or gain in the channels, thus presenting more of a mono signal to the following linestage.  I chose not to do this with the CORNET2 because I worried about about the stability of the cathode followers.  Call me paranoid.  In practice it is probably one of those 0.01% things, but to me they are not the best choice to run in parallel.  Other output stages sure, but not this one.  In a way, it's also the reason I don't use cathode followers to drive headphones...

The easiest thing is to not do anything at all.  Just play that mono album as is. 

jh