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I have a few mono records but have always refrained from purchasing them as I don't have a mono cartridge (or room for another tonearm to take one) or a pre/phono with a switchable mono function.

 

Does anyone know what a mono switch actually is? Is it something with an opamp and ultimately is it possible to retro-fit a mono switch to a phono?

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Not sure, but I recall Geoff at Aurealis selling a box that converts for mono.

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17 minutes ago, muon* said:

Not sure, but I recall Geoff at Aurealis selling a box that converts for mono.

Yeah that does ring a bell. I just couldn't imagine adding another box and another set of interconnects in the chain. The SUT makes it complicated enough.

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I've currently got two mono cartridges, a phono stage with a mono switch, and have in the past owned a dedicated mono phono stage with a turntable set up just for mono. I don't use any of them.

 

The whole mono thing is overdone. First, it is really only an issue if you have mono records dating from before  the early 60s. Mono records after that date were cut with stereo cutting heads, and play fine with stereo cartridges.

 

If you do have genuine early mono records, there is some benefit in a mono cartridge but even these mono records should still sound fine with a stereo cartridge. A mono switch - which I understand is basically just summing the channels to produce a mono result - I usually find does not sound as good. It does remove the sense of the sound coming from the central point between the speakers, but can also often produce some tonal flattening of the sound.

 

I've owned a few mono cartridges from entry level to extremely good - Lyra Dorian and Ortofon Cadenza. A mono cartridge still has its own sound and unless the mono cartridge is as good as your stereo cartridge, you may prefer the sound from the stereo cartridge anyway. I generally do.

 

So don't be too concerned about buying new mono records - particularly recent reissues - they will sound fine with what you have.

 

 

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I built my own mono switch, it works well.  The main benefit is reduced surface noise and a more solid sound field.  I just Googled a schematic, went to Jaycar and purchased all the bits and got busy soldering and drilling.

 

I have attached a pic of it and a YouTube link to a needle drop from a mono record I did on my channel.

 

IMG_3447.thumb.JPG.a10e3b61eb6e2e50088d71fa798eb8d7.JPG

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The mono switch can be (mechanically) simple or complex. 

 

In it's simple form, it looks like the pic above.  Input and output sockets, and all the switch does is to short-circuit the two positive wires (L+R).  In most cases this will work, and some people will achieve the same thing by using a "double-Y" rca lead adapter (although this doesn't have a switch). 

 

However, one thing I learned several years ago on SNA, is that although this is a simple solution it is not an electrionically good one.  This circuit should have a few resistors.  Without them, the inputs start operating as outputs and there are impedance problems and a whole lot of technical issues which are beyond my limited understanding (I hope my memory got some of it correct there!).  There are some (albeit rare) situations where short-circuiting the two +ve channels may cause some equipment not to work or even do damage.  An often-cited paper on the internet is by Rean, titled "Wye not Wye", which is getting hard to find on the internet, the work firewall prevented me from accessing a copy to post a link here (edit - the text, or most of it and diagrams, are here, but the link on that page to the pdf has died).  Hopefully the SNA person with the tech knowhow will read this thread and explain (sorry, I can't recall who it was). 

 

Looking on the internet I noticed that there were some complicated mono circuits out there, some of which used opamps.  From my (limited) perspective, I would think some RCA sockets, as switch and some resistors would make a good one.  Note- I think the resistors also attenuated the signal slightly, but that's a small tradeoff for better sound. 

 

In terms of using the switch, it should occur after the phono stage.  Between pre and power amp would be good, or via a tape monitor, or after the phono stage going to (pre/integrated)amp. 

 

 

 

Edited by audiofeline
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