Need some turntable guidance

The modern mono cartridge feeds the signal, (vertical vibrations totally ignored), to both channels, so it goes to a standard stereo phono input and your existing stereo amp. You get full room sound, dual mono, frequency balanced as you have already solved. 

So, using the mono amp might be fun, but not needed, and send the cartridge dual mono output where, how to a single mono amp, then to a single speaker? Unless you get a vintage single channel cartridge.

Not being critical of your idea, just letting you know my experience.

I have a pair of tube mono blocks (and spare), but far from integrated, they were made in 1958, so power switching, input switching, speaker out/in, all had to be independently solved. It was fun to have these 35 wpc tubes beat my 305 wpc McIntosh SS EVERY TIME! I sold the SS Preamp and Amp and got tube tuner/preamp from 1962 into modern integrated tube amp.

Another advantage of not using a stereo cartridge to play mono lps is that the grooves are different, and Mono cartridges are conical or elliptical, modern microline stylus are not 'right' for those grooves.

elliottbnewcombjr :

OK, so two channel mono (?) with a modern mono cartridge can be solved two ways:  One is a Y adapter, and the other is just use one channel off the cartridge and load the other with the recommended impedance.  The second method is probably preferable, as the differences between the two stereo parts of the chain could possibly introduce unwanted channel differences.  The one channel then stays mono straight to a single speaker.

I'd like to hear more about your DIY speed controller.  How did you do that?

xaak,

It's simple, really.

All you really need is a signal generator, and a way to amplify the signal to deliver 120 volts. Actually, between 60v and 130v is better because you can tune the voltage to provide adequate drive at the lowest motor vibration possible.

Keep in mind, this is for 120v synchronous motors only.

The signal generator is the easy part. You need to find one that provides adequate granularity so that small adjustments to the output frequency are possible, and it must output sine wave.  I have an old Leader signal generator that works OK for now.

The trickier part is amplifying the output of the signal generator so that it can output up to 130v @ roughly 10w (vpi motor needs 7.5 I think).  For this, I used a Kicker IX500.4 car stereo amp I had laying around and an old 15v laptop power supply (I never throw anything out :) ).  This easily allowed ouput in the range of I was looking for, to output 12w, a safety margin over the 7.5 needed for the motor.

So now I had to turn 5 to 7 volts into 120v.  Looking at my parts drawers,  I found a 6V center tapped line transformer, which normally turns 120v into 6v.  Reversing it and driving the secondary with 6v (not using the center tap), it turns 6v into around 120v.  Then I hooked the primary to a standard wall receptacle, and plugged the motor into the wall receptacle,

With the gain on the signal generator set to 0 and frequency set to 60hz, and the gain on the amp set to maybe 20%, I slowly increased the gain on the signal generator, while monitoring the voltage on a true RMS multi-meter until the platter started spinning.  It took a minimum of 75 volts to start the platter, and once started, it would maintain speed at anything over 60v.

There you have it.

I'm not into vintage for the sake of vintage, most of my stuff was fairly current when I bought it (been doing this a long time). I wouldn't be looking to ditch the VPI for older DD or idler wheel tables.

chakster:
Thanks for the info.

You're welcome. Let me assure you that any of those vintage turntables I have mentioned are much better than VPI or any modern belt-drive at this price. Technics SP 10 mkII, Luxman PD-444, Denon DP-80... those turntables are all HIGH-END direct drive and you will never find anything equal today in terms of price/performance. Garrard will cost more without being any better. 

When I mention any vintage gear (turntable or cartridges) in my posts i'm referring to the best turntables and best cartridges at certain price category TODAY (imo). Not because they are good looking or vintage, but only because they are better. 

You don't have to buy the latest gear when it comes to analog.
But you have to buy the latest gear when it comes to digital.