SH Spotlight If you have a turntable you need to play your mono records in true MONO. How to do it cheaply..

So I recently got a "new" receiver, or new to me anyhow. It's a Harman/Kardon 75+ circa 1973. Yep, quad.

interesting behavior though, the "mono" mode actually only selects the left channel and pans it to both speakers, which is a bit of a nuisance.

Why would anyone design a mono function like this? Is it due to the mono incompatibility of some quad mixes?

 

So it seems that all I needed to do was switch the location of the mono box from between the phono stage and the amp to between the turntable and the phono stage. Not sure why it would make a difference, but my problem went away once I switched them.

 

Probably because the output of the phono stage was presented with too low of an impedance. The left output was driving the right outputs low output impedance and visa- verse.

There should be no problem with a "y" cable at the cartridge output because it halves the source impedance, halves the load impedance, and doubles the capacitive load making everything balance out. As long as there are no loading resisters in the switch box. then you are changing the cartridge loading a somewhat.

 

Did you check your speaker phase? and all the cabling?

If anyone needs an interim "switch" while waiting for parts, a cheap a/v 2 or 3 way unit should work, like this one:

http://www.meritline.com/audio-video-switch-selector-box-splitter---p-120728.aspx

 

See post 899.

 

So does it matter where in the chain I hook them up? Either before or after the phono stage. My initial thought is to put them between the turntable and the phono stage, simply because for me those wires are more accessible. If they need to be somewhere else I can do it but not as easily.

Thanks
Mike

 

The mono switch was intended for use with a mono turntable.

Odd to find that on a '70s quad amp. This was more common in the late '50s/early '60s, when people were transitioning from mono to stereo, one component at a time.

I had an early '60s VM tube amp with a mono switched wired that way; it was simple and easy to convert to a conventional mono switch.

 

apparently it can, depending on your gear's impedance output/input requirements, if you're just using radio shack y cables, line level (pre out to amp) should be fine, depending on your phono/tt out and pre-ins, you may need to pad it with something like this:

http://allenk.home.infionline.net/techref/splitter.html

 

Hi action,

I can't say I'm 100% on board with the idea that mono buttons (on stereo amps) were designed for use with mono turntables. I mean the phono input *is* stereo on these amps, right? Plus, even if the mono signal from a mono tt was split for the inputs of a stereo amp, there would be no reason to sum that signal because it would be identical in both channels already...?

 

Then why would anyone design a mono switch for sending only one of two inputs to mono?

 

I had mine between the phono stage and the amp and got nasty distortion when accidentally playing stereo records in mono. I switched it to between the turntable and the phone stage and it went away. YMMV.

 

Maybe I misunderstood your comment. I thought you were talking about the "sum" mono button, like the one on my Marantz. Are you talking about those buttons like the ones on the vintage McIntosh amps that give you the option of sending either the left or the right to both channels? Hoffman has said on here that that was if anti-skate or a scratch had done more damage to either side of the groove wall but not both. But I suppose it could also be utilized for sending a mono signal to both channels. Even so, it seems to me that the "sum" mono button would have been designed with the intention of summing the stereo channels of a stereo turntable/stylus playing a mono record.

 

I'm referring to a very specific mono switch circuit where, when switched on, takes the signal from just one input (usually the left channel) and sends it to both outputs. If you played a stereo pressing of "With the Beatles," you'd only hear the backing tracks from the left channel, and none of the vocals on the right channel, coming from both speakers.

This was not a common configuration, but that's how the early '60s stereo Voice of Music tube amps were designed. I hated it and eventually rewired mine to act like a "normal" L+R summing mono switch.

 

Actionpact is right, according to the manual it does say that to connect a source to use in mono that it MUST be connected to the receiver in the left input - I figured that didn't mean much of anything but as it turns out of course, the right input is actually unused.

It's a minor annoyance, but whatever. I'm guessing they did this to allow people to use whatever surviving mono gear they had lying around that might have only accepted one plug, but if it was a true mono switch would it really have mattered which input it was plugged into.... Should've been designed that way, that's my one complaint about this amp. Anyhow I think there's something I can do with one of the tape loops, which shouldn't be a big deal because I don't use either of my tape machines to record to other sources or have the desire to hook up any EQ or effect boxes.

 

I decided to try and take it a step further to try and make it a permanent setup so I could just flip a/b when going between mono and stereo

I ordered a mediabridge y adapter setup

http://www.amazon.com/Mediabridge-U...1&sr=8-1&keywords=mediabridge rca y connector
and
http://www.amazon.com/Mediabridge-U...7&sr=8-2&keywords=mediabridge rca y connector

as well as a cables to go switch
http://www.amazon.com/C2G-Cables-28...415891090&sr=8-1&keywords=cables+to+go+switch

I also had a set of radio shack piggyback cables which are like the ones in the link below:

http://www.amazon.com/PcConnectTM-a...=1415891198&sr=8-1&keywords=piggy+back+cables

I took the L+R from the turntable and inserted them into the female part of the piggyback cable
I used those ends and hooked up the double Y connection and inserted that into 1st input on the switch.
I used the other male ends of the piggyback cables and plugged them into the 2nd input section on the switch.

I connected the output of the switch box into the input of my Pro-Ject Phono Box

I left the output from the Phono Box to my receiver the same as it was so all connections were made between the turntable and the Phono Box

There is a ground cable attached to the L+R RCA cord coming out of the turntable which I left connected to the Pro-Ject Phono Box.

Is there anything wrong with how set this up? Will I get any loss of fidelity using the piggyback cables? Will there be fidelity loss as a result? I am starting to think there is a loss in volume as a result of doing it this way. Is there an easier way to do the permanent setup without using the piggyback cables?

Thanks for any guidance you can give

Mike

 

I finally got around to doing this! Thank you, Steve! It is worth it!

 

If you are listening to a mono needle drop, would it make a difference if you connected a Double Y Cord from the CD player outputs to the preamp inputs?

 

No, unless it was dubbed in stereo. In that case, import it into Audacity and convert it to mono, and then re-burn the CD.

 

I'm curious about this set up. Did this work out for you?

Are you now able to switch from stereo to mono without moving any other cables around? Was there any loss of fidelity?

 

How do I determine for sure if it was dubbed in stereo?

 

Listen to the background noise! Headphones help.

If you can tell if it's stereo or mono, don't worry about whether or not to listen in mono mode.

 

Forum member xmas111 (John) builds these and has some for sale.
I have one they work great and really simplifies things.
http://forums.stevehoffman.tv/threads/stereo-mono-switch.386061/page-6#post-11480754

 

I'm confused. If the stereo/mono switch sits either between the turntable and the phono preamp, or between the phono preamp and the preamp/integrated amp/passive preamp, and the digital source is connected directly to the preamp/integrated amp/passive preamp, then how is the switch in the digital signal path?