Mono Blend Switch needed to align phono cartridge

[docbob52]

I need and advice and a schematic on how to wire a mono blend switch on my phono stage or my BeePre, in order to align my cartridge azimuth and anti-skating using the Hi-Fi News test record using the out-of-phase "null test.

Is it best to place the switch on the phono amp or the BeePre.  At present I am using my Transcendent Sound phono amp.  I plan on trying the Eros as soon as possible.

Yes, I know the the oscilloscope is the best route, but I have got to bone up on that before I try it.

[Grainger49]

Doc Bob,

All you need to do is Y-Adapt the two channels from your table into one channel of your system.  That gives a solid sum of the two channels from the table. 

If you go through your system in stereo you run a chance that an imbalance will throw your adjustments off.

Then adjust for minimum output.

[fullheadofnothing]

I added a mono switch to my FPIII. IIRC, I used a SPST switch. One lug has the hot left output of the selector switch tied to the left input of the circuit. The other lug has the right side the same. When the switch is in the "off" position, the left output goes to the left side of the circuit, the right output to the right side. When the switch is in the "on" position, the channels are summed nicely. Works a treat for mono records, and makes electronically re-processed for stereo records listenable. If all you want a mono switch for is to check azimuth, it's not really worth the effort; do Grainger's suggestion about summing with y-cables (although I'd do that at the input of the line or headphone stage (don't bother doing most of the HFNRR tracks with speakers, btw) for reasons of cartridge loading).

Azimuth is the fiddliest parameter to adjust, and on most arms it is so fiddly as to be basically un-repeatable and useless (if the adjustment is there at all). Also with the cartridges I've used, I haven't been able to perceive much if any difference dialing in the azimuth. The utility of this setup parameter will really be determined by your cartridge and your arm more than how easy it is to sum channels.

[docbob52]

Thanks for your advice Granger, 

I was reluctant to do this after reading of impedance issues when combining 2 stereo signals without using a summing box could trigger current limit overload.  (http://www.rane.com/note109.html ).  But now I realize that this would not be an issue since the HFNRR alignment track is not stereo, but is 2 MONO signals recorded out of phase.

So I will run the test track and use 1 Y connector connected to the 2 outputs of the phono preamp and measure the output voltage with my DMM or scope for the lowest reading.  Correct?

[docbob52]

Thanks Josh for your help. Yes it is way to much trouble to add the switch to the preamp.

The physical location of my TT  limits my ability to view the stylus head on for visual adjustment.  I can't move it around easily as it is a very heavy mass plinth for the Garrard 301 so I just roughed it in visually and am opting for the electrical adjustment to fine tune it.

I agree with you that small adjustments don't seem to make a whole lot of difference sonically to my ears.  I have a Ortofon 2m Black on the SME 3009 II imp. Fortunately the fixed headshell has a set screw that allows me to rotate the cartridge quite easily.

Why would measuring the voltage across the speakers load the cartridge?

Robert Howard

[Grainger49]

    .  .  .     Azimuth is the fiddliest parameter to adjust, and on most arms it is so fiddly as to be basically un-repeatable and useless (if the adjustment is there at all).

Amen!  My problem is that I loosen the set screw and it is still so snug that I over adjust.

[fullheadofnothing]

First - I'd highly recommend finding a new spot for your turntable. If you can't get a good enough view to adjust azimuth, I'd be surprised if you could see it well enough to get proper alignment on the protractor. Now that does make a difference!

Also sorry for the confusion in the nested parenthetical statements. What I meant was that you should use the y cables later in the chain than the input of the phono stage, so you are not altering the loading on your cartridge. The other thing I was saying was that you cannot do most of the tests on speakers. Headphones are an absolute necessity for the VTF, azimuth, and anti-skate tests.

[Grainger49]

Joshua,

How about he uses a meter or scope on the speaker leads of the one functioning channel?  Similar to the hum balance pot.

[fullheadofnothing]

I've never tried it. I'd think it'd need to be a 2channel oscilloscope, as you would need to see the phase cancellation. Maybe it's possible with two multimeters with black and red reversed on one channel, but they'd need to be really accurate.

I'll still contend that azimuth needs to be ballparked and then move on.

[docbob52]

Granger,

Fortunately, I don't have the problem twisting the headshell of the SME as it was well constructed with very tight tolerances.  I Just wish it was not the improved low mass model so that I would have more couches of cartridges, especially of the low output MC variety.

Josh, my scope is a dual trace, but I still have do a bit of practice learning how to use it before I fry something cherished or expensive.

Yes I wish I could relocate the TT, but it is really not possible in my small room because of the intervening fireplace.  At present I can view the front of the cartridge from 10 deg. off square.   I will try later moving it over about 6" which will give me a better view.  Really the problem is the age of my eyes.  At 62 years old it is just not the same looking through trifocals up close.  My pediatric telescopes at 2.5 and 4.5 power only help just a bit.

Also Josh, makes sense what you are saying about where to take the reading and I agree.

Josh, and Granger, what headphones do you recommend as best bang for the buck?

[Big Al 954]

If you're using a CRO for phase check as we would for tape head alignment you would be feeding one channel to each cro channel and in XY mode tweak for a diagonal straight line. This would be using a normal in phase tone record.If the phase is reversed on one channel then you would be looking for a perfect circle on the CRO.A great trick I've used for azimuth checking in Broadcast land is using a Howe  Phase-Chaser , the 2300A with the big LED display and adjusting tape heads watching that. Really nifty in the days when I had 40 NAB cart decks and 30 1/4" machines to keep up to spec for On-Air. Not to mention the 16 track decks in  the  production studios.