Melos SHA-gold photentiometer replacement DIY

You might want to consider replacing that photentiometer with a better one, if it's possible. Go over to the DIYAudio forum and do a search on "lightspeed attenuator". Besides being a stand alone attenuator with single input/output. Some DIYers have used this type of LDR attenuator in place of the inferior one that was in their preamp. If anything I'm sure George Stantschleff the Lightspeed designer will be able to verify if the swap is possible and maybe give you some pointers on how it can be accomplished.

I've read page after page about the SHA-gold the thought was the light controlled volume was the best. But there have been many issues that have come up with many of the units. When Melos went under and MAR (melos audio restoration) opened up (started by one of the melos guys) all the work they did lead them to replacing the volume control with stepped units. The places were spec diagrams were kept on the net have dried up as ha MAR. I'm not planning on doing any work until I know I can get it right. I have had some issues with the pho-tometer here and there, if there's away to swap that out I;d like to do it, other mods will happen down the road when time and cash flow allow me to figure it all out and do it.

Have you talked to Chris Johnson at partsconnexion.com?
try info@partsconnexion.com and he will get back to you.
If anyone would know, he would.

The volume pot in that Melos SHA may be special ... it is light coupled or a LDR ... notice the "phot" in Photeniometer meaning light

Some feel that these light coupled volume controls are better sounding than resister based controls and most likely why Melos chose to use them

You may want to do some homework about the Melos SHA before swapping for a basic Volume control

If you are trying to upgrade with ....

.."right one of these"..

... you may end up taking a step backwards

If you are having a problem with the volume control ... you may want to Google for help

Agree with Manistory.

You need to test with DMM to check a correctess of your DIY otherwise if you just turn it on, you'll have a large possibility to burn something in the circuit board especially with tube equipment. Also it's good to know what is Votage V, Current I, Resistance R, Impedance Z, Reactance X, Inductance L, Capacitance C, Freequency W, Power P, Measurements units of above listed.

Start with cheap equipment first to practice soldering, measurements (I to actually feel that you're not ready to DIY mod your preamp and practicing on cheap equipment will actually give you a cursory look to estimate yourself) etc and than exersize your DIY when you feel ready to take a risk.

Also having a camera to picture 'before' scenario would be very helpful in any tech DIY projects. I use Nikon D3000/Nikkor 18 - 55mm lens.

Disclosure: I'm part-time studio tech/full time software engineer.

If you're 'rather clueless' and do not own a DMM, I am not sure you should be performing these mods yourself...you could do your amp, or worse, yourself, quite a bit of damage.
Just sayin'...
byron

I do want to do the all the mods I'm planning myself...
Upgrade the attenuator, caps, resistors, tube sockets and power supply

Sorry the DMM is a digital multi-meter. If you don't have one and don't know how to check resistance,skip that suggestion.

The schematic for your preamp which I found on the web shows a standard stereo pot. "potentiometer" 6 pins. One ground, one input and one output per channel.

Take a look at it. It should have a sticker on it somewhere that says 50k or 100k. Those are the most common values anyway. Or if your going to have the work done for you have them check it for you. If it is indeed 50k and you have the physical room for that stepped attenuator it will work and be a nice improvement.

I am rather clueless here... DMM? I dont have one.
Can anyone confirm that the KHOZMO-74447 will work?

Thank you for pointing me in the right direction

I am pretty sure that used a 50k stereo Nobel pot. Take a look at it and make sure. You can also measure it with a DMM.

KHOZMO-74447 should be the right one.