• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Suggestions Please

coolzero

Member
2009-09-04 11:36 pm
UAE
Can our good experts suggest some improvements to this phono/pre schematic? Not just part swapping but something theoretical.
 

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  • Yaqin-ms-12b-schematic.jpg
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Every design has its compromises. The tweaked RCA setup I've uploaded will interact badly with a few carts. and SUTs, due to the high CMiller of the 12AX7 triode. OTOH, the tweaks fix the so/so bass extension and WRETCHED drive capability of RCA's original.

BTW, the fellow who made the original drawing (from a narrative I provided), loves "boutique" parts, but good quality, industrial, stuff is fine. Notice the changes in blue.
 

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coolzero

Member
2009-09-04 11:36 pm
UAE
Yaqin MS-12b?

jeff

I checked the threads on this model. But nothing solid. All about just replacing parts.

Two things I noticed so far without doing anything to the internals. When using a SUT, sound changes drastically. Transformation was from OK to really nice. I think this constitutes to the fact that the input of this phono is not properly loaded for MC cartridges. I am using a DL103 so 100 ohms resistor in the input would change the sound I believe.
Replacing 12AU7 to 12XT7 changes the sound positively. Assume it is because of the difference in gain of two tubes.

I am a novice in to tube electronics so can someone guide me where to start? I am reading Morgan Jones these days to find some clues but I am an impatient person when comes to DIY :)
 
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Two things I noticed so far without doing anything to the internals. When using a SUT, sound changes drastically. Transformation was from OK to really nice. I think this constitutes to the fact that the input of this phono is not properly loaded for MC cartridges. I am using a DL103 so 100 ohms resistor in the input would change the sound I believe.

It won't have enough gain without the SUT using a LOMC like a DL-103, so just leave the loading at 47k.

Replacing 12AU7 to 12AT7 changes the sound positively. Assume it is because of the difference in gain of two tubes.

There are a lot of lousy sounding 12AU7's out there. 12BH7 would be a better tube, but draws double (IIRC) the heater current, which could be an issue for the PS trans.

jeff
 

lilc

Member
2012-06-21 2:08 am
US
I've spent a few weeks listening to my "Les Box" (converted Yaqin MS22-B, see Hi-Q's link), and I'm back to let you know my thoughts. There is mega DETAIL here, the sound is open and big and the unit is very quiet now, it sounds excellent. Also, I want to say that Les's (Hi-Q) abilities and efforts in transforming this unit, along with documenting the procedure for others, has been outstanding and it needs to be mentioned. I can tell you from my experience, that he is a very generous and all-around good guy. Obviously, doing this conversion is considerably more involved than replacing a few caps, but if one is qualified and up to the task, the results are absolutely worthwhile. It's difficult for me to imagine that the MS22-B could be taken to an appreciably ( if any) higher level beyond this.
LesBox ftw

http://www.diyaudio.com/forums/tubes-valves/216979-yaqin-ms-22b-phono-amp-5.html#post3342427

http://homepage.ntlworld.com/lez/Yaq...n MS-22B.pdf
 

lilc

Member
2012-06-21 2:08 am
US
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