I am looking for a valve phono pre-amp as a starting point for my system, does anyone have any experience or feedback on the Yaqin MS-12B MC/MM phono amp, the price is certainly right and it looks good enough but how does it sound?
I am happy to mod it so I can accept some shortcomings if the base unit is good enough.
I am happy to mod it so I can accept some shortcomings if the base unit is good enough.
I recently acquired one of these and after some minor work I can say that it does sound very good, especially for the cost (paid £100 plus cost of my mods.)
Basically, you have to check the 12AU7 heater voltage first - this was a serious issue and could ruin some expensive valves. This was alarmingly high at 15.4V here in the UK with 240V mains on a 220V unit. These heaters are fed via a resistor from the unreg supply and I think the resistor was incorrect, even for 220V mains. It was 15R and I replaced with a 22R and the voltage is now much better at 12.90V, with 240V mains. This also cured a small hum problem and some very hot valves! A better option would be to fit another regulator but it was a bit tight.
Next, I replaced the 1uF coupling caps with ICEL 1.0uF 10% 400VDC. These are very cheap but seem to have a very natural sound, although they won't appeal to those who swear by PIOs! Well at least they fit.
Finally, the output coupling caps, also 1uF, were replaced with ICEL 4.7uF 10% 400V. This improved the bass extension when driving solid state amplifiers.
The simple mods made the MS-12B sound like it would challenge a much more expensive unit. So far, the stock Chinese valves have been used and they do improve a lot with use. I will try some more refined ones next.
Another comment, I am beginning to love this as a pre-amp buffer from my home brew DAC. It improves the dynamics and everything sounds more solid. I am not sure why yet.
The only problem I can report is that it takes a while to strip and re-build the unit to work on it.
Paul.
Basically, you have to check the 12AU7 heater voltage first - this was a serious issue and could ruin some expensive valves. This was alarmingly high at 15.4V here in the UK with 240V mains on a 220V unit. These heaters are fed via a resistor from the unreg supply and I think the resistor was incorrect, even for 220V mains. It was 15R and I replaced with a 22R and the voltage is now much better at 12.90V, with 240V mains. This also cured a small hum problem and some very hot valves! A better option would be to fit another regulator but it was a bit tight.
Next, I replaced the 1uF coupling caps with ICEL 1.0uF 10% 400VDC. These are very cheap but seem to have a very natural sound, although they won't appeal to those who swear by PIOs! Well at least they fit.
Finally, the output coupling caps, also 1uF, were replaced with ICEL 4.7uF 10% 400V. This improved the bass extension when driving solid state amplifiers.
The simple mods made the MS-12B sound like it would challenge a much more expensive unit. So far, the stock Chinese valves have been used and they do improve a lot with use. I will try some more refined ones next.
Another comment, I am beginning to love this as a pre-amp buffer from my home brew DAC. It improves the dynamics and everything sounds more solid. I am not sure why yet.
The only problem I can report is that it takes a while to strip and re-build the unit to work on it.
Paul.
Yaqin MS 12 B Mod
Can someone please tell me where the 15R is so I can replace it with a 22R. I don't have the schematics for it. I' pretty handy with a soldering iron. My 12AU7 can get pretty hot at times. This is what I've done so Far.
http://www.expo29.com/audio/yaqin/ms12b/_DS26556.jpg
Thanks in advance!!!
Cheers!
Can someone please tell me where the 15R is so I can replace it with a 22R. I don't have the schematics for it. I' pretty handy with a soldering iron. My 12AU7 can get pretty hot at times. This is what I've done so Far.
http://www.expo29.com/audio/yaqin/ms12b/_DS26556.jpg
Thanks in advance!!!
Cheers!
Thank you so much Juergen! I lived in Heidelberg, Germany for 12 years and both my sons were born there. It's about gluhwein time!!!
Hi Juergen,
Yes, I know its watts but I'm going to have to open it up again to see if its 7 watt or 1 watt. I can't tell from the photo. Also what kind of Resistor? Wirewound? Carbon Film? I'm Learning alot or re-learning. Alot of Fun... Unfortunately, I don't have a local Electronic supplier. Cheers!
Thank for your Help Jurgen! I really appreciate it! I ended up getting a:
MRA-12 22R 1% MILLS
RESISTOR (12 watt.)
I have acouple of other ideas for this phono preamp. If anyone has suggestions, That would be wonderful. Below is what I plan to Mod if I can or if it makes a difference.
Here is the schematic for the MS12B. I have one, but the sounds is a little bit too muddy and mushy for my taste (compared to a Pro-ject Tubebox I had and an Aikido phono amp I currently use), I didn't try to modify it, other than changing the stock tubes to NOS.
Attachments
Thank you so much. Well for me its all about learning and venturing to the unknown. Great Hobby...I'm having great fun reading about mods with Capacitors, resistors etc..etc.. I used to be a generator Tech for the Army some 20 years ago and used to read schematics like nothing. I was great at it and Its all coming back slowing, very slowly..lol.. this is my first Phono preamp but I'm sure it won't be my last. I'm sure there are way better phono preamps out there for less.. Cheers and thank you again!!
Hi Migkiller ,
as the other Forummembers said , there is only little advantage to mod the thingie .
For that money you better invest in a other Phono-Stage .
If Sand is no problem , the simple Salas N J-Fet RIAA is the simplest Phono i can
think of and recommend . I would like to see a PCB for newbees or starters at the
DiyAudio-Shop , maybe in the future the dream come true .
Greetings and enjoy your black disks
Juergen
as the other Forummembers said , there is only little advantage to mod the thingie .
For that money you better invest in a other Phono-Stage .
If Sand is no problem , the simple Salas N J-Fet RIAA is the simplest Phono i can
think of and recommend . I would like to see a PCB for newbees or starters at the
DiyAudio-Shop , maybe in the future the dream come true .
Greetings and enjoy your black disks
Juergen
Hi Everyone,
Back again. This phono amp is sounding sweeter and sweeter. I guess it takes time for those Caps to break in. I'm amazed on how the sounds changes when using different tubes. Thanks to Audiotux for helping me with that risistor. I can listen to vinyl for hours and the chassis is nice and cool... I have pairs of 12ax7 and 12au7 tubes coming in next week. Which comes to my second question. GRID STOPPERS. I'm getting slight oscillation "only" in certain tubes on the output. Looking at the schematic that TOUFU kindly put up. Should I also add Grid stoppers to the 12ax7? if so, I figured that 1k carbon Comp Resistors should be soldered directly on pins 2 and 7. Pin 2 (L) Pins 7 (R) goes to the input and pin 7(L) Pin 2(R) goes after the 2M resistor? after would be closer to ground or at the 2m symbol? Do I need to cut the circuit on the pcb? Pin 2 and 7 on the output (12au7) is where I get totally lost. Usually pin 2 and 7 are soldered to a 470k type resistor?
Danke, Thanks
Back again. This phono amp is sounding sweeter and sweeter. I guess it takes time for those Caps to break in. I'm amazed on how the sounds changes when using different tubes. Thanks to Audiotux for helping me with that risistor. I can listen to vinyl for hours and the chassis is nice and cool... I have pairs of 12ax7 and 12au7 tubes coming in next week. Which comes to my second question. GRID STOPPERS. I'm getting slight oscillation "only" in certain tubes on the output. Looking at the schematic that TOUFU kindly put up. Should I also add Grid stoppers to the 12ax7? if so, I figured that 1k carbon Comp Resistors should be soldered directly on pins 2 and 7. Pin 2 (L) Pins 7 (R) goes to the input and pin 7(L) Pin 2(R) goes after the 2M resistor? after would be closer to ground or at the 2m symbol? Do I need to cut the circuit on the pcb? Pin 2 and 7 on the output (12au7) is where I get totally lost. Usually pin 2 and 7 are soldered to a 470k type resistor?
Danke, Thanks
To tell you the truth I'm not really worried about the 12ax7 (would Be nice) but I really need to put grid stoppers on the 12au7. I get slight oscillation when I used my Ribbed Telefunken 12au7 (which I love) but none with the Cheap Chinese, or the Jan phillips or the a pair of baldwins which I don't like. I have some NOS RCA Clear top coming in. Looking at the schematics, I think I have to cut the pcb track to the grid. I also know that these grid stoppers should be put after the grid-to-ground resistor.
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