Yaqin MS-22b Phono Amp

[pegwill]

MS-22B - Hi-Q Mods

During the week I had my MS-22b returned after the Hi-Q mods. I have been listening at every chance since and my first impressions still hold. This is what I thought then:

"The amp arrived yesterday so I was listening till late night and it sounds excellent. More musical and 3D with instruments spread out across the sound stage. I like lots of different types of music from rock to jazz and tried them all. So as you might guess I won't be returning it for the mods to be reversed."

As my ear has become tuned to the new sounds its even better than that. I'm now hearing things in recordings that I didnt know were there in the first place.

A great job.

Regards

 

[DF96]

Just to clarify for those who haven't bothered to read the thread: the Hi-Q 'mods' are actually a complete rebuild which just happens to use some of the same components and lives in the same box. This is not a 'tweak' to a good design, but a complete replacement of a poor design by a quite different good design.

 

[lilc]

I've been listening to my converted (see Hi-Q's notes) MS22-B for only a couple of days now and I know that's not a lot of time to form an opinion but I wanted to share my early thoughts, it's stunning!
I'd like to listen and report back with more specifics after spending a little more time with it but for now... holy ****!

 

[Hi_Q]

WARNING ALL MS-22B OWNERS

I found this whilst doing a recent upgrade (No- not yours Bill or Rod).
This wire is the only wire connecting any of the metalwork to the Earth pin of the power connector. With this open circuit there is an extremely high risk of an electric shock! All owners are advised to check that there is an adequate connection between the Earth pin of the power connector and the metalwork of your unit. Note that no solder has been applied to the tag

Also if you are in the UK - DO NOT use the 13A plug that comes with the unit.
It has an illegal sleeved Earth Pin and no visible fuse in the plug
Dump the lead and fit a proper British Standard approved item.

Bill, Rod and Steph you can relax as your units now have a 5 point earthing arrangement.

 

[Violator]

Hi everybody!

Just want to say thank you for this useful thread! I bought a Destiny Tube Phono some weeks ago and tried a lot of things to eliminate this hum. I did not find a solution.

I did the modification described in post #68 and the hum has completely gone!!!

Regards,
Boris

 

[lilc]

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://homepage.ntlworld.com/lez/Yaqin MS-22B/Putting 'Life' into the Yaqin MS-22B.pdf

 

[troutmask123]

I just finished converting my MS22B and wanted to thank Les for his design. I always thought the MS22B was missing something, like there was a big hole in the sound. I have very little experience working with electronics and was a little hesitant about doing the conversion. Now that it's finished I can't imagine ever buying another phono pre. Thanks a bunch Les.

 

[UberTube21]

Another MS22B rebuild by Les (Hi-Q) - apparently Yaqin had fixed the hum on their latest model - but with the extra tube and a host of new components as detailed in Les' comprehensive PDF guide (see above) the difference is literally between Night and Day. I was somewhat underwhelmed with the original unit - now I'm hearing stuff in the mix I didn't know was there and a kind of brittleness most noticeable on vocals is essentially gone - I'm back to enjoying my vinyl. Thanks to Watford's DIY audio genius!

 

[coolzero]

A word of appreciation

I have converted my 12-B phono with help of this excellent document provided in the thread. I am really grateful for the author and everyone contributed for it. Thank you Rod for letting me know about this document. Effort of this change is well worth and I am thoroughly enjoying it every moment when I listen to a vinyl. Now Yaqin is challenging my modified MF-VLPS.

BTW, one addition I did was to put this step-up in the input. Best 15$ ever spent. Try and see whether it will suit your unit too.

http://www.ebay.com/itm/Shure-Transformer-steps-up-a-LO-Z-element-to-Hi-Z-harp-Mic-Mic-transformer-NEW/111066517785?_trksid=p2047675.m1850&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D11%26meid%3D892782033267826597%26pid%3D100011%26prg%3D1005%26rk%3D1%26rkt%3D5%26sd%3D121073300814%26

Regards,

Kanishka

 

[Hi_Q]

Kanishka Did you fit Mosfets? or fit another tube? or make use of one of the two tubes already present.

If you fitted Mosfets, you will gain another lift in performance if you can use another tube.

I would have liked to have acquired a MS12b myself to see how best to modify this unit too.

Regards, Les

 

[coolzero]

Kanishka Did you fit Mosfets? or fit another tube? or make use of one of the two tubes already present.

If you fitted Mosfets, you will gain another lift in performance if you can use another tube.

I would have liked to have acquired a MS12b myself to see how best to modify this unit too.

Regards, Les

Les,

I used the MOSFET. Didn't do much of other changes. I also believe it is still possible to improve 12-B further.

regards,

Kanishka

 

[Hi_Q]

Yes Kanishka, you could do it by isolating the grid of the last (Buffer) Triode using a switch which then connects it to the Gate connection of the Mosfet, which you would have to remove. However, the volume controls would now be out of circuit. The alternative is to hide, if internal space permits, another double Triode inside with the Plate, Grid and Cathode connected in place of the Mosfet at its Drain, Gate and Source pads respectively. Les

 

[coolzero]

Yes Kanishka, you could do it by isolating the grid of the last (Buffer) Triode using a switch which then connects it to the Gate connection of the Mosfet, which you would have to remove. However, the volume controls would now be out of circuit. The alternative is to hide, if internal space permits, another double Triode inside with the Plate, Grid and Cathode connected in place of the Mosfet at its Drain, Gate and Source pads respectively. Les

Les, Thank you for these valuable suggestions. Do you have any schematic done for these changes? I don't mind trying them and see the magic

 

[coolzero]

Les, There is a relay in between gate and the grid just before the volume control already. So are you suggesting to bypass both of these?

 

[Hi_Q]

Hi Kanishka, It all depends on what conversion work you have done so far, I assume it is as depicted in the first Jpeg.

As a quick test (and the easiest to do) to hear what the improvements are, you could simply isolate the Grids of the 12AU7 and route them to the Gate connection of the Mosfet. The Mosfet MUST BE removed of course. See the second Jpeg.
If it works OK, you could even try fitting a 12AX7 in place of the 12AU7 as an experiment.
The other inputs including the volume control will no longer work of course and you would have to fit a separate switch to change over. Alternatively, you may be able to fit an additional Relay to automatically do the switching for you.

The other option is to replace the Mosfet with a fifth Tube, hiding it away somewhere inside perhaps if space permits. Due to the awful way the heater supplies are run to the 12AU7, fitting an additional Tube onto its filament supply will require the 15 Ohm 7 Watt resistor to be reduced to 10 Ohms 7 Watts.

Be prepared to be seduced by the new sound you may achieve then you can curse me for having to fit either an extra Tube or Relay to your unit Les

 

[coolzero]

Hi Kanishka, It all depends on what conversion work you have done so far, I assume it is as depicted in the first Jpeg.

As a quick test (and the easiest to do) to hear what the improvements are, you could simply isolate the Grids of the 12AU7 and route them to the Gate connection of the Mosfet. The Mosfet MUST BE removed of course. See the second Jpeg.
If it works OK, you could even try fitting a 12AX7 in place of the 12AU7 as an experiment.
The other inputs including the volume control will no longer work of course and you would have to fit a separate switch to change over. Alternatively, you may be able to fit an additional Relay to automatically do the switching for you.

The other option is to replace the Mosfet with a fifth Tube, hiding it away somewhere inside perhaps if space permits. Due to the awful way the heater supplies are run to the 12AU7, fitting an additional Tube onto its filament supply will require the 15 Ohm 7 Watt resistor to be reduced to 10 Ohms 7 Watts.

Be prepared to be seduced by the new sound you may achieve then you can curse me for having to fit either an extra Tube or Relay to your unit Les

Thank you Les for this detail explanation. I did the exact changes mentioned in first schematic.

Apart from the changes you suggested, 20K B+ series resister was reduced to 10K (B+ is 204V which I did not try increasing) and bypassed the 5K1 resister in the output and replaced the 12K with a 270K. Hope these changes are fine. Please share your thoughts on this.

BTW, in your opinion what would give more superior sound out of these two methods (direct connection+replacing 12AU with 12AX Vs adding the 5th tube)? 5th tube seems to be a cumbersome task considering the space but don't mind trying this if it gives far better SQ. Otherwise if SQ is marginal, I would stay with the first option. Appreciate your advice on this.

 

[Hi_Q]

Hi Kanishka, I think using the present output 12AU7 would be the way I would go as you would then remove an un-necessary stage of buffering. Of course this would involve using an extra relay to do the switching. The internal volume controls would be out of circuit for phono use of course but you could preset the phono volume using your main amp controls and preset the CD input using the MS12 controls - just a thought.

I have amended the circuit with the extra relay, I am assuming that on switch-on the ms12 defaults to Phono/RIAA input. You may need to select a good sensitive double pole changeover relay with a high resistance coil as the present transistor only has a gain of 30 though the maximum collector current of 200mA should be adequate.

Please Please place a diode across the relay coil! Yaqin should have done this as otherwise the back emf from the relay when it turns off does not do the present transistor a lot of good.
Even if you don't fit another relay, please put a diode (1N400x series) across it as shown, cathode (normally marked with a silver ring) to the power rail.

I agree with your increase in resistance to 270k on the output and you may have found a slight increase in Bass by doing this.

If you adopt using the 12AU7 as the final buffer it will free up a 1uF capacitor and I suggest that rather than waste it, you place this in parallel with the present one fitted on the final buffer.

Feel free to remove the Mosfet though on each channel and hard wire to the 12AU7 grid wire just to hear what it sounds like. Then if you are happy, you can proceed to add an extra relay or suitable switch.

Have you tried winged =c= 12AX7's in the front end? They are the long nickel Anode ones currently going for a song :-
12AX7 SVETLANA 'WINGED C' BOX ANODE | eBay

Les

 

[coolzero]

Hi Kanishka, I think using the present output 12AU7 would be the way I would go as you would then remove an un-necessary stage of buffering. Of course this would involve using an extra relay to do the switching. The internal volume controls would be out of circuit for phono use of course but you could preset the phono volume using your main amp controls and preset the CD input using the MS12 controls - just a thought.

I have amended the circuit with the extra relay, I am assuming that on switch-on the ms12 defaults to Phono/RIAA input. You may need to select a good sensitive double pole changeover relay with a high resistance coil as the present transistor only has a gain of 30 though the maximum collector current of 200mA should be adequate.

Please Please place a diode across the relay coil! Yaqin should have done this as otherwise the back emf from the relay when it turns off does not do the present transistor a lot of good.
Even if you don't fit another relay, please put a diode (1N400x series) across it as shown, cathode (normally marked with a silver ring) to the power rail.

I agree with your increase in resistance to 270k on the output and you may have found a slight increase in Bass by doing this.

If you adopt using the 12AU7 as the final buffer it will free up a 1uF capacitor and I suggest that rather than waste it, you place this in parallel with the present one fitted on the final buffer.

Feel free to remove the Mosfet though on each channel and hard wire to the 12AU7 grid wire just to hear what it sounds like. Then if you are happy, you can proceed to add an extra relay or suitable switch.

Have you tried winged =c= 12AX7's in the front end? They are the long nickel Anode ones currently going for a song :-
12AX7 SVETLANA 'WINGED C' BOX ANODE | eBay

Les

Thank you Les. You are really helpful.

Since I don't use much of digital audio, I would rather reserve my 12-B completely for RIAA. In this way I could avoid putting anything additional in between the signal. Just connect the gate to grid and have a happy listening. Just order the "Winged C" so by the time it arrive, I could keep my 12-B ready I suppose.

However I have a small query on your earlier suggestion of replacing the final 12AU7 with 12AX7. Wouldn't this require changes to B+/heater supply?

Regards,

Kanishka

 

[coolzero]

Les, apologies for asking too many question. Hope you don't mind clarifying below my queries too.

1. Don't we need a coupling cap/grid leak resistor for 12AU7 in the latter half?

2. Is it feasible to use the first half of 12AU7 seperatly as a CF buffer for CD/DVD input as below? We could use 0.2V out for this by decoupling it from the rest of the circuit I suppose. In this way I think it is possible to eliminate the use of a switch/relay.

An externally hosted image should be here but it was not working when we last tested it.

 

[Hi_Q]

No No Kanishka, no grid leak! Both the Yaqin and my circuit are DC coupled directly to the preceding Triodes Anode. In the case of the Yaqin this is direct but in my circuit it is via the 180k resistor RAE.
This is what makes it much easier to try. Les

P.S. Don't forget to remove the Mosfet first