Modifying a SinglePower MPX3 Power Supply

[Frihed89]

Has anyone modified the power supply in their MPX3. I have a Slam SE model. My basic goal is to increase the filtering capacity by a lot and then do whatever I can to improve the dynamics. Has anyone tried switching out the input transformer?

I don't have a schematic (and can't get one unless you have it) so I am sort of guessing where things are. Any help there would also be appreciated.

 

[nikongod]

1: Its the POWER transformer./ AFAIK no SP headphone amp has ever used an input transformer.

2:by SE do you mean a MPX3 with a supra power transformer, or some new definition of that term?

The mpx3 has an uberrrrr regulated supply. aside from improving the quality of a couple film caps, there is not much to do to it.

you could duplicate the regulators and make the amp "faux-dual-mono." I would NOT put bigger caps in. the stock caps are already plenty big.

 

[n_maher]

I would also like to throw out a big caution that if you've never worked on HV amps before that you really should leave well enough alone. I can't remember exactly what the B+ is on the MPX3 but it's certainly enough to do serious damage/death.

 

[Frihed89]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif 1: Its the POWER transformer./ AFAIK no SP headphone amp has ever used an input transformer. 2:by SE do you mean a MPX3 with a supra power transformer, or some new definition of that term? The mpx3 has an uberrrrr regulated supply. aside from improving the quality of a couple film caps, there is not much to do to it. you could duplicate the regulators and make the amp "faux-dual-mono." I would NOT put bigger caps in. the stock caps are already plenty big.

Power transformer, sorry.

Yes it has the supra power supply effectively minus the Jensen coupling caps.

I was just wondering how/if to increase the filtering.

Yes, I have electrocuted myself a number of times. The last time was in the US Navy in 1969 when I used my hand in place of an SCR in the powwer supply of AN/SQS 26BX Sonar. I have no memory of the day or event.

I have this thing about power supplies. I guess i should get a Supra with a seperate power supply SDS-T type thing.

Thanks

 

[luvdunhill]

I've increased the filtering capacity using Black Gate capacitors. It's a PITA to remove the circuit board, so you have to get creative. I have the same MPX3 as you do. So, yes it's doable.

 

[Frihed89]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif I've increased the filtering capacity using Black Gate capacitors. It's a PITA to remove the circuit board, so you have to get creative. I have the same MPX3 as you do. So, yes it's doable.

That's where I am stuck. Did you add more or replace existing ones, which ones?

 

[nikongod]

have you upgraded the various cathode caps yet? I would do that before upgrading the power supply. I did not change the power supply caps in my MPX3, but did the cathode caps. the sonic changes were not subtle.

I agree that the power supply of the amp is very important, and so often overlooked. on the other hand, the power supply in the MPX3 has a nice voltage regulator, so im not 100% sure how significant these changes will even be.

I personally would not go for bigger caps in the power supply if you do decide to change the electrolytics.

The caps in the MPX3 are already plenty big for the amp, especially considering the fact that it has an active regulation stage.

Maybe improve the quality of the PS caps after the regulator. odds are good that you can get by with LESS capacitance after the regulator although I have not tried it personally.

 

[luvdunhill]

Quote:

Originally Posted by Frihed89 /img/forum/go_quote.gif That's where I am stuck. Did you add more or replace existing ones, which ones?

both replaced and added... I replaced the CRC for the heaters, cathode caps, plate cap, bypassed the output caps, etc... I lost track. I have Black Gates everywhere they'll work, large NOS polystyrene caps for the cathodes, and Nippon Chemi-con for many of the rest, where the WV is higher than I could find in the BG line.

 

[mrarroyo]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif have you upgraded the various cathode caps yet? I would do that before upgrading the power supply. I did not change the power supply caps in my MPX3, but did the cathode caps. the sonic changes were not subtle. I agree that the power supply of the amp is very important, and so often overlooked. on the other hand, the power supply in the MPX3 has a nice voltage regulator, so im not 100% sure how significant these changes will even be. I personally would not go for bigger caps in the power supply if you do decide to change the electrolytics. The caps in the MPX3 are already plenty big for the amp, especially considering the fact that it has an active regulation stage. Maybe improve the quality of the PS caps after the regulator. odds are good that you can get by with LESS capacitance after the regulator although I have not tried it personally.

Hi there, my MPX3 is supposed to arrive tomorrow (fingers crossed) so I can take it to CanJam. Anyways two of the mods that Mikhail did was to take the MPX3 transformer and replace it with the Supra, plus he took out the two 650 uF power caps and replaced them with two 2,400 uF power caps.

Based on my understanding of your statement the replacement of the power caps for much larger ones may not yield an improvement. Did I understand you correctly? Thanks.

 

[nikongod]

Quote:

Originally Posted by mrarroyo /img/forum/go_quote.gif Based on my understanding of your statement the replacement of the power caps for much larger ones may not yield an improvement. Did I understand you correctly? Thanks.

first off, and i probably should have said it before: i am inclined towards using smaller caps when possible in tube amps. This is my prejudice. it is based on some stuff i have built and may also be biased by my average listening levels which are on par with an average conversation.

i would have gone for the smaller caps and done something else. i dunno if you upgraded the cathode caps, but thats a HUGE difference.

FWIW, my supra has 3300uf caps

the thing NEVER runs out of steam.

 

[luvdunhill]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif FWIW, my supra has 3300uf caps the thing NEVER runs out of steam.

sweet...

Have you played around with the interstage coupling caps?

 

[nikongod]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif sweet... Have you played around with the interstage coupling caps?

not yet.

im torn between trying to fit Russian teflon's in the case, and the cost of v-cap teflons. odds are good that i'l eventually cave and buy the v-caps.

 

[luvdunhill]

Quote:

Originally Posted by nikongod /img/forum/go_quote.gif not yet. im torn between trying to fit Russian teflon's in the case, and the cost of v-cap teflons. odds are good that i'l eventually cave and buy the v-caps.

heh, I just sold the v-caps that I played with to someone else.... there's lots out there, just have fun trying various things. I think the Russian teflons would fit, I'd go ahead an do the end removal and connect the leads directly to the foil if you go that route. I think I'm finally happy, and now am turning to finishing up my 12v supply mod.

 

[Frihed89]

I took off in the middle of this thread and I apologise. I have been side-tracked by some new equipment.

OK, according to SP, I have:
Black Gate Cathode Capacitors
Black Gate Power Supply Capacitors
Power Supply Upgrade
Supra Power and High Bias Option
2 Mono Gold Point Stepped Attenuators
High Voltage Option
Two Single-Ended Input Sets
Preamp Out Option

Now, what I think i want to do is enlarge the two external reservoir capacitors to be the same size as the Supras and to increase the filtering capacity in the power supply. But I am not sure how easy or wise that is. I also am confused about the language used to describe some of the upgrades on the Moon-Audio Page:

Jensen PIO upgrade - OK, but where or are there just one set of coupling caps?
Audio note silver foil in oil caps - where?
Extra large Audio output caps - ?
Black gate output caps - ? Are these the same as above.

Anyway, in a while i will take the cover off and take some pictures.

Thanks

 

[luvdunhill]

Quote:

Originally Posted by Frihed89 /img/forum/go_quote.gif I took off in the middle of this thread and I apologise. I have been side-tracked by some new equipment. OK, according to SP, I have: Black Gate Cathode Capacitors Black Gate Power Supply Capacitors Power Supply Upgrade Supra Power and High Bias Option 2 Mono Gold Point Stepped Attenuators High Voltage Option Two Single-Ended Input Sets Preamp Out Option Now, what I think i want to do is enlarge the two external reservoir capacitors to be the same size as the Supras and to increase the filtering capacity in the power supply. But I am not sure how easy or wise that is. I also am confused about the language used to describe some of the upgrades on the Moon-Audio Page: Jensen PIO upgrade - OK, but where or are there just one set of coupling caps? Audio note silver foil in oil caps - where? Extra large Audio output caps - ? Black gate output caps - ? Are these the same as above. Anyway, in a while i will take the cover off and take some pictures. Thanks

yeah, easier to point these things out in the pictures honestly. You have my e-mail address. We have the exact same options on our MPX3s.

The Jensen and Audio Note upgrades are mutually exclusive. I'm betting you already have the Black Gate output caps.