Mezmerize B1 Buffer Preamp

[batty]

The pre has a look of Copland about it I think. The power amp will be the M2X when all the parts arrive.

 

[Stuey]

Hi Salas, I have a blue Mez board built up with 10R current setting resistors and wanted to briefly test the PSU section before soldering in the 4 matched fets...can I get away with not sinking the IRFP's for this test? Or will they heat quite quickly?

 

[Salas]

Because they are big you can get away for 30 seconds. Have your probes ready, power up, check, power down quickly, move your hands fast like Colibri wings

 

[Stuey]

Cheers, thank you for the quick reply!

 

[rookakoma]

Why is the 20k pot impedance ideal for DCB1?
Is the gate capacitance the reason?

 

[Salas]

Certainly interacts, it's a bit less transparent with 50k pot in my experience. But still not bad at all.

 

[rookakoma]

Thanks Salas.

 

[RCruz]

What do you think about 10k pots ?
In my last build it seems to add some detail and bass insight.

 

[Salas]

10K Log is not a bad choice. Personally I found it more on the contrast side than on the coherence side, at least with those pots I tested values back then.

Its not only about value but also what kind of pot material, total system synergy, preference. The available source equipment must feel OK on 10K loading is one other valid consideration.

 

[bubba177]

Salas, just finished my Mezmerize B1. I want to thank you for all the help you gave me. It is replacing a regular B1 driving a F5. I was not prepared for this level of transparency and front to back depth. Just blown away!!! Thanks again, great work i appreciate your effort.

 

[Salas]

Salas, just finished my Mezmerize B1. I want to thank you for all the help you gave me. It is replacing a regular B1 driving a F5. I was not prepared for this level of transparency and front to back depth. Just blown away!!! Thanks again, great work i appreciate your effort.

You are welcome. Congratulations!

 

[batty]

I'm guessing that I have done something wrong if the 2 x 5 groups of LEDs are not lit.

 

[Salas]

Even only one wrongly oriented or grilled during soldering is enough to break the chain. Fortunately you can test them before desoldering anything. A DMM that has enough voltage to turn on an LED in diode test mode or a 9V battery with two wires to briefly touch their pins at the bottom layer and see which ones light up and in what direction.

Also given the opportunity since you will lift the board, check again that the MOSFETS are the right types at the right sides as printed on the board near each one's pads.

 

[batty]

Thanks Salas, I'll check

 

[Salas]

Are the two MOSFETS near the lit triplets mildly warm? There should also be voltage drop already across the 18Ω resistor pairs at the sides of the reservoir caps. By the way, recheck that the BC550 is not a BC560 and vice versa while you are at it.

Good luck and let us know.

 

[batty]

I think I know what I have done (at work atm and looking at the pic, I think I have one of each mosfet on each side of the board. Will check tonight when I get home.

 

[batty]

Yep, got them crossed up and now they won't come out!

 

[batty]

Done, all LEDs lit.

DC offset at the output is R: 1.9mV L: 5mV

 

[batty]

Sounding great going through my valve HP amp and HiFiMan HE-4xx

 

[batty]

I'd like to thank everyone involved in this project for the design and improvements and most of all the help.
Cheers guys, a special call out for SALAS.