My MOSFET MAX Build

[dbfreak]

Quote:

 
Very nice indeed. So ......
 
Where'd ya get the carbon fiber for the panels?
 
How'd ya cut the perfect vent holes, and what
 
kind of screen is that?
 
I've been going back and forth between the MOSFET and the MINI
 
and (think) I've decided on the MOSFET. I've been looking for a
 
tube-based transportable amp, and I think this will fit the bill.
 
I've read that the MOSFET works well with Grado's, but in what
 
way? Does it help tame the highs, or emphasize them. Also
 
wondering if it would work well with DT770/600's. Or, would the
 
MINI be a better choice?

Carbon fiber is from DragonPlate (online shop)
Cut vent openings with a Dremel
Vent screens are from an old steel mesh office trash can I had laying around.
 

 

[funch]

 
That's pretty steady-hand work with a Dremel.

 

[dbfreak]

 
Pic of underside

 

[dbfreak]

Quote:

 
That's pretty steady-hand work with a Dremel.

It's finished up with a file.
 

 

[Pricklely Peete]

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Thanks, Peete.  This will be the third project using these K42y caps, and I've liked them every time.  If I remember right I bypassed them in one project with iridescent baby-blue ER 0.043uF polypropylenes.  That helped the bass - maybe it was the color! 

  The other one was Jim Hagerman's "Ripper" USB ADC.  This will be the first project that uses so many of them, though.  I've also used grenade-sized K75 10uF caps (in the Pass B-1), and they took a while to settle, but I eventually switched them out in favor of Jupiters.  Small difference, but I liked the beeswax better.
 
I've another noobische frage for ovrclkd (or anyone else) - what is the two-position terminal block for by the DAC relays?  It doesn't appear on the schematic as far as I can tell, and in your pics there's no wires connected.  (TomB's pics have wires but I can't tell where they're headed - maybe to the other half of the power switch?)  It looks like it's for a switch, but I couldn't figure out why you'd need to put a switch there when the master power switch would suffice.....

  Is it for powering the relays and thus switching the DAC (if present) into the circuit?  Part of the problem is that I can't locate VRS1 on the schematic, and...well, I'm just confused.

You might want to try bypassing the K75-10's with T-3 Teflons. The combination is magical IMO. On their own they are good but combined it's my fav coupling cap combo (in tube gear).
 
Looks like you have the situation well at hand. The K40's are a slight improvement over the K42 series I have found but not enough to pull the k42's from gear I've already installed them in.
 
Peete.

 

[schubert]

Well, believe it or not I did have the K75's bypassed with FT-3's, and those same caps are now bypassing the Jupiters.  This wasn't tube gear, and there was a hint of graininess at first (before adding the FT-3's) that lessened as they settled in.  I've put the FT-3's in everything that has room for them - they're great.

 

[schubert]

YIPPEE!!!!  It works, I didn't fry anything important, and it sounds great right out of the box.

  I've only listened for 10 minutes or so, so first impressions only - there was some unpleasant hardness in the upper midrange on a piano CD (Messiaen "Vingt Regards", Stephen Osborne) which I imagine will go away eventually (maybe the effect of those Muses?).  However,the brass opening of Liszt's Dante Symphony (Barenboim/Berlin PO) was hands-down-jaw-droppingly-mind-blowing!

 
One grouchy nitpicking point - the template on the website for the back panel puts the power jack right in back of the power caps, so during one biasing session I blew the fuse because the board was pushed back too far (I don't have it completely cased up yet) and something shorted out back there.  Yeah, I wasn't as smart as dbfreak, who must have actually thought things out and so put the jack in the middle of the panel instead of over to the side. So let my experience be a warning to those who haven't done case work yet - the back panel template is probably a carryover from the first version!  Put the power jack in the middle!
 
After another 10 minutes of listening - more Dante Symphony - the orchestral sound is smooth and well-balanced, and I feel I could listen to this amp for a long time.  Nice body to the sound.  I'll try the piano again later and report back.

 

[tomb]

Congratulations!  Glad you're enjoying it. I'll take a look at that template on the website, but I built one, too, and didn't have any trouble in that particular area, so I'm curious about your statements, re: the power socket and the power supply caps.  I'll look into it, though and let you know.

 

[schubert]

I made it workable (I didn't want to have to drill another hole!) by rotating the jack a bit and clipping off an unneeded tab.  It's still kind of close, but I don't think it will short again.  Of course it helps that I covered up all the exposed solder joints!

 

[dbfreak]

Yeah, power jack looked kind of close so I put it in the middle.

 

[schubert]

Another caveat about the old templates - the adjustment holes for RA1R & RA1L in the top plate are in the wrong place for the new board, so if anyone drills those holes adjustments need to be made.

 

[ovrclkd]

Quote:

Another caveat about the old templates - the adjustment holes for RA1R & RA1L in the top plate are in the wrong place for the new board, so if anyone drills those holes adjustments need to be made.

Great to hear everyone's loving this amp like I do ... as shuberth said "it sounds great right out of the box".

 

[dbfreak]

Some clarification regarding the MOSFET MAX measuring points (MOSFETS) - Taken from web page:
 
 

Measurement Points:	TB1L or TB2L tu TA2L, TB1R to TB2R with TA2R

[td=colspan:2] MOSFET Bias[/td]

 
I read this as positive probe of DMM on TB1L or TB2L and negative probe on TA2L (left channel).  Positive probe on TB1R or TB2R with negative probe on TA2R (right channel).  Please correct me if I'm not reading this correctly.

 

[tomb]

 
Quote:

Some clarification regarding the MOSFET MAX measuring points (MOSFETS) - Taken from web page:
 
 

Measurement Points:	TB1L or TB2L tu TA2L, TB1R to TB2R with TA2R

[td=colspan:2] MOSFET Bias[/td]

 
I read this as positive probe of DMM on TB1L or TB2L and negative probe on TA2L (left channel).  Positive probe on TB1R or TB2R with negative probe on TA2R (right channel).  Please correct me if I'm not reading this correctly.

Yes - looks like I need to correct the "tu", but polarity doesn't matter.  What you're reading is the voltage across the RB10 resistor in one case and the RB11 resistor in the other - for each channel.   The readings will be slightly different, because there are complementary differences and slight errors in matching/resistors, etc. - but they should be fairly close within the same channel.  It really ends up being an "either-or" type thing.  Although, I personally find which one reads higher and then use that for safety's sake.
 
Divide the voltage reading by the value of the resistor (they're 2.2R) and that gives you the milli-ampere bias.  I would try to get them up to 120ma (~264mV).

 

 

[dbfreak]

Thanks much for the speedy reply!