[tomb]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif It just clicked...... I'm guessing you don't have to worry about turn off thump with the new relay system?

I'll check it again tonight to be sure, but with 1800uf's there's no measureable offset (thump) at turn off. I've been using the circuit on a MiniMAX for some months now and tried measuring it every which way, with no results. It's a slight click that's heard as opposed to a small whoosh or thump as before.

You're correct to question whether my maxxed out capacitors on this MOSFET-MAX made a difference, but I'll let you know for sure.

All I had until a few days ago were some 1/2A slo-blo fuses and it went through those like a soldering iron melting solder.

I finally bypassed the fuse to get it biased and have been running it like that since.

 

[Beefy]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif All I had until a few days ago were some 1/2A slo-blo fuses and it went through those like a soldering iron melting solder.

How hot does Vreg get?

 

[tomb]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif How hot does Vreg get?

Vreg stays fine at 150ma bias - no more than about 45deg.C. The weak point is the MOSFET that ends up between the two middle heat sinks. It's at about 60deg.C., while the other one is at about 50deg.C. The outer MOSFETs are about the same as the Vreg. Because of the positive temperature coefficient, the bias may drop when I case it up. So I'm setting it up with tip jacks on all bias points just as I did the very first MAX prototype. That should give us some better info.

 

[kugino]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif For MAX or MiniMAX? I'm getting my threads mixed up these days. Those suggestions are for a MiniMAX where the height is restricted to 1" (25mm). If you're building a MAX and can go as much as 1-1/2" height, then a whole range of other caps can be used. I put 3300uf 35V Panasonic FC's on the V1.2 prototype MAX.

tom, i'm building a MAX...i'm not sure what version board i have, though, as it was given to me by a friend. i'll go with the 2200uf caps just to be safe...thanks again.

 

[BoilermakerFan]

Quote:

Originally Posted by kugino /img/forum/go_quote.gif tom, i'm building a MAX...i'm not sure what version board i have, though, as it was given to me by a friend. i'll go with the 2200uf caps just to be safe...thanks again.

If it's a MHM board from Beezar, it's a version 1.0. Tom has the only V1.2 PCB right now, much to my dismay and repeated offers.

Quote:

Originally Posted by tomb /img/forum/go_quote.gif EDIT: Sounds like some outstanding casework you have going there, BMF! Looking forward to seeing them!

Thanks Tom. I finally succeeded in getting the V1.2 drawing to print out to the correct scale so I can locate all the screw and vent holes I need to drill in the bottom before paint. Also need to add a few more holes in the back for RCA and the IEC cutout. Decided to try to get one top prepped for paint too, but I need to see if he'll leave it without clear coat for me to do a little pin striping on the top after it's painted. Then I'll bring it back for clear and cure. It will definitely be one of a kind and hoping to match the level of work set by MrMajestic's so long ago.

 

[Listen2this1]

Does it hurt anything if I run two set of headphones at one time. One pair is Grado 325i's (32Ω) and the other pair is D7000's (25Ω)? I know the combo will be a really low load for the Max.

 

[tomb]

Quote:

Originally Posted by Listen2this1 /img/forum/go_quote.gif Does it hurt anything if I run two set of headphones at one time. One pair is Grado 325i's (32Ω) and the other pair is D7000's (25Ω)? I know the combo will be a really low load for the Max.

No, I doubt it. The real issue would be with sound if those impedances were more of a mismatch - Sennheisers with Grados, for instance. The combined impedance of what you mentioned is 14 ohms - I doubt seriously that the MAX will have any trouble with that.

 

[Listen2this1]

Well I will give it a shot.

 

[tomb]

Quote:

Originally Posted by Listen2this1 /img/forum/go_quote.gif Well I will give it a shot.

The last time cetoole and I discussed it, he's pretty much been using his MAX to drive a couple of desktop speakers (8ohm). That's mostly because he's into all sorts of electrostatics these days

, but he still uses the MAX for his orthos, too. At any rate, 8 ohms is fine for a MAX (within reason, of course - it's still a headphone amp).

 

[BoilermakerFan]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif The last time cetoole and I discussed it, he's pretty much been using his MAX exclusively to drive a couple of desktop speakers (8ohm). That's mostly because he's into all sorts of electrostatics these days , but he still uses the MAX for his orthos, too. At any rate, 8 ohms is fine for a MAX.

He has a couple MB Quart dynamics in the heard and he'll be demo'ing RS-1s and ESW9s shortly...

 

[tomb]

I posted this in another thread, but it really belongs here. It's just that they were talking about the MOSFET-MAX. At any rate, a good report - it was the KZ's!

Just an update on the MOSFET-MAX V1.2 - I came to the conclusion that I hate Muse KZ caps. I replaced the KZ's on the outputs today with a pair of Silmic's at 1000uf 35V (big caps, but there was room!). It sounds wonderful.

I even backed it down from 150ma bias in the buffer down to 125ma. It still sounds wonderful.

Next up is testing the BantamDAC on the board with the switching relay, but I've got to do some more building first. The Starving Student PCB version blew out another one of my BantamDACs.

 

[BoilermakerFan]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif I posted this in another thread, but it really belongs here. It's just that they were talking about the MOSFET-MAX. At any rate, a good report - it was the KZ's! Just an update on the MOSFET-MAX V1.2 - I came to the conclusion that I hate Muse KZ caps. I replaced the KZ's on the outputs today with a pair of Silmic's at 1000uf 35V (big caps, but there was room!). It sounds wonderful. I even backed it down from 150ma bias in the buffer down to 125ma. It still sounds wonderful. Next up is testing the BantamDAC on the board with the switching relay, but I've got to do some more building first. The Starving Student PCB version blew out another one of my BantamDACs.

Quote:

Originally Posted by tomb /img/forum/go_quote.gif One of the things Colin suggested is that the gate capacitance on the Z24/Z34's is too much for the tubes and this style of buffer. We talked about a lot of different things, though. Still in the next few days, I'm going to change those out to the IRF510/9510's and some Zetex's for the input JFETs. We'll see if that makes a difference.

That is great news! Especially since I've been planning to use my Cerafines for my MOSFET-MAX with the IRF510/9510 DBs. Still planning to swap in the Zetexes?

Oh, and Starving Students don't need DACs, they need food! You might as well build a few extra BantamDACs while your at it.

 

[Jrossel]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Just an update on the MOSFET-MAX V1.2 - I came to the conclusion that I hate Muse KZ caps. I replaced the KZ's on the outputs today with a pair of Silmic's at 1000uf 35V (big caps, but there was room!). It sounds wonderful. I even backed it down from 150ma bias in the buffer down to 125ma. It still sounds wonderful.

I will make a note on the KZs for my kit BOM. Were they 1000 uF as well?
Lots of people asking about MAX kits. Are we getting close to a release?

Your proto board looks pretty cool.

JR

 

[soloz2]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif I posted this in another thread, but it really belongs here. It's just that they were talking about the MOSFET-MAX. At any rate, a good report - it was the KZ's! Just an update on the MOSFET-MAX V1.2 - I came to the conclusion that I hate Muse KZ caps. I replaced the KZ's on the outputs today with a pair of Silmic's at 1000uf 35V (big caps, but there was room!). It sounds wonderful. I even backed it down from 150ma bias in the buffer down to 125ma. It still sounds wonderful. Next up is testing the BantamDAC on the board with the switching relay, but I've got to do some more building first. The Starving Student PCB version blew out another one of my BantamDACs.

glad to hear it! I'm still struggling to believe that there could be a better 'budget' DIY amp than my current MOSFET Max!

 

[tomb]

Quote:

Originally Posted by Jrossel /img/forum/go_quote.gif I will make a note on the KZs for my kit BOM. Were they 1000 uF as well? Lots of people asking about MAX kits. Are we getting close to a release? Your proto board looks pretty cool. JR

Thanks, Jeff! Sorry about the comments on the KZ's. I just never tried them before, believe it or not.

There must be some bad combination that results from their "hard etched sound" that combines badly with Millett tubes - or perhaps the VitQ's that we use for output bypasses. The MOSFETs definitely contribute to this, because they do seem very fast.

To be specific, no on the 1000uf - the KZ's I tried were 470uf 50V. Keep in mind this is only in the CA7 positions - the direct output couplers. Sound quality means everything at that spot. To sum up again, I used the following:

PS - 2 x 2000uf 50V Panasonic FC
CA4/CA5 Decouplers - 3300uf 35V Panasonic FC
CA2 - 1000uf 25V Elna RFS Silmic II
CA7 - 1000uf 35V Elna RFS Silmic II
Wima MKP10 bypasses all around, except 0.22uf 100V 196P-series Sprague VitaminQ at CA8

MOSFETS are Z24/9Z34 with Toshiba JFETs 2SJ74 and 2SK170 at Q2/Q3 buffer signal input positions.

Thanks for the comments on the board! Yes, we are getting very close. The PS tests just as good as the MiniMAX, the sound is great with the combo I'm using now. The only thing left is to test the BantamDAC mounting and the input-relay switching. I'll try to get to it this weekend, but you know how things go - I've got the Starving Student I've got to release for sale on Beezar, too.