[tomb]

Verifed.

 
I'm sorry guys - I will fix that DigiKey section first chance I get.  There's just not enough time these days, it seems.

 

[Aalelan]

JK,
Yeah, I am lucky, its not the best store but it has things..  Thanks for catching My JFET error, iron is heating up now..
Also while the iron is hot I'm going to put in the R1 10Ohm I have .  I'm still reading through the 400+ pages of this post so I'm learning as I go
 
As for RB14L/R I was gonig by the current BOM where Tom said jumper out unless you are having noise issues or desire greater gain reduction.. so I was starting without them..  Looks like I might need to see if my local shop has some, I didnt order them.
 
Man you guys post faster than I can type..  No, I didnt realize that CR4 was wrong till today..  I have powered it up to make the LEDs come on.. what is the downfall to keeping it tantalum ?
 
Tomb,
 
Dont worry about time, it seems you put some much blood sweat and tears into this project and site, I cant even imagiane!!  Oh and I just orderd my GrubDAC today, thanks again for answering my standoff question email..

 

[Aalelan]

ok, my de-soldering skills, well lets just say they are bad I may need to reorder those JFETs
 
EDIT:
Yep, I pulled a leg off one of the J74's  Just emailed Tom to see if he can add to my order I put in this morning for my GrubDAC Kit..  I sure hope so, I'd really like to have this thing going by next weekend to start burning it in

 

[jdkJake]

ok, my de-soldering skills, well lets just say they are bad I may need to reorder those JFETs

Did you use braid or a pump? I am partial to braid, but, lot's of folks like the pump. Using a little bit of flux to speed things up can help as well. In general, I find it easiest to suck up as much as possible before trying to pull the part clear from the board. It can be tough with transistors, especially since they are so heat sensitive. I use alligator heatsinks when I put them in as well as when I pull them. They are cheap and work well to protect the part.

You can order some high quality resistors from beezar that work great at RB14. They stock multiple sizes, I used the 22R that TomB used on his build. Sounds wonderful. Unfortunately, looks like you might have to reorder JFETs, so, at least you can get them all in one shot.

BTW, be careful powering up a partially populated board. All kinds of bad things can happen depending upon which parts are still missing. I would not recommend doing that in the future.

jk

 

[tomb]

Quote:

I used BJT. I've never found a mosfet amplifier I like. My M3 included. And, as the MM uses more or less the same buffer as the M3 I decided to stick with BJT. I have to state that I'm a committed thermionic amp estimator and builder but  can't find any subjective ground backing the claim mosfets sound more like triodes than SS (because supposed 2nd harmonic distortion dominance).
 
This time I used the 2344/101 whilst my other MM uses 2238/968. I also, this time, splashed on prp and mills resistors.
Like Thomas says the 2234 gives amazing drumming. I will wait to see if the lower frequencies will get more body as I'm super spoiled with my old MM on K42Y+2239/968. I used tapped heat sink this time to make power BJTs replacement less painful.
 
This MM makes my Beyer DT48S Nagra, and my self too, extremely happy.
 
 
Cheers,
A
 
 
 

Oops - I didn't see all of these posts before - been busy with those grubDAC kits!
 
Again, I have to apologize - but there's no particular instructions (yet) for connecting the Bantam or grubDAC to the PCB.  The punch down blocks should be clear for two sets of L/R/G input connections - use one set for RCA inputs and one set for the onboard DAC.  The two-position terminal block is there for a SPDT switch.  I can't remember which is which, but connect the switch and the DAC/RCA inputs to different sources and it's easy enough to tell which one goes to which switch position.  You can also use a DPDT switch instead, and wire the LED on the onboard DAC to the front panel.  I did that with the MOSFET-MAX V1.2 I was showing at CanJam.  A red LED indicated that USB was connected, while throwing the switch to activate the onboard DAC input lit a green LED, instead.
 
I'll detail all this stuff on the website when I get a chance.

 

[TBomb06]

 
Quote:

Did you use braid or a pump? I am partial to braid, but, lot's of folks like the pump. Using a little bit of flux to speed things up can help as well. In general, I find it easiest to suck up as much as possible before trying to pull the part clear from the board. It can be tough with transistors, especially since they are so heat sensitive. I use alligator heatsinks when I put them in as well as when I pull them. They are cheap and work well to protect the part.

You can order some high quality resistors from beezar that work great at RB14. They stock multiple sizes, I used the 22R that TomB used on his build. Sounds wonderful. Unfortunately, looks like you might have to reorder JFETs, so, at least you can get them all in one shot.

BTW, be careful powering up a partially populated board. All kinds of bad things can happen depending upon which parts are still missing. I would not recommend doing that in the future.

jk

 
 
So, I've been running my Max for a couple of years without R1 or RB14 installed, but after reading some more recent posts, I've decided to install them both. For RB14 I ordered some Kiwame 22R resistors, but for R1, I can just use any old 10 ohm resistor, right?
 
I'm interested to see if I will notice any loss of impact or signal degradation with the RB14 resistors in place. I listen to Grados, so it will be nice to have a little bit of a reduction in the output, especially since I like the 12AE6 tubes with the higher gain, but I don't want to lose any of that awesome slam
 

 

[Aalelan]

Quote:

Did you use braid or a pump? I am partial to braid, but, lot's of folks like the pump. Using a little bit of flux to speed things up can help as well. In general, I find it easiest to suck up as much as possible before trying to pull the part clear from the board. It can be tough with transistors, especially since they are so heat sensitive. I use alligator heatsinks when I put them in as well as when I pull them. They are cheap and work well to protect the part.

You can order some high quality resistors from beezar that work great at RB14. They stock multiple sizes, I used the 22R that TomB used on his build. Sounds wonderful. Unfortunately, looks like you might have to reorder JFETs, so, at least you can get them all in one shot.

BTW, be careful powering up a partially populated board. All kinds of bad things can happen depending upon which parts are still missing. I would not recommend doing that in the future.

jk

Well I used some braid but it was just not in the cards for me that day I think.. I have a pump now to, I never used one but I was at the shack looking at knobs and such and got one..
 
For now I don't have / didn't order any nice resistors for RB14,  I have some carbon ones I will put in till I make another mouser-key order 

.
 
I will be carefull, I had seen other pics of powered on boards and didn't think twice about doing on my not finished one for some reason!  How about running a done board without tubes, what would that do if anything, besides not make any sound

 

[jdkJake]

 
 
 
So, I've been running my Max for a couple of years without R1 or RB14 installed, but after reading some more recent posts, I've decided to install them both. For RB14 I ordered some Kiwame 22R resistors, but for R1, I can just use any old 10 ohm resistor, right?
 
I'm interested to see if I will notice any loss of impact or signal degradation with the RB14 resistors in place. I listen to Grados, so it will be nice to have a little bit of a reduction in the output, especially since I like the 12AE6 tubes with the higher gain, but I don't want to lose any of that awesome slam
 

Do you have a BJT build or a MOSFET build? Also, what voltage are you running at? 24V or greater?

As I understand it, R1 only comes into play if you are running over 24V. Reference:

http://www.diyforums.org/MOSFET-MAX/MOSFET-MAXheaterResistor.php

You will need at least a 1/2 watt resistor or greater if using 10ohm at that position.

As for RB14, I doubt you will hear any noticeable attenuation until that value starts to approach 100R or greater. The 22R is there to help keep the MOSFET's from oscillating ( provided you have a MOSFET build ).

jk

 

[jdkJake]

Well I used some braid but it was just not in the cards for me that day I think.. I have a pump now to, I never used one but I was at the shack looking at knobs and such and got one..
 
For now I don't have / didn't order any nice resistors for RB14,  I have some carbon ones I will put in till I make another mouser-key order 

.
 
I will be carefull, I had seen other pics of powered on boards and didn't think twice about doing on my not finished one for some reason!  How about running a done board without tubes, what would that do if anything, besides not make any sound

As far as I know, it should do no harm. The main key on first power up is to insure the bias on the MOSFET/BJT is set as low as possible until you have a chance to set it. With the current parts and artwork, this is fully clockwise on the RB12 pots.

jk

 

[tomb]

 
Quote:

 
 
 
So, I've been running my Max for a couple of years without R1 or RB14 installed, but after reading some more recent posts, I've decided to install them both. For RB14 I ordered some Kiwame 22R resistors, but for R1, I can just use any old 10 ohm resistor, right?
 
I'm interested to see if I will notice any loss of impact or signal degradation with the RB14 resistors in place. I listen to Grados, so it will be nice to have a little bit of a reduction in the output, especially since I like the 12AE6 tubes with the higher gain, but I don't want to lose any of that awesome slam
 

I prefer nothing but jumpers (or sometimes 10R) at RB14 with a BJT MAX.  Please note that my statement about RB14 resistors being required has to do with a MOSFET-MAX, only.  As I stated, the MOSFETs will oscillate - the 2.2 power resistors ((RB10/RB11) are not enough to keep the MOSFETs stable.
 
You don't have any MOSFETs in a BJT MAX - two different animals.
 

 

[BoilermakerFan]

Quote:

My question would be, which BJT's to use? I know some of the toshiba parts are rarer than rare, does anyone know a potential source for something like a 2238/968 combo? BoilermakerFan, where did you source your set (if you do not mind me asking)?


jk

 
Sorry for th elate reply, but I was out for the last week on a fantastic family vacation...
 
I have a couple of sets I acquired from Tom over the span of 2 years.  I have a couple more, but I can't yet confirm if they are genuine Toshibas.
 
My plan is to roll them into the new MOSFET-MAX to see how they sound against the IRF24/34s and IRF540/9540s.  AMB used BJTs on his old MOSFET-MAX and really liked how they sounded, so I'll try it and see though I do plan to eventually use for pairs for a nice little hybrid 35w/ch amp in the future.
 

 

[TBomb06]

Quote:

 

I prefer nothing but jumpers (or sometimes 10R) at RB14 with a BJT MAX.  Please note that my statement about RB14 resistors being required has to do with a MOSFET-MAX, only.  As I stated, the MOSFETs will oscillate - the 2.2 power resistors ((RB10/RB11) are not enough to keep the MOSFETs stable.
 
You don't have any MOSFETs in a BJT MAX - two different animals.
 

Right, I realize the difference between the two configurations I just wasn't sure as to the need for the RB14 resistors. So, if they are only used to keep the MOSFETs from oscillating, what is the point of putting 10R resistors there on the BJT build if they don't offer any attenuation? Also, since I'm only running 27V at the power supply, is it necessary for me to use R1 either? Perhaps I took all of those suggestions out of context...

 

[tomb]

 
Quote:

Right, I realize the difference between the two configurations I just wasn't sure as to the need for the RB14 resistors. So, if they are only used to keep the MOSFETs from oscillating, what is the point of putting 10R resistors there on the BJT build if they don't offer any attenuation? Also, since I'm only running 27V at the power supply, is it necessary for me to use R1 either? Perhaps I took all of those suggestions out of context...

10R resistors do provide some quieting.  Trouble is, they will also cut some of the detail.  It's a balancing act.

  It can also help lower the cutoff frequency a bit on lower impedance phones such as Grado's or Denons.  On the other hand, the MOSFETs in a MOSFET-MAX are running such high currents that the output resistors don't seem to impact the detail, but my ears can detect ringing with only jumpers on a MOSFET-MAX (oscillation).
 
R1 at 10ohms is optimum when running 27VDC.  This is explained here:
http://www.diyforums.org/MAX/MAXheaterResistor.php
There is a similar page on the MOSFET-MAX and MiniMAX websites, too.  The heaters like to run at their rated voltage - 12.6V.  Lower than that, and you get reduced performance.  Higher than that, and you get reduced life.  Without the resistor at 27V, each heater is seeing 13.5V.
 

 

[Aalelan]

OK, I have it all build except for the replacement JFETs for the ones I killed, They are on there way..   Oh and RB14L/R are just carbon for now till I put in another order for stuff..  
 

 

 

[TBomb06]

Quote:

 
10R resistors do provide some quieting.  Trouble is, they will also cut some of the detail.  It's a balancing act.

  It can also help lower the cutoff frequency a bit on lower impedance phones such as Grado's or Denons.  On the other hand, the MOSFETs in a MOSFET-MAX are running such high currents that the output resistors don't seem to impact the detail, but my ears can detect ringing with only jumpers on a MOSFET-MAX (oscillation).
 
R1 at 10ohms is optimum when running 27VDC.  This is explained here:
http://www.diyforums.org/MAX/MAXheaterResistor.php
There is a similar page on the MOSFET-MAX and MiniMAX websites, too.  The heaters like to run at their rated voltage - 12.6V.  Lower than that, and you get reduced performance.  Higher than that, and you get reduced life.  Without the resistor at 27V, each heater is seeing 13.5V.
 

 
Okie doke. I'll definitely put in the 10ohm R1, and then try out the 10Rs for RB14. I'll hang on to the 22Rs I got for when I inevitably end up building a MOSFET Max I just haaaadd to come back here and see what's been going on that I've missed out on...