[tomb]

Quote:

Scratching head here..  Playing around here at my desk and I figured I would check my voltages.. my FET bias had droped about 12mv from last night so I tweaked it up again..  then I checked my tubes, left was at 16v!! and the right was at 14v..  I got the right back down to 13.5 but the left will not go down at all for some reason..  I checked the PS output and it was at 24!?!  so I check the AC side of things and the wall wart is only putting out 22.8v  where it was running at almost 27V loaded up.  The most I can get out of the PS adjusting the 1K is 25.4v
 
Everything seems to be going whacky on me, any ideas??
 
EDIT: just to note the wall wart is the 50va one from Beezar, so it should be plenty hefty enough.
 
AA

The tubes may very well change bias as they break-in.  That's not unusual.  As far as the left one not going down, that doesn't sound normal.  However, the biggest issue may just be your line voltage.  Is it possible that your area has some scheduled brown-outs?  This is the time of the year for those things - or just power sags, period.  It would explain a lot.
 
Try checking it later tonight and see if things have calmed back down.

 

[Aalelan]

Quote:

The tubes may very well change bias as they break-in.  That's not unusual.  As far as the left one not going down, that doesn't sound normal.  However, the biggest issue may just be your line voltage.  Is it possible that your area has some scheduled brown-outs?  This is the time of the year for those things - or just power sags, period.  It would explain a lot.
 
Try checking it later tonight and see if things have calmed back down.

Ok, partial answer and more questions  
 
I moved up to my office where that circuit is know to be on the verge of overloaded all the time..  The wall voltage there is 108VAC, down the bedroom and living room I get 120VAC.. Move the Wall wart and voltage comes out ok..
 
So for the questions:
 
1)  how much can the MAX 1.2 PS bump up the voltage?  is that why I could not adjust up past ~25 when I was only getting 23 from the wall wart?
 
2) So how about that left tube?  I know they take time to break in and they seem to always read high before they warm up..  but they had been fairly stable the last few days (right at 13.5 - 13.6)..  what would cause just that left tube to shoot up so high and not come down?  I have not got it below 15v even with the trimmer all the way in
 
3)  I cant seem to remember now, started talking the wife mid post and lost it
 

 

[tomb]

 
Quote:

Ok, partial answer and more questions  
 
I moved up to my office where that circuit is know to be on the verge of overloaded all the time..  The wall voltage there is 108VAC, down the bedroom and living room I get 120VAC.. Move the Wall wart and voltage comes out ok..
 
So for the questions:
 
1)  how much can the MAX 1.2 PS bump up the voltage?  is that why I could not adjust up past ~25 when I was only getting 23 from the wall wart?

 
The PS regulator "floats" by regulating to a voltage difference. It's that difference that's regulated, not the specific value of the output voltage. This works fine in most instances because we're really only interested in removing the noise to provide high-quality audio. All of the major headphone audio linear-regulation schemes work this way. It only becomes a problem when we have something like the MAX/MiniMAX with several specific voltages that need to be set.

Actually, there's only one specific voltage: V+. The tubes are simply biased at 1/2 of that, whatever that is. In any event, the 27VDC recommendation for V+ is based on the walwart supplying at least 24VAC to the terminal block under load. You can actually push it to 28 - 28.5VDC before you lose regulation ability under the best of conditions, but that's why we dropped it back to 27VDC for most scenarios.  Frankly, I've been a bit surprised at a couple of instances lately where there are problems in meeting this voltage.  As mentioned earlier, I suspect that there's some brownouts occuring during the peak of the summer season and that's raising this issue to the forefront.  Just as likely - as you mention - may be a localized circuit that turns out to be heavily loaded.  I would not want to plug one of my MAXes or MiniMAXes into the circuit that feeds my color laser printer, for instance.

2) So how about that left tube?  I know they take time to break in and they seem to always read high before they warm up..  but they had been fairly stable the last few days (right at 13.5 - 13.6)..  what would cause just that left tube to shoot up so high and not come down?  I have not got it below 15v even with the trimmer all the way in

Again, the bias is directly related to the V+ voltage.  If that changes, then the bias changes.  The changes should be consistent between the tubes, though - but this is not always the case, unfortunately.
 
Have you tried turning the trimmer the other way? Sometimes the bias changes direction on the trimmer, depending on which side of the resistance the bias has altered. If that doesn't work, then it may be one of those infrequent (thankfully) occasions where the tube went bad. Let me know and I'll replace it if it was a Beezar tube.
 

3)  I cant seem to remember now, started talking the wife mid post and lost it
 

 

 

[Aalelan]

Tomb,
 
That left tube is still acting up YGPM..

 

[TBomb06]

Well, I got my MOSFET Max built today and I'm listening to it now. My experience building my first BJT Max helped me out a lot this time around, as everything fired up perfectly and worked right out of the box, which was a relief. Once I get this one all cased up I'll post some photos, and once it's broken in I'll do a comparison to my BJT build and see how much difference I can hear with the MOSFETs. I know those red boards sure are pretty...I'm thinking I'll have to do a lexan top so I can show off the beautifully designed circuit board.
 
Thanks for all the help guys, I appreciate you making my life easier

 

[Nakattack]

Hey guys, I'm having problems with a MAX I received on loan today. I power the amp up, and one of the channels doesn't work, but if I switch the amp off and play with the tubes I can change which side receives a signal. Any ideas on how to fix this?

 

[Aalelan]

Quote:

Hey guys, I'm having problems with a MAX I received on loan today. I power the amp up, and one of the channels doesn't work, but if I switch the amp off and play with the tubes I can change which side receives a signal. Any ideas on how to fix this?

 
Well if play with the tubes means you swap sides with them, I would say it sounds like you have a dead tube.  Also the fact that you can get it to switch would lead me to believe that none of the solid state parts are dead/damaged.
 
Not what you wanted to hear I bet but thats my opinion on whats happening..
 
AA

 

[tomb]

A tube that's not biased will also act like a dead tube.  Does the tube glow?  Look for an orange glow near the top in the center of the tube.  If it glows, it's probably OK - at least it would produce some sort of signal if it were biased correctly.

 

[funch]

 
Aw crud!  I was listening last night, and all had been well for about an hour or so. Suddenly, the sound distorted, the volume dropped, and 'click',
everything went dead. The distortion sounded like the situation when you power an amp down with the music still playing and after a few seconds
the PS caps run out of reserve, the sound distorts, and the music stops. I'm visiting out of town right now, so don't have access to my meter so
I won't  be  able to troubleshoot 'till Monday. BTW, it happened in both channels simultaneously. Any thoughts?

 

[jdkJake]

 


Aw crud!  I was listening last night, and all had been well for about an hour or so. Suddenly, the sound distorted, the volume dropped, and 'click',


everything went dead. The distortion sounded like the situation when you power an amp down with the music still playing and after a few seconds


the PS caps run out of reserve, the sound distorts, and the music stops. I'm visiting out of town right now, so don't have access to my meter so


I won't  be  able to troubleshoot 'till Monday. BTW, it happened in both channels simultaneously. Any thoughts?

Check the fuse?

Did you use a fuse?

 

[funch]

Fuse still intact. LED's still light. No fireworks/smoke.

 

[Nakattack]

Quote:

 
Well if play with the tubes means you swap sides with them, I would say it sounds like you have a dead tube.  Also the fact that you can get it to switch would lead me to believe that none of the solid state parts are dead/damaged.
 
Not what you wanted to hear I bet but thats my opinion on whats happening..
 
AA

I wasn't swapping them, just wiggling them around a little bit. I managed to fix it by wiggling them, I think the tube sockets are loose? I'm scared to move it now, just incase a tube moves and I lose another channel. So far it sounds good, but the only real improvement I've heard over the headamp of my Maverick D1 is a little more bass punch. I'll have to do a critical listening sesh soon, and maybe some better RCA's.

 

[rarebear]

Is this still the AMP to build ?
If yes or no where can I get the info I need to buy and build the kit..
 
Thanks Much

 

[Aalelan]

Quote:

Is this still the AMP to build ?
If yes or no where can I get the info I need to buy and build the kit..
 
Thanks Much

Not so much a kit but  you can get the board here http://beezar.com/  and the build of materials are here http://www.diyforums.org/MOSFET-MAX/MOSFET-MAXbom.php
 
I suggest going with the mouser side of the BOM as there are still a few "errors" on the Digikey side..   This is a great amp to build I had a blast doing it and it sounds great!  IMHO if you have any kind of soldering skills at all and can read you can do this with some patients.  Just take it slow and easy..
 
AA

 

[rarebear]

Thanks Very Much,
I have some skills  
I think I'll give it a try, I just wanted to make sure it was not out of date...