[tomb]

Hey again! I know I have been bothering for a while but another problem came up -___-. Is it normal to have a 120hz hum all the time? This hum is apparent when im at a very low gain, as well as if I crank the volume up all the way with or without a source connected. The volume is constant which kinda tells me that it bypasses the volume pot? Also I tested changing the tubes and detaching any ground (volume pot and RCA). Also I tested the source (DAC) and its clean. Even if I don't have any connection at all I would still hear it, and although with music its barely noticeable, when it gets pretty quite in the music or in video dialogues it gets distracting... I really don't bother with most amp hiss but this hum is quite distracting. Is this normal? could it be a filter capacitor gone bad?

Thanks in advance.

You should never hear any ripple with a Millett MAX. The power supply noise is down in the 45 micro-volt range.

You definitely have a problem.

 

[FJJB]

So you think its the power supply stage which might be defective? I will try to swap most of the caps (although they look fine), some rectifiers and at the most extreme the ps lm317t. But this will have to wait until summer because I dont have any tools where I am right now.

 

[tomb]

  So you think its the power supply stage which might be defective? I will try to swap most of the caps (although they look fine), some rectifiers and at the most extreme the ps lm317t. But this will have to wait until summer because I dont have any tools where I am right now.

 
No, I'm not implying that at all.  The power supply is a superior design.  Swapping caps is not going to do anything, either, unless they're 30 years old or you bought something seriously cut-rate.
 
The point I was trying to make is that if you built the power supply correctly, that is NOT the problem.  Look elsewhere.

 

[ultraman31]

 
So over two weeks of work (had to wait for parts), finally came to end (still not quite done yet), At first, there's really loud hum noise, but found out it was the grounding issue. Quick fix and then it sound amazing!! I'm waiting for the heat shrink and heat gun to wrap up the connection and it should be good to go! One thing I noticed is the left LED is blinking time to time. It doesn't affect the sound, so I think it might be faulty LED. Also, I would like to thank @tomb for all the help! Without his help, it would have been rather difficult project!! 

 

[ultraman31]

Also, I just got the volume knob which I bought from ebay, but apparently, it's too loose... it has some screw but missing head, so no way to tighten it up. Can anyone recommend the volume knob? I don't want this to happen again...

 

[FJJB]

Just found where the 120hz hum was coming from! I just took some measurements to the power supply and although it was on the 27vdc I used a closer measurement on the DDM and it showed that it was at 27.4~ and so I lowered that value to 26.9vdc and the hum went away. I guess that the variable resistor was too open and wasn't attenuating much of the ripple coming from the PS. Hopefully this post will help future MMM builders troubleshoot a similar problem if ever encountered.

 

[tomb]

Just found where the 120hz hum was coming from! I just took some measurements to the power supply and although it was on the 27vdc I used a closer measurement on the DDM and it showed that it was at 27.4~ and so I lowered that value to 26.9vdc and the hum went away. I guess that the variable resistor was too open and wasn't attenuating much of the ripple coming from the PS. Hopefully this post will help future MMM builders troubleshoot a similar problem if ever encountered.

Yes - the LM317 has to "burn" some volts to provide regulation. Regulation is largely the mechanism that removes ripple.

 

[FJJB]

Good to know. Thanks again for helping out on the forums! Hopefully I won't have any problems as to bother again. Now some 

 

 

[tomb]

 
Good to know. Thanks again for helping out on the forums! Hopefully I won't have any problems as to bother again. Now some 

 

Well, thanks, but I probably shouldn't have been so definite that it wasn't the power supply.  Maybe "properly setup" was implied, but not stated.

  This has been a problem before, though, and I should add some notes on the website(s) about it.
 
My typical method is to always adjust for the highest voltage I can get with the trimmer.  When you make a half-turn and the voltage no long changes, stop, then dial it back by a full 1.5V at least.  That usually ensures the LM317 is in the range where it is still regulating.  If this voltage is still higher than 27V, then dial it back to 27V.
 
Anyway, I apologize for not mentioning this possibility as a reason for the hum/ripple you were hearing.

 

[3lectroD4ve]

Hello,
Will someone please point me to the JFET (2SJ74B, 2SK170B) matching procedure?
Thanks

 

[tomb]

Hello,
Will someone please point me to the JFET (2SJ74B, 2SK170B) matching procedure?
Thanks

http://www.diamondstar.de/transistor_matching_jfet.html

 

[3lectroD4ve]

Thanks!

 

[3lectroD4ve]

Got it working tonight! A little hum but otherwise the sound is sweet.

 

[tomb]

Got it working tonight! A little hum but otherwise the sound is sweet.

 
A Millett Max should NEVER hum.  Either you have bad tubes or your power supply is not operating correctly.  Turn the trimmer until the voltage no longer goes up.  Then turn it back down by at least 1.5V.  That will ensure that the LM317 is in a regulation mode and that it's not adjusted outside of its voltage capability.

 

[tedk84]

hello guys im the new one, dennis, 32 from germany.

i think i made a mess out of my build i accidently switched qb8l and qb9l, operated the build WITHOUT a fuse (... yeah, i know, i know). after two or three secs, i saw smoke, think it was near the left tube socket (having the volume pot directing towards me).
now i have the following readings:

v+ and gnd adjusted to 27v.
ta2rl and tb1 are 0v from the beginning,
ta2rl and tb2 have 10mV then slowly drop to zero.
gnd to ta2l/r are near (edit this in later since im on a train atm).

Can you guys help me fix my build?
Thanks in advance

Dennis