[RedLeader]

Was cleaning out my desk and had forgotten an almost-finished SSMH.  Took an hour or two to get it all together, and here it is!  Seems I've got about a 20% channel imbalance and some buzzing in the right channel that is pot-independant.  I'll have to do a thorough look through later, it's a p2p job, so a bit of a rats nest.
 

 

[monkeyevil]

Quote:

C7 and C8 go parallel to the resistors. When installed they increase gain.
 
A copy & paste answer from way back in this thread:
 
"[size=12.0pt]That cap is right in the signal path and will thus influence sonics. However, it also lowers rp a little and increases gain, so there are times when one might want it.[/size]
 
[size=12.0pt]Without the caps there is a small amount of degenerative feedback that reduces gain. The caps bypass the AC signal which eliminates this thus increasing gain[/size]
 
[size=12.0pt]Also, only use this cap if you need more gain. Otherwise, leave it out.[/size]

Thanks
 

 
Quote:

Yes, pin 9 connects to the middle tap of the heaters and is not used in this schematic. If you look at something like the Bravo V2 amp 12AU7 it utilizes each triode of one tube by using the center tap.
 
I don't know about C7/C8... you can try searching this thread.
 
Caps c5a and c3a are bypass caps, film caps to bypass the electrolytics. You can also search to get more info on bypass caps.
 

Thanks
 
 

 

[monkeyevil]

Done with case work (need to modify the tube socket nuts for clearance) and maybe halfway done with wiring.  Still couldn't resist seeing how it will look finished.
 

 

 
 

 

 

[c12mech]

Looks good so far.  It will look even better when the tubes start to glow. 

 

[the_equalizer]

@monkeyevil  and @RedLeader:  Cool looking builds!  Congratulations!

 

[c12mech]

Since I've had mine together for almost a year I should probably get around to actually finishing the case work.  I got it working and started listening to it and that was all  needed.  As we say at work, "It may not be pretty but it is effective." 

 

[RedLeader]

Alright, I'm a little baffled.  I've swapped out the pot, switched the tubes and double checked the jack and everything else.  I still have a 20% channel imbalance and buzzing in the quieter channel.  Sounds like a grounding issue to me, but I've checked all the ground.  I am, however, just using a piece of copper as the ground.  Do you guys think that running the grounds across other wiring like that is what is causing it?  Should I add another ground plate on the opposite side?
 
EDIT: I've added a second ground plate (which seemed to increase the noise floor in the normal channel) and replaced both of the mostfets.  Nothing I do makes any difference.  I must be missing something obvious here, because this is really not that complex an amp.
 

 

 

[Danthrax]

Quote:

 
Just because I had a hard time figuring out what parts I needed, I'll post this.
 
For the 9 pin and 17EW8 or similar the only real substitution from the original parts list (besides any of the optional stuff.) is the 390omh resistors in R2 & R8. Correct?
 
This is the current parts list I have on order for mine.  I subbed 63volts 470uF 20% general caps for the audio ones suggested because they were back orderd.  Not saying it's all correct, but I had a hell of a time figuring out what I needed and what I didn't from the 370 page thread
 
http://www.evilmonkeymedia.com/dl/SSamp.htm

I noticed that you have 100Kohm resistors but no 50Kohm resistors is there a reason for this substitution? I was also wondering where the LEDs would be connected
 
http://www.diyforums.org/SSMH/variants/SSMH-12AU7.gif <-- that parts list is for this schematic correct?

 

[Beftus]

LED.
 
Adjust RLED to set current through LED. Maximum current for a standard LED is usually 20mA. Don't run LED @ 20mA though, lower is better for LED life. A power status LED needs a few mA (3- 5 mA). Tube LEDs need more (10 mA or more).
 
Use LED calc here: http://led.linear1.org/1led.wiz

 

[Danthrax]

Oh ok so do 2 LEDs connect there or just 1? And also the bigger question I still have is the reason for the 100Kohm resistors that I am going to assume replace the 50Kohm in the picture that are connected to the left and right input.

 

[the_equalizer]

 
Quote:

Alright, I'm a little baffled.  I've swapped out the pot, switched the tubes and double checked the jack and everything else.  I still have a 20% channel imbalance and buzzing in the quieter channel.  Sounds like a grounding issue to me, but I've checked all the ground.  I am, however, just using a piece of copper as the ground.  Do you guys think that running the grounds across other wiring like that is what is causing it?  Should I add another ground plate on the opposite side?
 
EDIT: I've added a second ground plate (which seemed to increase the noise floor in the normal channel) and replaced both of the mostfets.  Nothing I do makes any difference.  I must be missing something obvious here, because this is really not that complex an amp.
 
 
 
 

I can only think that maybe some of the resistors are not at their correct values, or maybe the coupling cap is open... . Measuring the voltages at the tube plates and grids, as well as MOSFET gates and drains could point you in the right direction. Both channels' measurements should be the same (or very close). IIRC, for a 12AU7 version, plates sit at ~27 V, grids at ~ -1 volt, MOSFET gates at ~ 17 volts, MOSFET drains at ~48 volts and MOSFET sources at ~ 12 volts.
 
cheers!
 
 

 

[monkeyevil]

It's done! Works great on the first try with no troubleshooting... woot!
 

 

 

 
In it's new home...

 

[c12mech]

monkeyevil that looks real nice.  Hope you enjoy listening to it as much as I like mine.  This thing cannot be beat for the price or time involved.

 

[Danthrax]

Nice hopefully mine will look somewhat like that except my case will probably not be as good.

 

[the_equalizer]

Very nice work with your amp, monkeyevil !  Enjoy!