[capernicus]

Amp #2 - need help on this one too (unfortunately I'm just not getting a break on these things...)
 
So I actually built 2 of these amps as Christmas presents...  The first one featured earlier is for the lovely Mrs Capernicus.  Number two is for the bro-in-law.  I had my father in law build the box (another woody) and I wired it all up.
 
 
Amp #2 Problem:
Left Channel is there but only about half as loud (maybe less) than the Right but it is certainly there.
 
Observables:
-All of the voltages check out - closely match amp #1 across the board.
-I checked all of the resistances - R17, R15, R12, and from the negative side of C4 to GND - all checks out and measures same as working side.
-I tried swapping tubes - weak channel did not follow the tubes
-MOSFET voltages look good...
-measured resistances through POT and both channels track nicely
-I checked the CD source - even flop flopped the L vs R and nothing changes.  (I know the source is OK because it works as expected with Amp #1)
 
I am stumped... what have I missed?
 
 

 

[nikongod]

 
Quote:

So I have my 2k resistor at the other end of the wire from the mosfet - not right on it as you suggest.  How critical is it to put the resistor at the mosfet?  My limited understanding of all this would suggest that either way you have a 2k load on the gate and considering the distance we are talking is very small being right on the gate or 2" away shouldn't matter.  I'd like to understand this better - i haven't worked much with MOSFETs...
 
Thanks again Nikongod for the troubleshooting assistance!
 

I would say the importance is either 0 or 100%. It either makes no difference, or all the difference in the world. 
 
The idea behind the resistor is that mosfets can osciilate when they have RF on their inputs. By putting the resistor directly on the pin there is no antenna to pick up RF, and thus the likelihood of the mosfet oscillating drops. 
 
If the wires are very short, it probably doesnt matter.

 

[proid]

I'm planning on using Panasonic FC 1200uf/63V for C1,C6, Wima MKP10 0.47uf/400V for C2, C4, C3a, C5a, will that be fine?

 

[tomb]

Quote:

I'm planning on using Panasonic FC 1200uf/63V for C1,C6, Wima MKP10 0.47uf/400V for C2, C4, C3a, C5a, will that be fine?

Seems fine if you want to go with moar farads.

 
 
So, what are you proposing for C3 and C5?
 

 

[capernicus]

Quote:

 

I would say the importance is either 0 or 100%. It either makes no difference, or all the difference in the world. 
 
The idea behind the resistor is that mosfets can osciilate when they have RF on their inputs. By putting the resistor directly on the pin there is no antenna to pick up RF, and thus the likelihood of the mosfet oscillating drops. 
 
If the wires are very short, it probably doesnt matter.

Interesting -  Thanks for the response!
 

 

[proid]

Quote:

Seems fine if you want to go with moar farads.

 
 
So, what are you proposing for C3 and C5?
 

Just because i can't get lower farad 63V cap 

I'll use Philips BC 470uf/63V for C3 and C5

 

[TestSubject]

My Stripboard SSHM amplifier. Layout here LINK
 

 

[Starfire]

Figured I'd add mine to the thread, though I think I'll sell it.
 
First time I've really done a full point to point, I almost always use a perfboard, also used some navships teflon wire for all the audio signal.  Sound great though!
 
Outside:
 
 

Inside:
 

 

[proid]

i have just turned on the amp without un-plug my headphone for about 2-3 minute. I think my headphone now sound not different than before but i'm still worry ...

 

[nikongod]

[joke]How do you know its not the amp that sounds different due to different amounts of current going through the caps to allow for the turn on thump?[/joke]
 
Seriously:
I would not loose sleep over doing this once, especically if your headphones sound the same as before. I would certainly not make a habit of it, but relax. Damage from turn-on-spikes is pretty obvious.

 

[proid]

Quote:

[joke]How do you know its not the amp that sounds different due to different amounts of current going through the caps to allow for the turn on thump?[/joke]
 
Seriously:
I would not loose sleep over doing this once, especically if your headphones sound the same as before. I would certainly not make a habit of it, but relax. Damage from turn-on-spikes is pretty obvious.

In fact, i have just tried to turn off my amp then turn on and mesure the output and it's only around 5mv DC? Another problem i have is that when i solder the leds to the board, my amp sound very very tiny, even after i turn volume all the way up, i still can't  get comfortable volume. When i desolder leds, problem has gone but i want to use these leds, they look damn good (my amp is the modifed pcb version to use with 12au7)

 

[capernicus]

So how hot is too hot with respect to the heatsink?  After about an hour the heatsink is so hot that I can only touch it for about 1 second before I need to take my hand away...  is this normal?
 
 

 

[nikongod]

Quote:

In fact, i have just tried to turn off my amp then turn on and mesure the output and it's only around 5mv DC? Another problem i have is that when i solder the leds to the board, my amp sound very very tiny, even after i turn volume all the way up, i still can't  get comfortable volume. When i desolder leds, problem has gone but i want to use these leds, they look damn good (my amp is the modifed pcb version to use with 12au7)

It sounds like you soldered the LEDs to the wrong places, or maybe skipped some resistor. Im not too familiar with the 12au7 boards, but that is where I'd start looking. 
 
Quote:

So how hot is too hot with respect to the heatsink?  After about an hour the heatsink is so hot that I can only touch it for about 1 second before I need to take my hand away...  is this normal?
 

Mosfets can run hot enough to burn skin for a VERY long time. Cooler is better, but hot isn't necessarily unacceptable. 
Do you have an IR thermometer, or some other way of getting an accurate temperature measurement? I would strongly advise against touching stuff in a live circuit, but since you already did and it did not burn your skin I'd bet that the mosfet is pretty much OK. 

 

[Ikarios]

I believe the MOSFETs are rated for at least 80C continuous, maybe up to 105C. Obviously you would not want them to run at such a high temperature for long periods of time, but that is what they are rated for. I thought my amp ran pretty hot too (uncomfortable to touch but not unbearable), but I decided to check it with an IR thermometer anyway, and got a measy ~38-40C at the heatsinks. I'd say anything under 50C would be just fine, 60C you probably want to look into better heatsinking, vent holes, etc.

 

[rodneywimberly]

I have to brag to someone cause my wife just don't care. It's 2:00 AM and I just got my amp finalized, and tested. It's f_cking AWESOME. I gotta go to work early but I can't quit listening. Thanks to everyone in these posts and Pete Millet.