F6 smokes with preamp

[rock12]

My pass F6 has been playing for years. Just built sp14 tube preamp and when hooked to the F6 buzz and smoke from back right corner. Had this same problem with the NAD steamer preamp. It works well with my phone dragonfly red and nodi 2

 

[Rodeodave]

Is it a FW amp or a diy build? I'm guessing you would want to know what went wrong?

With troubleshooting it's always best to post a reference schematic and a couple of well lit, in-focus pictures of the build.

 

[rayma]

Your preamp likely outputs a large pulse upon turn on and turn off.
Verify this with an oscilloscope. You will need an output muting circuit for the preamp.

 

[Dennis Hui]

Was the F6 already on when you power up the preamp?

 

[Rodeodave]

Your preamp likely outputs a large pulse upon turn on and turn off.
Verify this with an oscilloscope. You will need an output muting circuit for the preamp.

I would've guessed parasitic oscillation. Guess we'll find out.

 

[rock12]

My f6 is a diy build. I had my sp14(another Diy with 6ns7 tube) already running and playing my tube lab SSE turned my pass F6 on and proceeded to hook up the pre already running and saw slight smoke. Thankfully my F6 is still working and running fine off the nodi 2.playing a little Larry carrolton Last night album

 

[Soundhappy]

Tube preamp without capacitors at the outputs ?

 

[rayma]

Nah, that F6 would have been a cinder.

 

[Ben Mah]

...... turned my pass F6 on and proceeded to hook up the pre already running and saw slight smoke.

Never a good idea to hook up components when they are on.

 

[rock12]

33uf caps at out put. The odd thing is it did the same smoke with the NAD 658 streamer dac I will open the F6 up later and retry to find out what is overheating. What amount of voltage does the F6 handle at input

 

[rock12]

It appears to be in my power supply. I hooked my sp14 preamp to the f6 but did not turn it on. Turned on the f6 and both power lights( red led) came on, within seconds the right light dimmed smoke came off the resistors and the light went out. Hooked up nodi2 wcerything works fine.

 

[rock12]

Could this be some kind of grounding issue since the preamp is not turned on?

 

[rock12]

Did one more experiment by switching the connection (red to white ) the same led started to dim and I pulled the one input connection and left the other in for a second thus bring smoke from the transistor area. Amp still works. Afraid to try other experiments for a while

 

[Ben Mah]

So it smokes with two of your sources but not with one?

Do the two sources that cause smoke have safety ground (3 prong plugs) and the one that does not smoke only has a two prong plug?

Please post a picture showing all of the amplifier (an overall shot).

Something is causing excess draw on the V- part of the power supply and the excess draw is burning the resistors.

 

[Rodeodave]

Excess draw is putting it mildly

The four 0R47 in parallel will give about 0R12. Let's say they each dissipate their rated power (given the discoloration likely more), that's 4*3W, and with P=12W=U*I=R*I^2, thus I=(12W/0.12R)^.5=10A of current!

Something's not right.

 

[Bare]

When I first built my F6.. I used my venerable George Wright triode type Tube pre.
The F6 sounded BAD. Couldn't believe it.
Finally unplugged the Pre and ran a stepped attenuator direct from sources and the sounds were/are exquisite.
Tube pre clearly didn't work with the F6.
Don't know why, don't care.
It's doing closet duty.. for the rest of My life.

 

[JeffYoung]

When one of the resistors starts to smoke are the other 3 really hot or cold? It looks like several of them didn't get enough heat when soldering to flow to the other side of the board.

 

[KevinHeem]

@rock12

What rating is the fuse in your amp?

 

[egellings]

Hang a scope on it.