Starving Student II Headphone Amplifier

That was pointed out to me by 6L6... on the next batch I made the pads bigger. Sorry about that!

Pete

Looks like I have to go back to the bench - a few oddities after a day of use: 1) Noticed that the turn on delay doesn't (hear a pop when first powered on - then about 10 min into listening, everything goes quiet for 10-15 sec). 2) Had one channel go completely silent (suspect an issue around one of the tubes).

I suspect some solder joint issues. Hard to actually see issues on inspection, so will trace out the circuit to find out where they are.

Most probably "operator" error.

Rich
 
Looks like I have to go back to the bench - a few oddities after a day of use: 1) Noticed that the turn on delay doesn't (hear a pop when first powered on - then about 10 min into listening, everything goes quiet for 10-15 sec). 2) Had one channel go completely silent (suspect an issue around one of the tubes).

I suspect some solder joint issues. Hard to actually see issues on inspection, so will trace out the circuit to find out where they are.

Spent some time tracing out the circuit - no problems found. Reflowed a few suspect solder joints & all the tube socket connections.

Appears to be working perfectly now.

A little more careful listening (SSII -> ACA -> Klipsch Cornwalls - playing Grissman/Garcia CD) - really nice combination, combines really well with the ACA and provides plenty of drive.

I would definitely recommend the SSII/ACA combination.

Rich
 
Spent some time tracing out the circuit - no problems found. Reflowed a few suspect solder joints & all the tube socket connections.

Appears to be working perfectly now.

A little more careful listening (SSII -> ACA -> Klipsch Cornwalls - playing Grissman/Garcia CD) - really nice combination, combines really well with the ACA and provides plenty of drive.

I would definitely recommend the SSII/ACA combination.

Rich

Cool, glad it's working well for you.

Pete
 
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I managed to build one today. Some of the pads on the pcb are
quite small so it would have been easier if I had thinner solder on hand.
Also it took a bit of effort for me to put the tubes in.

I'm currently trying it as a preamp after listing to its headphone
output for a couple hours. I encountered one minor issue. I
toughed the volume know and I felt a bit of static and both channels
went silent. Perhaps the relay was somehow triggered. Anyway,
after turning off and on, it is behaving ok again.

Dennis
 

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Dennis: I'm sure you'll enjoy it.

I had some issues building mine - I was using a very (very) old soldering iron with a suspect tip - I think some of the solder joints on the small pads (especially the ones connected to ground) were not good. I picked up a new soldering station (moved to the modern world) & carefully reflowed all of the solder joints - everything is fine now.

Rich
 
I built one a few days ago. I also had trouble with soldering using my 20+ year old inexpensive soldering station, which worked fine on the other gear I built. After soldering the resistors I finally figured I was building enough audio gear to buy a better soldering station. That helped a lot, but I still had to check everything carefully, as some of the pads and holes are so small.
 
The supplied Raytheon tubes are "made in Japan". Are those NOS? …..how old?

They are NOS from a large master case. I cannot tell exactly when or where they were manufactured. Probably early 1960's - Raytheon farmed out most of their small tube manufacturing to Japan around then.

In general there was much cross-production and labeling, especially in the 60's, so it's very hard to tell exactly what manufacturer really made what tubes.

I have examples that have just about every tube manufacturer's name (RCA, Sylvania, Westinghouse, Raytheon, etc.) and some made in USA, Japan, and Canada.

They all look and measure pretty much identically...

Pete
 
Input problems?

I just got my SSII kit built and testing it now. There is a problem with the input. Plugging in either the right or left RCA connector from source gives me output to both left and right headphone out. Plugging in the other (either left or right) RCA input lead I get the hollow remains of the input source. Wondering if anyone is reporting a similar issue. Source is phase correct and works correctly with my other systems. Headphones also working correctly with other sources.
 
I just got my SSII kit built and testing it now. There is a problem with the input. Plugging in either the right or left RCA connector from source gives me output to both left and right headphone out. Plugging in the other (either left or right) RCA input lead I get the hollow remains of the input source. Wondering if anyone is reporting a similar issue. Source is phase correct and works correctly with my other systems. Headphones also working correctly with other sources.

Problems like this are often an open ground connection on the volume control. Try reflowing those pins.

Pete
 
I've been listening the SSII as a headphone amplifier for a pair of headphones which have an impedance of 300 ohms. It sounds decent, but I have very little adjustment room on the volume control, as it quickly becomes quite loud within a ten degree turning radius. I am wondering if anyone knows of a different volume control with a more usable taper that will fit on the board.

Thanks
 
Are you missing the little blue jumpers (shunts), or the 3-pin headers? Or both?
Both are normally packaged in the "other parts" bag, with the connectors, relay, etc.
Pete



Hi Pete


It was both the 3-pin and blue jumpers. I ordered some locally at RS Components. So now the jumper will become black. Hope that does not change the sound :) seems spacing is 2.54 mm.
Interesting with those NOS tubes. May get some extras while they are available.
 
What am I doing wrong?

I'm at step 20 - smoke test.
VT1 pin3 to headphone ground measures 43.3 volts.
VT3 pin3 to headphone ground measures 19.05 volts.

My soldering looks very clean and solid (no bridges or cold joints) so I'm guessing I have a defective or wrong part somewhere.

The most likely error is that the grounded end of R11 isn't really soldered to ground. It's easy to get a solder joint that looks good, but actually has not flowed onto the grounded pad. It's connected to a large copper area that sinks heat away, so it is difficult to solder.

If this happens, the gate of Q3 is biased to 48V, so the source (and VT1 pin 3) goes to 48V - Vgs(th) or about 43V.

With power off, use an ohmeter to confirm that R11 is 200k, and R15 is 221k. And measure from the grounded end of R11 (on the resistor lead) to ground to see if it is connected.

Also check for solder bridges on Q3.

Pete