starving student blows up dacs?

[pistolsnipe]

hey i have built a starving student amp, and have read in a few scattered places that it has a problem of frying sources (aliens and bantam), hence i have not used it very much. my question is has anyone come up with a solution, or a safer way for me to operate my amp? i dont really have a cheap dac to sacrifice to using this source.

i have heard:

there is dc offset passed to the source
input resistors may help
not disconnecting anything on the amp may help

has anyone actually confirmed any of this to work?

is there dacs that would be safe to use with this amp? it is pretty much useless to me at this point.

 

[FallenAngel]

uhm... now that would be something!

Why on earth would an amp blow up a DAC? Unless you shorted something, the input wiring goes through the pot and into the tube, that's it.

 

[dBel84]

It has happened to several folk, has to do with the way the B+ is set up and DC somehow bleeds back to the input. I am not familiar with the design but know from Ludoo that he sacrificed several dacs..dB

 

[DKJones96]

DC should be blocked by the output caps on the Bantam. Curious as to how those died. The DC from a tube should be a slow-on and slow-off so it can't be startup surge.

Damn non-existent grid-leak resistor!

 

[pistolsnipe]

yeah apparently it was one of the things they were trying to work out before releasing the pcbs at beezar, but i dont think anyone has a definite answer

 

[cfcubed]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Why on earth would an amp blow up a DAC?

Perhaps tomb can chime in on this since at one time he found earlier(?) SSMH PCBs doing this: "The Starving Student PCB version blew out another one of my BantamDACs."

 

[sachu]

This is the main reason I got rid of my Starving Student millet hybrid.
It was the only millet hybrid that was even worth a listen as unlike the rest of the millet hybrids this actually sounded half decent and a low cost.

The lowing of DACs just wasn't reassuring enough to keep it around.

 

[dsavitsk]

My best guess: there is a small amount of capacitance on the Cisco PS between output ground and safety ground. If this gets charged up, it seems to be enough to toast some chips -- particularly the one in the Bantam -- if the output of the DAC touches the Starving Student ground before touching signal input.

 

[tomb]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif This is the main reason I got rid of my Starving Student millet hybrid. It was the only millet hybrid that was even worth a listen as unlike the rest of the millet hybrids this actually sounded half decent and a low cost. The lowing of DACs just wasn't reassuring enough to keep it around.

Geez - there's no reason to take a swipe at other Milletts! The market and numbers of happy Millett Hybrid/MAX/MiniMAX owners disagree with you.

The SSMH is a great little amp, but is not superior to a properly constructed MiniMAX or MH with DB's (ortho's excepted) - nor should it be at the price.

Dsavitsk is correct and I think his explanation is the best one so far. I have blown a number of Alien DACs with a Starving Student and a Bantam as well. Try disconnecting the RCA jacks on a Starving Student while music is playing - a charge, resulting in severe hum will occur and won't stop until something discharges the charge on the RCA jacks. This discharge will fry an Alien/BantamDAC under the right circumstances. It's one of the reasons we suggested perhaps always leaving the DAC connected to the amp, but I'm not certain that's a solution.

DC blocking caps offer no protection in this scenario.

Note that DACS that are not AC coupled have no issue with this. I've had Starving Students connected to Motherboards/typical sound cards in almost every conceivable scenario and haven't come close to blowing one of those.

 

[holland]

I was just wondering what this was all about as I've been OK. It's out of rotation now, but when it was in use, I had it connected all the time and no issues for a few months.

Would a different PS resolve the issue?

 

[tomb]

Quote:

Originally Posted by holland /img/forum/go_quote.gif I was just wondering what this was all about as I've been OK. It's out of rotation now, but when it was in use, I had it connected all the time and no issues for a few months. Would a different PS resolve the issue?

Unknown - we suspected that the Cisco PS had a floating ground at one point, but tests for that were inconclusive. I tend to suspect that it has something to do with the grounded/biased MOSFETs instead, but can't say for sure.

If you leave the DAC connected under all scenarios, it's possible that you'll never have a problem - but I can't say that for certain. It's been the connecting/disconnecting where the issue occurs.

 

[sachu]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Geez - there's no reason to take a swipe at other Milletts! The market and numbers of happy Millett Hybrid/MAX/MiniMAX owners disagree with you. The SSMH is a great little amp, but is not superior to a properly constructed MiniMAX or MH with DB's (ortho's excepted) - nor should it be at the price.

Since when is it wrong to voice an opinion on a public forum like this? Its not like I am making statements without ever having heard the other millets..I have built the SSMH and actually quite liked it a LOT unlike my personal view aout the other millets. And it is understood that it is my opinion. Not everyone will like every single component you know. lighten up.

Was only pointing that out as i thought it was a great sounding little amp that cost next to nothing to build save for the blowing of DACs part.

 

[nullstring]

hrmmm..

I wonder if my ipod is safe.
I would sure hate to blow that.

 

[tomb]

Quote:

Originally Posted by nullstring /img/forum/go_quote.gif hrmmm.. I wonder if my ipod is safe. I would sure hate to blow that.

AFAIK, ipods are nor direct AC-coupled to the outputs of the DAC. I think the DAC chips in an ipod have internal protection, too. Remember, they're designed to have headphones plugged in and out constantly - shorting occurs in the jack all the time.

 

[tomb]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif Since when is it wrong to voice an opinion on a public forum like this? Its not like I am making statements without ever having heard the other millets..I have built the SSMH and actually quite liked it a LOT unlike my personal view aout the other millets. And it is understood that it is my opinion. Not everyone will like every single component you know. lighten up.

You lighten up!! Since when was "Geez" used to voice real anger? Maybe you should check that tone before reacting so vigorously. So you voiced an opinion ... did that mean you couldn't be called on it?