[Beefy]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif That was somebody else; lid on or off doesn't seem to bother my build.

You know, I might need to retract this......

The amp was sitting with the top panel open this morning, I powered it up and there was no buzz. This wasn't that unusual, because it doesn't buzz every single time. But thinking back to studeb's issue I put the lid back on, powered it up, and it did buzz. Lid off, amp on, no buzz. Lid on, amp on, buzz. Very reproducible, until the amp warmed up enough such that the buzz with lid on stopped.

It has definitely buzzed in the past with the lid off - the recording I made yesterday was lid off - so there is more to it that just that. But it is certainly an interesting phenomenon. I will ground the heatsinks tonight.

 

[runeight]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif That was someone else, but I can ground the PSU heatsinks easily enough. Just focusing on a single rail though, the LED is brighter while the buzzing is happening. It dulls a touch when the buzzing stops. So perhaps the buzzing indicates extra current moving through the shunt. Though I suppose this could be an issue with regulation, or the FETs supplying extra current. I recall reading that the 'Max' modification increases gain at some point. Could this be unique to Max builds? That was somebody else; lid on or off doesn't seem to bother my build. But I will ground the heatsinks to see if this helps.

Thanks. Could you guys please remind me whether the buzzing builds are hybrids or SS. Or one of each.

Just to eliminate possibilities, in the hybrid, before the tubes conduct there will be different current relationships among the parts and less current draw from the PS which means more shunt current until the tubes warmup. Although there is no reason for this to be a problem since the bjts can handle amps.

 

[Beefy]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Thanks. Could you guys please remind me whether the buzzing builds are hybrids or SS. Or one of each.

Ah, crosspost....... as I said just seconds ago, the case lid does have an effect.

Mine is solid state.

 

[runeight]

Then it can't be the warmup period, so I'm back to suspecting heatsink coupling issues. If can find time to ground them all that would be the next step. If your output G from the PS terminal block goes to the star ground then wire the heatsinks to that point on the board.

 

[Beefy]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Then it can't be the warmup period, so I'm back to suspecting heatsink coupling issues. If can find time to ground them all that would be the next step. If your output G from the PS terminal block goes to the star ground then wire the heatsinks to that point on the board.

Sounds like a plan!

 

[Beefy]

Well grounding the heatsinks didn't seem to help...... but I didn't get much testing done after something sparked/popped on power up

It was something in the area of R1, R3, R5, R9, Z1 and Q1. In-circuit resistances of the resistors checks out and since nothing is in parallel they should be good. For Q1, C-B resistance is >10Mohm, C-E resistance is >10Mohm, B-E resistance is 118ohm (P1 + R1 +R3, so no dead short). The only thing I can't test is the zener.

LEDs still light, output voltage seems stable, but the voltage across T1-T2 was unstable. I wasn't game to try keep it going for any length of time though, just in case.

Any additional suggestions before I continue?

 

[WilCox]

Quote:

Originally Posted by WilCox /img/forum/go_quote.gif Speaking of problems, I am curious how much offset Stax headphones can tolerate. My eXStatA SS has about a 12-15V balance misalignment in one channel upon power-up the settles to less than 1V after 20-30 minutes. (The other channel is <1V from the start.) Will this harm my phones?

Just asking this again in case someone here has some experience or insights they could share.

Thanks!

 

[Beefy]

Well I checked everything on the PSU very closely, and could not find a single fault, no burnt up components, nothing. So I gave it a clean up with isopropanol, wired it back and, and every reading was A-O-K. So I don't know what sparked... maybe a hair or piece of dust?

In any case, I'm a bit frazzled tonight, so will re-test the heatsink grounding tomorrow.

 

[BoilermakerFan]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif Well I checked everything on the PSU very closely, and could not find a single fault, no burnt up components, nothing. So I gave it a clean up with isopropanol, wired it back and, and every reading was A-O-K. So I don't know what sparked... maybe a hair or piece of dust? In any case, I'm a bit frazzled tonight, so will re-test the heatsink grounding tomorrow.

No buzz after the reassembly?

 

[Beefy]

Yes, still buzz.

 

[runeight]

Quote:

Originally Posted by WilCox /img/forum/go_quote.gif Just asking this again in case someone here has some experience or insights they could share. Thanks!

I am not a stat headphone expert but it seems to me that we have headphones that are designed to handle 1000V or more between the stators so 15V for a few minutes seems harmless to me.

Beefy, probably right, a piece of something or maybe solder flux. Spacing can be close on these boards, even though all spacing conforms to the recommended values for coated PCBS.

I really don't know what the deal is with your PS. I wish I could offer you better help.

 

[BoilermakerFan]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif Yes, still buzz.

Just to rule it out completely, can you turn your trafo 90 degrees or remove it from the chassis all together and patch on extensions? Your transformer is just a hair undersized and that would only be an issue at start up during the inrush and while everything settle down, but mechanical vibration and larger EMI fields occur when a trafo is fully loaded or overloaded. It's a shielded and potted unit, but that doesn't completely eliminate EMI. Turning it should matter since it's a toroid, but that may be easier than removing it initially.

It's a low probability, but might as well eliminate it.

 

[spritzer]

Quote:

Originally Posted by WilCox /img/forum/go_quote.gif Just asking this again in case someone here has some experience or insights they could share. Thanks!

DC has almost no effect on the cans besides lowering their efficiency and in the grand scope of things 15V is nothing. All the Single Power ES amps shipped with a fixed offset of -100VDC or more and some designs have a rather high offset but compensate by increasing the bias voltage. Just look at the DC-coupled sibling of the GES which sits at +200V.

 

[runeight]

Quote:

Originally Posted by Beefy /img/forum/go_quote.gif Yes, still buzz.

Have you tried firing up in the dark to see if you can see any arcing? You may need to look at both top and bottom of the board.

 

[WilCox]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif I am not a stat headphone expert but it seems to me that we have headphones that are designed to handle 1000V or more between the stators so 15V for a few minutes seems harmless to me. Beefy, probably right, a piece of something or maybe solder flux. Spacing can be close on these boards, even though all spacing conforms to the recommended values for coated PCBS. I really don't know what the deal is with your PS. I wish I could offer you better help.

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif DC has almost no effect on the cans besides lowering their efficiency and in the grand scope of things 15V is nothing. All the Single Power ES amps shipped with a fixed offset of -100VDC or more and some designs have a rather high offset but compensate by increasing the bias voltage. Just look at the DC-coupled sibling of the GES which sits at +200V.

Thanks guys! You are confirming what I hoped/expected.

I really enjoy this amp and its performance with both 404LE and O2 is outstanding in view of its meager cost.