Electrostat help! Stax SRM 717 Distorting on Unbalanced Inputs Only
Oct 1, 2016 at 10:27 AM Thread Starter Post #1 of 2

Drewligarchy

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Hi All -
 
Could use the help of any Electrostat/Stax Experts.
 
I have a Stax 717 I bought used on head-fi a few years ago and it's always worked flawlessly. Ran into an issue last night with the unbalanced inputs. They began sounding like the amp was being overdriven. Confirmed it wasn't the phones as I heard the same behavior with my 009 and HE60.
 
DAC is an Auralic Vega and Source is an Auralic Aries.
 
Reason I am using single ended is I like to use the amp in bypass mode, with a CI Audio PLC 1 passive preamp so I have remote volume control, which is single ended only.  I also have the balanced outputs connected to another amp. Removed the preamp from the chain and no difference. I would also prefer not to use the digital volume of the Vega, as the passive sounds better.
 
I figured that the amp itself was broken, but when switching to balanced XLR, the sound was flawless.
 
Things I've tried:
 
- Checked the single ended output of Vega with another amp and no issues.
- Checked both the input and output of the preamp with another amp and no issues.
- Reduced volume on the Vega itself to determine if the signal was too hot.
- Took the 717 out of balanced mode and drove with the preamp, leaving the 717 pot at 12 o'clock.
- Ran vega directly to 717 and used the 717's volume control.
 
None of these solved the issue.
 
One piece of interesting behavior was after I had tested the balanced outputs and they worked, I tried the single-ended again, and they worked but started distorting again after 15 minutes. The amp has been driven from the Vega for a few weeks single ended (Recently purchased the Vega) with no previous problem.
 
I know that the Vega has relatively hot output at 4 vrms on both single-ended and balanced, so my initial thought was that the 717 can accept more voltage on the balanced input. That said, not sure why it's worked, and now does not - and why that behavior only occurs on the single ended input.
 
I was thinking of using an RCA to XLR adapter into the 717 so I could still use the passive pre-amp since the level is already hot, but don't want to damage the amp - and assume I'd also run into impedance issues. I have a Henry Matchbox HD or could use a transformer, but it would seem to defeat my attempt to keep the signal chain as uncluttered as possible. I have a Violectric v281 I've used as a preamp, but any additional gain stages seem to negatively color the sound - which was my reasoning for going passive.I'd  really like to use CI Audio Passive as it's a great piece and the amp sings with this preamp when working correctly.
 
Any suggestions as to what might be wrong or if it's fixable - or any other workaround around as described above? I am not opposed to upgrading amps at this point, but really want to stay with solid state (mostly in regards to maintenance as opposed to sound). 717s and KGSS's aren't readily available - and I know the 727 needs to be modded to sound it's best and I am not comfortable doing myself.
 
Would love to pick up one of Birgir's amps but they are balanced only so not sure what's out there that I could replace it with - relatively quickly if there is absolutely no fix. I wouldn't mind having a second electrostatic amp for a setup in another room, especially as the 717 is quite old at this point and may be slowly breaking down.
 
If anyone has some suggestions on what might be wrong, workarounds, or a solid state electrostatic amp I could buy with single ended input that pairs well to the 009 (I like the slight warmth the 717 provides), please let me know!
 
Thanks in advance for reading, and any help you can provide.
 
Best,
Andrew
 
Oct 1, 2016 at 12:58 PM Post #2 of 2

Drewligarchy

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I should really give myself time to figure things out before I write a long rant like this.
 
Turns out the Stax in combination with the CI Audio Pre is so sensitive because of the Passive Pre that anything else plugged into the pre, additional amps as outputs, other inputs than the one source - cause the distortion. It's only caused this behavior on the Stax and no other amp/headphone combo.
 
While I'd obviously like to use the other inputs and outputs for the pre - it's main purpose was remote volume control for the 717 without an additional gain stage - and it now sounds great.
 

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