The Stax Thread III

[Menkau-ra]

A nice KGSSHV Mini posted in the Classifieds.

Don't blink.

The seller has 0 feedback.
do you know who built it?

 

[paradoxper]

The seller has 0 feedback.
do you know who built it?

He has sold a Carbon of JR Audio.
I surmise this is JR Audio as well.

The layout denotes 0x01a of July 21 which conveniently correlates to a Head-Case user from '18.

So the origins are likely opaque.

 

[Klankliefhebber]

Little late to reply, but did you verify that it is the earspeakers that are the issue and not the amp or source? I would do that before tearing anything apart (further). Do you have access to another E-stat amp or energizer to try, or have you tried just reversing the RCA inputs to see if the imbalance stays the same or follows the swap?

And @KDS315, I would not jump to the conclusion that the driver is defective just yet...

Hi, thanks for the reply.

Electrostats are quite rare in these parts, so I haven't been able to a/b die headset/energiser with another working set. I have made plans to do so in 'n few days however, then I'll know for sure which one it is.

I have tested the source, cables, and everything else. The problem must lie in either the energizer or in the headset.

Could this possibly be caused by a faulty transistor or something on the energizer?

 

[KDS315]

The following is a good idea, just had assumed that done...

Have you crossed the RCA cable (right to left, left to right) on your amp ONLY to see if the problem moves to left channel ? If it does then the amp has a problem. If not then the headphones have an issue.

 

[AudioCats]

Try swapping L/R at the amp output. Open the amp and swap the wires. I think stax color code is (according to the 007t schematic)
yellow=L+
Red=R+
Green=L-
White = R-

swap L+ to R+, and L- to R-, either at the 5-pin socket or the board (probably easier at the PCB, it might even have marking to show the color wire so it is easier to swap back after the experiment)

If the weak/strong channels flips then the problem is the amp/source, if it stays the same then it is the phone.

 

[KDS315]

Crossing the RCA CABLES does the same ... But it is too easy and lacks the fun of soldering on the phones :LOL:

 

[AudioCats]

if the imbalance flips after swapping RCA L/R, then the source is causing the problem. But it doesn't tell if there is something going on in the amp (say, excessive flux residue on the board or at the socket, causing some kind of (high resistance) partial short (if humidity is high) and causing some kind of overload ==> distortion).

try the RCA first to see if the source is bad. then do the amp output L/R swap and see if the amp has problem.

 

[Klankliefhebber]

Thanks for the further advice, I've started tinkering a bit further. At the moment I don't have any soldering equipment or anything which which I can test the current/resistance on the circuitboard, but I did open it to check for anything obvious, and I did find one thing:

I noticed that the screws/settings were out of alignment. It's not quite visible on the foto but there is an indicator on each of the screw-heads. I also noted that the one of the right channel was set "lower" than the one on the left. I adjusted it (the photo was taken after I made the adjustment).

Having set everything up again, I can hear that the channel imbalance is much improved, but perhaps not quite gone. But now I'm not sure whether this had anything to do with the adjustment on the board, of whether it is because I left the headphones and amp disconnected and in a box for a few days (as that whole static-build-up theses would suggest).

Anyone know whether those things I adjusted are actually settings of some sort, of they just screws that hold down that particular component?

 

[capetownwatches]

Before you go bedondered pulling things apart, wait until you can test with another earspeaker and/or energizer.
That is the easiest way to determine where the problem lies.
Just my R0.02...

My guess is definitely the earspeaker, based on my experience.
What to do about it if so is another discussion.

 

[KDS315]

Omg don’t do stuff if you don’t know what you are actually doing!!

These “screws” are potentiometers and those are used to balance some electronic circuits. Could be that they needed adjustments (doubt it though) - but since you played with them I would advice to have them PROFESSIONALLY re-adjusted correctly!! Which needs experience and some metering equipment.

I’m out now here....

PS: STAX amps use high voltages inside even after switching off and disconnecting power the charged high voltage capacitors hold enough charge to be deadly dangerous if touched!!!

 

[Klankliefhebber]

Omg don’t do stuff if you don’t know what you are actually doing!!

These “screws” are potentiometers and those are used to balance some electronic circuits. Could be that they needed adjustments (doubt it though) - but since you played with them I would advice to have them PROFESSIONALLY re-adjusted correctly!! Which needs experience and some metering equipment.

I’m out now here....

Ha, I suppose you're (KDS315, Capetownwatches) right. I should just be patient.

I'm going to stop messing with stuff now and just wait until I can do an A/B test and then either replace or have professionally repaired.

Thanks for the help/advice anyway.

 

[kevin gilmore]

those are the balance pots and if you turn them too far you will blow up both the amp and the headphones.

you are going to need a voltmeter to reset those pots. stop now until you get the correct tools.

 

[Klankliefhebber]

those are the balance pots and if you turn them too far you will blow up both the amp and the headphones.

you are going to need a voltmeter to reset those pots. stop now until you get the correct tools.

Yeah, I did some post-facto research and realized that. Seeing as the headphones still work without any noticeable issue I don't think I changed the DC-bias too much, but I've arranged for an engineer with a good multimeter to check everything out so that we can make sure the bias is correct. Luckily I have the working (left) channel as a reference point for all the values.

One interesting thing though, and I'm not sure what this indicates, but I've noticed that the balance issue does get worse as the amp, or possibly the headphone "warms-up". Each time I have the set switched off and plugged out for a day or so, the balance issue is much improved when I switch them on (85-90/100 to sound level), and then it starts to get progressively worse the longer the set is powered on (not sure if it has to be actively playing something or just be powered) eventually ending back at 63/100 after about 10 minutes.

 

[KDS315]

That's called "drifting" and the reason why it is important to set the balance pots correctly..

 

[capetownwatches]

One interesting thing though, and I'm not sure what this indicates, but I've noticed that the balance issue does get worse as the amp, or possibly the headphone "warms-up". Each time I have the set switched off and plugged out for a day or so, the balance issue is much improved when I switch them on (85-90/100 to sound level), and then it starts to get progressively worse the longer the set is powered on (not sure if it has to be actively playing something or just be powered) eventually ending back at 63/100 after about 10 minutes.

Sounds more and more like I may have to revise my initial assessment to the energizer being the source of your issue rather than the earspeakers.
As the amp plays longer, it would seem as if the current output to one channel is decreasing slowly.

It may be time to call in the big guns and enlist the help of a professional, although just where such a person may be found locally I do not know.
That said I'm sure there must be a few okes on AVF who are definitely qualified. Perhaps reach out there or contact the local Stax agents (The Listening Room).
Rodney or Victor may be able to recommend a good technician.