[Clarkmc2]

Spritzer - I know you do it for fun and I have great respect for you so no pressure - but if you could some day perhaps modify my SRM-727II that would be great - any service / parts fees and all shipping fees on me, of course.

None of my business, I guess, but I feel obligated to point out that any radio/TV technician you trust could do it in a heartbeat. Having the right tools for the job is key to taking any risk out of the proposition. In order, 1) Very simple proceedure 2) Stax amps, I was astonished to find when I opened my SRM-007tII, have the easiest service access in the electronics scene 3) A good desoldering tool removes the possibility of a disaster. Find a tech who has a functioning one and who knows how to use it. I have a separate one that looks like a soldering gun. It was about $200US and banished the anxiety of component removal instantly and completely.

I have imposed on Spritzer to experiment on my personal SRM-007tII, but that was to field test a new mod. I cannot imagine needing to send a 727 off to a busy man to do such a simple job when any local technician will do. Spritzer has emphasized how simple the mod is and how easily reversible it is.

 

[daveDerek]

Quote:

 I cannot imagine needing to send a 727 off to a busy man to do such a simple job when any local technican will do. Spritzer has emphasized how simple the mod is and how easily reversible it is.

 
what exactly is this simple mod to the SRM-727II?

 

[Clarkmc2]

what exactly is this simple mod to the SRM-727II?

Moving four resistors to restore the negative feedback loop Stax removed to align with the feedback free mania of the moment.

As to what Spritzer is up to now with the SRM-007tII, that is up to him to speak of it when he is ready to document it. He has my amp as we speak and he reports it sounds great.

I can say that owners are going to like the result.

 

[daveDerek]

Quote:

Moving four resistors to restore the negative feedback loop Stax removed to align with the feedback free mania of the moment.
As to what Spritzer is up to now with the SRM-007II, that is up to him to speak of it when he is ready to document it. He has my amp as we speak and he reports it sounds great.
I can say that owners are going to like the result.

 
oh, i thought from the sound of your earlier post, that the mod was out there in public. i just didn't know where it was and trying to search for it might not be so easy.

 

[spritzer]

I'm not going to modify any more as it doesn't make a whole lot of sense to ship a 5kg amp half way around the world to move 4 resistors.  The mod was posted over there with pics but I don't know if they are still there.  Should be...
 
The SRM-007t mod simply requires all traces to the tube sockets be removed (except the tube heaters) and wires added to make 6S4A's work instead of the 6CG7's.  These are far better tubes for the job and capable of handling the 700V going through them and they are single triodes so no issues with balance.  The 007t can actually drive the SR-007 now... 

 

[ericohgb]

Moving four resistors to restore the negative feedback loop Stax removed to align with the feedback free mania of the moment.
As to what Spritzer is up to now with the SRM-007II, that is up to him to speak of it when he is ready to document it. He has my amp as we speak and he reports it sounds great.
I can say that owners are going to like the result.

Hi Clark,
Sorry If this question may seem stupid, but what exactly was this fad to remove the negative feedback?
Thanks for making at least one person less ignorant.
Erico

 

[Clarkmc2]

Hi Clark,
Sorry If this question may seem stupid, but what exactly was this fad to remove the negative feedback?
Thanks for making at least one person less ignorant.
Erico

The question is not stupid, but the answer sort of is. I was not part of the progression, but I think it evolved like this.

Poorly designed amps usually rely on a lot of negative feedback to produce halfway linear frequency response. Well designed amps are linear by design and need very little feedback. This led to a general recognition that less is good and more is bad.

This led to designers trying to do without it at all. OK in a well designed preamp, not so great in a power amp. But by this time the buzz was out that negative feedback was bad, period. I think it was an ignorant supposition on the part of a lot of high end buyers and audiophiles. Not a very knowlegable bunch when it comes to things electronic. The high end suppliers feared they couldn't compete offering models with feedback, so Stax killed the feedback circuit on a model they had already designed.

Spritzer noticed the amp sounded messed up and was kind enough to figure out what was wrong and how to restore it.

 

[googleli]

Nicely explained - now if someone could dig out Spritzer's mod instructions... Always nice to have a backup for the BHSE...

 

[ericohgb]

The question is not stupid, but the answer sort of is. I was not part of the progression, but I think it evolved like this.
Poorly designed amps usually rely on a lot of negative feedback to produce halfway linear frequency response. Well designed amps are linear by design and need very little feedback. This led to a general recognition that less is good and more is bad.
This led to designers trying to do without it at all. OK in a well designed preamp, not so great in a power amp. But by this time the buzz was out that negative feedback was bad, period. I think it was an ignorant supposition on the part of a lot of high end buyers and audiophiles. Not a very knowlegable bunch when it comes to things electronic. The high end suppliers feared they couldn't compete offering models with feedback, so Stax killed the feedback circuit on a model they had already designed.
Spritzer noticed the amp sounded messed up and was kind enough to figure out what was wrong and how to restore it.

Thanks for the explanation.

 

[tiga3mata]

Quote:

 
I just updated the BHSE product page on Head-Fi for an easier-to-find spot: http://www.head-fi.org/products/headamp-blue-hawaii-se-electrostatic-amp
 
 
No offense but I'm not sure I'd recommend trying out tube-rolling if you don't know how to follow the directions I posted, because as spritzer mentioned there's high voltage levels in the amp. The BHSE comes properly biased for the stock EL34s so you don't need to worry about adjusting for them.

 
Fair advice...I wouldn't try unless I am reasonably sure. After reading it again, I think I understand. Now all I need is that insulated probe from Justin before I check out the different tubes in my inventory. Anyone here has any experience with tube rolling for the BHSE and Stax SR 009 combo? Any opinion about what sounds best?

 

[googleli]

You put your hands on the transformer all day!!!???  "Nice and warm" ???????
Quote:

About supposedly the BHSE running hot, I don't understand where some Headfiers have got this from, yes the tubes get hot but the chassis and the PSU get maybe slightly above warm. I could quite easily put my hands on both all day because like I say they are nice and warm, but hot, No Way.

 

[David1961]

Quote:

You put your hands on the transformer all day!!!???  "Nice and warm" ???????

Obviously I wouldn't be having my hands on either the BHSE's amp section or PSU all day, I'm just saying I could quite easily do that. When you have your BHSE see how long you can keep your hands on. please post how long you managed to do that.

 

[googleli]

Quote:

Obviously I wouldn't be having my hands on either the BHSE's amp section or PSU all day, I'm just saying I could quite easily do that. When you have your BHSE see how long you can keep your hands on. please post how long you managed to do that.

Is there going to be a reward for doing that?

 

[David1961]

Quote:

Is there going to be a reward for doing that?

No but I bet you can listen to all your CD collection before you need to take them off   

 
The point I'm trying to make is that some headfiers believe the BHSE gets hot, but since the day I got it I've learnt that is not the case.

 

[TheAttorney]

Quote:

The point I'm trying to make is that some headfiers believe the BHSE gets hot, but since the day I got it I've learnt that is not the case.

I'm very pleased about that. It was one of the things I was concerned about - the BHSE sometimes being compared to a space heater.
 
With around 250w power consumption,spread over 2 boxes, and a fair proportion of heat coming directly from the tubes, I just couldn't see how the boxes themselves could get that hot. Just not enough watts to go around. Justin increased the ventilation holes in the current 50 batch, so maybe the previous batch did get a bit hotter.
 
My BHSE is allegedly going to be "in the post" pretty soon now, so I'll find out for myself.