Stax SRM-T1 Repair

[Dusty Chalk]

Yeah, you obviously have some knowledge to impart (please don't part with it, I'm not sure what we'd do with it...), but please don't take attacks as personal, we correct each other all the time, and the best way to deal with it is with a thick skin.

They are just expensive with gold printing on black which has to mean they are good.  

(notes spritzer's black-on-gold avatar)

[Voltron]

 

My caps are way more musical than that rubbish from Jensen!

[CraigBuckingham]

Hey guys, my skin is thick, I just thought who the heck is this guy.

 

As far as it not being personal but about the post, well the post was written by me personally, so I have trouble seeing how a facepalm comment about my post could be seen as mutually exclusive from the person that wrote it.

 

I read the welcome PM carefully, trust me. I also did a little research before I posted to get a feel who was who and doing what. I know KG and am familiar with his work. He may remember me from another headphone forum, we had some correspondence, I provided him with an original Stax SRM-313 schematic which he did not have at the time.

 

As far as the caps, I choose caps on performance criteria, mainly dissipation factor. However the Jensens were just some of a few I tried. They were a lot better than the OEM caps in the SRM-313. The four poles better. It was the four poles I wanted to evaluate as that configuration I had not seen before, so I picked up some orange ones while I was at it. And the chokes made a very noticeable difference also. AFAIK, not many or may be any Stax use a CLC filtered power supply.

 

In terms of what people are doing, I don't see many designing their own circuits for amplifiers or other electronic gear. I see spritzer using op-amps in audio equipment, notably OPA2604. Op-amps have no place in high quality audio reproduction, yes they are ok for making cheap hi-fi, but if you are serious about good audio then op-amps won't get you there.

 

OPA2604 are so so as far as op-amps go, but the OPA627 or OPA637 (CL >5) leave them behind. It's a no contest. I gave up on op-amps about 15 years ago, because nothing you can do will fix up their problems. Not the least they use feedback and that's going to severely limit forward progress because of it, besides all their other limitations. I tried and I tried, including current sinking and sourcing the outputs for single ended class A operation and balancing the impedances seen by the input terminals. Both made big improvements, but a good discrete design relegated them into the spare parts box for repairs and non-audio work.

 

Dusty Chalk, if you don't want to learn from other peoples knowledge good for you. But to qualify that statement for any one else here that does I think is a little too generous.

 

Hope that's not too much writing in one post, but I tried to address everyone's comments in one go.

[Torpedo]

Maybe you read your welcome message, but it's obvious you didn't get it. Read it again. Once understood you might feel like refraining from posting here, mainly because if instead of writing you were reading, you would have known who is Spritzer in the first place. And yes, that's too much writing for a post around these lands.

[DefQon]

Spritzer using opamps in his system?

[CraigBuckingham]

Torpedo, the Introduction Message, mmmmm, are you referring to "Don't mistake our familiarity with each other as familiarity with you,......"

 

I am not sure if you noticed but it was spritzer who decided to exercise his familiarity with me, not the other way around.

 

So what is so special about spritzer that I should know, I read his posts, I can't find it? It wasn't in the introduction message. :popcorn:

[CraigBuckingham]

Oh my God, sorry Torpedo, I missed it, spritzer has a lot of posts, around 10,929.

 

Sorry not going to be able to compete with that. I can only value add with some design and engineering advice. But not the real good stuff, I am am too old and wise to give away hard earned experience. It's worth too much money and how I make a living.

 

 

 

[Audiojunkie]

Oh my God, sorry Torpedo, I missed it, spritzer has a lot of posts, around 10,929.

 

Sorry not going to be able to compete with that. I can only value add with some design and engineering advice. But not the real good stuff, I am am too old and wise to give away hard earned experience. It's worth too much money and how I make a living.

 

You really don't have a clue do you? 

[Torpedo]

You are way too glad of having met you to be able to understand what this place is about   Definitely not post count

[spritzer]

Post count means nothing here and it shouldn't mean anything... ever.  We welcome any good engineering but swapping caps really doesn't cut it here. 

[kevin gilmore]

 

In terms of what people are doing, I don't see many designing their own circuits for amplifiers or other electronic gear. I see spritzer using op-amps in audio equipment, notably OPA2604. Op-amps have no place in high quality audio reproduction, yes they are ok for making cheap hi-fi, but if you are serious about good audio then op-amps won't get you there.

 

not the spritzer i know. maybe you are thinking of someone else.

the stax mafia uses discretes for everything.  And yes we use opamps

for servo's, but that is it.  Even for the power supply its a discrete

opamp.

[skullguise]

Craig, you seem quite intelligent.  Sarcastic too (which I personally happen to like).  But letting sarcasm drop to cynicism won't get you far.

 

One of the things that the welcome PM should impart is the concept of how social this place is.  It's not always about what someone knows technically, but what one can contribute to just make this a more interesting place.  It happens to include cars, bikes, drinks, food, etc., and even audio.  This isn't the type of place that - no matter how experienced and intelligent you are - you come in and expect to be treated like royalty (IE, your comment about people being nice to you and you imparting knowledge).

 

As was stated, we have discourse and disagreements about many things, but it's something that's earned through participation and contribution.  And as Spritzer said, it's not about post count.  Continue the discussion on the SRM-313 if you will, but don't get so defensive - remember that thick skin you said you have - and enjoy the ride.  I'm sure there's a lot you can contribute, but also can pick up as well.

 

Something tells me it'd be nice to have you here over time.  We're an odd bunch, but a really great odd bunch.

 

My two cents.....

[spritzer]

not the spritzer i know. maybe you are thinking of someone else.

the stax mafia uses discretes for everything.  And yes we use opamps

for servo's, but that is it.  Even for the power supply its a discrete

opamp.

 

Only places I've ever used the OPA2604 was in the only cmoy I ever built (good project to do after building a Blue Hawaii or two) and when upgrading the Stax SRM-300 amps.  Better than the stock LF353... 

[Dusty Chalk]

Hey guys, my skin is thick, I just thought who the heck is this guy.

 

As far as it not being personal but about the post, well the post was written by me personally, so I have trouble seeing how a facepalm comment about my post could be seen as mutually exclusive from the person that wrote it.

 

I read the welcome PM carefully, trust me.

That's the problem right there.  You do, indeed, need to make that distinction.  There's a difference between arguments of fact (what is wrong) and arguments of ego (who is wrong).  When spritzer facepalmed your post, it was understood that it was his foray into the argument of fact (because he doesn't know you, and we knew that he didn't know you, so it didn't merit discussion).  We don't know if this is your own knowledge that you have legitimately accumulated through experience, knowledge you are regurgitating from a smart, close friend (we get a lot of those, too; I'll be honest, I'm one -- I don't know anything myself, so I tend to stay away from technical discussions), or knowledge you may have gleaned by googling (get a lot of those too).  (And of course, the ones who have no knowledge, who come in here and expect us to spoon-feed them the answers.)  So even if the facepalm was directed indirectly at you for being the source of the information, it doesn't mean it was directed towards you at a gestalt level, since that is but a small crumb of who you are.  And you're probably not even going to read this, so I'll just stick this here.

 

So, leave your ego at the door, argue the technical merits only, until you get an idea of who we are personally.  THEN you can start attacking us personally.  Well, not really, then we'll ban you for being a dick, but at least you can feel righteous in your exile.  

[acidbasement]

Anyway, if you stroke my ego in a pleasing fashion, yes, just like that, maybe a bit to the right, yes that's perfect... I may condescend to impart some of my knowledge to help you improve your audio system.

 

FTFY.

 

Gee, that sounds like a wonderful offer, Mister Buckingham.  Where do I sign up?

[CraigBuckingham]

Last one first, eeeeeekk - acidbasement, you obviously don't practise law for a living.

 

I like your diplomacy skullguise. The introduction letter is right, there are some good people around here.

 

Thanks for the intro guys. Nothing like a good jostle. Torpedo, I understood your last post this time, but I can assure you that is not the case.

 

As far as throwing egos and reputations around, I can see none of you gentleman would engage in such an exercise, not the least on someone else's behalf.

[CraigBuckingham]

Now onto some engineering which is of more interest to me.

 

spritzer, I don't have a schematic of the 323. I know the layout of the 313 however so I will provide a response to your assertions on how to improve it based on that.

 

No issue on increased class A biasing. Well known to improve performance generally. However safe operating areas and ripple current increases on existing designs need to be recalculated to ensure reliability. I am sure KG wouldn't miss that.

 

Finding good capacitors is necessary if you want to obtain quality audio reproduction. If you are not going replace sub-standard ones in existing designs then there may always be a limitation. As to the Jensens being garbage, maybe they have changed since 2006. But the gold Jensens were much better than the standard IIRC Nichicon in the 313, and Elna cerafines. It was an easy pick out of the bunch. I had/have some cheap Taiwanese brand that beat all the best audio grade caps I have put against them. But they were not available in high voltage versions and I didn't have time to muck around with a relatively expensive headphone set that were being challenged by some garage sale $10 AKG-340s. Sure the Stax just pulled ahead after the mods, which included some customs chokes I designed and had made.

 

I apologise if I missed your posts on your choke modified power supplies spritzer. I am interested, how did you find choke based unregulated supplies versus regulated ones when you did A/B testing with the same unit?

 

In my experience regulating the supplies can be an improvement, but it's 2 steps forward and one step back. And that one step back can't be fixed unless the regulators are removed. This may appear cryptic, let me explain another way. There are better ways to improve the power supply rejection of the amplifier, series pass regulators using an active device from my experience are about the 4th best way to do it. There are at least another 3 ways to improve on that.

 

The advantage of the differential amplifier design is that power supply noise induced into the amplifier circuit can be made to be virtually all common mode. If the power supply noise is analysed in the differential and common mode domains a lot of optimisation can be made by thinking of it that way.

 

Single ended circuits can also benefit by some of these methods, even though there is no common mode domain.

 

Servos are another can of worms. If at all possible they should be avoided which I am sure most would agree is common-sense. I know KG believes in not putting the correction back into the node used for the feedback loop. But even the terrible artefacts that IC op-amps display when used as amplifiers can be heard when used as a servo in high resolution systems. By putting them on a DC node used for bias stabilisation is better but there are ways to decouple them so the output is not directly used.

 

Spritzer, sorry if I missed your optimised servo designs. Can show me where to find the ones that you optimised over the ones KG uses on the DC nodes of the current sinks/sources.

 

Too big a post again? I'll end it here.

[DefQon]

AKG 340's....by this you are referring to the K340 from the 80's electrostatic (actually really just a mini electret tweeter) dynamic headphone, right?

 

Maybe something was wrong with your 313 (which is essentially an Xh with a bigger transformer), but I would no way in hell say a K340 is better then a 303/404 + SRM-313 (Xh) combo. Not to mention the 340's suffer from a lot of imbalance issues (have a K340 with imbalance in the upper mids, Tyll's measurements on 2 pairs on Innerfidelity also proves my point. Most probably the electret tweeter is losing it's charge).

 

I'm interested in your choke mod. 

Edited September 4, 2014 by DefQon

[CraigBuckingham]

Yes, it was the K340s of 79 vintage.

 

The 313/404 combo I had were brand new in the box from a distributor in Japan. They probably measured well, but lacked colour and sounded grainy. The K340 weren't perfect but were a lot more musical and smooth. Since the source was the same I put it down to the 313. The caps and chokes were enough to make it jump ahead of the K340s, but not enough in my opinion to justify the price to performance ratio. The feeling I had was that amplification for the the electrostatics was possibly going to be challenging using semiconductors and that a vacuum tube (or hybrid) design was maybe the better way to go. I didn't end up using them for R&D work and instead used a speaker setup.

 

The choke mod was a pi CLC network. So, rectifier -> parallel electo -> series choke (inductor) -> parallel electro. The chokes made a big improvement over the standard filter capacitor arrangement. I A/Bed that, only took a few seconds to win me over. Still have those chokes in my spares somewhere. Local transformer manufacturer made them to my specifications.

[luvdunhill]

Tl;dr

[CraigBuckingham]

I apologise, I can read and type fast so it doesn't seem so long to me. I suppose it's a blessing to be able to read, some people can't read at all, so you could take some solace in that. If this is par for the course I'll try and slow the pace down if that helps.

[nikongod]

CLCAC FTMFW. 

/thread

[CraigBuckingham]

CLCAC FTMFW. 

/thread

"Head Case" forums  .

 

I completely missed the significance of the website and forum name until I read your and luvdunhill's posts.

 

Thanks for the laugh guys.

[CraigBuckingham]

Spritzer, I was waiting for your engineering experience on the topics that were raised. You were after all lecturing me on how to do it and criticising my endeavours. I mean you have a truck load of posts here, I can't find it though.

 

You only contribution was a disparaging vague initial post towards me. You came out all guns blasting and then lost interest real quickly and went posting elsewhere.

 

Seems like the introductory letter doesn't work both ways.

[grawk]

that's correct. it only applies to people we don't know. which it pretty clearly spells out.