kgst

[JoaMat]

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Edited November 11, 2015 by JoaMat

[mwl168]

Thanks guys! That's really helpful.

To be clear; with the stock CCS value (Rk = 300 ohm), each channel of KGST draws 20mA from each of the HV rail. That's 40mA for the two channels combined.

That's less than the ~ 52mA (two channels combined) which KGSSHV Consumes.

I am trying to understand why it's not recommended to use the more sophisticated kgsshvps8g PSU to power the KGST.

[kevin gilmore]

its all about the size of the box. if you go with a bigger box you certainly

can use the more extensive power supply which is far more voltage stable

and substantially less noise.

[valve5425]

its all about the size of the box. if you go with a bigger box you certainly

can use the more extensive power supply which is far more voltage stable

and substantially less noise.

 

I'm just sizing up my chassis, so, is the KGSSHV PSU a "must do" or "could do" for the KGST?

 

I'll be using the KGST psu initially, just to get up and running, but if it's going to be worth the effort, I'll leave some space to change psu's later. I've ordered a TX with 0-280-330v secondaries, so I'm assuming that would just get me 350V from the KGSSHV psu. My mains supply is consistently around 247v, so, with 230v primaries, I've some extra headroom.

 

If this is feasible, I'll monitor the thread regarding the latest board until they know it's not going up in smoke!

 

Thanks!

[mwl168]

its all about the size of the box. if you go with a bigger box you certainly

can use the more extensive power supply which is far more voltage stable

and substantially less noise.

Thanks Kevin!

[Kerry]

If you use the KGSSHV PS you should set the pre-reg zener string to about 400v. You'll need some head room above that so the transformers should produce a peak voltage of at least 430v. I'd use the 330v tap on the transformer.

[mwl168]

Thanks Kerry.

 

I am hoping to use an off-the-shelf transformer. Antek has a 100VA transformer with 2 x 350v/120mA and 2 x 6.3v/3A secondaries. Would this provide enough headroom for the KGST? I'm especially concerned about the 120mA current rating. They have another 100VA transformer that has 2 x 300v/170mA secondaries but the rectified voltage is below your 430V minimum.

 

I will have to source a separate transformer for the 15V rails if  I go this route.

Edited March 22, 2015 by mwl168

[sorenb]

I wouldn't use the KGSSHV psu as it just doesn't like that load. No mods possible with that PSU board which is why we are slowly working on a new one.

Can you elaborate a bit on that Birgir?

As far as I understand the load from kgst is less than kgsshv, or do i miss something?

[JimL]

If you look at the posts just before Birgir's post #662 of 1/10/15, I think you'll find that Birgir was talking about building a Blue Hawaii (#652) nopants was talking about building his Blue Hawaii (#653) and asking about whether the KGSSHV supply would work for that (#661).  I believe Birgir was addressing nopants question (#662), and not saying that the KGSSHV PS was not suitable for the KGST.  At least that's the way I read it.

Edited March 22, 2015 by JimL

[Amar]

Apologize for slightly OT, Could use a quick advice: I'm looking to replace my screwd-up KGSS PSU board with a mini-PSU, Only question is about the heatsinks for the current source transistors, in my case 2SA1968 are coupled to the same sinks as the power mosfets and I noticed in two varaitions of the boards thus far that use either a smaller single-sided sinks or a single shared double-sided sink. Would these solutions be effective for handling 2SA1968's?

 

Also, if someone has a spare board I would love to know.

[spritzer]

If you look at the posts just before Birgir's post #662 of 1/10/15, I think you'll find that Birgir was talking about building a Blue Hawaii (#652) nopants was talking about building his Blue Hawaii (#653) and asking about whether the KGSSHV supply would work for that (#661).  I believe Birgir was addressing nopants question (#662), and not saying that the KGSSHV PS was not suitable for the KGST.  At least that's the way I read it.

 

Yeah, that was for using it on a BHSE.  I will draw up a new psu just for the BHSE when I can find some time. 

 

For the KGST I just can't see any reason to use the HV psu.  Why use a PSU which was setup to run +/-500V at 350? 

[Kerry]

To Birgir's point, I always modify the PS for the intended use.  For a 350v supply you can remove half the capacitors and the associated resistors.

 

I like the performance of the design though it has a very high drop-out voltage. 

 

You can certainly get away with the 300V 100VA transformer, but you need to tweak the zener string.  I find you need at least 20V higher on the pre-regulated voltage over the output voltage plus you want another 20 or so volts over that coming from the transformer.  Problem is that the zener string moves 10 - 15 or so volts from cold to warm-up. 

 

I use the Antek 350V 100VA transformer on my KGST, but I run the output at 400V.  The power is not an issue.  Runs silent.

[valve5425]

If you use the KGSSHV PS you should set the pre-reg zener string to about 400v. You'll need some head room above that so the transformers should produce a peak voltage of at least 430v. I'd use the 330v tap on the transformer.

 

 Thanks Kerry. 

 

Yeah, that was for using it on a BHSE.  I will draw up a new psu just for the BHSE when I can find some time. 

 

For the KGST I just can't see any reason to use the HV psu.  Why use a PSU which was setup to run +/-500V at 350? 

 

See your point spritzer. Just wondered if anyone had tried both psu's and found the change worthwhile. 

[mwl168]

To Birgir's point, I always modify the PS for the intended use.  For a 350v supply you can remove half the capacitors and the associated resistors.

 

I like the performance of the design though it has a very high drop-out voltage. 

 

You can certainly get away with the 300V 100VA transformer, but you need to tweak the zener string.  I find you need at least 20V higher on the pre-regulated voltage over the output voltage plus you want another 20 or so volts over that coming from the transformer.  Problem is that the zener string moves 10 - 15 or so volts from cold to warm-up. 

 

I use the Antek 350V 100VA transformer on my KGST, but I run the output at 400V.  The power is not an issue.  Runs silent.

Thanks Kerry!

[JimL]

Yeah, that was for using it on a BHSE.  I will draw up a new psu just for the BHSE when I can find some time. 

 

For the KGST I just can't see any reason to use the HV psu.  Why use a PSU which was setup to run +/-500V at 350? 

 

WHAT!!??

 

Isn't overkill the motto of the Stax Mafia?

 

Here's spritzer on 4/16/14 on the KGSSHV design:

 

"The whole goal of the KGSSHV was never the high voltage, that was just a side product of the parts available.  The main focus was the new PSU design and indeed the CCS for the third stage..."  

 

So if the PSU for the KGSSHV is an improvement over the KGSS PS (which is basically the same as the KGST mini PS), shouldn't using a modded KGSSHV PS (with decreased output voltage) be an improvement for the KGST, assuming you have the space to do it?

Edited March 22, 2015 by JimL

[valve5425]

Guess I'll stand back and watch this one go!!

 

I have a confession. I do like to get carried away with power supplies, but only if there's a chance of improvement. I mean, we don't want wimpy stuff do we. If the lights don't dim when you turn it on, is it big enough?

[JimL]

[kevin gilmore]

about overkill...

if you want 350v out, then the error amplifier really should get 400v from

the zener string, which compensates for the hot/cold

and then the unregulated input voltage should be 450v and that is

right at the limit of a 450v cap. So while 2 caps in series is overkill

you can always pick lower voltages and higher capacity, say

2 x 250v caps. Or 1 x 500v cap, and the 500v caps seem to go

in and out of stock often.

running things with less clearance on the voltages ends up raising

the noise level. Still its much less than noise than the simple supply

and the amplifier is definitely subject to power supply noise

[spritzer]

This is DIY, you can do what ever the fuck you want.  I for one am tired of people coming up with stupid crap and then asking me to fix their fuckups when it inevitably comes crashing down on them.  Overkill is well and good but it's often thrown around as an excuse for stupidity, using a 400VA transformer for a 50W circuit and stuff like that. 

 

I for one have tried the KGST with every PSU I have here and I'm sticking with my KGSSHV mini unit. 

[valve5425]

........................................................................................................................................

............................................running things with less clearance on the voltages ends up raising

the noise level. Still its much less than noise than the simple supply

and the amplifier is definitely subject to power supply noise

 

Thanks for that Kevin.

 

This is DIY, you can do what ever the fuck you want.  I for one am tired of people coming up with stupid crap and then asking me to fix their fuckups when it inevitably comes crashing down on them.  Overkill is well and good but it's often thrown around as an excuse for stupidity, using a 400VA transformer for a 50W circuit and stuff like that. 

 

I for one have tried the KGST with every PSU I have here and I'm sticking with my KGSSHV mini unit. 

 

Yep, that's fair enough, I'll stick to getting a  KGST built and working for now. 

[JimL]

That's cool.  At some point overkill doesn't make any difference - it just makes the rubble bounce higher.  Sounds like the using the KGSSHV PS is technically better but may not make much if any sonic improvement.

[Earspeakers]

Edit: on overkill, it usually does come with downsides - cost and difficulty for one. But just a simple example, it's popular here to go for thick boards with 4oz traces. Good right? Yeah, until you try to solder them. Unless you have a Metcal station they're a pain to solder and take careful technique. You're more likely to end up with a cold joint, and for what? A thick board which still probably has a bit of that fiberglass bend in it. 

 

Anyhow ...

 

I'm looking for a source of 2SA970 or MPSW56, can I trust these?

 

http://www.ebay.com/itm/100pc-PNP-Transistor-2SA970-A970-TO-92-hfe-GR-Low-Noise-Audio-Amplifier-TOSHIBA-/140730909646

 

They do show a Toshiba box at least. Any other suggestions?

Edited March 22, 2015 by Earspeakers

[spritzer]

I've bought from them in the past and they were good.  I just bought another lot so we'll see. 

[Earspeakers]

I've bought from them in the past and they were good.  I just bought another lot so we'll see. 

 

Thanks spritz. Rhetorical question: do the Mafia ever produce an amp that doesn't take an obsolete part?   

 

Well I do love your work; about to finish a KGST, a KGSSHV is partially done, a Megatron has been started, and just assembled the parts for the T2. 

[PretentiousFood]

I'm not sure if it's suitable in this build, but the 2SA1163 is basically a current production 2SA970 in a surface mount package. You might be able to use it with an adapter like this. Its complement is the 2SC2713.