The ultimate DIY? A Stax SRM-T2!

[GeorgeP]

yeah, where are the caps from? That should tell you right away.

 

[nopants]

secondhand, I wasn't sure if the strip alignment was uniform for the whole series. the casing looks pretty shitty too so I should have been more suspicious.

fuck

what's a good way to desolder these without opting for a second iron? I don't want to fuck up the board too much but I've only one iron at the moment

[Pars]

Big enough tip on your iron (3.2mm is what I have) and a good soldersucker, something like this

Edsyn Soldapullt

I got mine at Frys.

Edited September 29, 2015 by Pars

[GeorgeP]

are they supposed to be United Chemi-Con? i've just never seen "negative black" before.

I received some counterfeit panny caps before - by themselves I had doubts but when compared to the original, it was clear - the casing and print just were "off".

 

[chiguy]

I've used a hot air station to desolder caps before.  Need to be careful not to burn the PCB by holding in one position for too long.

[b0bb]

I've used a hot air station to desolder caps before.  Need to be careful not to burn the PCB by holding in one position for too long.

That is a good idea, use hot-air to preheat the joint and adjoining PCB area slowly, once the solder starts to melt use a desolder gun or one of the solder suckers mentioned earlier.

Always keep the wand moving and never leave it in more than 1 spot for more than 2-3 seconds. I set my air temps to 350-380degF

Be careful to not pull out the plated sleeve that connects both sides of the board.

[nopants]

I was able to get it out cleanly by slowly rocking it out of place by heating and reheating the joints.

I just found out my octal sockets don't fit, does anyone have a link to what they know fits the board?

Also looking at the Bakelite sockets, what are the dis/advantages of this over ceramic/teflon?

[s_r]

I bought my teflon octal sockets off ebay, pretty sure this is the same item.

[Earspeakers]

I can recommend a Metcal station with desoldering gun, you can build a kit off eBay for cheap (I got the gun new for something like $100). Just hook it up to an air compressor, get a few tips and it beautifully makes rework easy. 

 

Weller and others have similar solutions. 

[G600]

Today I triggered my PSU.

Before I had a chance to measure high voltages, I heared something boiling. The two 4700µF were hot and their tops are now convex.

Sounds like an overvoltaged cap, right ?

Maybe the center tapping is confusing me, but why a 25v rating for those ? Isn't the 30-0-30 rectified to 42v ? This way 50v seems to be the minimal requirement...

 

Any thought ?

Edited October 6, 2015 by G600

[spritzer]

It is 30VCT so 15-0-15V not 60VCT like you have. 

Edited October 6, 2015 by spritzer

[G600]

OK, there is the culprit.

So I jumped both feet into Lil Knight's error (boards markings, etc...).

Would you share a solution, other than reworking the secondary ?

I could put 63V caps, but max DC for the 7X12 is 35V...

Edited October 6, 2015 by G600

[spritzer]

You could put in large resistors to drop the voltage but the only sensible thing would be to get a new transformer.  This isn't a project where you worry about 200$ or so... 

[G600]

I'll see what Mr Monaghan can do then...

[GeorgeP]

what about adding a small 15-0-15? Don't know if such exists - but space could be an issue.

[spritzer]

A small 2*0-15 with the center secondary leads tied together does the same thing. 

[G600]

Yep, i found a small 30va rcore with dual 15v secondaires. Will mesure if it fits.

Half the price of the trafo rework, not mentioning the lead time.

But i still feel dumb...

[kevin gilmore]

i will look at the board layout later, but i thought it said 36 vac center tapped which is the

same as 18-0-18  from now on, i will make that clear. the fat hvsic supplies are probably mislabeled too.

[s_r]

So I've now been able to replace the 10k trimmers with PTF56 resistors. The batteries adjusted just fine too. However the background noise is still there. Could the PSU be the culprit somehow?

[spritzer]

Could be but I doubt it.  Has to be the resistors acting up. 

[iwik]

Try Kevin suggestion of way back. Turn out the lights and see if there is any arcing.

[8street]

So I've now been able to replace the 10k trimmers with PTF56 resistors. The batteries adjusted just fine too. However the background noise is still there. Could the PSU be the culprit somehow?

Probably the noise from the current source 2sk246 - 10k. Test it: touch a isolated metal screwdriver to 10k pot and also the circuit between 10k and 2sk246 (don't touch the soldering place). Noise should disappear or minimize by touch one battery and maximize in other battery.

 

And do not forget to change resistors R24, R31 to 20 ohm in PSU.

Edited October 10, 2015 by 8street

[s_r]

Yea, I ordered some 22ohm resistors to put in the -500V supply as well. I assume you mean touch the legs of the 10k PTF56 or the 2SK246 and not the point where it's soldered, right? Do you mean the noise would maximize in the other channels batteries, or in the other battery in the same channel? Either way it sounds like I'm looking for a change in the noise by touching these points.

[nopants]

What are you guys using for interfacing the brackets? Was looking at Keratherm red but it's almost 100 USD for enough sheets

[s_r]

I used silicone thermal paste, specifically this stuff.