STK-0050 replacement for SX-780 and others

[rcs16]

Nice to hear.
As per the service manual, Adj R7 on module for 15mV(34mA) across R263/Q4e & R265/Q1e which represents about 34mA of bias current (0.034*0.44ohms). It can be increased to be as much as 80mA of bias which would be 0.08*.44ohms=35mV, with increased HS temp, but I think that there is lots of margin in this design.
Use some retractable clips so it is easy to connect to your DMM. Volume is to be set at zero, wait about 15 minutes for the HS to warm up and the ckt to thermally stablize.
With R7 being a 500 ohm Bourns 3362-R-502, the pot is turned fully CW to start, for 0 bias, then CCW to turn bias up.

 

[Awesomeaudio]

Thanks guys rcs, Zeb, and other’s, got my 4th unit up and running tonight with the new modules. All hail the 780!!
I do find if you torque down the MJE,s too hard you get continuity between the collector and the aluminum plate. Had to back off a little on a few of them, not sure why. Awesome fix nonetheless. Thanks.

View attachment 1014310

Damn those kits look like they came from the factory ! Excellent work. I am going to have to get myself a kit for my 780.
So who do we contact exactly regarding the kits ?
Zeb or Rick and Co ?

 

[rcs16]

http://www.ebay.ca/itm/STK-0050-Mod...e=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649
and get the parts from the Mouser BOM or the BOm on the web as above. Probably will have to get some subs as Onsemi parts seem to have back orders these days.

 

[Awesomeaudio]

http://www.ebay.ca/itm/STK-0050-Module-W-Power-to-operate-sets-up-to-100-Watts-Open-Source/122649581190?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m1438.l2649
and get the parts from the Mouser BOM or the BOm on the web as above. Probably will have to get some subs as Onsemi parts seem to have back orders these days.

Cool ! Thanks Rick.
Just made my purchase of one pair.
Now to get the bits on the BOM.

 

[tsd71]

Rick both MJE15032G and MJE15033G are in stock at Mouser

 

[rcs16]

Then use the Fairchild parts.
Post 131

 

[jeffV]

ok, ran into an issue. left channel is distorted pretty badly, what should I check on the modules?

also, really weird issue:
all output ceases depending on where I am physically in the room...?? If I approach the receiver at a certain angle, it goes out until I move. ???? what is that??

 

[rcs16]

Hard to say for sure, have to check a number to things before you suspect the modules.
1) really need a scope to be able to look at signals throughout the signal path
2) check the signals at o/p of pre-amp, before/after the relay
3) check bias/offset again with no signal input
4) that all sources do the same thing, phono,aux,AM/FM
See where this gets you

 

[torinogt]

Hi, Will these modules work to replace a STK0029 in the SX-580? Mine still has the originals and they are working fine at this point, but would nice to know I have an option to replace them when the time comes.

 

[rcs16]

well hopefully we do not have to fix your 580
electrically speaking, I can't say for sure if the stk module would work, the 780 design is different, the 580 has a bootstrapped voltage amplifier stage, where the 780 is a constant current loaded source type.
from the 580 sch I see that the VAS current is 26.6V-25.3V.0.6V(Vbe of q303/4) = 0.7 /100 ohm = ~7mA
i am not sure of the 780 vas current, my ltspice sim env is broken as my old computer died. I'd have to get it going again and run some sims to be sure of operation.

mechanically i'd have to take a good look at the innerds to see if the module would fit and how to install. post a good pic of the existing stk mounted on the heatsink.
you could print out a 1:1 of the existing module and see how it fits in the 580

 

[torinogt]

the modules in the 580 are socketed. I will have to pull the cabinet take some pictures.

 

[rcs16]

re: 580
not sure if the ic sockets need to be removed, have to figure out how to wire from module pt holes to ic socket, it is on 4mm centers.
Got my win10 computer running ltspice sim again, have to use the 780 design as a template to mod for the 580 design.,time consuming ,

Anyone want to learn some ltspice design simulation, can start by entering the schematic, the sim is already set up to run, i've already started the entry part, a good hour or so of work left to do.

 

[torinogt]

Here are the pictures of the 580

 

[rcs16]

pic is not very good.

 

[zebulon1]

 

[rcs16]

Looks tight to wire new module with AL plate to existing holes for stk using the existing mounting holes. Might have to modify the AL plate to make it fit better (raise it up) or screw the module(s) directly to the exiting HS and not need a AL plate, only 5 holes/module

 

[torinogt]

that was my first atempt at posting a picture

 

[torinogt]

 

[rcs16]

Much better pics, still need to simulate this design to see what goes.

 

[zebulon1]

I wanted to inform the thread that I (we) just sold the 40th kit from the auction listing.
Most of guys will buy two sets/kits.
Several of the guys have repair shops and are tired of sending the costumers away due to the unreliability of the current modules on the market.
The feedback has only been very positive.
The only question I get is; Can the module work for the higher wattage sets?
I'll steer the buyer's to the Thread. I wonder how many new members we have added to the rolls?
I set up the process so I have minimal work in packing and shipping, so it's not a chore to handle.
I'm going to have to re-up an order for the heatsinks and PCB's.