STK-0050 replacement for SX-780 and others

Not sure if I'm allowed in Canada, I've been told Drunk Driving offenses count as felonies over there and they don't let "felons" in

 

yeah, it would be chancy, do not know until you try and it may depend on the border officer = risky. I think it is the same for us too, kinda stupid, but we live in a stupid world these days.
We shall see if they reject pot smokers too, time will tell after it is legalized here in the summer, so they say.

 

I acquired a 100 watt Fisher CA-880 with the STK-0080 modules and plan to build the up the higher power modules discussed in post # 364 and subsequent. Look to fit the Fisher BA-6000 rated at 100 watts, using the STK-0100 and +-57v rails.
To the 100 watt Fisher RS-2010 using the STK-0105 and +-56.9 rails.

 

Good luck with these efforts. I am confident they should work, it just the mech stuff to sort out.
the bassblaster guy got his amp (CA-800) sorted out, it was the ips diff pair after all, not the new modules
If you want, I can give you the CA-800 ltspice schematic or any of the other ones I have done (SX-870). You can change it to match the ones you are trying? it predicts bias voltages, power dissipation, current drawn, thd .... something to learn to use this valuable design tool.
Cheers
Rick

 

PM sent

 

Hi!
I'm trying to save a Technics SU-V4 for a friend, There is another thread where I tried to replace the whole amplifier section with a mx50 se kit but so far the results aren't that great (got a 100hz hum that just won't go away). I have a second amp and would like to try and see if this option is doable. The SU-V4 has stk-8050's in it with synchronous bias new class A as they called it. I can probably toss out the bias circuit all together so I don't think that's a problem but would this discrete replacement for the stk-0050 work in there as is (by adding a couple of emitter resistors). The power supply rails are a bit higher than in the sx-780 (+/-48v). It would be connected like this :

 

Most probably could be made to work, but the VAS (voltage amp stage,Q314,316) current into the Vbe multiplier ckt could be different, which could mean some component changes necessary to get the correct O/P stage bias current.
I would have to simulate the design to see how it would work in this design to have a better understanding. I am also not sure where your hum is coming from, so can not say if using this module would solve that problem.

 

It would be great if you could do that .
Before replacing the whole thing with that mx50 kit, one of the two stk's was working and I had no hum so it's probably due to something not being quite right with the way I did things. Also this way I will be able to keep wiring to a minimum and mount the whole thing to the heat sink easily. As I have two amps, I will be able to keep the one I was working for later and try the second one with this option.

 

Lets see if I have some time for this one. Does anyone else around here know how to use ltspice?

 

Okay, I took a stab at it, see the attached schematic of the sim for Technics SU-V4. Based on the sim results, it looks to be working.
I did not include the tone control using IC303 in the sim.
Good luck
Rick

 

That was quick, thank you ! From what I read the tone controls shouldn't disturb the output stage in any way, I will try without first and see next if they will work as is. Thanks again, will update in a week or two with the results. I see you left out C307 (308), is there a particular reason for this ? Also for R6 and R14 there are two values 75R and (150R) for R6, 1.3K and (1.2K) for R14 ?

 

I agree replacing the ops should not make any difference.
C307 is done by C5 on the module, C307 can be left on the pcb.
on the module, use 75R for R6 and 1K3 for R14.

 

Great, thank you.

 

It was a long trying week, glad to have some down time this weekend.
I'm building two orders. One for Mouser and the other DigiKey. A ton of components needed for other work but some for the modules. I'm glad I didn't hit the order key. Every time I turn around another component needs ordered.
I might be able to pull the order triggers tomorrow.

 

Cool, take care guys, while I play with this SA-8800 NSA design. I can see why people have had difficulty getting them to bias when they change the original parts. basically can not use the STV-2, need only one diode to make it work.

 

Hello everyone! I have been all through this thread and I must say that I am super impressed with the knowledge about this particular issue. I have an SX-780 open on my work bench right now and I am looking at these Darrington Power Packs because I think they are the source of my issues. I was looking at the connections and I noticed that pins 4-7 weren't soldered on. It's that normal. There seems to be some residue on 6 and 7 from a past soldering job. I have posted some pictures to explain. Should these be soldered?

Quick diagnosis on the unit is that it powers I and all the fuses and lights are good but I get nothing from the meters on any channel. I started it with a good clean and it still does not work.

 

Only three pins on each side of the modules are used. 0, 1, 2 and 7, 8, 9.
Measure the DC voltage at those pins. Plus and negative voltages are expected. Some maybe less than one volt.
Report the readings.

 

So. I was reading about a few things in other threads and realized that I am a bit out of my depth on this one. For safety's sake, I am just going to have a tech do this job. Thank you for the reply.

 

Read up on the use of a DMM. In this case, reading DC voltages. Practice on a battery. The black probe is grounded to the chassis and the red probe contacts the pins on the module. Tape up the red probes metal tip so only a small amount of metal tip is exposed. This will prevent the probe from contacting two pins at the same time (Bad). A steady hand is still required. Have someone else read the meter, that way you can concentrate on the matter at hand.
You do need a descent meter to read the voltages accurately. Some of the guys have said the Harbor Fright meter isn't too bad.
You got this far, you must have some interest/knowledge, why stop now?
At the very least, you'll know whats wrong with it.

 

Oh I am tremendously interested. The reasoning behind my knee jerk is that I was reading another thread from about 10 years where someone was asking the exact same questions and the guy answering got really alarmed and just told him to close it up because he was not going to be part of his electrocution. So I took that to heart a little. I will have to watch some more videos to make sure I get it down. I got a kiddo on the way and I can only take so much of that current, ya dig?