Ashly SC-50 Black Face Schematics?

[user 40373]

Does anyone have a readable scan of the Ashly SC-50 schematics (black face model). I picked one up recently and plan on doing a complete rebuild to clean it up, because they are a little noisy.

 

[user 40373]

Ashly was kind enough to e-mail me a schematic, I'm not sure what revision it is.
http://img685.imageshack.us/img685/7222/sc50schemolder.jpg

 

[user 40373]

According to Ashly, this is the only schematic in their archives but it should be pretty close no matter which revision you have.

 

[pvision]

Looking for a schematic for an early SC-50 compressor - does anyone have it?

Nick Froome

 

[shot]

Here you go!


btw... I love that comp! I have SC-55 (same but dual channel) - the best thing on electric guitars!

 

[pvision]

Had a very helpful - and very prompt - reply from Ashly to my email. The schematic above is for the early version of the SC-50 which uses matched pairs of transistors in a metal can. This is the type I have. The later version uses a dbx chip

According to Jim at Ashly: "If you do have the original version SC-50 with the matched dual can transistor VCA, it is important that no substitutions be made concerning the IC chips. The circuit was designed around a special mode of operation only available in the 301 IC"

Thanks for the help, shot & Jim

Nick Froome

 

[disssa]

Is there any chance to get the schematics for the SC-50 again?

 

[CalavoBob]

Here's an Ashley SC50 schematic I have.

 

[disssa]

Thank you!

 

[CalavoBob]

You may notice that the op amps used in the stock SC50 are not the greatest by today's standards. A few months ago I did a comprehensive mod on a pair of SC50s that addressed this. The 4558 used to make the balanced input can be replaced by a THAT 1200 balanced input chip. These offer a great solution to the difficulty of achieving the promise that balanced lines try to achieve. The quad 4136s are basically (4) 741s in a single package and suffer from low slew rate, higher distortion, poor signal to noise, low current delivery and offset current and voltage. I stacked a couple of 8-pin sockets onto each 14-pin socket with some crazy cross wiring to accomodate a pair of LM4562 duals to replace them. The SC50s balanced output is a nutty stack of 4558 sections to try to drive balanced lines. I might have used one of the TI-Burr-Brown DRV 134 balanced output chips. Since the LM4562s have a much higher bandwidth than this circuit needs, I trimmed the negative feedback resistors to cut off at 159kHz to they won't amplify every radio station in town. I also added several 0.1 uF supply bypass caps at several spots in the circuit. It came out sounding very good. I'll look through my files for details and photos of how I stacked those chips, etc, if you're interested.

 

[MidnightArrakis]

You may notice that the op amps used in the stock SC50 are not the greatest by today's standards. A few months ago I did a comprehensive mod on a pair of SC50s that addressed this. The 4558 used to make the balanced input can be replaced by a THAT 1200 balanced input chip. These offer a great solution to the difficulty of achieving the promise that balanced lines try to achieve. The quad 4136s are basically (4) 741s in a single package and suffer from low slew rate, higher distortion, poor signal to noise, low current delivery and offset current and voltage. I stacked a couple of 8-pin sockets onto each 14-pin socket with some crazy cross wiring to accomodate a pair of LM4562 duals to replace them. The SC50s balanced output is a nutty stack of 4558 sections to try to drive balanced lines. I might have used one of the TI-Burr-Brown DRV 134 balanced output chips. Since the LM4562s have a much higher bandwidth than this circuit needs, I trimmed the negative feedback resistors to cut off at 159kHz to they won't amplify every radio station in town. I also added several 0.1 uF supply bypass caps at several spots in the circuit. It came out sounding very good. I'll look through my files for details and photos of how I stacked those chips, etc, if you're interested.

[the op amps used in the stock SC50 are not the greatest by today's standards] -- Ya think???.....I once had 3 6-channel mixers that used LM301's for its ICs!!! Can't complain though.....at the time, that is all of what was available to use in audio designs.

[quad 4136s are basically (4) 741s in a single package] -- Revolutionary at-the-time!!!

[and suffer from low slew rate, higher distortion, poor signal to noise, low current delivery and offset current and voltage] -- OH!!! THE HORRORS!!!.....

[I trimmed the negative feedback resistors to cut off at 159kHz to they won't amplify every radio station in town] -- I gotta say!!!.....There's nothing more exciting than having a trucker on a CB-radio come blasting through your PA-system during a "LIVE" show!!! >> 10-4, Good Buddy!!! <<

[I'll look through my files for details and photos of how I stacked those chips] -- I'd settle for an updated schematic that shows all of your updated modifications!!! Howzat???.....

/

 

[CalavoBob]

Well here goes. I found my SC50 mod notes. The marked up schematic shows what ICs I wired into each location and has sideline notes about which chips go where too. It also describes how I cut the traces to send a balanced cable to the output jack. I think I used a SSM2142P as the balanced output driver, but they may not be available now so you could use a DRV134PA instead. it looks like I used a LM4562 on the balanced input, but you might consider the excellent THAT 1200 there. There's also a page that describes how I did the wiring to stack two 8-pin dip sockets onto a 14-pin dip socket so I could plug the whole assembly into sockets on the pcb. Notice there are two different types of stacks. This was really tedious but it works. I had to trim several pins off of the upper 8-pin sockets so they wouldn't pass through, but about half of the upper pins did go to correct locations in the 14-pin sockets below. Notice that since there's 16 pins on top and only 14 pins below, there are two that hang off the end. In the construction diagram, the squares and circles indicate pins that pass through. The "x"s and "alpha" symbols indicate pins that must be removed. I found the the trimmed pins often still made contact to the metal below them, so I cut out tiny insulators from plastic sheets I had to insulate the trimmed upper pins from the 14-pin socket pins below. There are several photos that shows the wiring details of the two stack types that needed to be built, the pcb trace cuts for the output cable, and the location of the capacitors I added under the board. Luckily, the caps they used in parallel with the feedback resistors cut the frequency response to an acceptable frequency for stability. The end result worked really well and the studio I make it for says it sounds great. You have to possess some excellent soldering skills to pull this off. This project is not for newbies. Good luck and have fun.

 

[HerbertR]

Wow...... Awesome. You ve upgraded this ugly sounding thing. Holy crap...Respect^10.

I have one SC50 lying around. But this challenge is beyond my capabilities...Cheers