Hey there,
I’m repairing this beautiful rotary mixer for a friend, I’m not very experienced / oriented with these kind of repairs, but still see it as a fun way to learn and wanna do my best to succeed on my own.
So, the problem is that the inputs (Phono 1, phono 2 and tape) are weak/unbalanced to varying extent. I did my best to show in these pictures below. Upon cue:ing through headphones, Phono 2 has a right channel that’s weak/dropping out. Phono 1 struggles with both channels: thin, rather bad sound lacking bottom, and also here the right channel is the worst of the two.
Tape 1+2 worked for a second, then went silent.
I tried listening both through headphones and through Program (master) out, and same issues.
My question would be if anyone has a schematic over this mixer, and if anyone would be able to point me in a direction of what components to be looking at checking? Preferably explained on a beginner’s level (like I am).
Thanks!
I’m repairing this beautiful rotary mixer for a friend, I’m not very experienced / oriented with these kind of repairs, but still see it as a fun way to learn and wanna do my best to succeed on my own.
So, the problem is that the inputs (Phono 1, phono 2 and tape) are weak/unbalanced to varying extent. I did my best to show in these pictures below. Upon cue:ing through headphones, Phono 2 has a right channel that’s weak/dropping out. Phono 1 struggles with both channels: thin, rather bad sound lacking bottom, and also here the right channel is the worst of the two.
Tape 1+2 worked for a second, then went silent.
I tried listening both through headphones and through Program (master) out, and same issues.
My question would be if anyone has a schematic over this mixer, and if anyone would be able to point me in a direction of what components to be looking at checking? Preferably explained on a beginner’s level (like I am).
Thanks!
The RCA's look really ugly, it can be hard to convince them to make contact. Get new gilded ones, cheap from Aliexpress or buy the same localy for 10x the money.
Make more, good pictures before you start!
Then replace the 10uF/35Volt caps, they will be out of spec after such a long time. Same for all the other electrolythics. Mind the polarity. Don't touch the other components.
If there are still problems after new RCA and caps, get new pots. These have an Ohm rating and will be linear or log type, mostly the last.
That should do the trick. Dont try to improve or "tune" this gear.
Estimated cost for the parts is about 20-30 € depending of source.
Make more, good pictures before you start!
Then replace the 10uF/35Volt caps, they will be out of spec after such a long time. Same for all the other electrolythics. Mind the polarity. Don't touch the other components.
If there are still problems after new RCA and caps, get new pots. These have an Ohm rating and will be linear or log type, mostly the last.
That should do the trick. Dont try to improve or "tune" this gear.
Estimated cost for the parts is about 20-30 € depending of source.
Sounds good, these things I'm fairly confident with doing. Will start with re-capping and change / check the RCA:s properly. I also contacted that guy on Reddit offering schematics, will see if I get a reply. Thanks!
I would also offer up gently reseating the socketed devices.
Edit: and cleaning the sockets with something good like Deoxit
Edit: and cleaning the sockets with something good like Deoxit
...
I'm planning on replacing all 7 in/out-puts while at it, I happened to stumble across an old listing at Reverb with a similar restauration (not that I'm planning on making those upgrades, though): https://reverb.com/item/65456071
Best,
Arvid
My unfamiliarity begins to show already. Would these ones be fitting? https://www.aliexpress.com/item/1005007792874706.html?
I'm planning on replacing all 7 in/out-puts while at it, I happened to stumble across an old listing at Reverb with a similar restauration (not that I'm planning on making those upgrades, though): https://reverb.com/item/65456071
Best,
Arvid
The RCA's are what I would suggest. If you would be able to find anything that "sounds" better than these, I would be very surprised.
The "tuning" is what I feared you would find and try to do. The outcome will be something else than what it once was. Maybe better, maybe worse, you will never know until you have a second, identical device at factory spec to do a A-B comparison. Of course on some reverence amp and speakers. In most cases fitting more expensive and larger sized parts will have no audible effect at all, but null the historic value of the object. Using capacitors from reputated brands instead of cheapest China brands should be enough of a tuning and an acceptable modificaton.
I can't see the whole cirquit, but from maybe fitting some 1uF extra film capacitors in parallel to the power supplys electrolythic (on the solder side of the PCB if the case has room for them), I would not change anything.
Any further "tuning" is very questionable. Expect it to sound much better than know, just by doing these repairs, while keeping it's value. Electrolythics have a limited life time and these should be too old now.
PS MOUSER is a good source for quality components even in consumer size orders, You should find any size and value of cap for this board. Stay away from eBay and Ali for those!
The "tuning" is what I feared you would find and try to do. The outcome will be something else than what it once was. Maybe better, maybe worse, you will never know until you have a second, identical device at factory spec to do a A-B comparison. Of course on some reverence amp and speakers. In most cases fitting more expensive and larger sized parts will have no audible effect at all, but null the historic value of the object. Using capacitors from reputated brands instead of cheapest China brands should be enough of a tuning and an acceptable modificaton.
I can't see the whole cirquit, but from maybe fitting some 1uF extra film capacitors in parallel to the power supplys electrolythic (on the solder side of the PCB if the case has room for them), I would not change anything.
Any further "tuning" is very questionable. Expect it to sound much better than know, just by doing these repairs, while keeping it's value. Electrolythics have a limited life time and these should be too old now.
PS MOUSER is a good source for quality components even in consumer size orders, You should find any size and value of cap for this board. Stay away from eBay and Ali for those!
Yeah, I was just wondering what type of RCA plugs to purchase, what exactly am I searching for? Are these alright? https://www.aliexpress.com/item/1005007792874706.html?
if deoxit or a good quality contact cleaner on the jacks and controls doesn't restore proper function i'd stop there.
i don't understand the reverence for Sound Workshop stuff, their recording consoles where not great, weak EQ's, patch bay and buss problems not to mention high noise floor.
they where far less $$$ then other stuff so became the go to for independent fledgling studios in the mid seventies.(disco era which is why the 421 was found in so many hotel/clubs)
just cuz it's vintage doesn't make it great...
i don't understand the reverence for Sound Workshop stuff, their recording consoles where not great, weak EQ's, patch bay and buss problems not to mention high noise floor.
they where far less $$$ then other stuff so became the go to for independent fledgling studios in the mid seventies.(disco era which is why the 421 was found in so many hotel/clubs)
just cuz it's vintage doesn't make it great...
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here's a link to another source of inexplicable fascination with vintage gear http://www.muzines.co.uk/articles/hot-rodding-an-mm-mixer/6373
the lynch pin with these MM mixers is that the faders are in the feedback loop of the op-amp that drives the buss so any faults at the faders can result in full rip output...learned that the hard way.
i still get a chuckle out of reading the label on the front panel of that SW 421 where it says "Broadcast-Disco Mixer" ...nothing broadcast quality 'bout those!!
the lynch pin with these MM mixers is that the faders are in the feedback loop of the op-amp that drives the buss so any faults at the faders can result in full rip output...learned that the hard way.
i still get a chuckle out of reading the label on the front panel of that SW 421 where it says "Broadcast-Disco Mixer" ...nothing broadcast quality 'bout those!!
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There's fun and satisfaction in simply repairing something, regardless of the perceived quality of the item involved. Plus the knowledge gained.
that up to the OP to decide.
i'm just advising caution not to go all in on cash outlay for parts unless that really what he wants to do.
i'm just advising caution not to go all in on cash outlay for parts unless that really what he wants to do.
Yup, that's all definitely up to the OP to decide.
Anyways, I would definitely not stop at just cleaning the controls and jacks. @F3rdy I've had good success over the years solving problems by performing a pull/clean/reseat of socketed ICs, checking out any funky wiring, and reflowing of suspect traces where that makes sense.
Good luck with it, interested in how it turns out!
Anyways, I would definitely not stop at just cleaning the controls and jacks. @F3rdy I've had good success over the years solving problems by performing a pull/clean/reseat of socketed ICs, checking out any funky wiring, and reflowing of suspect traces where that makes sense.
Good luck with it, interested in how it turns out!
RCA plugs corrode and loose tention, capacitors dry out and change capacity while producing distortion. Switches can be cleaned and potentiometers should be replaced because of wear, dirt or both. Cleaning will not recondition them for long is my experience.
This object was build from usual, cheap industry quality parts, so no need to use highest audiophylic boutique components to restore it.
If you take good standard, branded quality from a reputated seller, the thing should sound better than ever. The PCB looks quite clean and should give no problem replacing parts if some care is taken. Don't take the 120Watt soldering iron you use to fix the roof with, 15W will do, a simple vacuum press and some "no clean" solder. Don't mess with any soldering liquid or paste!
The IC OP-amps should be pulled before soldering anyway, when you insert them later, the action should clean the contact. No need for WD40 or the like.
The whole project looks like a simple job. There is nothing to see that would indicate it sounds bad, also nothing that would make it special. Sure no high end audio thing, should be transparent with a little hiss, something no one cares about when the music is playing.
Link to the phono OP-amp: https://bg-electronics.de/datenblaetter/Schaltkreise/HA-4741.pdf
This object was build from usual, cheap industry quality parts, so no need to use highest audiophylic boutique components to restore it.
If you take good standard, branded quality from a reputated seller, the thing should sound better than ever. The PCB looks quite clean and should give no problem replacing parts if some care is taken. Don't take the 120Watt soldering iron you use to fix the roof with, 15W will do, a simple vacuum press and some "no clean" solder. Don't mess with any soldering liquid or paste!
The IC OP-amps should be pulled before soldering anyway, when you insert them later, the action should clean the contact. No need for WD40 or the like.
The whole project looks like a simple job. There is nothing to see that would indicate it sounds bad, also nothing that would make it special. Sure no high end audio thing, should be transparent with a little hiss, something no one cares about when the music is playing.
Link to the phono OP-amp: https://bg-electronics.de/datenblaetter/Schaltkreise/HA-4741.pdf
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Yeah but you can test most of the problems without spending on new parts or doing a deal of work that might be in vain.
Put a signal direct to the wiring rather than through the socket - if it works then you can replace the socket.
Pots usually go noisy, only occasionally fail due to no contact or broken track.
Clean, operate vigorously, test end to end and end to slider with ohm meter.
Sure, replace if it's crackly but not if that isn't the fault.
Above all, replace one or two parts at a time then retest.
Replace all the parts in one go and find a fault - you don't know where you went wrong.
Make it work first, then you can replace grubby sockets & crackly pots.
Put a signal direct to the wiring rather than through the socket - if it works then you can replace the socket.
Pots usually go noisy, only occasionally fail due to no contact or broken track.
Clean, operate vigorously, test end to end and end to slider with ohm meter.
Sure, replace if it's crackly but not if that isn't the fault.
Above all, replace one or two parts at a time then retest.
Replace all the parts in one go and find a fault - you don't know where you went wrong.
Make it work first, then you can replace grubby sockets & crackly pots.
The cost of new potetiometers may be less than the postage for a second order. So if uses Mouser or the like to get quality capacitors, that will not make much of a difference. The problem with old potentiometers, as well as RCA plugs is that they are unreliable. A spray can of high quality pot cleaner will cost more than new potentiometers. Even cleaned old components may work when plugged in a few times or freshly cleaned, but fail in producing distortion after a little time (the RCA) or work only in certain positions (the pots). This is not worth the hassle if the mixer is disassembled anyway.
Second, he is doing it for a friend. So he doesn't want it to fail after a week or two, just because he saved 12$ in parts while repairing it.
I have a whole cabinet of old gear, I experienced this many times first hand.
You are right about the risks of a beginner doing soldering work, but that is not the point. He may do a good job just by practicing a few things as shown in many video tutorials, before going for the actual object. My kids, when about 8 years old, soldered small PCB kits in good quality, after practicing for about 10 minutes on my lap.Good quality like you get from China, if you are lucky. He may as well have no talent, refuse to practice and overestimate his personal skills, ruining this perfect looking, simple old mixer, but that is out of our reach. Just like him ignoring the need for correct tools and material or confusing wires and capacitor polarity.
What helps, the mixer was done with "good" solder, so the usual "lead free" problems should not occur. As long as he uses leaded solder for the repair as well.
PS this is about all you will ever need to do a perfect repair on such a simple object. Just replace the solder for leaded quality. 20$ on Amazon
Second, he is doing it for a friend. So he doesn't want it to fail after a week or two, just because he saved 12$ in parts while repairing it.
I have a whole cabinet of old gear, I experienced this many times first hand.
You are right about the risks of a beginner doing soldering work, but that is not the point. He may do a good job just by practicing a few things as shown in many video tutorials, before going for the actual object. My kids, when about 8 years old, soldered small PCB kits in good quality, after practicing for about 10 minutes on my lap.Good quality like you get from China, if you are lucky. He may as well have no talent, refuse to practice and overestimate his personal skills, ruining this perfect looking, simple old mixer, but that is out of our reach. Just like him ignoring the need for correct tools and material or confusing wires and capacitor polarity.
What helps, the mixer was done with "good" solder, so the usual "lead free" problems should not occur. As long as he uses leaded solder for the repair as well.
PS this is about all you will ever need to do a perfect repair on such a simple object. Just replace the solder for leaded quality. 20$ on Amazon
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Wow, quite a buzz I totally missed over here. Replacing the mentioned parts is fine for me. It's still something I was planning on doing anyways, so if the problems would persist afterwards, I'll take it from there. I'm using vintage leaded solder which works well... The soldering station needs an upgrade, but for this time it will do the job...
I haven't gotten around to even ordering parts yet, but I'll update on results here later. And regarding the quality of the mixer model and worthyness of fixing - I don't specifically put any personal value in it. This is all about fixing it as the friend (who's lacking any sort of technical knowledge) wants to sell it. Noise floor or not, people are still nuts about these vintage rotary mixers...
Thanks everyone!
I haven't gotten around to even ordering parts yet, but I'll update on results here later. And regarding the quality of the mixer model and worthyness of fixing - I don't specifically put any personal value in it. This is all about fixing it as the friend (who's lacking any sort of technical knowledge) wants to sell it. Noise floor or not, people are still nuts about these vintage rotary mixers...
Thanks everyone!
If you want to sell it, a repair my look different. I would not replace the worn out RCA's (look close at the plastic inside) with golden ones, but get silver colored. A buyer may not like the "non original" gold plating.
Whether a buyer will like and honor high quality capacitors, like Panasonic, may depend. Anyway, if you can't solder as good or better than it was from the factory, amateurs work will devalue the object close to zero, working or not. I, for example, never buy anything with repairs visible, except for a few $ to use parts or the case. I don't think that amateur work will get you more money for it (or for your friend) than in the current state.
Whether a buyer will like and honor high quality capacitors, like Panasonic, may depend. Anyway, if you can't solder as good or better than it was from the factory, amateurs work will devalue the object close to zero, working or not. I, for example, never buy anything with repairs visible, except for a few $ to use parts or the case. I don't think that amateur work will get you more money for it (or for your friend) than in the current state.
I think I may have undervalued my own skills in the initial post, I am quite confident with soldering, so I don't view that as an issue. I've repaired and re-sold many objects successfully before, mostly locally to DJs (like I am myself), and I don't see why this wouldn't be doable with this one. Better repaired and re-sold than laying to rot in my friend's wardrobe.