Shure M62V Level-Loc Repair Questions

Hey all,

Just got this box and it had a 9v to DC jack (like for a guitar pedal wallwort) adapter connected. I then connected the wires directly from that wallwort adapter to the locations in the circuit where the battery wires were. It _had not_ passed or generated any signal when engaged prior to now. The signal passes through without issue when in bypass. When I did this mod and engaged the compressor, it made an oscillating to stabilizing squeal type of sound and passed no signal from the input microphone. The sound persists with the input gain at any level including zero, with no change in amplitude.

Any ideas of what this sounds like it could be?

Thanks very much in advance.

Mark

Here’s a link to the manual and schematic in case this helps!

http://www.freeinfosociety.com/electronics/schematics/audio/shurem62v.pdf

Thank you,
Mark

Bump to you kind souls who might help me make sense of this  ;D

The battery deal is a bit confusing.......
??

That unit is a cheap peice of crap, dont waste time on it.

scott2000 said:

The battery deal is a bit confusing.......
??

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Thanks for replying. What I don’t know is if, when using a dc plug like you would use on a guitar pedal, does that supply more voltage or current than a 9v battery would? So am I potentially putting too much power in it? The output right now sounds like a walkie talkie squelch sound - not white noise but like a saw tooth oscillator moving a bit then settling on a frequency. Almost like a metal detector sound or something.

I’m in my first year of taking my electronics understanding from general to much more in depth, so what would a more experienced person test next to help solve this riddle?

radardoug said:

That unit is a cheap peice of crap, dont waste time on it.

Click to expand...

I’m a mixer and I know exactly what role and sound I want from this. Cheap or shitty isn’t my concern. It would cost me money and time to build a clone and I’d rather hear the original if I can get it working.

Thanks much,
Mark

MrG said:

Thanks for replying. What I don’t know is if, when using a dc plug like you would use on a guitar pedal, does that supply more voltage or current than a 9v battery would? So am I potentially putting too much power in it? The output right now sounds like a walkie talkie squelch sound - not white noise but like a saw tooth oscillator moving a bit then settling on a frequency. Almost like a metal detector sound or something.

Click to expand...

I'd have to read up on it more so don't have an answer this minute....... It almost seemed to me when glancing that the aux input should be 28V......and that the 9v battery supply should be disabled when using it........ but that would mean you are wiring in 9v where there should be 28v??? then there's that battery eliminator deal??? Like if you want to use an ac current??

Hopefully someone can chime in ... I'll look further to see what the heck I'm talking about....

scott2000 said:

I'd have to read up on it more so don't have an answer this minute....... It almost seemed to me when glancing that the aux input should be 28V......and that the 9v battery supply should be disabled when using it........ but that would mean you are wiring in 9v where there should be 28v???

Hopefully someone can chime in ... I'll look further to see what the heck I'm talking about....

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Thanks again. I’m actually going in the battery inputs - so i clipped the 9v battery leap “pad” and soldered a female dc guitar pedal wall wort cable to the battery input locations. I took red to red and black to black, but maybe would the color coding on the dc walleort power plug be backwards, and could that matter?

Thanks,
MG

MrG said:

would the color coding on the dc walleort power plug be backwards, and could that matter?

Thanks,
MG

Click to expand...

Yes it would matter....that would mean some nasty happenings I'm sure since the bypass is just in to out , no circuitry but, not certain what's up.....


make sure to test polarity if you're thinking about it....

Its designed to run on the battery at 9 volts. There is a 10K resistor in series with the input socket. You could remove this resistor and feed 9 volts in across the battery terminals. Polarity is important. The 9 volt supply needs to be very well filtered and provide a reasonably accurate 9 volts. Lots of plug packs wont be suitable. Let me know how many hours you spend on it, and whether it was worthwhile in the end.

radardoug said:

The 9 volt supply needs to be very well filtered and provide a reasonably accurate 9 volts. Lots of plug packs wont be suitable.

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Good point..... Could he plop a cap in there somewhere???

radardoug said:

Its designed to run on the battery at 9 volts. There is a 10K resistor in series with the input socket. You could remove this resistor and feed 9 volts in across the battery terminals. Polarity is important. The 9 volt supply needs to be very well filtered and provide a reasonably accurate 9 volts. Lots of plug packs wont be suitable. Let me know how many hours you spend on it, and whether it was worthwhile in the end.

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Thank you very much for your insights. So you mean a 10k resistor in series on the battery input? I’m assuming it’s safe to surmise that a 9v battery is more stable than a plug pack, which I didn’t know - is this correct? I’d be happy to just feed it batteries if that solves this issue.

How would you recommend filtering and stabilizing a plug pack? Is there another method you’d recommend instead of either?

Thanks,
Mark

First of all: it is a hundred years old, and cheap when new. Squealing suggests the power supply capacitors are past their peak freshness.

Not-knowing the polarity of things is a Real Problem. (At the start of my career I was stalled 3 months when red/black did not mean what I thought they meant-- I do the dumb thing less often since then.)

The 28V feed has a resistor in it which will drop the voltage. The current demand is not on the sheet, but a quick look-over suggests 0.5mA here, 1.2mA there, maybe 2mA total. 28V through 10K at 2mA gives 8V, so the quick guess is not wrong. You remove the battery because occasionally a battery getting "charge" will leak-out, especially since you will forget it is in there.

PRR said:

First of all: it is a hundred years old, and cheap when new. Squealing suggests the power supply capacitors are past their peak freshness.

Not-knowing the polarity of things is a Real Problem. (At the start of my career I was stalled 3 months when red/black did not mean what I thought they meant-- I do the dumb thing less often since then.)

The 28V feed has a resistor in it which will drop the voltage. The current demand is not on the sheet, but a quick look-over suggests 0.5mA here, 1.2mA there, maybe 2mA total. 28V through 10K at 2mA gives 8V, so the quick guess is not wrong. You remove the battery because occasionally a battery getting "charge" will leak-out, especially since you will forget it is in there.

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Thanks for this PRR. I’ll look into the caps.

Regarding your last paragraph, so you’re saying that tha guess of 9v working in this circuit is a reasonable one? In other words, you think my approach of using a wallwort 9v supply is an acceptable approach? Any suggestions on how to filter it?

Yes, I’ll check those leads. And hopefully I’ll find I’m wrong!

Thanks,
Mark

MrG said:

Regarding your last paragraph, so you’re saying that tha guess of 9v working in this circuit is a reasonable one?

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The circuit runs on 9v. The 28v option is dropped using a resistor to get to the 9v if you went that route.....so yes, reasonable... I think I read some guys try to mod/run it higher like 12v  but the benefits???I don't know....... I don't even know if I read that now that I'm thinking about it.....

Wall warts are used all the time .......

Some can be made differently, some noisier  than others, and they can get old and hokey too so,  after you replace  the  caps in circuit , if you still have problems, maybe check a different wart.....??

and do make sure it's rated for at least the couple of ma....which is tiny ....

There are lots of articles out there about filtering a wall warts....maybe look around and post ideas you have to get some input??? I'd be interested in this.....

....... I used a cap to ground one time for some tube heaters being powered from a wart as recommended to me and it worked pretty well...... but not sure it's relevant...

Hopefully you don't need to change the leads.....

_I_ would use a battery until you get the howling resolved.

For all we know it is your "wort" which squeals.

Ah yes, the old squealing wart... 

Good news: I took voltages last night and indeed the colors of the DC plug lead were wired backwards - black for hot, red for cold! Switched them and voila, it’s alive!!!

The power seems to be steady and clean. It’s a Korg 9v 600ma brick. I’d be happy to hear any critique of that thinking.

I’m happy also because I considered the polarity of the power after only several days of being stumped. Next time I’ll know to verify this right away!

FWIW, the box seems recently recapped and the aux out at line level is very quiet. I’ll be destroying drums in no time. (Don’t hate me, I’m actually an old school big tone freak)

Question regarding one mod I may do and the theory behind it:

Regarding impedances versus resistances when it comes to resistor pads, if the Level-Loc wants to see mic input at ~150 ohms, and I want to pad line level down to use this like that, I’m considering adding like a 3.3k resistor to get about 30dB padding. But re impedances, would this mean the input effectively is seeing an unhealthily high source impedance? Or does the source see a more healthy (approaching) bridging impedance?

Thanks so much in advance,
Mark

Ha!  I remember buying an MXR Distortion+ for 25 cents at a flea market.  Took it home and of course it didn't work.  Replaced the chip, caps, and damn near every other part before realizing that someone before me had replaced the 9v snap and got it backwards!  :

Regarding the input, do you have the manual?  I believe the high impedance setting on the back bypasses the input transformer and gives you a bridging input.

mjrippe said:

Ha!  I remember buying an MXR Distortion+ for 25 cents at a flea market.  Took it home and of course it didn't work.  Replaced the chip, caps, and damn near every other part before realizing that someone before me had replaced the 9v snap and got it backwards!  :

Regarding the input, do you have the manual?  I believe the high impedance setting on the back bypasses the input transformer and gives you a bridging input.

Click to expand...

Glad I’m not alone in this!!!

I do have the manual. It seems it’s just a 50k mic input, which accepts a microphone output up to 10v.

I’m more interested in a line input level signal, approximately 150 ohms coming from my D/A, being bumped down to work with this box. Would a 3.3k ohm resistor work? Approx 30dB?

Thanks!
Mark

Close, the 50k input accepts signals *from* microphone level *to* 10v.  I don't know of a mic that can put out a 10v signal, so that would be line level.  Then use the input level control to adjust.