Quantum Audio QM 22/20 Questions

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Michael A

Well-known member
Joined
Mar 9, 2006
Messages
67
Hi All,

I picked up a Quantum QM 22/20 broadcast/production mixing desk today sans power supply. Can anyone give me any info on the voltages and pinouts I would need to replace the power supply? The connection appears to accept some sort of ribbon wire connector.

Any other info and opinions would be welcome too. This board uses QM-2201 channel strips. They have 75101-1 input transformers. I'm guessing these are Cinemag units. Seem right? Opamps are mostly NE5532N and NE5534N. Faders are Penny and Giles type PGF.

I can provide other information on the physicals if you wish.

Thanks,
Michael
 
I forgot the other important question. Is it worth building a power supply for or should I just consign the good bits to the parts bin and chuck the rest? I guess in a sort of sentimentality for older equipment I forget to ask that one a little too often.

Thanks,
Michael
 
I'm probably going to part my 8 channel quantum board out, mostly for the cinemags. I don't know too much about it though, just that it's noisy and several channels don't work. I'd rather have the iron for my API 312 clones.

Anyway, we're talking about different models.
 
Any idea the cause of the noise? Does yours have the same QM-2201 channel strips? Does it have an external power supply? If so, could you pass along the voltages and pinouts?

When I was searching for info here I noticed the inputs could be used for the API 312 project. I must say that is a consideration too.

Thanks,
Michael
 
Sorry, no extrenal PSU on my board.

It's also not a modular design, probably not the same channel strips.

I don't really know too much about it, it' spent most of it's life in our storage closet.

You could try Dave Hecht's forum, I think some folks over there might have experience with Quantum stuff.
 
[quote author="Michael A"]I picked up a Quantum QM 22/20 broadcast/production mixing desk today sans power supply. Can anyone give me any info on the voltages and pinouts I would need to replace the power supply? The connection appears to accept some sort of ribbon wire connector.

Any other info and opinions would be welcome too. This board uses QM-2201 channel strips. They have 75101-1 input transformers. I'm guessing these are Cinemag units. Seem right? Opamps are mostly NE5532N and NE5534N. Faders are Penny and Giles type PGF.

I can provide other information on the physicals if you wish.[/quote]

I used a similar board at Channel Nine -- in fact, I specified it. Very decent-sounding, and I made some nice recordings on it. I'd try to clean it up and use it.

I don't know exactly what the supplies were, but if you started with +/- 16V plus phantom you'd probably do fine. Do these have discrete transistor output boosters?

Also, what does the board use for EQ amplifiers? Some Quantum boards used 4136 quad opamps, which had a non-standard pinout; I used to replace them with TL075s, which had the same weird pinout. Much better sound.

Peace,
Paul
 
So, I guess I will try to figure out a minimum power supply. I think there are a bunch of pins on the input, but I haven't taken it apart far enough to see if they are all active or if the outputs are transistor boosted for that matter.

The IC's in the strips are all socket mounted and the equalizer section has the TL075CN part. So I can't really say if they were original or have already been replaced.

On a side note I took my other board, a Ramsa WR-DA7, out this weekend and did my first live multi-track recordings at a local festival. This pointed out my continuing need for 8 channels of mic pre for my MOTU 2408 analog inputs. Maybe this will ultimately live on as those 8 discrete channels in a small mainframe. Any opinions on that idea?

Thanks,
Michael
 
Well, I've got all the modules out and parts of the mainframe apart. I don't see any transistor output boosters. All of the outputs are transformer coupled. The output transformers are labeled 7393PC. Any idea who might have made these?

Phantom appears to have been an option. The input connector boards have traces for it and there is an empty hole in the back panel for each pair of input channels that was probably for a switch. There are no resistors installed, except for two channels that were labeled "KM84" with grease pencil on the outside.

I'm fairly confident I have correctly located the input pins for the pos and neg rails and the ground. Also the phantom.

There is another pin on the power input connector that connects to one or two pins on the channel strips and output boards that I haven't figured out. There are CD4053BE parts that are multiplexers or switches on all of the boards. Could these be the control voltage for these?

Also there is a button labeled start on each strip and a connector on the back panel that is labeled "remote start" so I suppose there was some sort of TTL trigger voltage there. Another couple of power connector pins come in to test points on the main buss board, but I can't find out where they go from there.

In any case, I think I know enough now to get power to the opamps. So is +/- 15V the suggested supply? Hopefully I will get signal to go somewhere and then I can figure out the other parts.

Sorry for the long ramble.

Thanks,
Michael
 
Somewhere in the back of my mind I recall +/- 16V as the supply voltage. Even if it isn't, it'll work fine.

What part of the country are you in? This sounds like it might be my old board from Channel Nine. Although they very seldom let anything escape.

Peace,
Paul
 
Paul,

I'm up in Iowa. The board was last used in a college radio station. I don't know what it's history was before that. Everything appears to be in good shape with it. There might have been a few mods for monitor outputs. But I guess I don't know anything about it really until I can get it to pass a signal.

You wouldn't have any idea if the multiplexer part needs power to get the signal onto the buss, would you? That would complicate my plans a little.

Thanks again,
Michael
 
I dug through some of my pile of junk last night and came up with a small Lambda linear power supply with +/-15VDC output. Plugged it onto my selected inputs on the board and the voltages were on the right pins of the ICs.

So this morning I put it back together enough to get a mic plugged in and the output channels. Connected it to my MOTU A/D and on to the monitors. Seems to be absolutely quiet. With no input and both strip and output fader set to 0 dB the noise floor is everywhere under -100dB. Changing the strip fader makes no change and moving the output fader to max shows -90dB or lower. Mind you that is with only one channel strip installed.

Sounds very clean as well. And the VU meter works. So now I guess I need to figure out what I ultimately want to do with it.

Michael
 
I've not built a power supply for SS equipment before, so I could use some help/advice/suggestions here.

I put an ammeter in the positive leg of the Lambda supply I was using to test with and found that the output strips use 150mA at 15V supply. The channel strips measured 67mA each. That gives a total of 1.3A. Seem in the ballpark?

I dug into my junk box again and came out with a transformer that has dual 20-0-20 secondaries rated at 2A each. I also found some LAS15U and 18U adjustable pos and neg voltage regulators that are rated at 1.5A. Would these be parts suitable for use here? Is there a better regulation scheme to use here? I also have a small variac I could use in front of the transformer to lower the dc output from the rectifiers and lighten the load on the regs, but I would prefer to avoid using it if possible.

Also I need 24V (AC or DC?) to run the indicator lamps and 48VDC for the phantom. Could I use two half wave circuits on the other secondary to give me these?

I have a pretty big junk box, but very little cash so I would prefer to work with the former and not the latter.

Thanks,
Michael
 
Well, you could use the Lambda for the audio circuits and just build a 48V supply...

But that transformer should work. Build a full-wave center-tapped rectifier on one winding, and you'll get about 25.8V nominal, 23V when the wall voltage is -10%. Build a 2-stage supply with a 2.7 ohm 10W dropping resistor -- give it lots of air -- and use a couple of LM317/337 regulators for each leg, maybe one for the channel strips, one for the outputs. Set their outputs at 16V. Use TO3 packages and heatsink like crazy. At +10% line voltage your first filter stage will be at 28.6V and your second stage at 24.6V so each regulator will be dropping 8.6V worst case.

Use the other winding for a full-wave rectifier, no center tap. At -10% wall voltage your DC should be about 48.4V, not leaving much room for regulation. You could use Shottky diodes for less drop in the bridge, or you could use a TL783 set to 46V, which is well within the tolerances for phantom supplies and leaves you enough slop room for staying in regulation even with low wall voltage. Or you could do both.

Peace,
Paul
 
Paul,

Thanks for your nicely worked out example. So if I understand this correctly, what I want to do is size the resistor such that at my specified low line voltage (-10% in your example) and maximum current draw the input to the voltage regulator would be just above it's dropout voltage. And at high line voltage and minimum current draw the input voltage to the regulator is such that it is still within power dissipation limits. I think the LAS parts I mentioned are very similar to the LM317/337. Not quite as good on the regulation, but still 1% or so.

Did the current use that I measured seem ballpark? The Lambda is only rated 0.5A on the 15V outputs so needless to say I was very disappointed when I measured the current that one strip and the outputs was using. I'll try it again just to be sure I read it right. I've only built tube circuits in the past and half an amp goes a long way there.

For the phantom and lights, will the suggestion I had work or is that a no-no. I calculate the light at around 0.8 amp/24V at the maximum.

Off to record the last concert of the season at the downtown mall.

Thanks again,
Michael
 
[quote author="Michael A"]Paul,

Thanks for your nicely worked out example. So if I understand this correctly, what I want to do is size the resistor such that at my specified low line voltage (-10% in your example) and maximum current draw the input to the voltage regulator would be just above it's dropout voltage. And at high line voltage and minimum current draw the input voltage to the regulator is such that it is still within power dissipation limits. [/quote]

More or less, yes, but you also need to check what happens at maximum current draw and high line voltage. That's where the worst stress on the regulator will happen.

I think the LAS parts I mentioned are very similar to the LM317/337. Not quite as good on the regulation, but still 1% or so.


The thing about LM317/337 is that, properly implemented, they have a nice low output impedance, which ICs really care about. One thing that occurs to me, though: are there regulators inside the Quantum, either on a regulator card or on the individual cards? If so, then you want to present them the right voltage so *they* won't drop out, using the same calculations as above.

Did the current use that I measured seem ballpark? The Lambda is only rated 0.5A on the 15V outputs so needless to say I was very disappointed when I measured the current that one strip and the outputs was using. I'll try it again just to be sure I read it right. I've only built tube circuits in the past and half an amp goes a long way there.

Yes, it seemed reasonable if I remember it right.

For the phantom and lights, will the suggestion I had work or is that a no-no. I calculate the light at around 0.8 amp/24V at the maximum.

I think it might be worthwhile picking up a Radio Shack 24V transformer (or looking for one in the basement) and running the lights on AC, assuming the wires don't go anyplace near the low-level signal wires. Pulling another supply, 0.8A at that, out of the same transformer you're using for the phantom supply strikes me as not a good idea.

Peace,
Paul
 
Got the supply mostly done. I'd post a pic, but the procedure is frustrating me again. Anyway, I have regulated +/- 15 at the moment. It is adjustable. There is also regulated 24VDC for the lights. But the lights are working now without it being connected, except for the VU meter lights. So I am confused about that and don't want to add the 24V until I figure out what is going on since 24V is over the rating for about everything in the strip. The phantom winding is there, but I didn't put in the rectifier/filter or regulation. Since I have to add resistors and switches to get phantom going anyway I figured I would wait until that is done for a few channels.

Now another problem appears though. Channels 1-8 have lots of gain. Channels 9-16 seem to be 20 or 30 dB down from that. If I were a suspicious person I would see a pattern here and suspect someone has added pads to those channels. I've only tested the mic inputs.

Seems quiet still. Haven't gotten much further.


Michael
power%20supply%20resized.jpg

edit: Think I got the pic to work
 
In absence of anything better to do this evening I made a few measurements of the 26/20. I used Rightmark Audio Analyzer software and did the A/D and D/A with a Motu 2408 Mk II at 24 bit and 48kHz sample rate. Mostly I was interested in a look at the noise floor. This is from the line input. I have to make a pad to test the mic input as the signal is too hot even at minimum gain setting on the trimpot. Channel faders and Master faders are both hovering around the 0 mark. All other channels are muted.
Noise%20spectrum%20line%20in%20Channels%206-7.jpg


I haven't quite figured out how this program works as far as the dB scale goes. I measured the output voltage from the Quantum board during the 1kHz THD test signal and it was 2.8 Vrms. The program considers this to be -3dB full scale. So I guess that means that 0 dB on the graph is 12dBu. Anyway, the programs says this is 0.010% THD and 0.013% THD+ noise (unweighted).
THD%20at%201kHz.jpg


So what do you folks think? Only numbers and pictures, I know. I'm hopefully supposed to have a female vocalist and acoustic guitar in next week. So I guess I will see how it sounds then.

Michael
 

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