Double Bass Canary 16/2 mixing console for preamp

[Big Nyz]

Hello all!
Greetings from Finland. We have -22celsius outside so I´m spending my days inside soldering...

I posted in the Simms-Watts-thread about half a year ago, asking about a rare power amp modelled "Simms PS500". I am planning on using this as a bass head amp. Now, I could buy - or build - a preamp for it, but for experimental and learning purposes I would like to try to salvage an inlet strip and the main part from a mixing console I have laying on the floor right now.

It is a Canary 16/2 mkII, an English make, and it looks like this:

Like the Simms PA-head, this also seems to be a rare breed with little info on the Internet. The power jack confused me for a while, but then I found this pic of a similar 10/2 desk:

I removed the XLR-jack and mounted a standard jack, like in the picture above. It fitted exactly and it was clear that the desk had one of those originally.

Then I got stupid and plugged it into the wall. It blew the safety and the diode bridge and two resistors inside burned.

Now, do any of you know how this thing should be powered? It obviously needs a transformer...
There is no phantom power. As I said, there is a diode bridge inside coupled with a 2000uf capacitor, but nothing that resembles a transformer.

I don´t have any money in the desk, I´m just trying to wrap my head around it. I like to build and fix things and the idea of recycling stuff gets me going.
I would be very grateful for any input in this matter!

Best regards,
Mathias

 

[DoubleMIDI]

You might follow the connections from the rectifying diodes to a voltage regulator or if there are none and no Zener-diodes to the opamps, get the data sheets and you should know the voltage and go back to decide which AC input voltage you need.
I'm afraid there are more components damaged by the high voltage than you can see...

 

[Big Nyz]

You might follow the connections from the rectifying diodes to a voltage regulator or if there are none and no Zener-diodes to the opamps, get the data sheets and you should know the voltage and go back to decide which AC input voltage you need.
I'm afraid there are more components damaged by the high voltage than you can see...

Hey DoubleMIDI, thanks for the response!
I´m afraid so too... But I hope the damage is only on the main card, which is not that big.

The scenario looks like this:

There isn´t anything that should be regulating voltage before or after the diodes (you can see them right in front of the big capacitor). No more diodes after the bridge either, only resistors, kapacitors, IC-circuits, and power transistor.

I was hoping maybe somebody here have the scematics for it, or maybe even personal experience from using it?

 

[DoubleMIDI]

I'm afraid this is the wrong site for asking that kind of questions. Of course you can try, but don't be too disappointed if you don't get here what you were wishing.
Most opamps use +/- 15 volts, but check the numbers on the ICs and get the data sheets. Often they could be used in a certain voltage range and other parts might determine the voltage needed. Also check the bigger electrolytic capacitors for maximum voltage. Usually the real voltage is below that, not reaching the maximum.

Good luck reviving your desk.

 

[Big Nyz]

I'm afraid this is the wrong site for asking that kind of questions. Of course you can try, but don't be too disappointed if you don't get here what you were wishing.
Most opamps use +/- 15 volts, but check the numbers on the ICs and get the data sheets. Often they could be used in a certain voltage range and other parts might determine the voltage needed. Also check the bigger electrolytic capacitors for maximum voltage. Usually the real voltage is below that, not reaching the maximum.

Good luck reviving your desk.

Ok, thank you very much! I will try to find a more studio-oriented forum then Good tip though about checking typed voltage range for the IC:s. At least the big capacitor says "35VDC", that much is clear.

Thanx alot, have a nice day!

 

[DoubleMIDI]

Get the data sheet for the opamps. If the rectifier + goes to opamp Vcc+ And the rectifier - goes to opamp -, then it could be 30 V at the rectifier output and 30V divided by sqrt(2) for the AC transformer output.

 

[Big Nyz]

Get the data sheet for the opamps. If the rectifier + goes to opamp Vcc+ And the rectifier - goes to opamp -, then it could be 30 V at the rectifier output and 30V divided by sqrt(2) for the AC transformer output.

Actually I already did, and things got much clearer! Found this for the opamp CA741E, which is the first one in the board layout:

Absolute Maximum Ratings Operating Conditions
Supply Voltage (Between V+ and V- Terminals)
CA741C, CA1458 (Note 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . 36V
CA741, CA1558 (Note 3) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44V
Differential Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30V
Input Voltage (Note 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _15V
Offset Terminal to V- Terminal Voltage (CA741C, CA741) . . . . _0.5V
Output Short Circuit Duration . . . . . . . . . . . . . . . . . . . . . . . Indefinite


And yes, the connections go exactly as you say... At least I know now 36v is the roof.
But I don´t understand the difference between "Differential Input Voltage", "Input Voltage" and "Supply Voltage"... ?

For example, does rectified 15V AC become +-30V DC? Or the other way around???

 

[DoubleMIDI]

Supply voltage is the is the voltage from the power supply.
Differential input voltage is the voltage between the + and - inputs to the opamp (signals to be amplified). I guess input voltage is the voltage to either + input or - input (signal inputs).

15V AC rectified becomes 15V * sqrt(2) = 15V * 1.414 = 21.21V DC (!)
30V DC / sqrt(2) = 21.21V AC (!)
36V DC / sqrt(2) = 25.46 V AC

So ideally you take 21V AC, should not exceed 25.4V AC. But with a low load the transformer might deliver a higher than the rated voltage, so better use a 20 to 22 V transformer, even a more common 18 V AC transformer may do the job.

But you still have to find out the current. If there is no power amplifier in there, a few ampere might be enough. If you have a transformer with a high ampere rating, you can connect it and measure the current. Multiply this by two and that current should be OK for your board if a lot of signals go through. But use the same voltage or scale the ampere with the changed voltage factor if you test transformer has a differing voltage than your final one.

BTW, the 741 opamp is a very simple and noisy one. Think about if it really makes sense to revive this board. Of course, you can change them to less noisy types (check pinout and voltage ratings), but that would cost money again.

 

[Big Nyz]

Ok, I did some studies and now I understand that I have to count the transformed AC *1.414 to get the correct DC. Damn, it´s so fascinating to learn new things, isn´t it

I opened up a tiny guitar amp to take a look at the trafo. I measured it with my multimeter and found out it gave 26V AC. That makes 36V DC. What surprises me about this is that on that board I found three capacitors marked 25V... The two big ones after the rectifier is marked 35V though.

The reason I noticed this is that yesterday I found, on my mixing desk, several 25V capacitors (All input plugs deliver signal through 25V 100uf capacitors). There is also another 25V cap on the "main" power supply board. I took this as a clear sign that I should not use a trafo delivering more than 18c V, but maybe not?

There is a power transistor, BD241A (it also got burned when I overloaded it with 230V), maybe it can give a clue about current? At least the spec sheet says "Peak current 5A":

Absolute maximum ratings
VCER Collector-emitter voltage (RBE = 100Ω) 70 V
VCEO Collector-emitter voltage (IB = 0) 60 V
VEBO Emitter-base voltage (IC = 0) 5 V
IC Collector current 3 A
ICM Collector peak current (tp < ms) 5 A
IB Base current 1 A
PTOT Total dissipation at Tcase = 25°C 40 W
Tstg Storage temperature -65 to 150 °C
TJ Max. operating junction temperature 150 °C

OK, so the 741 is not optimal... I understand they have a fairly standardized pinout? But actually I´ve been considering building something like a gainclone t oreplace this main board, and coupling it to on or two strips from this mixer to get a preamp wit h the possibility of running two inputs.

I see you´re from Germany, I like that! I´m from Finland myself, been over there a few times. I studied in Norway in the year 2000 and one of my best friends there was from Fulda. I actually visited him a couple of years later when I did kind of a trans-Germany rail trip . I had a period in my life that I fancied Wartburgs, so I wanted to make a pilgrimage to the city of Wartburg, first to climb up to the castle, then to visit the car museum. I even got to shake hands with the director of the Wartburg mudseum... was a great moment

Great people, you germans. I also took german lessons in the gymnasium and been using it every now and then since then. Wherabout are you living?
'

 

[DoubleMIDI]

I'm no expert in analog circuit design, I'm happy if I can understand some stuff. So don't ask me for the transistor. Together with the resistor on collector or emitter you might be able to determine the maximum voltage. But I think that would be higher than the maximum voltage you already found from the capacitor.

It depends how the 25V electrolytics are connected if they determine the maximum DC supply voltage. If they connect to the + and - from the supply rectifier, then that is the maximum. But two in a row (serial connection) from + to - would half the supply voltage for each. Could be to make a virtual ground for the signals.

I'm located close to Cologne. Lot of bass players over here...

 

[Big Nyz]

Every input signal xlr has three active pinuts: one is grounded, the other two signals to the strips, each over a separate 25v capacitor. That means, they are not in series but for separate pins into the strip board.

The other 25v capacitor is at the other end of the main board so it is not related to the rectifyer.

 

[DoubleMIDI]

The capacitors from the XLR just say no input signal above +/- 25V, which is rarely the case. But they should be bipolar ones anyway since the signal goes above and below ground. Anyway that doesn't mean anything for the supply voltage.

If a capacitor is just at the other end of the board doesn't't mean it is not connected to the power supply output. It could be there to buffer the supply voltage because (!) it is so far away from the power supply. But it also could have a different function, of course.
That's the problem ...
The standard for opamp supply voltage is +/- 15 V, sometimes 18V, sometimes 12V, very rarely 9V. I would try to find hints for one of them.

I have an old mixer desk (monophonic) with 741 opamps. There is more hiss comping out than signal. Might be useful for a punk band ...

 

[Big Nyz]

The capacitors from the XLR just say no input signal above +/- 25V, which is rarely the case. But they should be bipolar ones anyway since the signal goes above and below ground. Anyway that doesn't mean anything for the supply voltage.

If a capacitor is just at the other end of the board doesn't't mean it is not connected to the power supply output. It could be there to buffer the supply voltage because (!) it is so far away from the power supply. But it also could have a different function, of course.
That's the problem ...
The standard for opamp supply voltage is +/- 15 V, sometimes 18V, sometimes 12V, very rarely 9V. I would try to find hints for one of them.

I have an old mixer desk (monophonic) with 741 opamps. There is more hiss comping out than signal. Might be useful for a punk band ...

Tried changing out the 741?


I bought an interesting power supply unit today at a flea market:

It´s old and rudimentary but seems to work ok. I think the text on the cover is written in romanian. The interesting thing about it is that the secondary AC side has a "potentiometer" as you can see... I measured it and it leaves from 7,2V up to 18 Volts. It says only 200mA on the cover, but I figure I can use it for pedals supply. I think I will build a new diode bridge though, and maybe add a digital voltsmeter...

 

[DoubleMIDI]

I have a different older 12-channel stereo mixer desk, where most 741 opamps were changed except for two channels, I think they were changed to TL081, but I'm not sure about the type. I thought the 8-channel mono desk was a stereo one when I bought it used. Not worth anything then and now, I think.

The power supply you got might be useable for pedals, but simple power supplies can inject some amount of hum and noise into a pedal. It depends if there is some voltage regulation inside the pedal or not. Usually there is almost no regulation inside a pedal, because the battery delivers a clean voltage.

200 mA is definitely not enough for a desk. I assume something between 1.5 to 4 ampere.

But this is not the forum to discuss this. You can contact me by private message, this is of no interest to the bass community.