Bench testing setup for console modules

Hey,

I'm starting to work more often with different console modules which are sent to me and I would like to workout a good way to test them on the bench as far as audio I/O and power connection.

What would be the best approach for this? attaching connectors to the IDC cables? Are the IDC cable pinouts universal for each console brand?

I would appreciate any tips and suggestions.

Thanks for your time

It is not simple... First you must provide the appropriate PS voltages.

You can do simple troubleshooting by injecting signals into inputs of a powered module and following them with a scope, but to perform comprehensive testing you need to set up a dedicated test fixture, perhaps even connected to a master section and other strips. To confirm that the bus sends are working properly and to spec.

Chasing down subtle faults are best done using an extension cable with the subject strip plugged into the actual console.

JR

Hey John,

thanks for your reply.

I completely understand the fact that the channel strip should be tested in the original environment. I was just looking for some beginner tips on powering them and testing stand alone units. Something that will make my work easier.

Well designed console strips may add extra parts to not go crazy in a test environment.. but it's an extra cost unappreciated by customers. 

You need to inspect the schematic for the console including the strips that will be receiving signals sent by the strip.

Some external logic signals (like solo-pfl) need to be provided from external sources.

I can imagine a different fixture for each strip...

JR

A different fixture for each channel strip sounds good (pretty much required, given the range of connectors and the like), but I'd also like to put a vote in for a 'lab type' power supply that can provide whatever voltages you need along with an accurately settable current limit. This is useful so that you can prevent things from going really wrong, by setting a predictably 'reasonable' current limit on the power supply rails. These supplies typically provide a readout of the actual current consumed by the load, so you can see what your module is doing, see if it's preparing to 'launch' from excess current consumption, and see if it's within your expectations of how much current it's supposed to be drawing.

You still have to do some thumbnail engineering to determine what the chips (or circuits) in the module are supposed to draw, but that's part of verifying a module anyway. If you set your conservative limit a little too low, there's no harm, but you avoid the possibility of 'blasting out' a somehow defective module with excessive power supply current.

I'm fond of the HP/Agilent bench supplies, but there are a wide range of offerings out there, and I think they're worth it, not only to generate exactly the voltages you need, but also provide precisely settable current limits.

Thanks Monte,

A good bench PSU was something that I really needed, and just today I picked up a Thurlby Thander PL330DP dual PSU with current limiting for relatively cheap. What do you think about it? 32VDC should be sufficient for most solid state audio circuits.

Apart from that I do have a function generator, a Fluke DMM, Hitachi Oscilloscope and thats about it. I would love to invest in Lindos analyser along the way, possibly the little MS10/20 would be enough for now. I would like to do some testing when upgrading op amps/caps in the modules. I used before the RightMark analyser but I guess it can't compare with a stand alone dedicated device.

btw. as I'm still very much learning anyone has any good tutorials/books/websites on troubleshooting and repairing audio circuits? I know that nothing can substitute years of actually getting your hands dirty but I'm just looking for some general tips and guidelines.

Cheers

15+ years ago, I wandered into doing "custom racking" of console modules:

http://brianroth.com/custom/custom.html

I have since "wandered out" of that universe, since many other folks also had the same idea and pricing for our time became a "race to the bottom".  I decided that McDonald's pay/hour wasn't my cuppa tea.

However, I can throw in my 2 cents...

I built up a variety of edge/whatever connector harnesses for testing stuff on the bench.  Bench power??  A Heathkit I build back in the 1980's.  Bipolar (like me...ahem..lol!)  up to +/-20 VDC.  In series with the rails were simple inline fuse holders in case of a serious "oops" that wasn't obvious with simple Ohm meter testing.

Bri

thanks Brian,

I guess I will be making the connectors as I go along, after some time I should also get a nice collection that will cover most consoles.

I was also interested in racking strips, however I don't have any machining tools so it would be difficult for me. By now I need to grasp all the electronics side of things.

My new 32V 3A dual PSU just have arrived, unfortunately the seller with good intention packed it up in loads of polystyrene bits that have all crumbled up and stack to all the insides, so I have spent an hour just cleaning the thing. Initially the voltage output on the left channel was climbing very slowly but with load on it seems to be more responsive.

I have some untested and faulty Soundcraft Ghost channels lying around so I can start working on them straight away!

Ok, so I'm a little stuck with making the harness for the Soundcraft Ghost strips. I have the pinout, its just how to actually wire everything. I would like to be able to have control over mute and solos, ability to test the mix bus and obviously to power the strips.

Could you please confirm the following:

+17V - PIN 27,29,30 - tied together going into the positive output terminal 1 of the PSU
-17V - PIN 35,36,37 - tied together going into the negative output terminal 2 of the PSU
Earth - PIN 31,34,38 - tied together and split into two connectors going into earth terminal 1 and 2 of the PSU
Mix L/R - PIN 9,10
Solo - PIN 11 - ?
Mute - PIN ? - ?

I don't know if I'm missing anything for the main connector. I can't find the mute signals on this pinout. And I have one Solo signal, how do I activate/deactivate it?

Any help would be much appreciate!

AFL/PFL systems involve both an audio bus "and" and a logic bus so you can communicate status from a button press from the strip to the master section.

To fully test every aspect you need to replicate that external circuitry and connections (perhaps wire up a master section, perhaps a send return modules . )  Different consoles will require different hooks.

JR 

Thanks John,

Ok I understand.  Anyway I would like to start with simply powering the channel up and checking all the DC supply path, then the audio, and then I will try to figure out the rest.

Any comments on the above pinout?

Cheers

Aniol1349 said:

Any comments on the above pinout?

Cheers

Click to expand...

It looks like an edge connector,,, but you really need to looks at the schematic for the channel, and the other modules to really understand what is required to fully test everything.

I think I mentioned in one of my earlier posts, some designs will be more bench friendly and not go crazy without every connection properly terminated, some can do unexpected things.

You can connect power and look for smoke and do some basic debugging but be very careful about making ASSumptions about how it should behave, some path may be missing.

good luck you will definitely be smarter by the time you finish.  ;D

JR

Aniol1349 said:

A good bench PSU was something that I really needed, and just today I picked up a Thurlby Thander PL330DP dual PSU with current limiting for relatively cheap. What do you think about it? 32VDC should be sufficient for most solid state audio circuits.

Click to expand...

That supply looks very good - easily on par with the HP/Agilent stuff I'm more used to. The noise specs etc. seem very good, and it has all of the standard high end bells and whistles. 32V will be sufficient, and the only situation I've run into where more voltage is needed is the case of some older McCurdy modules that use a single 48V supply. To handle that, you can stack two channels of your supply together to get a 64V maximum, since the two supply channels are isolated.

All the best!

Aniol1349 said:

I guess I will be making the connectors as I go along, after some time I should also get a nice collection that will cover most consoles.

Click to expand...

I think that would be really hard, there's so many different desks, models, brands  and connectors that I dont think you will be able to have in stock test gigs for "most of the consoles" . Also that would be really expensive and time consuming.

As for the PSU,
your PSU looks great but you will need another PSU with more rails.
you will need at least a  48V rail, and one more negative and one more positive variable voltage rails. You can DIY a simple PSU for that with  this pcb:
https://pcbgrinder.com/index.php?route=product/product&path=59_73&product_id=98

for example a Studer 900 series module will need:
+15
-15
+48
-5
-24

Thanks for your reply Whoops,
I was perhaps a little over ambitious with this sentence

You are right about more rails I have possibly overlooked the fact that some consoles run on more than two rails, and I didn't take in account the phantom power also.

Thanks for the link to the varipsu, I can't seem to find any info about it, is there a thread for it here on the forum?

Whoops said:

Aniol1349 said:

I guess I will be making the connectors as I go along, after some time I should also get a nice collection that will cover most consoles.

Click to expand...

I think that would be really hard, there's so many different desks, models, brands  and connectors that I dont think you will be able to have in stock test gigs for "most of the consoles" . Also that would be really expensive and time consuming.

As for the PSU,
your PSU looks great but you will need another PSU with more rails.
you will need at least a  48V rail, and one more negative and one more positive variable voltage rails. You can DIY a simple PSU for that with  this pcb:
https://pcbgrinder.com/index.php?route=product/product&path=59_73&product_id=98

for example a Studer 900 series module will need:
+15
-15
+48
-5
-24

Click to expand...

If you think that's bad try making a jig for MCI 500 which can need &-36v, +&-32v,+&-24v, +&- 15v & 5vto test full functionality......
Yikes.

I did some testing on a DDA Q2 master module recently and its much easier just to hook up the power through the current limiting resistors.

What about testing each bipolar rail separately?

Aniol1349 said:

I did some testing on a DDA Q2 master module recently and its much easier just to hook up the power through the current limiting resistors.

What about testing each bipolar rail separately?

Click to expand...

You can do some preliminary troubleshooting without all PS but just applying a + rail without the - rail could cause unexpected behavior.

Proper testing requires all rails and expected terminations for buses, logic signals, and the like.

JR

You can do some preliminary troubleshooting without all PS but just applying a + rail without the - rail could cause unexpected behavior.

Click to expand...

Sorry my bad, I meant each pair of rails not each rail.

But yes I understand that basically to test everything properly I need to have my modules plugged into the actual console.

Aniol1349 said:

Hey,

I'm starting to work more often with different console modules which are sent to me and I would like to workout a good way to test them on the bench as far as audio I/O and power connection.

What would be the best approach for this? attaching connectors to the IDC cables? Are the IDC cable pinouts universal for each console brand?

I would appreciate any tips and suggestions.

Thanks for your time

Click to expand...

There is nothing common between console manufacturers as far as pinouts are concerned. Everyone did what suited themselves best for their particular product design. Within each console manufacturer there is seldom commonality between connector pinouts. The only place you are likely to get commonality is within a specific product type/range. It's all down to convenience and module facilities.

It's only worth building a specific test jig if you are going to be testing "N" number of a particular type of module, and preferrably on a regular basis to get long-term use/payback out of the test jig, where "N" is the tipping point between efficiency and the irritation of swapping and plugging numerous wires (and likely getting the odd one wrong and wasting time chasing non-faults).

This is a test jig that I have designed to test the Neve VR Equaliser sub-assembly. It is but one of a range of test jigs that are used in my business to make the job more efficient and repeatably accurate.
http://www.cmlaudio.com/ie1324-neve-vr-eq-ev11491-test-jig/#Images
In reality it is a very simple test jig that only does signal routing in and out of the EQ assembly and provides protected power, the point is that it enables efficiency and ensures repeatability.

Console channel test jigs are a bit more complex in that to do it properly and fully, you would need to simulate the interactions with the rest of the console, including:
Mix/sum outputs (auxes, groups, main, pfl, afl).
Control/logic (pfl, afl, solo). The more complex modules may have central command for mic/line switching, aux pre-post switching, fader swap, etc, etc.
The intereactions need to be accounted for as a 2-way street: If you press SOLO on the module under test, what does that do to the rest of the console, and likewise, if SOLO on another module is pressed, how does it affect the module under test?

Accurate documentation for the module under test is essential. If you are just starting out on this adventure, and with respect this line from your opening post suggests you are, "Are the IDC cable pinouts universal for each console brand?", then don't underestimate the value of the console tech manual. Even after 33+ years of audio electronics putting food on my table I will not work on a console (or individual modules) unless I have the schematics...... customers are not prepared to pay workshop rates for me to decypher and reverse engineer a module so as to fix a fault. For example, 4 hours or more of decyphering to do a repair that with the schematics would take no more than an hour is a model for business failure and customers feeling ripped-off.

Hope this helps by shedding some light from another perspective.

Gareth.