sonuus User Forum

Hello good people of Sonuus.

We at Stein-Time music are glad to have purchased this handy British product which works so well through a CME "MIDI to USB" converter directly to the audio application and the application identifies bass notes on channel 1 as "Velocity" from "28 to "63".

BUT! connect it directly to our Mackie interface, or a midi triggered keyboard, or through a Zoom 9050 (which we use for quick note identification) and the MIDI is not recognized!
However if we connect a MIDI thru, back from the CME PC interface in echo mode then it transmits fine to these devices.

There is also a feint audio hum from the audio whenever the MIDI lead is connected

We intend to use this for some on-stage experimentation so if we could get this working it would be awesome.

The serial no. is 2003410

I do not like to suggest one of your products is faulty on a public forum and I'm sure it's something simple, but you insisted that we don't send technical support requests via Emails!

Peace and respect and that.

Carlos Stein

I'm not sure what's wrong here, but some here's my thoughts...

Since the B2M is transmitting to the CME interface correctly, it suggests that the B2M is possibly working ok.

But, why doesn't it communicate with the other devices? And also why do you get audio hum?

MIDI was designed to avoid hum, by not allowing ground-loops to exist between interconnected devices. So, the transmitter (the B2M in this case) has the MIDI cable connected to its ground, but the receiver (your other devices) have the cable connected to an opto-isolator so that the ground of the MIDI cable is connected only to the opto-isolator and not to any other part of the circuit. This means it is not possible for any ground loops to exist between the two connected devices.

But, if the receiving device has a fault, or is not designed correctly, it could have a connection to ground, and thus give ground loops. This would cause hum and also transmission problems.

Why does it work with the CME's MIDI-Thru? It could be because it's ground connection is referenced to your computer, whereas the B2M is floating (it is battery powered) so the voltage differences are much less, and thus the ground-loop problems are much less too.

Buy why is this happening on ALL of your other devices? I can't answer that one, maybe you have some ideas on that?

Hi James, thanks for your reply.

Ground hum I can deal with and it's not necessarily a major problem, but without pulling the unit apart the presence of common-mode noise on an isolated line could possibly suggest a ground short on the isolated (B2M) side, or even an open circuit- which only manifests itself when the PC completes the circuit via the audio thru to our mixing desk? This could explain why the individual devices arn't "seeing" the MIDI - as they are supplied from an isolated PSU and arn't sharing the common audio ground, whereas the PC is grounded.

We have tried 2 different MIDI leads between devices but the PC connection is the only one which works, and only when the audio thru is connected!

If you could email me a schematic of the midi side we'd be happy to diagnose it at PCB level and let you know what we come up with.

I'm not sure what the warranty situation is, as it was purchased from your factory as a "refurbished" (which is why I gave you the serial number).

Let me know what you think. BTW Thanks for your swift response.

Carlos

Stein-Time Music

Warranty is not a problem. If there is something wrong with the B2M, we will repair or replace it for you. I just don't want go down that route without exploring other options first.

The MIDI at the B2M side is not isolated. Isolation only happens at the receiver, not the transmitter. So the MIDI ground and audio ground are common at the B2M.

Maybe you can first check the voltages from the B2Ms MIDI port, just in case it's not operating at 5V as it should be -- that would explain some devices working and others not working, but probably not explain the hum. At the MIDI connector, pin 2 (the top-middle) is ground, the next one to the right (pin 5) is the MIDI signal, and the one to the left (pin 4) is +5V. The outer two pins are not connected. So, measuring from pin2, to pin 4 should give you +5V. Measuring from pin 2 to pin 5 should give you also +5V, but which toggles if there is a MIDI signal -- if you can a scope, you should get nice clean rectangular pulses from pin 5.

Cheers James!

That's the kind of answer I was hoping for, I'm seriously impressed!

I'll run that on the 'scope later and see what happens.

Thanks for your support.

Carlos

Stein-Time Music

Hi James,

I had a moment to look at the B2M today. There is indeed 5v at pin 4 and square pulses on the MIDI out at pin 5 (wrt pin 2). Although I couldn't get a lock on the timebase it was enough to establish an active low signal of 3v with a train of negative going square pulses.

My only concern is your comment about the ground being common to both the audio and MIDI. The audio grounds are both common with the battery (-) but not the MIDI at pin 2.

All is not lost however because I discovered that 1 of the MIDI cables given to me by a (now EX) employee was not PIN to PIN (hint: always source your own cables!). If the above measurements are what you'd expect then I will assume the B2M is OK.

Carlos

You are correct about the grounds. Audio ground is common with battery ground, but this is isolated from the digital (including MIDI ground) by a FET. When powered on, the FET gives a low resistance and then it becomes common (there is only a small resistance between them when the FET is on).

Let me double-check the MIDI signals on as scope in the lab and get back to you. I will even try to get a screen grab for your reference.

It was the lead, well both of them in fact (as Carlos casually puts his multimeter away and tries to look smug).

Thanks for your help James.

Carlos Stein

Great -- the main thing is the problem is solved.

Hi James thanks for the solution you have provided. I had a similar problem in my computer and I have tried the solution you have provided here, which worked pretty well without any errors. Now everything is working perfect here. Great work guys!


Thanks