BlueClone - The Blue Room's Own Comms System

[sunray]

I don't have the schematics for a 721 here. Would you be willing to pop the lid and see what values of R and C they have in the termination networks. It a pair of series connected resistors, one around 200-500 Ohms, the other in the 4k7 to 10k range. The larger value has one end to ground and is bypassed by a capacitor of around 10uF.

 

You can compare with the BlueCom one documented here...

 

https://www.blue-room.org.uk/index.php?showtopic=59644&view=findpost&p=486728

 

When John and I designed BlueCom we looked at what everyone else did and found quite a wide variation in things like the audio level on the line and termination networks so ended up picking a middle set of values so that it should work with most systems.

 

The I/P network is 200, 4K7 & 10uF and measure 199.2, 199.3, 4692, 4689 across the 2 circuits of one 721. I don't have any ability to test the caps but a basic Wheatstone bridge at 1KHz indicated 208.8 & 212.6 ohms.

 

I'm surprised that a variation of 2% makes such a noticeable difference with the bluecom and unnoticed with techpro.

 

I don't have the 2nd 721 here to test, or my home made version but I think I used 270 ohm as shown in the schematic.

Edited February 22, 2019 by sunray

[sunray]

The I/P network is 200, 4K7 & 10uF and measure 199.2, 199.3, 4692, 4689 across the 2 circuits of one 721. I don't have any ability to test the caps but a basic Wheatstone bridge at 1KHz indicated 208.8 & 212.6 ohms.I'm surprised that a variation of 2% makes such a noticeable difference with the bluecom and unnoticed with Techpro.I don't have the 2nd 721 here to test, or my home made version but I think I used 270 ohm as shown in the schematic.

Just to clarify my tests, I knocked up a Wheatstone bridge using a couple of 680ohm resisters, a 50K 15 turn pot (which quickly got changed to a 1K 10 turn), the 4th leg being pins 1 & 3 of the Techpro and a sig gen/LMS. I trimmed for a null and measured the resistance of the pot. As the 680's weren't a perfect match, I then swapped the resisters, repeated the test and averaged the 2 readings. The whole thing was repeated for the second channel.

[sunray]

Last night I had my homemade psu back here and checked the values of the termination of 270R, 4K7 and 10uF measured as 340R, 4665 and a Z of well over 400R. I replaced the faulty 270 with a 200 (202.3)and Z comes up as 215 (average of 213.9/216.1).

 

This means that side tone wise our Bluecom packs are good to go on the home made psu and circuit A of above 721 and need about one turn of the side tone pot to use on circuit B.

 

Hopefully I'll be able to repeat the tests on the other 721 in due course.

 

I find I can use from one to 13 packs (6 Bluecom & 7 Techpro) on the bench with very short mic lead links without needing to adjust side tone and in the real world I've not yet run into cable length issues.

 

It's good to have got to this conclusion as I'd been struggling during use of 4 systems, almost simultaneously, and packs getting mixed up during the 2 week period.

 

Interestingly the frequency response of the anti side tone system is noticeably different (under test conditions but never previously noticed in real world use) between the 721 and home made on both Bluecom packs and Tecpro packs, I assume this is due to the termination Z being circa 200R at 1KHz and 2K at 10Hz.

Edited February 25, 2019 by sunray

[sunray]

I've been away all week and was a bit surprised one of 'the others' had a look at the remaining 721. From his chat:-  

 

Using Tecpro packs there was hardly any movement of the sidetone pot between the 2 circuits of the 721.

Using Bluecom packs he was unable to find a sensible setting to null sidetone.  

DC resistance of both circuits XLR's - about 5K but one circuit didn't have any capacitor kick so he changed the 10uF.

 

Now there is only a 'little bit of difference'(his words) between the circuits for the bluecoms and no adjustment for the Tecpro across all 3 PSU's.  

 

This last few weeks has been a useful exercise to get all of our PSU's to a reasonable match, hopefully we'll have another play in a little while (September always seems to be a good time for our projects) to see if we can balance them a tad better.

Sadly this will not include the other 4 PSU's we have access to as their owners don't have a problem with their Tecpro packs.  

 

Overall it seems strange that the Bluecom's are so much more sensitive to this issue than the Techpro's as they have relatively simmilar interface circuits.  

 

For what it's worth I have noted down most of the elements of the 721 circuit, but when I tried doing a full drawing I realised I don't have all the component numbers/values or full details of how the elements fit together. There is of course significant similarity with the BP1. I'll try to do a better job when I have the next one open.

Edited March 16, 2019 by sunray

[pedromigcruz]

Hi everyone, I finally made 5 beltpacks and 2 psu. I’m still missing the panels but that should be sorted soon.

So far my test went great except for one thing. If my volume knob is set at full volume, there is a lot of oscillation on the volume. when I press call, the led blinks and it can be heard on the headset. If my volume knob is at 50% nothing wierd happens. The led lights up and I can still communicate nicely. Only in between 75%-100% the led goes flashy and communications also get chopped.

Seems there is not enough juice for the amplifier. atm I’m using 12v 2A for 1psu and 2x beltpack.

Do you have any idea?

Headset I’m using is single ear Beyer Dynamic DT 108-200-400

Best!

[sunray]

Hi everyone, I finally made 5 beltpacks and 2 psu. I'm still missing the panels but that should be sorted soon.

So far my test went great except for one thing. If my volume knob is set at full volume, there is a lot of oscillation on the volume. when I press call, the led blinks and it can be heard on the headset. If my volume knob is at 50% nothing wierd happens. The led lights up and I can still communicate nicely. Only in between 75%-100% the led goes flashy and communications also get chopped.

Seems there is not enough juice for the amplifier. atm I'm using 12v 2A for 1psu and 2x beltpack.

Do you have any idea?

Headset I'm using is single ear Beyer Dynamic DT 108-200-400

Best!

The system is designed for 24V.

[pedromigcruz]

Hi Sunray! Thanks!

I see, but should that happen if I plug it to another main station? I plugged 2 bluecoms to an Altair WB-200 which is Asl/clearcom compatible and I have exactly the same results. I will try with 24v feeding the PSU, but my main target for these beltpacks is using them with other main stations as well :/

Cheers

Pedro Cruz

Edited March 30, 2019 by pedromigcruz

[sunray]

We have made 6 bluecom packs and we've only had the symptoms you describe during initial construction of a PSU (we haven't made the bluecom PSU)and due to a wiring error we had 18V or so which dropped off fairly rapidly as additional packs were added. We corrected it and the problem ceased to exist. We have used the packs with Tecpro PSU's and packs with no problems.

 

What impedance headphones are you using? Should be more than 30 ohms.

Edited March 30, 2019 by sunray

[pedromigcruz]

Hi Sunray, I’m using Beyer Dynamic Dt108 400ohm headphone single ear. ATM all 5 of them behave like this.

[sunray]

One of ours did something vaguely similar but that turned out to be a high resistance resister not applying enough negative feedback to a stage.

From that:

Are running too much mic gain/ do you require this much gain? I find we run the bluecom packs at well below 50% headphone volume.

Have you misread one of your resister colours and fitted the wrong value.

Edited March 31, 2019 by sunray

[pedromigcruz]

One of ours did something vaguely similar but that turned out to be a high resistance resister not applying enough negative feedback to a stage.

From that:

Are running too much mic gain/ do you require this much gain? I find we run the bluecom packs at well below 50% headphone volume.

Have you misread one of your resister colours and fitted the wrong value.

 

Sorry the late reply Sunray.

 

Well I noticed that if I use higher gain in microphone, and less volume amplification it gets better than the other way around.

I don’t believe I got it wrong with resistors value because they have the values printed in individual bags for each value. But of course ###### could have happen. I will try to check the values again.

Thanks!

[Brian]

When carrying out the tests are you wearing the headphones or do they just sit on the bench?

 

Could this be feedback? Either acoustic or mechanical?

[pedromigcruz]

When carrying out the tests are you wearing the headphones or do they just sit on the bench?

 

Could this be feedback? Either acoustic or mechanical?

 

Hi! No that wasn’t feedback. Thanks

 

I will start now the tedious task of double checking resistor values.

In case you wonder how my PCB looks like:

https://drive.google.com/file/d/1mcIIMAk3kK11cnHaeE0WE4Hiqv7EtE5y/view?usp=drivesdk

 

Thanks guys

[pedromigcruz]

So I double checked resistor values and all seems fine. Although the resistor colours are not the same as boatman pictures. Maybe is just a diferent labeling of the resistors.

[dmxlights]

I have had a quick look at your pic of the board there looks to be a few solder joints that may need doing again but I could be wrong.

 

I have ringed them in red.

 

When I work with double sided boards I always make sure it well sorldered as in it come out the other side as well.

http://mcgcs.net/pics/pack.jpg