MixBuzz500 build/support tHread

[Harpo]

they are showing 100K RIN and 100K ROUT values.
Should I set R6/R3 to 100K?

R6 and R3 could be decreased a little IMHO.
With THAT1246 in front, giving -6dB signal gain, voltage swing in front of the VCA can not be higher than Vsupply/2. For the max.allowed signal current of 500uA for (Iin+Iout), this is 250uA max.for Iin in bypass condition. 18V/250uA=min.value 72K for Rin. Pick next avail.standard value 75K. Same value for feedback resistor for unity gain, because the THAT1646 makes up the -6dB loss from the line receiver. Decrease 33pF compensation cap to 12-15pF.

 

[Igor]

Thanx Harpo! Great point. Yes, this will work better. IMHO 68K1 will be fine instead of 100k as well.

 

[Biasrocks]

Thanks for your help guys, much to digest.

Mark

 

[zayance]

Done Deal, tested, calibrated, Thanks to Igor for the Project, and to StereoKillah for his PPM scales and clarifications.

 

[ultra-alex]

nice knobs. where did you get those?
cheers, alex

 

[RedNoise]

HI Zayance , have you got the "inverted" ratios??
(2:1=10 , 4:1=4 , 10:1=2)

 

[zayance]

@Ultra Alex: These are Kilo international knobs, you can find them at Digikey, just type Kilo in the search field, these are 15.88cm knobs IIRC, anyway you'll find out.

@Rednoise: No when testing on the lab, Ratio were ok, a little high for the 2:1 the rest was ok.

Bad news for me  :'( :'(, everything was working nice in the Lab, so i inserted in the box, putting tabs for helping the PCB getting to the right pins, conclusion smoke  :'( :'( :'(, so turn off, and check the pins of the rack, and what the f..k, some crazy voltage 62v , at pin -16v, where is this voltage coming from...S..t, totally forgot to check that before inserting, and even when my box was finished IIRC, seem to be good on the PCB molex tough that i remember, i don't get it, anyway, some hours of troobleshooting, and well who knows maybe everything is smoked, visually all res were ok, only one 1646 seem to have burned, all the rest well don't know, BAD DAY FOR ME  

 

[Igor]

Nice knobs, very nice meter, now, relax.
10R resistors acts like a fuses. Check them at first.
THAT1646 probably shorted power supply rails and maybe nothing else did not blew out.
Take all chips out from sockets and check for power supply consumption.
Then, start to insert them one-by-one, continue checking if no smoke.
Than feed sound, repeat test pro, that's it. Please let us know.
I am very curious what really blew out.

 

[Harpo]

IMHO 68K1 will be fine instead of 100k as well.

Sure. Looking closer, a THAT124x doesn't swing rail to rail but typ.+/-2V off its supply rails. Supply voltage from psu probably is +/-16.5V (ignoring voltage drop in 10R fusing resistors) or a little lower, not +/-18V. Schematic differs from GSSL, where signal is always running thru the VCA. Your design is coming with hardwire bypass, so no VCA-bypassing and min.compression ratio is at least 2:1, allowing a 2/3 Iin to 1/3 Iout current sharing within the DBX202 VCA. Rin and Rfb might decrease further to (((+16.5V-2V)-(-16.5V+2V))/2) / (500uA*2/3) = min.43K5.

 

[zayance]

hmmm, i Absolutely don't get it, i just connected the boards alone in the rack, one board with chips out, all had good voltages on right pins, and tried with the other one that had the components all in, and everything is fine, no crazy voltages on the pins or whatsoever, DBX getting correct voltages all Socket pins getting correct voltages and no Smoke  ??? ??? ??? ??? ??? ??? ??? at least on one of the boards and Controller board not connected, didn't check sound passing still but very Weird issue, maybe a pin got shorted when inserting the card  ???, Now i need to check all the configuration in the box and not out of it, just to have a better look of that.

EDIT: 51x Rack not API

 

[AudioGimmer]

Are you fitting the mix buzz in a Lunchbox or 51x rack?

Its a pretty tight fit in a 6 slot lunchbox, making sure both cards sit properly in the backplane.
I had a problem the first time I assembled all the PCBs etc in the metalwork. One of the ribbon cables had got damaged and the sidechain was going nuts. I disassembled and rechecked everything outside the rack, and then very carefully put it all back together and it worked fine.

I'm sure you'll get it fixed.....

The gimmer

 

[reanimatorstudio]

Hi,

any suggestions on the silver mica caps?

All I can find is way to big. Is it correct that the schematic and the PCB component numbers don't correspond or is there an upgrade of the schematic?

No input and output caps, Is there a risk to put accidently 48V on it? Should we put clamping diodes?

BTW I love assambling this project.

 

[AudioGimmer]

The only micas I could find were physically large, and the lead spacing too big.

I very carefully bent the legs in an S shape to make them fit the board, and used some thin silicon sleeving to prevent any shorts.

I'd post a picture, but the mixbuzz is in my lunchbox hard at work at the moment...

The Gimmer

 

[reanimatorstudio]

some protection against 48V and RFI is suggested in the date sheet. I would strongly recommand this modification for reliability:
look at page 9 of:  http://www.thatcorp.com/datashts/THAT_1606-1646_Datasheet.pdf

 

[canidoit]

Done Deal, tested, calibrated, Thanks to Igor for the Project, and to StereoKillah for his PPM scales and clarifications.

Zayance, how does it sound? Have you compared it with other compressors?

 

[zayance]

@Canidoid: Well sounded Smokey  , still didn't repaired, so will let you know....

 

[oceres]

I'm trying to figure out what kind of ferrite bead is suitable for R4 and R39? Are there different ones?

 

[stereokillah]

just use resistor leg for each.

 

[reanimatorstudio]

R4, R39 is ferrite bead or jumper: It's a great thing Igor implemented this use it when you are going to use a fast opamp with high GBW. You don't want RFI.
RS stocknumber 226-8191  Panasonic  EXCELDR35C  or RS stocknumber 226-8185  Panasonic EXCELSA35

 

[oceres]

Thanks!

I found excelsa35 from DigiKey and it's 3.5mm x 5mm so it should fit just fine.