Feeler: ez760 - Compressor/Limiter/Expander/Gate

[salomonander]

hey Gustav

thanks. did you hear any compression/limit/expander before calibrating? it seems a little suspect that i hear no effects whatsoever at this point.....
yes, i copied your wiring now. all controls react as they should. i just can't hear it working - or its the most transparent comp ever built


ps: i left out all the filtering on the xlr pcbs and connected straight from the xlrs to the mainboards molex....

 

[salomonander]

ps: i have nothing connected to the stereo link molex. maybe thats the problem?

 

[Gustav]

ps: i have nothing connected to the stereo link molex. maybe thats the problem?

Im 100% certain it isn't .

Try calibrating, and see what happens. It doesn't make any sense at all to compare pre-calibrated units.

Gustav

 

[salomonander]

ok. i'll try tomorrow. but i have all my trimpots in a safe middle position and hear absolutely no effect - with the meter showing 20db of compression. but who knows - maybe it is a calibration issue.

 

[tonycamp]

Hi Guys.

Currently building one of these, and I can't find an available replacement for the 2N3820.

Any tips?

So far, I have found the following replacements for the rest of the discontinued parts. Please note, I have yet to try these in action, so I cannot vouch for the list. Double check the data sheets if you try them...

BC182B - > BC546B
BC184C - > BC549C
BC184L - > BC547C
BC212B - > BC560B
BC212L - > BC557B

Gustav

Hi Gustav, can you verify whether these are good options now that you've finished your pair? are the pinouts different than the parts they replaced? did you find a 2N3820 substitute? my bet is the original compex transistors had a very high HFE to them, the new ones always seem to be on the low side?

any info is appreciated as i'm ready to push through the sourcing process again, this time with a little more experience and patience under my skinny belt 8) If i have success with this, i will post a solid, cut and paste style sourcing bom to make it easier for guys to tackle this project, the compex f760 is one of the coolest compressors ever imo, it's awesome that you and Collin made this available to us! it'd be nice to see more of the fella's take advantage of the opportunity to create such a beast!

 

[Gustav]

Hi Guys.

Currently building one of these, and I can't find an available replacement for the 2N3820.

Any tips?

So far, I have found the following replacements for the rest of the discontinued parts. Please note, I have yet to try these in action, so I cannot vouch for the list. Double check the data sheets if you try them...

BC182B - > BC546B
BC184C - > BC549C
BC184L - > BC547C
BC212B - > BC560B
BC212L - > BC557B

Gustav

Hi Gustav, can you verify whether these are good options now that you've finished your pair?

Sorry, no. I "lost" that prototype and ended up getting some packs of the correct transistors off of various ebay vendors.

I packed up some transistor kits for convenience, but I currently don't have any in stock. 

any info is appreciated as i'm ready to push through the sourcing process again, this time with a little more experience and patience under my skinny belt 8) If i have success with this, i will post a solid, cut and paste style sourcing bom to make it easier for guys to tackle this project, the compex f760 is one of the coolest compressors ever imo, it's awesome that you and Collin made this available to us! it'd be nice to see more of the fella's take advantage of the opportunity to create such a beast!

Cant wait to see it, and thanks for the kind words. Its really just Colin's project. I simply played the role of the PCB fabbing monkey

Gustav

 

[salomonander]

hey guys

so i tried the calibration procedure today. and everything seemed fine until the point where i was supposed to read +10db. my meter (ntp) only goes up to +5db. so im kinda stuck atm. guess i'll have to invest in a proper voltmeter like an hp with dbu scale....

cheers

 

[Dr Gris]

Isn't +10 dBu = 2.4495 V RMS ?

Best
//M

 

[salomonander]

Isn't +10 dBu = 2.4495 V RMS ?

Best
//M

if only my multimeter did rms.... thanks for the tip though.

 

[Gustav]

Isn't +10 dBu = 2.4495 V RMS ?

Best
//M

if only my multimeter did rms.... thanks for the tip though.

Its equivalent to AC, which I bet your meter "does". 

You can use this calculator to convert any target values you need.

http://www.sengpielaudio.com/calculator-db-volt.htm

Gustav

 

[salomonander]

Isn't +10 dBu = 2.4495 V RMS ?

Best
//M

if only my multimeter did rms.... thanks for the tip though.

Its equivalent to AC, which I bet your meter "does". 

You can use this calculator to convert any target values you need.

http://www.sengpielaudio.com/calculator-db-volt.htm

Gustav

hey Guys
thanks. i still had to borrow a better meter - simply because mine is not accurate enough. and it looks like the one channel i did actually passed calibration. and it does compress - hurray! next channel coming up tomorrw.

 

[Dr Gris]

And btw 10dBu = 3.4636V AC peak to peak if meter doesn't read RMS if I'm correct.

Following this with interest, good luck!!!

Best
//M

 

[salomonander]

i do have two more noob questions im afraid:

- i have a 1k resistor installed for the vu leds (the hairball one). works nice but id like the leds to be way less bright. would i simply increase the resistor value? if so - what kind of (ballpark) value?

- am i correct that i'd want a dpdt switch for stereo link? is the unit in "stereo" when hot and cold of both units are connected - the shield being left as is?

thanks again!

 

[Gustav]

i do have two more noob questions im afraid:

- i have a 1k resistor installed for the vu leds (the hairball one). works nice but id like the leds to be way less bright. would i simply increase the resistor value? if so - what kind of (ballpark) value?

Just increase it.

- am i correct that i'd want a dpdt switch for stereo link? is the unit in "stereo" when hot and cold of both units are connected - the shield being left as is?

If you built them into the same case and already have a common ground, yes - it should work.

Gustav

 

[salomonander]

hey

so no luck with channel two im afraid. sitting here the whole day without any luck
the problem is obviously the comp ratio trim pot. which does not seem to react as it should. took the comp card out of the working channel zeroed it (argh) just to compare. the comp ratio trim works. doesnt on the second channel (only exchanging the comp cards here).
it does a little but way too little. anyone have an idea where to start my search. im kind of lost honestly. changed q42. no luck....
maybe someone has an idea?

 

[salomonander]

ps: on the working comp card this trim pot makes a change of about 20db. on the non working one only like 1.5-2db.
all other trim pots are all the way counterclockwise now (just for testing) and only the comp cards are exchanged. all transistors seem fine - looking not measuring. same goes for resistors and caps (i can measure those). i dont see any shorts either.
inserting the working card shows me about 16db of reduction while the none working card shows 6db. this is only changing the comp cards having trimmed all pots to fully counter clockwise.... nothing else changed. they react very different



all voltages measure a little different on the non working board. im wondering if there is one transistor that controls all the bas voltages?
i could not really measure the transistors nor zeners. everything else is good - i think so at least

 

[salomonander]

just got it working!
guess i got really unlucky and had a faulty pcb. one trace simply didn't conduct. bridging it solved the issue. thanks god - i went nuts after 12 hours of error searching

 

[salomonander]

anyone else see that there are three"wrong" transistors on the pcb?
the schematic is 100% the same as my original compex plan. except Q9 and Q39.
Q9 is a BC182B on our pcb while it is marked as a BC184C on the original schematic.
Q39 is a BC182B on our pcb again while it should be a BC212B according to the original plans.
Q8 is a 182B on ours but should be a BC212B again.

is there a reason for this or did someone make a mistake?

 

[Slenderchap]

Original schematics will be wrong.

Colin
www.audiomaintenance.com

 

[salomonander]

Original schematics will be wrong.

Colin
www.audiomaintenance.com

ok great. thx