I'm thinking of building an equivalent ov 202XL VCA for my compressor. I've studied the documents here: viewtopic.php?f=6&t=34
While circuits look simple enough, there're a couple of things I'd like to clarify. All circuits use 3300ppm tempco resistor. All tempco resistors in the range of 2700-3600ppm were made by Panasonic and are phased out. There are some high values tempcos available (1k and 2k), but here the value is 50-100R. Is there any recommendation regarding replacing this resistor?
Also, in the 2002T circuit there's a note regarding R2/R3 selection procedure. What would that procedure be?
THAT 202XL recreation
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Re: THAT 202XL recreation
I think in through-hole your choices are pretty limited.
You might follow this link: viewtopic.php?f=12&t=658
In surface mount you at least have more options.
The driving market (I'm guessing) for SMT tempco resistors might be LED drivers and Cellular base station RF power amplifiers.
In SMT KOA comes to mind: http://www.koaspeer.com/products/thermal-protection/
I used to stock the 1K PT-146 and they're big. http://www.precisionresistor.com/PT146- ... sator.html
What I might suggest is that you find a tempco you can readily source as close to 3300 ppm either negative or positive TC and then design the Ec driver circuit around the resistor.
I don't know the answer to your final question about the resistor selection but my hunch is that the input resistor is selected to match the 5 or 10% tolerance of the temperature sensitive shunt R.
You might follow this link: viewtopic.php?f=12&t=658
In surface mount you at least have more options.
The driving market (I'm guessing) for SMT tempco resistors might be LED drivers and Cellular base station RF power amplifiers.
In SMT KOA comes to mind: http://www.koaspeer.com/products/thermal-protection/
I used to stock the 1K PT-146 and they're big. http://www.precisionresistor.com/PT146- ... sator.html
What I might suggest is that you find a tempco you can readily source as close to 3300 ppm either negative or positive TC and then design the Ec driver circuit around the resistor.
I don't know the answer to your final question about the resistor selection but my hunch is that the input resistor is selected to match the 5 or 10% tolerance of the temperature sensitive shunt R.
Re: THAT 202XL recreation
I hate always being the wet blanket but WHY??????? (maybe I don't hate it, or I would stop doing it).ilya wrote: ↑Wed Nov 15, 2017 7:47 am I'm thinking of building an equivalent ov 202XL VCA for my compressor. I've studied the documents here: viewtopic.php?f=6&t=34
While circuits look simple enough, there're a couple of things I'd like to clarify. All circuits use 3300ppm tempco resistor. All tempco resistors in the range of 2700-3600ppm were made by Panasonic and are phased out. There are some high values tempcos available (1k and 2k), but here the value is 50-100R. Is there any recommendation regarding replacing this resistor?
Also, in the 2002T circuit there's a note regarding R2/R3 selection procedure. What would that procedure be?
I actually have a patent for a VCA (US04818951 roberts 1989), and stopped using my own after we (Peavey) could buy better ones from dbx....
The last generation IC VCA from THAT corp is superior to all the former stuff...
If you just want some distortion there may be easier ways to make that.
JR
PS: Tempco of resistors is probably about VCA gain tracking over temperature. May not be a big deal for small gain change range... or simple dynamics processing.
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Re: THAT 202XL recreation
There is a replacement need for failing VCAs with the 202 footprint in legacy consoles.
Re: THAT 202XL recreation
It would make the world a better*** place if the new VCA could be integrated into previous applications.mediatechnology wrote: ↑Wed Nov 15, 2017 4:24 pm There is a replacement need for failing VCAs with the 202 footprint in legacy consoles.
JR
*** lower noise, lower distortion
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Re: THAT 202XL recreation
But of course I'm not going to make a discrete VCA, this is just insane! What I'm talking about is an array of 218x chips (4 or 8 in 2002 and 202XL respectively) with a couple of op-amps. Tempcos are giving me a hard time though....JR. wrote: ↑Wed Nov 15, 2017 3:37 pm
I hate always being the wet blanket but WHY??????? (maybe I don't hate it, or I would stop doing it).
I actually have a patent for a VCA (US04818951 roberts 1989), and stopped using my own after we (Peavey) could buy better ones from dbx....
The last generation IC VCA from THAT corp is superior to all the former stuff...
If you just want some distortion there may be easier ways to make that.
Re: THAT 202XL recreation
OK I still would like to see new silicon...(better than 2180s too)
3300ppm Rs available in SMD but they are noted as end of life... so won't be available forever.
You can probably tweak tempco by mixing and matching values in series /parallel but seems like a lot of effort.
You can hand solder SMD resistors with care (I have before in prototypes).
JR
3300ppm Rs available in SMD but they are noted as end of life... so won't be available forever.
You can probably tweak tempco by mixing and matching values in series /parallel but seems like a lot of effort.
You can hand solder SMD resistors with care (I have before in prototypes).
JR
Cancel the "cancel culture", do not support mob hatred.
Re: THAT 202XL recreation
Sent a letter to THAT and it turned out I don't need tempcos for 2181 any more because it's already there on the chip. Now, if I understand correctly, I just remove the tempco (R8 in the 202XT circuit). Do I still need the R7 (6R8)? Can't figure what its function is.
Everything else seems to be pretty straighforward.
Everything else seems to be pretty straighforward.
Re: THAT 202XL recreation
I believe THAT published a white paper about upgrading old VCAs with newer ones... maybe check their website.
I would guess you still need the resistor, just doesn't need a special tempco.
JR
I would guess you still need the resistor, just doesn't need a special tempco.
JR
Cancel the "cancel culture", do not support mob hatred.
- mediatechnology
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Re: THAT 202XL recreation
I don't think that's correct.
If you look at the 2181 datasheet page 2 table 3 it shows a +0.33% gain control tempco.
You still need -0.33% to correct it.
Also see equation 1 on page 5 of the 2181 datasheet for the delta-T term in the denominator: http://www.thatcorp.com/datashts/THAT_2 ... asheet.pdf