BOSS TR2 Tremolo - second version with That2181 vca

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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby bajaman » 13 Sep 2019, 09:52

thanks to all so far, for the great info and thank you Manfred for your observations :thumbsup
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby george giblet » 14 Sep 2019, 00:31

The THAT chip has dB/V gain control instead of the linear control found on the earlier OTA's. The whole added circuit around IC5B, IC2B, is about undoing that. If the diode voltage shifts it will shift the gain of the THAT chip. The shape of the diode VI curve might also come into play. The That data gain graphs show about 0.167 dB/mV = 166 dB / V. So looking at the datasheet for the 1SS120, 1SS270 diodes the VI graphs show them to be identical. The yellow band 1SS133 has a 20mV lower voltage drop for the same current. 20mV amounts to 3.3dB! So the diode voltage needs to be controlled in this design.

I discovered one weird thing about the schematic it looks like the values of R38 and R21 have been swapped. R21 should be 12k and R38 should be 10k. This is the case for the THAT version and also the previous version. Unless there's a third version it appears someone has swapped the values on those - weird?

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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby bajaman » 14 Sep 2019, 01:56

Thanks George for that info - yes the THAT chip is an logarithmic controlled device - a lot of extra opamps needed to linearize it's gain curve !
I checked the picture and good spotting with R38 and R21 - the original version schematic on the internet is obviously wrong - here is the latest preliminary schematic.
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Boss TR2 second edition with THAT VCA preliminary 5.gif
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby george giblet » 14 Sep 2019, 04:50

the original version schematic on the internet is obviously wrong

It looks like the schematic was redrawn to clean it up and that error was introduced.
The original schematic on the web (2004) was scanned and has the resistors in the right place. The new schem is easier to read and I couldn't see any more differences.

So I've confirmed there are three versions of the TR-2,

Left = Version 1, 4xIC's and M5207L01 VCA
Right = Version 3 (the one in this thread), 6xIC's, THAT2181L VCA
Image

But then there's this one, Version 2, 5xIC's.
I'm fairly certain it's based on the THAT2181L VGA,

http://www.musicgarage.fi/mods-repairs/ ... -drop-fix/

IC5 near IC1
Added
- R's R53 1k, R46 120k?, R47 1k5
- R's R52 82k?
- D8
- C27 electro

The reason I think this is V2 is because it has a diode D8 and the one in this thread has D9.
R46 and R47 look like they belong to the THAT2181.
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby bajaman » 14 Sep 2019, 06:19

Hi George - yes, so this must indeed be version 3 - the pcb board is 70901390R0 whereas the 5 IC board in your link is 70901390.
Obviously the Boss engineers revised the voltage control section of the VCA for version 3 (R0) by adding a further dual opamp because their attempt with version 2 was not good enough !
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby george giblet » 14 Sep 2019, 06:38

Obviously the Boss engineers revised the voltage control section of the VCA for version 3 (R0) by adding a further dual opamp because their attempt with version 2 was not good enough !

Yes, so maybe V2 was a minimal change over to the THAT chip but then they found out it wasn't so simple had to fix it with V3. I've only seen one or two pics of that V2 board so maybe Boss realized there was a problem soon after the release of V2 and so V2 was very short lived.

Another thing I've noticed on the V3 boards is some have fixed resistors for R9 and others have a trimpot. Maybe Boss thought they could avoid volume issues by choosing a particular diode for D9 but later on that turned not to work so they ended up giving-up and putting in the trimpot for R9.
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby Manfred » 14 Sep 2019, 08:17

george giblet wrote:The THAT chip has dB/V gain control instead of the linear control found on the earlier OTA's. The whole added circuit around IC5B, IC2B, is about undoing that. If the diode voltage shifts it will shift the gain of the THAT chip. The shape of the diode VI curve might also come into play. The That data gain graphs show about 0.167 dB/mV = 166 dB / V. So looking at the datasheet for the 1SS120, 1SS270 diodes the VI graphs show them to be identical. The yellow band 1SS133 has a 20mV lower voltage drop for the same current. 20mV amounts to 3.3dB! So the diode voltage needs to be controlled in this design.

I discovered one weird thing about the schematic it looks like the values of R38 and R21 have been swapped. R21 should be 12k and R38 should be 10k. This is the case for the THAT version and also the previous version. Unless there's a third version it appears someone has swapped the values on those - weird?


Thanks Georg for pointing out that.
From that it will be seen that the application is depend on few Millivolts,
for me the conclusion of this is that the diode must be selected for the suitable VI curve of D9.

Consequently, D9 must be selected,
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby Manfred » 14 Sep 2019, 08:23

Consequently, D9 must be selected,

Sorry, typo.

Sometimes the EDIT-Button is not displayed in my browser, I don't now why.
Any idea, please give me a PM.
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby bajaman » 14 Sep 2019, 10:00

yes the edit button seems to have disappeared with the new software/ server introduced a few months ago - also the "view new posts" is no longer available UNLESS you go to the Board Index now :roll:
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby Manfred » 15 Sep 2019, 02:20

also the "view new posts" is no longer available

"view new posts" is available to me. :?:
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby bajaman » 15 Sep 2019, 03:01

view new posts is not available for me, when in a topic ! If I go to the top of this page, the only options are: User Control Panel and View your posts. I have to click on the Board Index before the option of View new posts appears - it never used to be like this a few months ago :!:
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby bajaman » 15 Sep 2019, 03:10

Ok - i figured out how to view new posts from inside any topics - after the reset a few months back my board style in Board Preferences was set to prosilver. i changed it to subsilver2 and now the View new posts is available from inside any topic
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby bajaman » 15 Sep 2019, 03:12

still no edit button though !
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby george giblet » 15 Sep 2019, 03:26

still no edit button though !

I haven't seen that for some time.

I found out a couple more things about the TR-2. It looks like the change from V2 to V3 occurred around 2006. I haven't been able to work out when V1 change to V2 occurred, not enough pics.

FWIW, Boss seem to have started batch numbering the PCB's around 2004/2005, not sure of the exact year. The PCB is marked with a YYWW format date code in a 7-segment/LCD display font; 0721 would be week 21 of 2007. Dating the M5207 Mitsubishi chips is a little ambiguous as the 6-digit codes start with the year units but (AFAIK) don't have the year 10's. So a chip marked as 5xxxxx could be 1995 or 2005.
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby Manfred » 15 Sep 2019, 10:38

bajaman wrote:still no edit button though !

Sometimes it works to me, maybe blocked by Firewall or another protection software.
Normally I use the Firefox, for this post I try the Microsoft Edge to see if the Edit button appears.
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Re: BOSS TR2 Tremolo - second version with That2181 vca

Postby Manfred » 15 Sep 2019, 10:42

Manfred wrote:
bajaman wrote:still no edit button though !

Sometimes it works to me, maybe blocked by Firewall or another protection software.
Normally I use the Firefox, for this post I try the Microsoft Edge to see if the Edit button appears.

It does not work either.
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