DOD - FX84 Milkbox Compressor

Post by **jstbrowsin** » 28 Sep 2011, 23:29

Thanks yes I agree our boards are the same but your schematic doesn't reflect that

pedalgrinder · Post by **pedalgrinder** » 29 Sep 2011, 04:53

Hi Ryanuk,

First of all can i say a big thanks and well done you have done a really good job tracing that board. Is there any chance of a pic of the track side just encase there is a mistake in the schematic (not saying there is) But we can have a look and verify rather than bug you. Thanks

ryanuk · Post by **ryanuk** » 29 Sep 2011, 08:13

jstbrowsin wrote:Thanks yes I agree our boards are the same but your schematic doesn't reflect that

Ok, so we agree that our boards are the same, but I'm still not sure what you meant in your earlier post when mentioned that "there is a bit of difference between my board and the schem". What did you mean? Happy to work with you to sort out any variances. What jumps out at you as being different?

pedalgrinder wrote:Hi Ryanuk,

First of all can i say a big thanks and well done you have done a really good job tracing that board. Is there any chance of a pic of the track side just encase there is a mistake in the schematic (not saying there is) But we can have a look and verify rather than bug you. Thanks

I tried to but the fine traces above the VCAs make it very difficult to take a good picture. That said, the pic Liquids poasted on page 1 is very good and you should be able to check the schem from there.

RyUK

ryanuk · Post by **ryanuk** » 29 Sep 2011, 08:29

jstbrowsin wrote:I really hope we get this done so I can piece back together my board also.[/attachment]

jstbrowsin - If you looking to simply get yours going, then I would buy/refit some J201s for Q2 to Q5. All being well, the circuit shoudl then function.

Have you got the original enclosure? If not then you could mount in a different enclosure, though you might need to replace DC jack and momentary switch with case mounted types and run fly leads to the respective pads.

Post by **jstbrowsin** » 29 Sep 2011, 11:12

thanks bud but its a bit more than that. When I had it given to me the guy said it was distorting when he increased the cream or pasteurization knob to be honest I can't remember which?? But I was a lot clueless back (not that much clued up now

) then about pedals so I just left it and as you see started stripping it for parts.

So if anybody has an idea why that would happen I really like to know. TIA

And yes I do have the original enclosure somewhere in the archives.

ryanuk · Post by **ryanuk** » 29 Sep 2011, 15:51

jstbrowsin wrote:thanks bud but its a bit more than that. When I had it given to me the guy said it was distorting when he increased the cream or pasteurization knob to be honest I can't remember which?? But I was a lot clueless back (not that much clued up now ) then about pedals so I just left it and as you see started stripping it for parts.
So if anybody has an idea why that would happen I really like to know. TIA

And yes I do have the original enclosure somewhere in the archives.

Not sure what you mean. Did the knob crackle which may only require cleaning? Or was the sound produced distorted? Bear in mind that there's a bit of boost available on this pedal. That could be where the distrotrion was coming from. Ill let you know if I experience the same thing.

Still willing to hear how your board differs from the schem.

Ry UK

strato56 · Post by **strato56** » 13 Oct 2011, 09:53

Hi,

Thanks for the schematic : can you specify the origin of “vr”?
Please check connection of pin 3 and 5 from IC4 to pin6 of IC5 : is that correct ?

ryanuk · Post by **ryanuk** » 13 Oct 2011, 12:06

strato56 wrote:Hi,Thanks for the schematic : can you specify the origin of “vr”?

Apologies - yes this is missing - "Vr" is the virtual ground created by the voltage divider (R3/4) and buffered by IC 1.1. All Vr points should be joined together and to IC 1.1 pins 1 and 2.

strato56 wrote:Please check connection of pin 3 and 5 from IC4 to pin6 of IC5 : is that correct ?

Im on the go at the moment and dont have the board with me, but looking at the pics posted, yes, you have spotted another error.

For clarity, IC4 pins 3 and 5 should NOT be connected to IC5 - pin 6 .
IC4 pins 3 and 5 should be connected to IC5 - pin 3 (which is Vr)
So, in summary, IC4 pins 3 and 5 should be connected to Vr.

Ill re-check and re-post the schem tomorrow when I can look at the board.

RyUK

Liquids · Post by **Liquids** » 06 Apr 2012, 01:28

I traced out your schem - good job I must say. It's a rather annoying circuit to trace (or maybe that is just me and my feeling about tracing in general).

Can you update your schematic to reflect the corrections noted above?

MY trace confirmed that (per your schematic component labeling, not MY board's labeling):
IC1.1 pin 1 is Vref
pin 3 IC4.1 and pin 5 IC4.2 connect to Vref
IC5.2 pins 6 and 7 are connected, and are connected to D5, but NOT to pin 3 of IC4.1 and pin 5 IC4.2

Also, not noted here, the ATTACK pot, VR1 - the CCW side of that pot and the wiper are joined. In other words, the attack pot is a variable resistor, not a voltage divider. Following, C21 and the A (anode) side of D5 are always directly connected to the Collector of Q4, Q5, and the Gate of Q6.

It would be cool if the schematics component labels for semiconductors and those components (most of the capacitors) matched the labeling on the board, but I was able to trace it out, and your pin-numbers were very helpful...I don't know that I would have done this from the ground up like you did, so thank you very much!!

Liquids · Post by **Liquids** » 06 Apr 2012, 01:45

And, oh yes - also a possible correction for R25: on my board, and the other picture in the thread, that resistor looks to be Purple / Green / Red / Gold, which would suggest a 7.5k 5% resistor, rather than 4.5k, if so.

It's potentially a minor difference, and reading it with a DMM in circuit would prove useless given the other components surrounding it having a major impact on it's apparent resistance...one side would need to be lifted to measure it, but 4.5k is close..not sure how significant this component value is. 6.8k or 8.2k are fairly close replacements...I'd go with 8.2k if I had to choose one, since there are other components essentially in parallel anyhow. into if one was without a 7.5k but wanted to come close with more common values, you could parallel an 8.2k+100k, or even 10k+33k.

mictester · Post by **mictester** » 06 Apr 2012, 10:44

... or two 15k resistors in parallel for exactly 7k5!

Liquids · Post by **Liquids** » 06 Apr 2012, 13:31

mictester wrote:... or two 15k resistors in parallel for exactly 7k5!

uh....oh yeah!

Though, I DO think of 15k as a 'level two' in terms of common values, while I think of 8.2x, 10x, and 33x as 'level one' common personally.
And a 7.5 value...well, it's kinda and obscure 'level 3' value IMO. (= Especially at 5% tolerance...which means it could be anywhere in the range of 7.1 to 7.8...7.1k is in the 5% range of a 6.8k resistor, 7.8 is in the 5% range of a 8.2k resistor... (= A DMM could reveal a component labeled as such to be as close as whatever I measured if I lifted one side of the actual resistor on my circuit board...

Of course, one could also do 6.8k+680R in series... or many others combinations. (=

On a completely different note - the schematic may betray, but if you look at the boss CS-3 schematic and wipe out the silly active tone control, you can see the 'core' circuit of both the cs-3 and the DOD are nearly identical - the boss uses the active tone control, the DOD uses the additional VCA for 'high expansion' or whatever, which to me looks like they use a HPF, mix the compressed high-pass filtered signal to the end mixing back with the the 'raw' compressed signal (which would be like the CS-3 signal, but pre-tone control or tone control centered), with the HPF also feeding the second THAT VCA with some kind of feedback (?) around it allowing you to dial in some control of the HPF/VCAd signal to affect the first VCA as well....or something. It confuses me, I'm just trying to make sense of it, some of the above may be partially true, someone who understands this all far more could correct me where I'm wrong and explain it all better & more accurately.

But in the end, the core compression circuit is near identical to the CS-2 outside of the 'range' of the compression control voltage divider, and the DOD controls the VCA via it's non-inverting pin and the Boss CS-3 controls it via it's inverting pin...which may or may not be a negligible difference, or merely due to the DOD's initial buffer is inverting, and the boss's is non-inverting....

twangster · Post by **twangster** » 05 Dec 2017, 17:45

Hi, if I wanted to replace the IC buffer which should be among those in the picture? Is a TL072 better suited for that purpose? I'm totally newbie

Sorry for my bad english, I hope you understand what I wrote

Lani · Post by **Lani** » 30 Mar 2020, 09:02

Anyone know if this schematic has been verified. I have a bunch of old DBX 2150a that I would love to try in this circuit. I belive they are compatible. I'm looking into building a SSL too!!

bugg · Post by **bugg** » 31 Mar 2020, 03:51

Lani wrote:Anyone know if this schematic has been verified. I have a bunch of old DBX 2150a that I would love to try in this circuit. I belive they are compatible. I'm looking into building a SSL too!!

I have some PCBs for it, but haven't had a chance to verify them yet.

Daniel · Post by **Daniel** » 18 May 2023, 00:31

Hi!!!

I have one of these pedals and it's great, but inspecting on it i think i found buffer is failing, can someone tell me which IC is the buffer so i can replace it please?

DOD - FX84 Milkbox Compressor [schematic]