TC Electronics - Dark Matter

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Re: TC Electronic - Dark Matter

Postby Ice-9 » 17 Feb 2012, 21:23

ppluis0 wrote:[quote="Ice-9]...there are far too many vias that just are not necessary on a circuit like this...[/quote]

I think that mostly of the vias are intended to create all the test points that can bee seen in your first photograph, and also a bunch of them are to connect the solder side ground plane with the component side ground plane.

Perhaps if you mark with a coloured sharpie the vias that really connect the few solder side active traces we seen in the first photo, and with another colours those used for GND and for test points, you can faster the process.

Cheers,
Jose[/quote]


Yes indeed your correct there is a huge amount od test points. It's just the constant board turning that takes time. Sharpie idea is coll to mark the ones that matter. :applause:
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 18 Feb 2012, 17:19

I have done a little work on tracing the Dark Matter this morning, I haven't got very far yet but have traced the input upto the tone stack. The input is a two stage opamp the second part being a unity gain inverting stage, after this the signal splits in two to drive the Baxandall tone stack using two opamps one has a capacitor in the feedback loop. The strange thing from all other bax tone stacks I have seen previouslt is that R43 and R44 in this one would usually be capacitors not resistors. Someone with more knowledge than me might be able to explain this.

The gain part of the circuit is based around two more opamps and is symetrical clipping but the whole effect isn't just a modded TS or DS type circuit. It is beggining to look interesting.

Another pcb picture.

Image

I'm having trouble with attachments at the moment so am unable to post schematic so far.
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Re: Another Reversing Contribution - Short Notice

Postby ~arph » 18 Feb 2012, 18:16

Chugs wrote:I believe some of the Voodoo labs pedals used an optopcoupler as part of the switching. Check out the link.

http://stinkfoot.se/archives/1005


I've used this method, it works like a charm. It eliminates a lot of footswitch problems too.. though technically it's not true bypass anymore.. ( I don't care )
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 18 Feb 2012, 19:51

This is the first part of the schematic , I am working on the distortion and gain section so will post that as soon as I have anything to add. The bax section looks strange as the output which normally would come fromm the middle lug of the treble pot boesn't seem connect to anything other than what is in the schematic I have drwarn up ??
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Re: TC Electronic - Dark Matter

Postby Dirk_Hendrik » 18 Feb 2012, 22:30

quick hints on first imression. You're doing a fine job so far.

- IC1.2 is to be biased somewhere to Vr. Suspect R6. R6 to GND is senseless.
- C2 as well unless it's in the pF range
- R4 as feedforward loop?? no way!
-C37 like this?? Must be more there.
- There's something going from the junction of R23 and C39 to an opamp input.

Keep on posting schematic updates. The more gets clear, the easier it is to point out the uncertainties.
Sorry. Plain out of planes.

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Re: TC Electronic - Dark Matter

Postby Ice-9 » 19 Feb 2012, 16:56

Dirk_Hendrik wrote:quick hints on first imression. You're doing a fine job so far.

- IC1.2 is to be biased somewhere to Vr. Suspect R6. R6 to GND is senseless.
- C2 as well unless it's in the pF range
- R4 as feedforward loop?? no way!
-C37 like this?? Must be more there.
- There's something going from the junction of R23 and C39 to an opamp input.

Keep on posting schematic updates. The more gets clear, the easier it is to point out the uncertainties.


Thanks for the hints Dirk, I was also wondering on those points too.

R6 to ground is not going to work but after checking several times it really seems to go to ground.
R4 As feedforward loop ? This is one that really confues me (it's not hard to confuse me) But there is a missing capacitor in this which is now in the next schematic.
C37 I have not got back to check yet but I will look around that part for something else going on.
R23 and C39 Junction is going to IC4 pin 6.

For R6 to ground and feedforward resistor R4 I'm wondering,as it looks like this PCB is used in other pedals (quite a few components missing)maybe that R4 resistor is just bypassing the opamp and R6 is just tying the input and output to ground ??? Is this possible ??

I have nearly finished the whole trace but it looks like I have done it chunks that are too big, as looking back at what I have drawn is just a bit messy. So I am going to start again by doing smaller sections at a time, if everyone can bear with me while I end up making regular posts that just add little bits at a time then it might be easier for anyone to spot mistakes and other ideas to get this one done.

For each section I will post two pictures - one of the schematic part and the second of the pcb with the relevent tracks and components marked out.

Ok i'm off now to draw up the first section of the circuit again and see how this looks this time, back soon.
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 19 Feb 2012, 18:01

Back to the start for a new try. I am posting two pictures, one of the pcb marked out to match the second of the schematic.

This bit is as Dirk Hendrik pointed out earlier a bit strange, so If any one can follow the pictures and point out if it looks wrong let me know please.

PART 1
Image
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 19 Feb 2012, 19:13

I have eventually found the bias for IC2.1 . It heads off to the voice switch there are some caps and resistors around this area so I expect it is just switching a different cap to ground around pin 2 of IC2.
I need to go and buy a desk lamp so I can see better. :D
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 19 Feb 2012, 19:14

Ice-9 wrote:I have eventually found the bias for IC2.1 . It heads off to the voice switch there are some caps and resistors around this area so I expect it is just switching a different cap to ground around pin 2 of IC2.
I need to go and buy a desk lamp so I can see better. :D


I meant to say a different cap to VR
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 20 Feb 2012, 01:50

Small update to schematic. IC2.1 looks like it is getting its bias from around R11 but i need to find out where it is going tobefore i can confirm this. R6 and R4 still look out of place, but no matter how many time I look at the pcb and meter it the result is still the same. :scratch:
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Re: TC Electronic - Dark Matter

Postby greigoroth » 20 Feb 2012, 19:13

As may be apparent from the usual nature of my few posts, I don't know a schematic from a sausage, but this is awesome watching Ice (and friends) piece together this schem - it's really instructive (and at the same time impossible to follow - see aforementioned sausage/schematic paradox). Mad props Ice-9!
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 21 Feb 2012, 12:41

greigoroth wrote:As may be apparent from the usual nature of my few posts, I don't know a schematic from a sausage, but this is awesome watching Ice (and friends) piece together this schem - it's really instructive (and at the same time impossible to follow - see aforementioned sausage/schematic paradox). Mad props Ice-9!


Hi, I'm not sure how much you do or don't know about following schematics but It might be worth looking up some info on opamp circuit design, it will help you follow the circuit through and the building blocks that are being used here. knowing this would definately make thing a lot clearer.
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 21 Feb 2012, 12:46

Another small update to the schematic , I have traced out some of the distorting circuit but i'm still having a hard time finding the correct bias points for the op-amps. I am sure it will become obvious as I get the rest of the circuit traced, but for now here is an updated schematic so far.
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Re: TC Electronic - Dark Matter

Postby greigoroth » 24 Feb 2012, 22:32

Ice-9 wrote:
greigoroth wrote:As may be apparent from the usual nature of my few posts, I don't know a schematic from a sausage, but this is awesome watching Ice (and friends) piece together this schem - it's really instructive (and at the same time impossible to follow - see aforementioned sausage/schematic paradox). Mad props Ice-9!


Hi, I'm not sure how much you do or don't know about following schematics but It might be worth looking up some info on opamp circuit design, it will help you follow the circuit through and the building blocks that are being used here. knowing this would definately make thing a lot clearer.


Thanks dude! I've just gotta start building some stuff instead of reading about building stuff - but with a young fella at home it's hard to get time in the cellar to build stuff, so I tend to steal a few minutes at the guitar when he's gone to sleep, then check the forums before I crash myself. In any case, good work dude.
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Re: Another Reversing Contribution - Short Notice

Postby R.G. » 26 Feb 2012, 06:30

Chugs wrote:I believe some of the Voodoo labs pedals used an optopcoupler as part of the switching. Check out the link.

:lol:
I wondered when the commercial world would start doing this. The following is an excerpt from "The Ins and Outs of Bypassing" at geofex.com, from 1998, almost 14 years ago:

Very recently, two methods of breaking the true-bypass versus LED-indicator impasse were found.

One is known as the "Clinton bypass" or almost-true bypass method. This method connects one pole of a DPDT to the output jack and its throws select the effect output or the input jack. The second section of the DPDT turns an LED indicator on as in the tone-sucking DPDT bypass, but the alternate throw of the indicator switch section also passes a control voltage to a simple switch which is wired between the input jack and the input of the effect. In the illustration, the simple switch is implemented by a P-channel JFET, switched between fully conducting and fully off by the control voltage. When on, the JFET may be a resistance of as little as 100 ohms depending the device type, and when off it is many megohms. This very large off resistance is almost as effective at isolating the input jack from the effect input as is an open mechanical switch, and so tone sucking is avoided. The switch behaves like a true bypass although some effect circuitry still touches the signal, hence the name. This trick can be done even more simply with the now-available LED/photo-FET optoisolators like the H11F1/2/3 by simply including the LED that turns the photo-FET on in series with the indicator LED, and substituting the photo-FET for the series P-channel JFET at the effect input.


I called it the "Clinton Bypass" after our illustrious leader, William Jefferson Clinton, who once said something (to reporters) which went "I don't think you can find any evidence that it's not true..."
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Re: TC Electronic - Dark Matter

Postby phibes » 26 Feb 2012, 06:56

Slick Willy for a slick bypass!
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Re: TC Electronic - Dark Matter

Postby coldcraft » 28 Feb 2012, 15:08

good effort so far! i second the idea to keep a reference of common opamp circuits near by.
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 28 Feb 2012, 16:08

yeah sorry for the delay in getting anymore done as I have had to put my spare time into rebuilding a motorcycle engine, I shall be back on Dark Matter circuit this week. :D
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Re: TC Electronic - Dark Matter

Postby Ice-9 » 02 Mar 2012, 10:46

I have been having difficulties with the Vref for a while on this as the voltage divider seemed to go to only to one of the opamps which is drawn in the schematic so far as IC2.2 and looks like a unity gain buffer to the next stage. After checking and checking for other traces and via's from the Vref it was apparent that there just wasn't one visable. This left me with the conclusion that this may be a 3 layer board and the Vref was hiding somewhere, but my head was telling me that there is no need or reason for a 3 layer board, So after a break to do other work Iooked at the drawings I had made and the PCB to find this missing Vref. It hit me straight away, IC2.2 isn't in the audio path as it looks drwan it is in fact being used as a Vref buffer :slap:

It's amazing what a few days away from something does to make what you have been scratching your head over is staring you in the face. So I will start a redraw to the schematic to see how this alters the rest of the scriblings I have. I'm sure it will make much more sense to me now and get this one finished quite soon now.

Thanks for all your patience.
It's fairly straight forward, if you want to start it , press start. You can work out the rest of the controls for yourself !

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Re: TC Electronic - Dark Matter

Postby coldcraft » 02 Mar 2012, 21:13

good catch! I can see that now in the schematic
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