Rocktek - DIR-01 Distortion  [schematic]

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Rocktek - DIR-01 Distortion  [schematic]

Postby JiM » 07 Dec 2008, 16:25

There's room for improvement on this one ...
I'ts a cheap distortion that i bought in a toy store almost 15 years ago, and it sounds great for 80's metal ... :slap:
It has no clean, no crunch, the tone control is inefficient, it hisses a lot, and reduces volume. Can be used with bass too. :mrgreen:
BUT there is a JRC4558DD inside, the input buffer is quite transparent, and the plastic case is really sturdy.

It looks like that, except mine has a pink battery cover/name plate (early version)

Link to some reviews : http://filters.muziq.be/model/rocktek/dir01

Don't search for "BC536" it's a mistake : Q1 has only "536 F2H" written on it, it's more likely a 2SC536 or 2SC536N.
I already reduced R26 who limits the DIST pot travel, in order to get some crunch back, but then it lacks volume.
Messing with diodes should be easy : removing them, asymetrical clipping, LEDs for more amplitude ...
Any idea to reduce noise ?
Or should i get into heart surgery and mod it into a Tube Screamer ?

PS : i almost forgot, here is the schematic :
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Re: Rocktek Distortion DIR-01

Postby cbriere » 07 Dec 2008, 17:38

mmm :scratch:
change clipping diodes for RED LEDS, reduce C20 and change opamp for OPA2134 for real Marshall type dist.
just a suggestion. :thumbsup
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Re: Rocktek Distortion DIR-01

Postby JiM » 08 Dec 2008, 00:05

Hey, you're right, the circuit looks a bit like a Guv'nor ! Thanks for pointing that.
A pair of red leds is the first thing i'll try ... :wink:

And maybe replace the tone control by the "controur" filter from the Valvestate series.
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Re: Rocktek Distortion DIR-01

Postby bay-fisher » 15 May 2010, 10:05

I have one of these beasts too and I'm keen to mod it into something remotely useable. Anybody done the mod suggested here or have any other ideas as how to pimp the pedal?
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Re: Rocktek Distortion DIR-01

Postby JiM » 15 May 2010, 22:39

The first mod i did was to short the 3.3k resistor next to the gain pot (R26) to lower the gain. This brings the pedal back in the rock'n'roll world. Beware, with the pot at zero there is no sound.

Then i wired an on-off-on switch to select either the original silicon diodes, a pair of red LEDs, or nothing. The latter provides quite a big volume boost, and a nice overdrive when you crank the gain. The LEDs have a nice sound, i'd say in between the other two : still distorted, but not as ear-piercing fizzy. Less distortion than Si, but less volume than bare. Quite Marshall-esque in fact.

Last week i went into some more mods, in order to even out the volume of the different diode modes. I did some Spice simulations, and eventually replaced the jumper across R26 by a 220k resistor (I shoud have made it a bit smaller) and used the other pole of my on-off-on DPDT switch to mess with R28 and get some volume back from the Si position. I'm not convinced by this latest mod, too much high frequencies, i needs more tweaking.

So, in this order : shunt R26, clip the diodes, enventually replace them with LEDs, and you won't look at this perdal as a "hair-metal crap" anymore.
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Re: Rocktek Distortion DIR-01

Postby bay-fisher » 21 May 2010, 09:22

I removed R26, D5 and D6 as shown in the above scematic and now have no sound when I switch the pedal on. Although no sound is better than the fizzy distortion it had before, I would like to get something out of it.
Do I need to replace the resistor or diodes with something, even a wire, to get some sound back? Do I need to put LEDs where the diodes were to recover some sound? At the moment I have nothing there.
I'm going to check my battery and cables to make sure I've not overlooked something there.
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Re: Rocktek Distortion DIR-01

Postby JiM » 21 May 2010, 16:40

bay-fisher wrote:I removed R26, D5 and D6 as shown in the above scematic and now have no sound when I switch the pedal on. Although no sound is better than the fizzy distortion it had before, I would like to get something out of it.
Do I need to replace the resistor or diodes with something, even a wire, to get some sound back?

Yes, you need to replace R26 with a wire.

bay-fisher wrote: Do I need to put LEDs where the diodes were to recover some sound? At the moment I have nothing there.

You need not, but you might like it. Or you can do like me, and keep the choice by adding a switch.
With no diodes, it's more like a booster : huge volume available, but maximum gain provides more overdrive than distortion. With leds, it's about in-between that and the stock sound.
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Re: Rocktek Distortion DIR-01

Postby bay-fisher » 22 May 2010, 08:07

Cheers.
I replaced the resistor with a wire and took out the diodes. The result is a nice clean boost in volume which works really well to push my Big Muff clone.
Thanks for the advise - a cheap pedal salvaged into something reasonable.
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Re: Rocktek Distortion DIR-01

Postby tasteless » 01 Jun 2010, 16:42

OMG ! I'd forgotten that I even have one of these.
I think I'll follow Your lead, However just glancing at the schem. I think I'll bump up the ceramics a bit.
I'm off to look for it now-Cheers guys !
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Re: Rocktek Distortion DIR-01

Postby debolestis » 16 Jun 2010, 00:24

How to mod this for Bass?
Thank you!
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Re: Rocktek Distortion DIR-01

Postby JiM » 16 Jun 2010, 20:51

debolestis wrote:How to mod this for Bass?
Thank you!

It depends on what you want to acheive ... some people would like it as is !

Letting more bass frequencies through usually involves increasing the value of series caps, but this can become muddy.
Another popular use of effects for bass is to mix some clean signal with the processed signal, either inside or outside of the pedal (with a dedicated box or a small mixer board). This can be done full-band, or with some crossover filtering : dry bass, wet treble.

So, which part of the sound do you dislike when using it with a bass ?
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Re: Rocktek Distortion DIR-01

Postby debolestis » 17 Jun 2010, 13:59

Hi, thank you much for your reply.
It didn't let any bass to output. So I changed C1 to 1uF, now it is a little basssier. Also I connected 0,047 uF cap on middle lug of dist pot. It removed hiss. This mixing of clean and processed signal seems like a good Idea. Can you give me an example of it. Can you draw it on dir-01 scheme.
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Re: Rocktek Distortion DIR-01

Postby JiM » 17 Jun 2010, 21:30

debolestis wrote:This mixing of clean and processed signal seems like a good Idea. Can you give me an example of it. Can you draw it on dir-01 scheme.

Here is a good example (and some further links included) : http://seanm.ca/stomp/bblender.html
Just wire the "send" to the input of the pedal, and the output to the "return".
Or keep it as a separate box for use with any other pedal, or a full chain.
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Re: Rocktek Distortion DIR-01

Postby debolestis » 13 Jul 2010, 23:15

Hi, in the end I like this pedal a lot it sounds great on my bass.
Now I want to rehouse it in aluminum case. I want a true bypass switch what do I need to do on this pedal?

Thank you!
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Re: Rocktek Distortion DIR-01

Postby mictester » 13 Jul 2010, 23:48

JiM wrote:There's room for improvement on this one ...
I'ts a cheap distortion that i bought in a toy store almost 15 years ago, and it sounds great for 80's metal ... :slap:
It has no clean, no crunch, the tone control is inefficient, it hisses a lot, and reduces volume. Can be used with bass too. :mrgreen:
BUT there is a JRC4558DD inside, the input buffer is quite transparent, and the plastic case is really sturdy.

It looks like that, except mine has a pink battery cover/name plate (early version)

Link to some reviews : http://filters.muziq.be/model/rocktek/dir01

Don't search for "BC536" it's a mistake : Q1 has only "536 F2H" written on it, it's more likely a 2SC536 or 2SC536N.
I already reduced R26 who limits the DIST pot travel, in order to get some crunch back, but then it lacks volume.
Messing with diodes should be easy : removing them, asymetrical clipping, LEDs for more amplitude ...
Any idea to reduce noise ?
Or should i get into heart surgery and mod it into a Tube Screamer ?

PS : i almost forgot, here is the schematic :


Reduce R28 (or put 10k in parallel with it) to get the level up a lot!
"Why is it humming?" "Because it doesn't know the words!"
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Re: Rocktek Distortion DIR-01

Postby bobo » 18 Jul 2010, 03:54

Hi..

How can I increase more bass.? The tone pot is too much treble.
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Re: Rocktek Distortion DIR-01

Postby debolestis » 20 Jul 2010, 10:19

I changed c9 to 22n, maybe 47n will be better, try it.
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Re: Rocktek Distortion DIR-01

Postby bobo » 21 Jul 2010, 01:25

Thank you for advise. I already tried 22n still too much treble, will try 47n
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Re: Rocktek Distortion DIR-01

Postby GuineaFowl » 17 Sep 2010, 12:31

  • The distortion of this pedal is always on. When you change the "Dist." knob all you're really doing is reducing how much of the first opamp stage is fed into the second. The "Dist." knob only attenuates the result of the first opamp stage it does not vary the distortion in a meaningful way.
  • Even with the "Level" knob at maximum you will get a volume decrease when you switch this effect on. R28 is at fault and serves no purpose!
  • Some people dislike the standard tones available through the "Tone" knob and I provide a set of graphs showing the frequency response curves with different values of C9 for those people.

I think JiM and others have put forward a good suggestion of using LEDs as clipping diodes to address the problem of not really being able to lower the amount of signal being fed through the clipping diodes. LEDs clip at a higher voltage than the stock diodes which makes it seem as if there is more "head room" before it starts distorting.

JiM also mentioned jumpering R28 as a way to increase volume but said that he felt it introduced too many highs. I wasn't convinced of this. I felt that R28 played a part in the level knob's function, not the tone knob's function. Using a Spice analysis I have proved that R28 plays no part in the tone control. It is simply in series with the volume knob. You can safely replace R28 with a jumper without altering the tone at all. I am not even sure why the manufacturer puts it there because a few seconds playing with one of these effects and anyone can hear it reduces volume. R28 is not necessary at all and you will get a volume boost when you jumper it.

Lastly, I put the tone control through a Spice analysis, varying the capacitance of C9, and took graphs at 10 equally spaced positions on the tone knob for each value of C9. (Thanks to Gauss Markov for his tutorial on the BMP tone stack analysis with Spice). Attached are the results of this analysis, if you don't like the stock tone curves (with C9 set at 10nF) then perhaps these images will help you choose a new capacitance value.

C9 at 10nF (stock)
Effect on Tone Control of C9 at 10n.JPG

C9 at 22nF
Effect on Tone Control of C9 at 22n.JPG

C9 at 47nF
Effect on Tone Control of C9 at 47n.JPG
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Re: Rocktek Distortion DIR-01

Postby tasteless » 17 Sep 2010, 18:59

Cool graphs ! Thanks !
Mine's still a work in progress, And I've actually been quite restrained in just making miniscule adjustments.
I have'nt touched the Distortion or Volume Yet ,Nor the clippers.
I wasn't sure how far to go with R28 - I think I dropped it to 10K with the intention to get back to it later.
I added some bottom end and decreased the gain ,But it is still quite noisy (well its a LOT quieter -But theres still a way to go).
I hav'nt got my notes with me right now But, I can tell You I increased C3,4,5,6,9 and 20 in very small steps.(didnt like C1-too fuzzy).
Havent done the interstage electros /did replace filter caps and voltage divider/bias resistors.
Decreased R16 to 1k /R15 to something smaller and I'm not sure about the gain at R10 and R14 But its lower.
I'm kind of going for a darker, crunchier ,Marshallier sort of thing and its sounding quite nice.
Oh yeah I socketed a TL072 which I think I prefer !
I reckon a lot of the noise could be tamed just by better quality components here and there.(ie- electros).
And maybe some foil !
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