Top Tone - Light Drive  [traced]

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Re: Top Tone Light Drive

Postby JOHNO » 19 Feb 2012, 11:49

I used your schematic from the previous page accept i used 990k for R12 and 120r for R13 and R14 i cannot go any higher than 1k or the squealing (oscillating) starts. I used the layout that i posted above and used RCA 741ca for both op amps. I changed out the second op amp for a UA741 but had the same result. I check over the layout and my build and it all checks out with the schematic.
P.S The good sounds come when i use 6.8k at R14 but it squeals. Maybe C12 needs to be higher. Or maybe C11 needs to be changed, I'm just guessing.
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Re: Top Tone Light Drive

Postby MWichni » 19 Feb 2012, 11:56

If I am correct you used as follows:
R11- 990k
R12- 990k
R13- 120R
R14- 120R
Right?

Maybe that 1nF capacitor is too much, try 10pF or 100pF as in first stage. If this will help try to put back 6.8k for R14.

EDIT:
I'll try my build today I hope. So later I'll report back what I achieved with this circuit.
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Re: Top Tone Light Drive

Postby JOHNO » 19 Feb 2012, 12:21

MWichni wrote:If I am correct you used as follows:
R11- 990k
R12- 990k
R13- 120R
R14- 120R
Right?

Wrong R11 is 1M. R14 is connected to my resistor wheel so as i can change the value on the fly. As i said earlier if i go above 1K on R14 the circuit starts to squeal. Here are the ic voltages i think they look ok but i dont really know. Supply voltage is 8.7V
IC1 IC2
PIN PIN
1-0.01 1-0.01
2-4.25 2-4.32
3-3.70 3-4.11 < is that right?
4-0 4-0
5-0.01 5-0.01
6-4.29 6-4.32
7-8.62 7-8.62
8-0 8-0

I'm thinking that C12 (1nf) maybe too small because if i up it to 4n7 the squealing subsides slightly.
How did you come up with the value of C11 (47nf) was that a guess or could you read the value of the component?

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Re: Top Tone Light Drive

Postby MWichni » 19 Feb 2012, 12:53

C11 was rather a guess, you can experiment with that value. With that 1nF you can experiment too. I couldn't determine them unfortunately.
That one higher voltage is the result of using 10k instead of 1M like it is in the first stage. But it shouldn't change anything much I think, a little bigger current is getting to the pin 3 of IC2. Besides that 10k value is read from the pictures and looks sensible in the place where it is used.

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Re: Top Tone Light Drive

Postby JOHNO » 20 Feb 2012, 05:09

Turns out that C11 was the culprit. I stuck a 2.2nf in there and the oscillation and the splattering went away. I had 6.8k in R14 but now i can go as high as 1m for R14 and no oscillating, so you can stab in the dark as to the value you put in there i guess. I still need to play around and tune C11 C12 and R14 a bit but, its rockin my fuckin sox off through my vht. Whether its the cornish SS-2 or not i like it alot. Thanks again for all you work MWichni.

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Re: Top Tone Light Drive

Postby MWichni » 20 Feb 2012, 08:20

JOHNO wrote:Turns out that C11 was the culprit. I stuck a 2.2nf in there and the oscillation and the splattering went away. I had 6.8k in R14 but now i can go as high as 1m for R14 and no oscillating, so you can stab in the dark as to the value you put in there i guess. I still need to play around and tune C11 C12 and R14 a bit but, its rockin my fuckin sox off through my vht. Whether its the cornish SS-2 or not i like it alot. Thanks again for all you work MWichni.


Hi JOHNO, it's great that you figured out what was the problem and how to prevent oscillation. Yesterday looking at the pictures I noticed that I can read one more value, so you can play with this one also. It's the value of the C7 which I marked 1nF following the MXR schematic while from the picture I can read 10nF. Unfortunately I hadn't time yesterday to complete and test my build but I hope to do it next weekend. Could you make a parts list using my schem numbering? It would be great to know what values you used. Thanks in advance.
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Re: Top Tone Light Drive

Postby JOHNO » 20 Feb 2012, 08:55

I used exact parts values as in your schematic the only differences are,

C11-2.2nf But haven't decided on a final value yet.
C12-1nf and upwards, haven't decided on a final value yet.
C13- 4.7uf for more bottom end. It's a little bright sounding on the low strings with 1uf. I think the G2 has 4.7uf too.
R14- 68K It hisses a bit more with 68k as opposed to 6.8k but it sounds more "grindy" if thats a word.

You should socket those components so you can tune them yourself.
FYI I put in a UA 741 for U2 and there was a massive volume drop as compaired to the RCA CA741. So i put back the CA741, go figure.
It isn't massively loud like some circuits ( think Big muff) but I get way more than unity gain with the volume dimmed. My MRX Distortion + clone only gets just over unity when i dime it.
Anyway i'm starting to ramble, good luck with your build.
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Re: Top Tone Light Drive

Postby MWichni » 20 Feb 2012, 09:26

JOHNO wrote:I used exact parts values as in your schematic the only differences are,

C11-2.2nf But haven't decided on a final value yet.
C12-1nf and upwards, haven't decided on a final value yet.
C13- 4.7uf for more bottom end. It's a little bright sounding on the low strings with 1uf. I think the G2 has 4.7uf too.
R14- 68K It hisses a bit more with 68k as opposed to 6.8k but it sounds more "grindy" if thats a word.

You should socket those components so you can tune them yourself.
FYI I put in a UA 741 for U2 and there was a massive volume drop as compaired to the RCA CA741. So i put back the CA741, go figure.
It isn't massively loud like some circuits ( think Big muff) but I get way more than unity gain with the volume dimmed. My MRX Distortion + clone only gets just over unity when i dime it.
Anyway i'm starting to ramble, good luck with your build.


68k hisses because you have too much gain. 68000/130= 523 of gain! 6800/130= 52 which should be just ok. Remember that R13 and R14 are determining the gain of the op-amp, and C11 cut DC as we only want to amplify the AC- our signal. Hope this helps.
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Re: Top Tone Light Drive

Postby Ghandi » 21 Feb 2012, 00:36

MWichni wrote:Yesterday looking at the pictures I noticed that I can read one more value, so you can play with this one also. It's the value of the C7 which I marked 1nF following the MXR schematic while from the picture I can read 10nF. Unfortunately I hadn't time yesterday to complete and test my build but I hope to do it next weekend. Could you make a parts list using my schem numbering? It would be great to know what values you used. Thanks in advance.


That would make perfect sense to me, I pimped my Distortion+ years ago by ear to get a smoother (more tube like) sound.

I ended with two changes,on the TT schematic:
C7 = 10nF
R8 = 8K2

makes a pretty big difference on how it sounds!

cheers
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Re: Top Tone Light Drive

Postby MoonWatcher » 21 Feb 2012, 13:28

MWichni wrote:
sinner wrote:Looks very much like two cascaded RAT's to me, am I right?


Totally not. If I traced it properly it is a Distortion + with added tonestack and second gain stage.


Hmm... :hmmm: sounds like the OCD to me. :lol:

Well, had to do the lineage, I guess. OD250/D+=>Voodoo Lab OD=>OCD.

I'd love to do a Rat stage followed by a decent recovery stage (TL071/NE5534/etc.). Always seemed like the output buffer wasn't doing enough at unity gain (could be tightened up a bit). It would even open up some options for the Filter control.
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Re: Top Tone Light Drive

Postby MWichni » 07 Dec 2012, 08:48

Hi, thanks to the thread about Skrydstrup ODR-2 I have corrected some values on my schematic. I have replaced few components on my pcb and now it works as it should. So I am posting the end result of the reverse engineering of this pedal.
I can also post corrected pcb for this one if someone is interested.
(C3 and C12 are not needed for this project so you don't have to mount them; I added a C15 to the input after the Skrydstrup ODR-2 and I recommend to mount this one; Skrydstrup also
don't have C5)

Here it is:

Image

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Re: Top Tone Light Drive

Postby MWichni » 07 Dec 2012, 09:58

PCB of course corresponds to the schematic. Resolution is 600 dpi.
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Re: Top Tone Light Drive

Postby JOHNO » 01 Jan 2013, 06:07

I decided to revisit this circuit today and what do I find? A new schematic? So I change a few bits and pieces in my old build an low and behold it works like a charm. No more squealing just lovely overdrive distortion.
So now im gonna be playing FREE's Cant get enough and drinking beer all afternoon. Thanks so much for all your great work MWichni your a champion.
My layout posted here earlier is now verified.
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Re: Top Tone Light Drive

Postby MWichni » 01 Jan 2013, 21:02

JOHNO wrote:I decided to revisit this circuit today and what do I find? A new schematic? So I change a few bits and pieces in my old build an low and behold it works like a charm. No more squealing just lovely overdrive distortion.
So now im gonna be playing FREE's Cant get enough and drinking beer all afternoon. Thanks so much for all your great work MWichni your a champion.
My layout posted here earlier is now verified.
Johno


Hi, great to hear some kind words from you. I'm also playing this overdrive a lot. It sound just great.
Regards,
Mariusz.
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Re: Top Tone Light Drive

Postby JOHNO » 02 Jan 2013, 01:30

atreidesheir wrote:BTW are you guys using 741 chips or others?


Yes i used a pair of CA741. I just love those noisy little buggers.

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Re: Top Tone Light Drive

Postby JOHNO » 02 Jan 2013, 08:25

I did this bread board layout for myself so i could dick around with this circuit, thought i would share it here in case any one is interested. I know its a weird thing to post but there it is. Be sure to wire the power rails to suit your bread board. The components in the top left corner i left out as they didn't make much difference to my ears. Also i left out C15 but you can try it if you like.
light drive bread board layout.png

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Re: Top Tone Light Drive

Postby MWichni » 02 Jan 2013, 10:33

I also used two 741. Cheers.
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Re: Top Tone Light Drive

Postby Amstel » 02 Jan 2013, 18:03

It sounds similar to a SS2 or not?
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Re: Top Tone Light Drive

Postby MWichni » 04 Jan 2013, 16:56

It is a SS-2. I reccomend you to build it and find it out yourself.
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Re: Top Tone Light Drive

Postby fakcior » 04 Jan 2013, 19:00

Technically it's SS-2 without Cornish's input buffer.
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