Help me to better understand the TS9/SD-1 circuit

grrrunge · Post by **grrrunge** » 22 Mar 2011, 17:57

Hi all!

I recently bought a TS9 as a substitute for my SD-1, and afterwards i thought i'd give the SD-1 a spin on the workbench, to see if i can get it to behave a bit more like i think it should.
I'm the kind of guy who learns best by writing stuff down while studying on the subject, so i thought that as i progress, i might as well write an entry level article about the various building blocks of the circuit (input- and output buffers, drive circuit and tone control circuit mostly), and list some of the crucial mod-points with audio examples along the side, so that n00b's like myself - at this point at least - can easily understand where to mod their SD-1 to get the sound they're after.

I understand that the SD-1 and the TS9 are almost identical circuit-wise, so a little TS9 reading as well as technical explanations about the structure of the various blocks, won't scare me off. I find myself capable of handling a fair level of abstraction

So far i've written an introduction to my SD-1 modification journey. I really hope you guys can point me towards some interesting reading about the various circuit "blocks".

Abstract:

My musical preferences drives me towards the use of modern hi-gain guitar amplifiers such as ENGL, Mesa/Boogie, Soldano etc. Even though these amps tend to deliver more than enough overdrive on their own, i really like the extra oomph they deliver, when i slam the front of the amp with a slightly overdriven, boosted guitar signal.
To do so, i have been using a BOSS SD-1 "Super Overdrive" for quite some time. Even though i like it a lot, i find it a bit insufficient for my use in the following points:

⁃ The high mids gets a bit too lo-fi for my taste.
⁃ The punchy lows that my amps provide on their own seems to disappear when i engage the pedal
⁃ As i only use the lower gain settings, i don't need blistering amounts of overdrive from the pedal, instead i would like to have more control of the lower gain area (from 6-11 0'clock on the stock SD-1)
⁃ On "higher" low gain settings, the sound tends to get a bit compressed. I prefer an open "breathing" sound from the overdrive section, as i can always use a compressor later in the signal chain.
⁃ The higher drive settings seem a bit too harsh for my taste

Project Description:

To suit my needs from the pedal better, i would like to replace existing components on the SD-1's PCB to achieve the following when the pedal is engaged:

⁃ Accentuate high mids
⁃ Retain the guitars natural low end response
⁃ Reduce overdrive, thus increasing control over the lower gain settings
⁃ Obtain smoother, less compressed overdrive

First Hand Experiments:

Before i started this project, i installed a DIP-8 socket in place of the JRC4558DD chip that came in the stock unit. I toyed around with various op-amps, and found that i liked the sound of the MC1558N better than the other chips i tried, including the stock JRC4558DD, JRC1458D, JRC5532D, CA3240E and a TL082CN. I have yet to try the OPA2134 stuff. I suppose that's gonna come around sometime too.

Peace out! /grrrunge

Post by **azrael** » 22 Mar 2011, 18:17

Have you read this?

http://www.geofex.com/article_folders/t ... sxtech.htm

For less compressed distortion increase the clipping threshold by changing out the diodes. Use diodes in series to give it a higher clipping threshold, to make it use 4 silicon diodes (1N914/1N4148). Try red LEDs, yellow LEDs....Lots of options here.

You will see that this also opens up your upper midrange a bit.

grrrunge · Post by **grrrunge** » 22 Mar 2011, 22:56

azrael wrote:Have you read this?

http://www.geofex.com/article_folders/t ... sxtech.htm

For less compressed distortion increase the clipping threshold by changing out the diodes. Use diodes in series to give it a higher clipping threshold, to make it use 4 silicon diodes (1N914/1N4148). Try red LEDs, yellow LEDs....Lots of options here.

You will see that this also opens up your upper midrange a bit.

Thanks! I remember seing this one before, but forgot about it again

Adding diodes in series is going to add their forward voltages, right? Like one 1n4148 diode has a clipping of about 500mV, 4 1n4148's in series wil clip at 2V, is that correctly understood?

DrNomis · Post by **DrNomis** » 23 Mar 2011, 08:07

grrrunge wrote:
azrael wrote:Have you read this?

http://www.geofex.com/article_folders/t ... sxtech.htm

For less compressed distortion increase the clipping threshold by changing out the diodes. Use diodes in series to give it a higher clipping threshold, to make it use 4 silicon diodes (1N914/1N4148). Try red LEDs, yellow LEDs....Lots of options here.

You will see that this also opens up your upper midrange a bit.
Thanks! I remember seing this one before, but forgot about it again
Adding diodes in series is going to add their forward voltages, right? Like one 1n4148 diode has a clipping of about 500mV, 4 1n4148's in series wil clip at 2V, is that correctly understood?

That's correct, Leds have a forward voltage drop that's equal to two, or four Si diode diode drops, but it depends on what colour Led you're using, a Blue led drops about 3 Volts.....

phatt · Post by **phatt** » 23 Mar 2011, 08:15

Quote from *grrrunge*
"hi-gain guitar amplifiers such as ENGL, Mesa/Boogie, Soldano etc. Even though these amps tend to deliver more than enough overdrive on their own, i really like the extra oomph they deliver, when i slam the front of the amp with a slightly overdriven, boosted guitar signal."

Then you simply have the wrong pedal!

Try a voltage boost instead! like the Fet mu boosters they simply make the signal larger.

If you want more distortion from a Valve Amp just send a bigger signal

Fuzz box circuits just add distortion but very little is added to signal swing which is why you end up goin in circles with pedals.

In the case of All SS amplification then you have no choise but to add preamp distortion So don't mix up the two.
You have to think in different terms when using the different types of Amplification.

TS9 is basically a fuzz box and this is not really much use for the tube Amps you mention.

A TS 9 sounds good in front of Early Valve Amps but is ugly in front of a lot SS Amps.
Phil.

grrrunge · Post by **grrrunge** » 23 Mar 2011, 15:12

phatt wrote:Quote from *grrrunge*
"hi-gain guitar amplifiers such as ENGL, Mesa/Boogie, Soldano etc. Even though these amps tend to deliver more than enough overdrive on their own, i really like the extra oomph they deliver, when i slam the front of the amp with a slightly overdriven, boosted guitar signal."

Then you simply have the wrong pedal!
Try a voltage boost instead! like the Fet mu boosters they simply make the signal larger.

If you want more distortion from a Valve Amp just send a bigger signal
Fuzz box circuits just add distortion but very little is added to signal swing which is why you end up goin in circles with pedals.

In the case of All SS amplification then you have no choise but to add preamp distortion So don't mix up the two.
You have to think in different terms when using the different types of Amplification.

TS9 is basically a fuzz box and this is not really much use for the tube Amps you mention.

A TS 9 sounds good in front of Early Valve Amps but is ugly in front of a lot SS Amps.
Phil.

I'm a tube amp guy

The reason i like a little bit of overdrive before the overdriven amps, is that i can roll the amp gain back a little, keep all the growl, and cut better through the mix. I'm playing low tuned rythm stuff most of the time, so cutting through without loosing too much bottom is crucial

I've tried several boosters, and none of them seems to do the trick for me.

grrrunge · Post by **grrrunge** » 23 Mar 2011, 15:16

DrNomis wrote:
grrrunge wrote:
azrael wrote:Have you read this?

http://www.geofex.com/article_folders/t ... sxtech.htm

For less compressed distortion increase the clipping threshold by changing out the diodes. Use diodes in series to give it a higher clipping threshold, to make it use 4 silicon diodes (1N914/1N4148). Try red LEDs, yellow LEDs....Lots of options here.

You will see that this also opens up your upper midrange a bit.
Thanks! I remember seing this one before, but forgot about it again
Adding diodes in series is going to add their forward voltages, right? Like one 1n4148 diode has a clipping of about 500mV, 4 1n4148's in series wil clip at 2V, is that correctly understood?

That's correct, Leds have a forward voltage drop that's equal to two, or four Si diode diode drops, but it depends on what colour Led you're using, a Blue led drops about 3 Volts.....

Looks like i'm gonna have to try out some blue LED's! Thanks for verifying

DrNomis · Post by **DrNomis** » 23 Mar 2011, 15:43

grrrunge wrote:
DrNomis wrote:
grrrunge wrote:
azrael wrote:Have you read this?

http://www.geofex.com/article_folders/t ... sxtech.htm

For less compressed distortion increase the clipping threshold by changing out the diodes. Use diodes in series to give it a higher clipping threshold, to make it use 4 silicon diodes (1N914/1N4148). Try red LEDs, yellow LEDs....Lots of options here.

You will see that this also opens up your upper midrange a bit.
Thanks! I remember seing this one before, but forgot about it again
Adding diodes in series is going to add their forward voltages, right? Like one 1n4148 diode has a clipping of about 500mV, 4 1n4148's in series wil clip at 2V, is that correctly understood?

That's correct, Leds have a forward voltage drop that's equal to two, or four Si diode diode drops, but it depends on what colour Led you're using, a Blue led drops about 3 Volts.....
Looks like i'm gonna have to try out some blue LED's! Thanks for verifying

Try two 3mm Blue Leds as symmetrical clippers...

1oldsidewinder · Post by **1oldsidewinder** » 26 Mar 2011, 17:38

Try this for starters:
D4, D6 - 5mm red LED
D5 - jumper
C5 - .022uf
C6 - remove, don't jumper
R8 - 2.2k
Put a 47pf cap across one of the LED's for a smoother distortion if you want to.

These changes should get you close to what you're describing. The change to the C5/R8 network drops the corner freq to around 3.3k and allows more upper mids to pass. Removing C6 defeats a filter and gives a little more presence.

grrrunge · Post by **grrrunge** » 27 Mar 2011, 11:08

1oldsidewinder wrote:Try this for starters:
D4, D6 - 5mm red LED
D5 - jumper
C5 - .022uf
C6 - remove, don't jumper
R8 - 2.2k
Put a 47pf cap across one of the LED's for a smoother distortion if you want to.

These changes should get you close to what you're describing. The change to the C5/R8 network drops the corner freq to around 3.3k and allows more upper mids to pass. Removing C6 defeats a filter and gives a little more presence.

Thanks!

C6 is already gone

As far as i can read from the schematic, R7 and C4 forms a low pass filter after the drive section. I have removed C4, allowing all upper frequencies to pass through (sounds harsh like shit

), and at the moment i'm waiting for a bunch of caps to arrive in the mail. My plan is to replace the stock .018nF with a .01nF to raise the corner frequency of the post-drive filter to ~1.6khZ from the former ~880hZ. How does that sound in terms of brightening the circuit? Is it better/more efficient to chance the tone control?

Excactly how does that tone control network work?

1oldsidewinder · Post by **1oldsidewinder** » 28 Mar 2011, 04:29

I came up with those values while working on a low-gain version of analogguru's excellent Clay Jones mod for the SD-1. From your description, I thought they might be close to what you're looking for. I typically control the lows before clipping with the C3/R6 network. Higher values of C3 will give you more bass, lower for less. I haven't tried the values you mentioned for C4/R7. Sounds like an interesting experiment. For a good explanation of how the tone control works, check out the circuit explanation in Brian Wampler's "How to Modify Guitar Pedals". I don't want to quote him because it's copyrighted material, but it may be available as a PDF somewhere on the web. Beat of luck!

grrrunge · Post by **grrrunge** » 31 Mar 2011, 14:28

1oldsidewinder wrote:I came up with those values while working on a low-gain version of analogguru's excellent Clay Jones mod for the SD-1. From your description, I thought they might be close to what you're looking for. I typically control the lows before clipping with the C3/R6 network. Higher values of C3 will give you more bass, lower for less. I haven't tried the values you mentioned for C4/R7. Sounds like an interesting experiment. For a good explanation of how the tone control works, check out the circuit explanation in Brian Wampler's "How to Modify Guitar Pedals". I don't want to quote him because it's copyrighted material, but it may be available as a PDF somewhere on the web. Beat of luck!

Thanks for all this! I'll write back/post samples when i get the parts from WIMA. I was also wondering if replacing all resistors with a 1% metal film type would do any good? I would really like this to be as hi-fi sounding as possible

open, crisp and distinct are the keywords here.

grrrunge · Post by **grrrunge** » 06 Apr 2011, 09:39

Okay, so i found these two clips on youtube of Brian Wampler going briefly over the TS9/SD-1 circuit schematics.

I now understand that the tone pot along with C5 and R8 forms some sort of variable resonant filter. I understand how Wampler calculates the minimum and maximum values values, but i don't quite get how the filter works.
I also don't get how the frequency boosting occurs, unless the positive and negative inputs act like some sort of multiplying mixer.

At some point Wampler states that increasing R9 will give the pedal more volume.
I assume that with C6 removed, there is only R9 in the negative feedback loop? As far as i have understood, the greater the difference between the positive and negative input on the op-amp, the more the output signal will be amplified. Is that correct?

If anyone's got more sources of information, please chip in! I'm writing a noob-to-noob article here, so the better i understand the circuit, the better i will be able to explain it in laymen's terms

It's my way of learning stuff and giving back to the community

grrrunge · Post by **grrrunge** » 12 Apr 2011, 20:40

So, i was toying around with my MT-2 the other day, doing the 'remove nasal mids' mod from one of Wamplers boks, and guess what came out? The cap value i wanted to try out for C4 (0.01uF instead of 0.018uF) on my SD-1

That should raise the hi-cut after the clipping section from around 880hZ to around 1.5khZ

I popped it in to see what happened... It seems like it just opens the range of the tone control a bit towards the higher frequencies on the high tone settings. Turning the tone control below 12 o'clock still just seems like pulling a blanket over the amp.

I ordered a VHT special6 from thomann for home practice and mod testing purposes, and i'll post some progress clips once i recieve it. Sadly it's currently backordered

grrrunge · Post by **grrrunge** » 12 Apr 2011, 21:00

I guess this thread is becoming my own cut-and-paste board for the project... I just found this: http://www.muzique.com/lab/tstone.htm , which looks like a pretty good explanation of the tone circuit. I'll be looking into that tomorrov

Post by **azrael** » 12 Apr 2011, 23:05

so what's your current schematic look like?
I've been toying with the TS circuit myself, and mine looks mostly like a Timmy now, haha.

grrrunge · Post by **grrrunge** » 13 Apr 2011, 14:12

azrael wrote:so what's your current schematic look like?
I've been toying with the TS circuit myself, and mine looks mostly like a Timmy now, haha.

I'm playing around with the SD-1

C6 is removed, C4 changed to 0.01uF and D5 is jumpered for symmetrical clipping. It's still cutting a lot of low end when i switch it on. I'm still waiting for my caps to arrive from wima, and then those days are over

mictester · Post by **mictester** » 14 Apr 2011, 00:04

grrrunge wrote: but i don't quite get how the filter works.
I also don't get how the frequency boosting occurs,
As far as i have understood, the greater the difference between the positive and negative input on the op-amp, the more the output signal will be amplified. Is that correct?

The Filter (and the frequency boosting) - a capacitor works as a frequency dependant resistor. The "reactance" of a capacitor is the AC equivalent of resistance. At any given frequency, a capacitor will (effectively, and only to AC signals) behave like a fixed resistor.

The formula for capacitive reactance is Xc = 1/(2.pi.f.C) where f is frequency in Hz and C is capacitance in Farads. You'll see that the reactance (the "AC resistance") is inversely proportional to frequency.

Op-amp gain: There are two formulae for gain - one for the inverting and one for the non-inverting version: Inverting is simply the value of the negative feedback resistor divided by the value of the input resistor. The non-inverting version is one plus the negative feedback resistor divided by the resistor that goes from the inverting input to ground (usually through a capacitor in a single rail circuit)

You'll now realise that you can make your op-amp stages frequency dependant - putting capacitors in the negative feedback loop will give a lowpass characteristic, for example.

The best resource for reading up on all this is Horowitz and Hill's book "The Art of Electronics" which is big on worked examples and how to avoid silly mistakes.

grrrunge · Post by **grrrunge** » 17 Apr 2011, 11:27

mictester wrote:
grrrunge wrote: but i don't quite get how the filter works.
I also don't get how the frequency boosting occurs,
As far as i have understood, the greater the difference between the positive and negative input on the op-amp, the more the output signal will be amplified. Is that correct?
The Filter (and the frequency boosting) - a capacitor works as a frequency dependant resistor. The "reactance" of a capacitor is the AC equivalent of resistance. At any given frequency, a capacitor will (effectively, and only to AC signals) behave like a fixed resistor.

The formula for capacitive reactance is Xc = 1/(2.pi.f.C) where f is frequency in Hz and C is capacitance in Farads. You'll see that the reactance (the "AC resistance") is inversely proportional to frequency.

Op-amp gain: There are two formulae for gain - one for the inverting and one for the non-inverting version: Inverting is simply the value of the negative feedback resistor divided by the value of the input resistor. The non-inverting version is one plus the negative feedback resistor divided by the resistor that goes from the inverting input to ground (usually through a capacitor in a single rail circuit)

You'll now realise that you can make your op-amp stages frequency dependant - putting capacitors in the negative feedback loop will give a lowpass characteristic, for example.

The best resource for reading up on all this is Horowitz and Hill's book "The Art of Electronics" which is big on worked examples and how to avoid silly mistakes.

Thanks for a great answer! I'll try and find the book somewhere

Just to clarify: Capacitive reactance is the capacitors resistance at a given frequency, right?

I understand how RC-network high- and low pass filters act as shown here: http://www.muzique.com/schem/filter.htm , but how about when they're connected in series or parallel?

RnFR · Post by **RnFR** » 17 Apr 2011, 12:19

this site has the answers, but gets pretty deep.
http://www.play-hookey.com/ac_theory/
look up first order vs. second order filters for the series answer.
this site has a lot of good info as well.
http://www.electronics2000.co.uk/