Need some TS reassurance please!!

[Govmnt_Lacky]

SO I built a TS clone..... Surprise  

My question is about the clipping diode section. With the 1N914s installed it is typical TS tone all the way however,

I also included switching to change to 3mm Red LEDs. My problem (maybe) is that when I switch to have the LEDs in the clipping section, I am getting hardly any clipping at all  

I thought the LEDs would provide a bit more bite to the OD/Distortion. Am I wrong on this?

I measured and made sure the LEDs were, in fact, "in the circuit" and there are no shorts, opens, etc. so I know they are in there. I just thought it would be more pronounced.

Thoughts??

EDIT: Used the GGG TS layout BTW. The one with clipping switch here: https://www.generalguitargadgets.com/pdf/ggg_its8_lo.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

[bluebunny]

I thought LEDs gave slightly softer clipping, rather than more "bite".  But this threads suggests modding the nearby resistor if you go for LEDs.  And elsewhere, R.G. suggests reading all of Geofex (!) to find out all about clipping.   

[pakrat]

In my experience LEDS give less gain, but louder volume. I personally like the sound of one 1N914 and one blue LED. I also have a TS with only blue LEDS and there is definitely clipping there but I have found that on all of my TS builds I need to change the 4.7k resistor to 2.2K and it's associated cap to .1uf or I have hardly any gain.

[Jazznoise]

The voltage drop of LED's can be quite different to standard diodes. Anywhere up to 1.4V. What's the drop on those?

[R.G.]

In my experience LEDS give less gain, but louder volume. I personally like the sound of one 1N914 and one blue LED. I also have a TS with only blue LEDS and there is definitely clipping there but I have found that on all of my TS builds I need to change the 4.7k resistor to 2.2K and it's associated cap to .1uf or I have hardly any gain.

Do not confuse distortion with gain. You're using "gain" to mean the amount of distortion.

A circuit with LEDs as the clippers may have more or less gain, but the LEDs will not clip until a higher signal voltage is reached. So there is a bigger signal (i.e. more volume) and it clips later, only after the signal is bigger.

Gain is not equal to distortion.

[pakrat]

Thanks R.G. I should have remembered that having read another one of your posts just a few days ago on that subject. I'm so used to the term "gain" when talking about distortion, it's hard to change 

[HOTTUBES]

I don't know the technical stuff , but i like this in my TS builds !

1n4001 + 1N34A Germ in series ( Do this for both )

This to me sounds and feels warmer like a tube amp should imo ...

[Govmnt_Lacky]

The reason why this confuses me is because I originally put symetrical 1N34s in the circuit and I barely got any clipping at all. Even with the Output and Gain dimed out I was seeing very little signal clipping. I removed the 34s and they both measured at about 0.35 FV. I then replaced them with the 3mm LEDs and it seems that I did get a boost in output however, the clipping was still very weak.

Over all, I am pleased as I have a clean volume boost to slight overdrive with the LEDs and I have the typical TS overdrive with the 914s.

I just found it odd that the 34s and the LEDs responded almost the same (the LEDs had a larger output signal) when it came to the clipping. 

[slacker]

Read R.G's technology of the TS carefully. The answer to how the LED's and Germanium diodes behave is in there. Took me a few reads before it clicked.

[J0K3RX]

I think it has a lot to do with the forward voltages

[Mark Hammer]

In my experience LEDS give less gain, but louder volume. I personally like the sound of one 1N914 and one blue LED. I also have a TS with only blue LEDS and there is definitely clipping there but I have found that on all of my TS builds I need to change the 4.7k resistor to 2.2K and it's associated cap to .1uf or I have hardly any gain.

Do not confuse distortion with gain. You're using "gain" to mean the amount of distortion.

A circuit with LEDs as the clippers may have more or less gain, but the LEDs will not clip until a higher signal voltage is reached. So there is a bigger signal (i.e. more volume) and it clips later, only after the signal is bigger.

Gain is not equal to distortion.

Drives you crazy too, eh?    Some days I want to line up all the ad copy folks, all the underinformed magazine writers, all the music store people who spout that stuff, and "go Moe" on them (we watched the recent Three Stooges movie the other week).

What I will recommend to those interested is to simply insert a 10-25k pot in series with one of the Si diodes in the feedback loop, and use that to vary the asymmetry. Has an interesting effect.  Alternatively, do what so many other pedal-makers do (and the list ifs fairly lengthy, but includes many well-loved TS-spinoff pedals) and use a 2+2 1N4148 configuration instead of stepping up from a pair to a pair of LEDs.  Makes a noticeable difference, but doesn't bump you outside of clipping territory.

[Govmnt_Lacky]

I have read through RGs anatomy article.

What I do not understand (in laymen's terms I guess) is why the 1N34s have about 1/2 of the FV of 1N914s, the LEDs are about Double the FV of 1N914s.....

So why do I get the same (about the same) clipping in this circuit when I switch to symetrical 1N34s -OR- 3mm Red LEDs? It stands to reason that 1 of them should give more and the other should give less  

Am I missing something?

[Mark Hammer]

Am I missing something?

Yes, your amplifier.  There's a reason why Ibanez called it a Tube Screamer.  The intent was to push the input of tube amps harder to extract more clipping from them.  Granted, the pedal has some tone of its own, but you ARE plugging it into a guitar amplifier, right?  And not a Crown or McIntosh or QSC power amp?

[Govmnt_Lacky]

...but you ARE plugging it into a guitar amplifier, right?  And not a Crown or McIntosh or QSC power amp?

Absolutely...

Peavey Valveking.... Tube amp.

[midwayfair]

Greg, can you post pics of both sides of your board?

A germanium will have quite a bit of distortion, and far less output; a Ge will clip even a unity level signal with some pickups, meaning that at 0 on the gain you might get a little bit of distortion. LEDs need to be slammed quite a bit harder. If you're really not hearing a huge distortion difference between the germanium and LEDs, there may be something wrong on the board that you haven't spotted. I'd start checking continuity and all that good stuff.

[Govmnt_Lacky]

Greg, can you post pics of both sides of your board?

A germanium will have quite a bit of distortion, and far less output; a Ge will clip even a unity level signal with some pickups, meaning that at 0 on the gain you might get a little bit of distortion. LEDs need to be slammed quite a bit harder. If you're really not hearing a huge distortion difference between the germanium and LEDs, there may be something wrong on the board that you haven't spotted. I'd start checking continuity and all that good stuff.

I thought that the germs should clip harder than the silicons. I had the 1N34s in the circuit and pulled them to install the LEDs. When I removed the 1N34s, I tested them and one read 0.34 and the other read 0.36 FV.

Maybe it was a bad solder joint??  I know the traces are good because I tested when the LEDs were installed and all is good.

Mybe tonight I will give the 1N34s another go but, I will be running the risk of lifting traces 

[pakrat]

Gov, try changing the 4.7k resistor to 2.2k and the .047uf cap to .1uf. It works, I swear!

[slacker]

I thought that the germs should clip harder than the silicons.

Germs clip less than silicons in a TS. This from the tech of the T.S explains why

"....So as the diode turns on, the gain of the opamp stage changes, going down to just over 1 if the diode can be considered a short circuit compared to the 4.7 K resistor on the (-) input. Even if the Drive control is set for a gain of 100, the diodes conducting cause the gain to drop to 1 for only those portions of the signal where the product of the input signal and the gain exceeds the diode threshold. This means that the signal is "clipped" at the forward voltage of the diode; because there are two opposing diodes, this happens for both signal polarities. "

The important bit is the gain going down to 1 part, this means that the peaks of signals that are near or above the forward voltage of the clippers, get no gain so the loud bits don't sound distorted. In reality the gain won't go all the way down to 1, the diodes don't go short circuit so they get a bit of boost. This is why it sounds like the TS mixes some clean in with the distortion, it doesn't it's just that the peaks don't get clipped much and quieter signals get clipped more.
If you lower the forward voltage of the clippers, say by using germs then more of the signal will be near or above the forward voltage and so gets clipped less, giving less distortion.

If you go the opposite way and use LEDs then you need to turn the gain up more before the signal get amplified enough for the LEDs to clip it.

[Govmnt_Lacky]

I thought that the germs should clip harder than the silicons.

Germs clip less than silicons in a TS. This from the tech of the T.S explains why

"....So as the diode turns on, the gain of the opamp stage changes, going down to just over 1 if the diode can be considered a short circuit compared to the 4.7 K resistor on the (-) input. Even if the Drive control is set for a gain of 100, the diodes conducting cause the gain to drop to 1 for only those portions of the signal where the product of the input signal and the gain exceeds the diode threshold. This means that the signal is "clipped" at the forward voltage of the diode; because there are two opposing diodes, this happens for both signal polarities. "

The important bit is the gain going down to 1 part, this means that the peaks of signals that are near or above the forward voltage of the clippers, get no gain so the loud bits don't sound distorted. In reality the gain won't go all the way down to 1, the diodes don't go short circuit so they get a bit of boost. This is why it sounds like the TS mixes some clean in with the distortion, it doesn't it's just that the peaks don't get clipped much and quieter signals get clipped more.
If you lower the forward voltage of the clippers, say by using germs then more of the signal will be near or above the forward voltage and so gets clipped less, giving less distortion.

If you go the opposite way and use LEDs then you need to turn the gain up more before the signal get amplified enough for the LEDs to clip it.

OK....

So according to the above, both the 1N34s and the LEDs will not clip as well as OR better than the 1N914s unless the supportive components are changed to accommidate it.

Is that a correct summation?

[Mark Hammer]

Germs clip harder than Si which clip harder than LED.  They ALL effectively become zero-ohm resistors when the forward voltage is reached.  They differ in how much of the overall signal will fall beyond the forward voltage.  So LED will generally confine clipping to the initial attack of most (but not all) notes, Si to a longer period of the note's lifespan for pretty much all notes, and Ge to an even greater period, given identically-set gain.

Since the actual practical amplification of the circuit will depend on the headroom afforded by a puny op-amp being fed by a puny 9v supply, SOME of the clipping you will hear will by from the baseline headroom limitations of the circuit in the complete and total absence of ANY diodes.

Since the total heard distortion/clipping will include both the pedal's actual intended clipping, and whatever happens when the amp is hit with an input signal of that amplitude, and when the output transformer and/or speaker is hit with the signal levels that come out the other end, it can happen that everything can bet set to produce greater heard distortion using LEDs than with Ge diodes.

The other element we never speak of is the listener bias that occurs when one switches from the louder output of LED-based clipping devices to the lower volume of Ge-based clipping.  The Ge may well be harsher, but the LED sound is more audible (because it's louder), so it can "sound" harsher.