4-knob Silicon Tonebender -- Schem and Vero

[Derringer]

Ok, so here's what I've been working on for a while now. It's currently breadboarded and I think it's time to commit it to an actual pedal! 

Here's the schem and my first attempt at a vero layout using the awesome DIY Layout Creator.

I know that the only way to be 100% sure that the vero layout is correct is to build it ... but I figured I'd show what I have to the community here first and see if anyone spots any problems. I did go through it and did correct a few mistakes ... but like I said, this is my first time going from schem to vero.

Thanks for any input and feel free to use the design (if you wish to) however you want.

[Naz Nomad]

I'm lovin' the porcine theme ... nice one

[Gus]

A few things that you might want to investigate, you posted it is still on the breadboard.  Have you built or looked at the Hot Si?

The first stage has a grounded emitter and and you have it marked and maybe needing an C to B resistor adjustment and you have the collector voltage close to 9VDC already.  Take a look at the Hot Si input section a "standard" textbook circuit fragment.
  With one transistor you can both control the gain and set the operating point you want.
Adjust the "top" base bias resistor in the Hot Si input to shift the collector voltage.

The output stage you might be able to combine R15 and R17(in parallel)  and move C10 to the other side of R15,R17 and adjust R16 to adjust the bias  OR you could set the output stage to load the tone section less with a higher Hfe transistor and different resistor values.

Did you try taking the output of the FF section to the tone control section off the collector of Q5?  This will allow the output section to operate at lower gain
or
Remove Q7s section maybe make R15 a 100K volume pot with a cap between R13 and R14 node and the pot and remove stuff to the right of R15.

What are the operation points of the transistors of the FF section with the use of the 5K gain?

How much hiss from the 100K input pot when turned closer to 100K?

Just some ideas for you to try you might like them or you might not.

[Derringer]

Naz .... Thanks buddy. I always dug the theme specific titles that designers sometimes give their controls. Now it's my turn 

Gus ...

A few things that you might want to investigate, you posted it is still on the breadboard.  Have you built or looked at the Hot Si?

I have looked at the schem but have not built it.

The first stage has a grounded emitter and and you have it marked and maybe needing an C to B resistor adjustment and you have the collector voltage close to 9VDC already.  Take a look at the Hot Si input section a "standard" textbook circuit fragment.
  With one transistor you can both control the gain and set the operating point you want.
Adjust the "top" base bias resistor in the Hot Si input to shift the collector voltage.

This is a little over my head. Are you referring to R1 in the Hot Si schem? And concerning the input stage of the Hot Si, it looks quite a bit like an LPB ... is that correct?

The output stage you might be able to combine R15 and R17(in parallel)  and move C10 to the other side of R15,R17 and adjust R16 to adjust the bias  OR you could set the output stage to load the tone section less with a higher Hfe transistor and different resistor values.

Again, over my head a bit ... are you saying get rid of R17 as it is and change R15 to ~11.4K ?

Did you try taking the output of the FF section to the tone control section off the collector of Q5?  This will allow the output section to operate at lower gain

have not tried this ... but I think I will ... I like the idea of less gain because there is PLENTY on tap right now

or
Remove Q7s section maybe make R15 a 100K volume pot with a cap between R13 and R14 node and the pot and remove stuff to the right of R15.

Would I lose volume?

What are the operation points of the transistors of the FF section with the use of the 5K gain?

Not quite sure what you mean by "operation points" ... but I am willing to learn
I'm using the 5K because I liked its range of sounds better than the 2K and the 1K that I had tried previously.

How much hiss from the 100K input pot when turned closer to 100K?

I was hoping the hiss was due to it being breadboarded ... but I think that I have introduced some noise into the circuit with the 100K pot. Is there an effective way to quell that hiss? Simple cap to ground perhaps ... or would that alter the frequencies of the whole thing?

Just some ideas for you to try you might like them or you might not.

Thank you very much for taking the time to reply to my post. This is the kind of information that I was hoping to get from the community here. I appreciate it 110%

[Gus]

The input of the Hot Si is the same basic circuit fragment as the LPB and many other gain stages.  You can find it in text books.  It does matter how you set it up.

  Your input stage is biased like the BMP gain stages.  However you the first stage collector at 8 to 8.5VDC it close to the 9VDC supply so you are operating closer to cutoff like a RM set to 7.5VDC at the collector  One bias setup is not always "better" than another with effects.  You might like to keep it as you have it drawn if, you like how it sounds.  The Hot Si input is setup for about a gain of X10, 10K/1K and the bias string should fix the operations points good enough for a X10 Si transistor gain stage in an effect

Output section maybe try connecting the tone section at Q5 collector and remove the parts R15 and every thing to the right.  Use a C10 after the tone control to a 100K volume pot.

Operation points.   If you know the resistor values and the voltages at the different points in the circuit you can calculate DC collector current and other thing using Ohms law.

[Derringer]

I was just tinkering with it and then saw your reply. I had directly connected the collector of Q5 to the tone section input and changed the attack pot back to 2KB. It sounds a bit more refined through my small amp here. I need to test it on my gigging amp though. The problem with my small amp (ax84 P1 EX) is that it's not as transparent as my big amp (Carvin X100b).

Before I put the lpb -style gain recovery circuit on the end of the design, I was achieving unity with very little left to go on the volume pot. For some this isn't an issue, but I like having all of that extra volume on tap at the end of the circuit because at different effect levels and different amp levels, you get different sounds. I like having that tweak-ability.

operation points: thanks ... that makes sense

Question 1: Earlier you refered to possibly using a higher gain transistor in the Q7 section so that it did not load the tone section. How would the frequency response be altered by using something like a 2n5089 in place of the 2n3904 ?

Question 2: By changing my input stage to a circuit similar to the Hot Si input, would the tone become less saturated? Or would I at least have the option of making it less saturated? Saturated is not a bad thing for the tones I'm looking for here, I just would just like to know how these different approaches work.

Question 3: do you know of any available sound clips of the Hot Silicon?


Thanks,

Bill

[Derringer]

also...

found this article (short)
http://www.rason.org/Projects/bipolamp/bipolamp.htm

how/why were the values of R1 - R4 chosen for use in the input stage of the Hot Si?
http://www.aronnelson.com/gallery/main.php/v/ulysses/ulysses_layouts/dh_hot_silicon/dh_hot_silicon.gif.html


Thanks

[Derringer]

So here's where I'm at now. It's sounding much more refined and articulate.
Plus, there's a lower parts count!

There's plenty of volume on tap now so the original booster at the end is not needed. I also plucked a transistor from the final (previously piggybacked stage) and found that I like the tone better with the higher hfe at Q5. I also decided to move around/change a few caps.

I'm getting around 6v on the collector of Q1. I did toss in a pot and scaled it back to 4.5v, but I didn't hear any noticeable difference, so I left the 10k resistor as it was. Is there any reason to bother biasing the collector of Q1 to 4.5v ?

Thanks a ton Gus.

Now to try making another vero layout ...

[Gus]

Try it with just Q1 no Q2.   You don't always want to be 1/2 of the supply voltage sometime 2/3 or 1/4 or.... clip and or bend the waveform causing different harmoincs.  If you have a scope and a signal generator feed circuits triangle wave and look at what happens and then test it by ear.  Look at "The Art of Electronics" for some ideas.  Read R.G.s treble booster PDF. 

[Derringer]

There's a subtle difference without Q2, but I prefer having it in there. It gives a more ... airy? quality to the sound.

Thanks for the treble booster reading suggestion That cleared the biasing question up very nicely. I had assumed that biasing away from 1/2Vcc would lead to asymmetrical clipping ... but it's good to read that and have it confirmed.

I was also able to d/l a .pdf of "The Art of Electronics." Just looking at the table of contents I can see that there's A LOT of information there!

So I've decided to ditch C1 and C2 as well. I thought C1 would be a clever way of retaining some highs when the soft pot was dialed up ... but then that kind of defeats the purpose of the soft pot if I'm letting certain frequencies pass through uninhibited. It also didn't seem to make all that much of a difference. C2 was there because I based my design off of the MKII. I notice that the Hot Si didn't have a 0.01uF cap going to ground from the input so I decided to see if it made a difference being there ... it really didn't.


Thanks for all of the input Gus!

[Derringer]

Ok. So here's what I finalized it with.



I ran into a problem with the trimpot. Maybe I gave it too much heat but it would only complete the circuit when I squeezed it top-to-bottom. So I replaced it with a resistor of value that I cannot remember. Luckily I had the 50K pot that I had used on the breadboard and was able to take a measurement of its resistance to approximate the required resistor. I'll get back with the actual voltage it's running at now if anyone is interested.

I also had an odd intermittent problem where I was getting a short between + and ground ... heating up batteries and what have you. I touched up all mu solder points and triple checked for bridges and that seemed to fix the issue. So, I think that I can call the vero "Verified."

If I ever build it again I may design the tone control so that it only cuts highs, not add them as well. The pedal is plenty bright without the high frequency boost available. I prefer dark and punchy tones.
here's a quick and dirty clip of it

Hot Neck HB Tele> GCB95 wah w/buffer>Bent Pig>Clean Channel Carvin X100b>Avatar 2X12

The sm57 was just thrown haphazardly infront of the speaker and was recorded with a Tascam 424 4-track cassette, no EQ'in in the recording

the clip simply goes single-notes ... wah with notes ... chords
it's just a few pieces of a jam with just me and my drummer

It's not a beautiful clip but I think it gives a pretty good impression of what the pedal sounds like

http://www.mediafire.com/?mhmccy8gzuv

Thanks again for all the help Gus.


oh yeah .. and the outside shot ... going to paint it, install the led and a DC jack when my DC jacks arrive

[Gus]

To be clear.  The Hot Si is Doug's.  Doug took a three Si transistor tonebender idea of mine and tuned it a bit different and added a stage.  Doug is very good at tuning circuits.

  One could look at a circuit like this and think it is just a FF type with a boost before it and you would correct: however you did find out the it is the details that make you smile when you use the circuit.  I had fun reading and posting with this thread and I am happy to read and see you kept some of the piggyback transistors and you tuned it to what you wanted that is what the DIY is about IMO.
  Funny thing I have built a few FF types with a tone control and I find I tend to like it as a mild treble cut.  Often I use a rolloff cap across the "top" collector resistor in the 2nd  transistor in the FF section with no tone control.  I think I hear that type of high end roll off sounds better than the C to B cap(s) sometimes used.

[Derringer]

To be clear.  The Hot Si is Doug's.  Doug took a three Si transistor tonebender idea of mine and tuned it a bit different and added a stage.  Doug is very good at tuning circuits.

Gotcha. When I get to it, I'll update the acknowledgments.

  One could look at a circuit like this and think it is just a FF type with a boost before it and you would correct: however you did find out the it is the details that make you smile when you use the circuit.  I had fun reading and posting with this thread and I am happy to read and see you kept some of the piggyback transistors and

Absolutely, it's basically a FF with a boost in front. But as I'm learning, these circuit patterns are building blocks ... when I'm breadboarding I liken it to building with legos oh so many many years ago ... so what does one do with building blocks? One builds things. And the details are what make these designs unique.

I'm relatively new to this, but two concepts have really grabbed me: piggybacking and FET/Triode emulation. I'll soon be packaging up a very simple fet design that sounds great on my P1 EX.

you tuned it to what you wanted that is what the DIY is about IMO.

right on

Funny thing I have built a few FF types with a tone control and I find I tend to like it as a mild treble cut.  Often I use a rolloff cap across the "top" collector resistor in the 2nd  transistor in the FF section with no tone control.  I think I hear that type of high end roll off sounds better than the C to B cap(s) sometimes used.

note taken

When you say across the collector resistor .. that also means parallel to the resistor right?

How exactly does that work to attenuate the high frequencies? Would that cap simply capture the V+ that would be used to create the high frequencies?