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Author Topic: Phabb Tone....  (Read 4933 times)

kevin b

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Phabb Tone....
« on: April 11, 2013, 03:56:29 PM »
Hello...

First post from a long time lurker. 
After reading a lot of posts and listening to a few sound samples I got interested in Phil Abbots Phabb Tone, DCC and Presence circuits.
I PM'd Phil and he kindly replied to my questions and also gave some pointers and interesting opinions (especially about the use of Compressors and Noise Gates.....)  (And Phil just when I get my schematic ready, I see you have a new version of the DDC - is there any difference in tone between  the old circuit and the new one??)

I finally found time to redraw Phil's posted schematics, the only difference is I want to use a bipolar supply (Just because I have a 15-0-15V transformer sitting on a shelf and would like to use it!!). 
I am posting my redrawn schematics here, hopefully so more informed person would be kind enough to look them over to see if I have carried out the conversion to a bipolar supply correctly, before I start destroying some IC's. 

If the schematics are complete I will draw up some layouts for them.

PS. if anyone is familiar with Bajamans optical limiter (available from freestompboxes  http://www.freestompboxes.org/viewtopic.php?f=13&t=2369&p=217265&hilit=limiter#p211584) could this also be converted to a bipolar supply?  The link is to a post I made, showing my proposed modification.

Regards to everyone

Edit

Made the attachments smaller
« Last Edit: May 05, 2013, 05:54:14 AM by kevin b »

Roly

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Re: Phabb Tone....
« Reply #1 on: April 12, 2013, 11:44:34 AM »
Welcome in from the cold of your lurkatude!

I've just given your drawings a quick once over and I can't see anything obviously wrong.

As you may already know the main difference between single and split rail operation is that there will be DC isolating caps you no longer need.  If they are not needed for bandpass shaping then you can also eliminate C20 and C14.

Another thing that happens is that outputs will now idle at ground and go both ways in polarity.  This makes the use of electrolytics at C28, C15 and C32 problematic.  C28 at 10uF might be a problem in a non-polar, but the other two can easily be changed to non-polar types.

Your link requires membership, so perhaps you could hotlink to, or post, the circuit?

HTH
If you say theory and practice don't agree you haven't applied enough theory.

kevin b

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Re: Phabb Tone....
« Reply #2 on: April 12, 2013, 12:19:16 PM »
Hi Roly

Welcome in from the cold of your lurkatude!

Lurkatude! I like that one....  :)

Thank you taking the time to look over the schematics.

C14 and C20 - I think they are required for bandpass shaping.  C20 is in Phil's Original PhAbb DCC  - mods for Nobels SST1, so I think that is part of his mods to the Nobels circuit.  The SST1 was powered by a +6V 0 -6V bipolar supply.

C15, C28 Would a bipolar cap be OK? I have 2u2 and 10uF....

C32 can be 1uF film no problem.

re the link I will post Bajaman's schematic and my proposed mods in a separate post.
What I am actually asking about is converting a single supply circuit to a bipolar one so it may be better to have that subject covered in a separate post.

Thanks again
Kevin




Roly

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Re: Phabb Tone....
« Reply #3 on: April 13, 2013, 01:25:45 AM »
High value bipolar caps are basically two polar caps back-to-back in the same case.  These should be okay but I'm not keen on them generally.  For the 2.2uF you can use a couple of 1uF non-polar caps, like film, in parallel, and if you shop around you may be able to find something similar for the 10uF.

The basic problem here is that electrolytic caps like to have at least around 10% or their rated voltage to "form up" and maintain their insulating layer properly, and with the split supply they will idle at zero volts.  I don't see this as a big problem, but it's not really ideal if you can avoid it.  Worst case, if it goes leaky you could get "paper rustling" or "popcorn" noises.

Not a suggestion but an observation; sometimes you see two electrolytics in series of double the required value, and a large value bias resistor off to one of the supply rails to put a DC bias voltage on both.  While this works it also opens the possibility of introducing noise from the supply rail into the signal path (unless you split the resistor and bypass the mid point to ground with another electro, but that is getting needlessly complicated in this case unless you are into Hi-Fi Lily Guilding - try the bi-polar and see how it goes).
If you say theory and practice don't agree you haven't applied enough theory.

phatt

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Re: Phabb Tone....
« Reply #4 on: April 13, 2013, 09:25:37 AM »

Hi Kevin,
          Thank Roly for all the indepth tecky stuff,, constantly helping those who are still chipping away at the edges of the mountain of tricks in the trade. xP

Looks good to me,, maybe a 100 ohm resistor on the output of the DDC and Presence circuit to be safe. (kinda depends what comes after that)

Re the New circuit, I take it you mean the PhAbbZone?
Well that's a very different circuit.

Nothing wrong with the circuit you have but over the last 2~3 Years I've been trying to get these circuits to be more dynamic (some call it touch response) which is what I'm chasing.

It seems that triodes are quite unique in the way they respond and after many many attempts to replicate the effect with SS devices it just won't happen so why not just use a friggin Valve for first stage?

lo and behold halfway through testing the Phabbzone with great results,, That amazing chap (member KMG) posts some amazing revelations about using Fets.
Seems He has indeed studied the intricate details of this subject and has built some stunning units that come very very close to the response of a triode. :dbtu:

He has posted much on here,, Well worth a read.

Anyways with a Valve front end the DDC was making the preamp section far to clamped so I had to rethink the whole idea. The new circuit needs a much bigger input signal to distort/limit the signal and now it open up a lot better. But nothing wrong with the old one if you use it as a front end it just won't have quite the magic of a triode.

Triodes do this wonderful half wave clip trick as the signal gets big they still play clean but with a little rattle on the edge of big notes,, get the EQ right and they can do magic stuff. 
Not to sound like a bleeding heart story,, but as a novice with limited knowledge this stuff takes quite some years to get your head around what goes on inside circuits that makes them work.

It really comes down to what equipment you have already been exposed to and where you want your sound to go.
So if heavy metal is your trip then maybe go in a different direction. Though I've found that a simple graphic EQ after the DDC will get you close.

If all you learn from Me is that Tone shaping of the distorting sound is super critical to success of whatever sound you chase then I've likely saved you from a lot of torment. ;)
The use of tone shaping tools both before and after distortion is the key.
I've found the PhAbbTone circuit helped a lot.

Regards the optical limiter; (yes I noticed it over at FSB)
Don't remove the input buffer. When the LDR goes low R the input Z will change and cause you big hassles,, might not even work?
Better still take the time and get yourself a breadboard of some sorts and test all this stuff out. If all we do is copy we learn little,, by testing it yourself it often shows up weaknesses in these circuits.

That is how I discovered most of the circuits I have posted just by messing around with ideas from electronic mags in the old days and now of course anywhere and everywhere on the net but that probably makes it harder as there is just so much that you become lost in the maze. :duh
Phil.

J M Fahey

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Re: Phabb Tone....
« Reply #5 on: April 13, 2013, 02:42:27 PM »
 :dbtu: :dbtu: :dbtu: :dbtu:

kevin b

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Re: Phabb Tone....
« Reply #6 on: May 05, 2013, 07:17:18 AM »
Dober Dan

Sorry for taking my time in getting back to this got involved in other things - wife, kids, house, garden, work, you know how it is...

I have updated the schematics taking to account the comments of Roly and Phil.
So Electrolytic caps have been replaced with film, 100r resistors to outputs of DCC and Presence circuits.

I breadboarded the Presence and Phabbtone circuits. the Presence is a little noisy, used a TL071 anyone have a suggestion to other chips I could use... (Ne5534 or LM351?)

No issues with the Phabbtone circuit.

@Phil

Read a lot of your posts on Tone shaping and EQ'ing, that's what got me interested in the Phabbtone in the first place.
Yes I have read a lot of posts by KMG here and over on FSB -  I stand in awe, his web site is worth a visit some nice projects for the more advanced.

The other thing I have learnt from you is Breadboard, Breadboard Breadboard Breadboard  :tu:

Heavy metal is not really my thing.  I am after a specific sound. Billy Gibbons used a Scholtz Sustainer for the distortion sounds on the Eliminator and Afterburner albums -  listen to "Rough boy" and you will hear the sound I am trying to get.  The Nobels SST-1 that you based your DCC circuit on is a close copy/clone of the Scholtz rockman, which shared much the same distortion and fiter as the the Sustainer.  Thats why I am interested in the DCC. IF anyone has any of the Scholtz schematics and would be willing to share, I would be greatful I have the sustainer, but the others seem to have dissipated from the web.

I have drawn up some proposed layouts for the circuits -  hopefully someone will have time to give them a quick look over.  I have checked and rechecked but you know how it is.

Regards

Kevin
« Last Edit: May 05, 2013, 07:28:52 AM by kevin b »

Roly

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Re: Phabb Tone....
« Reply #7 on: May 06, 2013, 07:46:28 AM »
Gave the circuits a quick once over and can't see anything obviously amiss.

Thanks for reminding me about "Rough Boy".
If you say theory and practice don't agree you haven't applied enough theory.

phatt

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Re: Phabb Tone....
« Reply #8 on: May 06, 2013, 10:11:58 AM »
Hi Kevin, great effort mate. :tu:
Running out of time tonight but one quick Q.
Are you intending to etch and drill this at home?
If so it could be a little tight in places you may want to spread things out a little more and give yourself some margin for error when drilling.
More later,, Phil.