Professor tweed sound clips

[dschwartz]

I added two sound clips of my professor tweed build...they´re in my website:

http://diynoise.googlepages.com/home

i just added a little reverb...it was recorded miking the amp, the pedal was on the front (preamp), and before it a Boss DS1 for the boosted sound..

The boosted is really dirty, like it took the character of the DS1.. the PT alone sounded really good.. but avoiding the "farting" sound lowering the gain and going easy over the low notes.....i just gave up trying to get rid of that ugly buzz, seems that the best solution ys building/buying a jcm800!!..

do anyone thinks that a output buffer will help with the farting buzz? y already put a 0.1uF cap at the output thinking that it was DC offsetting the signal and uglyclipping my amp...but no...didnt help at all.

greetiongs!!

[John Lyons]

The Professor tweed clips alone sound nice!
The Boosted clips take on the tone of the DS-1 but the combonation still sounds good to me.
Adding a buffer will not help. A buffer is for preserving the impedance of the circuit.

The "buzzing" sound you are talking about. It this the hum over both soundclips? Is this coming out of your amp or was this because of the recording?
John

[dschwartz]

nop..is not the hum...the hum was because poor recording technique (sorry bout that)

The farting sound is not present on the demos cause i was easy on the low e string and set the gain rather low (12 o clock)

ill post the farting sound later so you can hear it..is a nasty clipping, very SS buzz..not useable....

[jakenold]

Cudos on the clips! Very nice playing and a great sounding pedal. I gotta try that one.

I too have pedal with a lot of farting - the RAT2. What to do about that?

EDIT: I was trying to ask: Is there a universal approach to stompboxes farting? .... christ, what a sentence 

[John Lyons]

I think the term may be one thing but the actual problem may be another.
"Blocking" distortion and  "farting out" are usually a matter of two much lowend in combonation with the gain being set higer. Early stages with to much low end. Reducing coupleing cap sizes or lowering Source resistance on FET circuits will help this. To get a smooth distortion sound you will generally need to cut bass in the early stages and cut treble in the later stages or at the end. This way the bass doesn't over modulate the signal and cause "farting". But only if this is the actual thing happening.

John

[dschwartz]

well john, i suspected that at first, so i added a 33nF bypass cap (in parallel w/the 1k source resistor) at the first stage to cut bass..
I thought that 33nf would do.. but still sounds like after a big beans and chilli dinner...do you think that´s enough bass cut?..

i suspect that the second stage does the farting though.....gonna check the schem now
please keep up this thread, i think it will help others too...

thanks!

[dschwartz]

aha!!
i noted that the first stage has a 22uF bypass cap...too large!!! i didnt noticed on the board so the 33nF is now in parallel with it, so i´m addingh even more bass..DUH!!
let´s see what happens if i change that cap to..hmmm 470nF?? is that ok?

[John Lyons]

dschwartz
For the PT alone sound the 22uf is fine as the PT sounds good by itself.
For a bass cut when it's boosted you would be better off making the coupling cap smaller instead of changing the source bypass cap. (the cap coming off the Drain to the next stage)
Adding capacitance in parallel to the source resistance is going to make the gain higher, But since you have a 22uf there it's not going to change much. If you are getting too much bass and that truly is the problem then you should make the coupling cap switchable. Smaller for boosted gain sounds, and the stock value for the PT by itself.

Once you have found what will work for both sounds you can put them on a switch. You may also find that the lower cap value works for both boosted and by itself sounds.

John

[dschwartz]

I guess your'e right, thought that bypass caps gave the low-end corner frequency..

I thought that cause comparing the DR boogie stages (that has a smoother drive) with the PT stages, i found that decoupling caps were the same (22nf), but the bypass Caps were smaller (1uF)...

i know that in fets, usig more than 2uF is not really usefull, cause the corner freq will be around 53Hz (with a 1.5k R)..lower than the E string, so 22uF gives 4.5HZ..totally subsonic..

so my guess was changing the bypass caps to a higher, "audio" range

[stm]

I've noticed that JFETs sometimes don't like to be driven hard directly by a low impedance.  I'd suggest placing a 220k resistor in series with the gate of Q2 and Q3, just after any preceeding component.

The above will not impact overall gain and shouldn't affect high frequency content to a significant extent since the expected miller capacitance is around 20pF, thus giving a 36 kHz approximate cuttoff.  Of course if you want a mellow sound you may use 470k resistors.

[dschwartz]

Thanks STM!!! i´ll try every mod and report the results..maybe they can be added to the prf tweed project as an update..

and hey..me puedes contestar en español tb..jaja

[John Lyons]

You can try to change the bypass cap as well. Maybe that would get you the sound.
Maybe actually it would be easier to put a switch on the bypass.
High gain 1uf
Low gain (PT by itself) 22uf.
1uf will be a bit lower gain than the 22uf so this may be your answer.
Try this first and see what you get.
On second thought the coupling cap should be your second choice to lower the bass content.

I'm not sure about the impedance issue. Seems that a low imp out DS-1 would work ok into a high imp such as the PT/FET input, but STM should know!

[dschwartz]

i think STM referred the 2nd stage impedance..i dont understand what you said about the DS1....

[stm]

i think STM referred the 2nd stage impedance..i dont understand what you said about the DS1....

As a matter of fact, 2nd and 3rd stages.

[John Lyons]

DS-1 = high imedance in low impedance out.
Professor tweed = High imp in low out.

If you drive the PT with the DS-1 the impedance at the input of the PT should be ok.
STM is talking about impedance after the first stage though I guess.
So changing the impedance in the inner part of the circuit will have an effect on the sound stm?

Seems like he was having problems with the low end effecting the blocking distortion of the PT.
I probably don't know my stuff but can you explaint this a bit?
Thanks

John

[dschwartz]

i just want to thank you guys, STM and John, you have been very kind helping on this issue..
i will report the results and maybe post the modified prof tweed schem when finished as my way to give back to the forum comunitty