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Author Topic: I need help with howie style pedal.  (Read 7120 times)

sjturbo

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I need help with howie style pedal.
« on: February 19, 2014, 08:07:33 PM »
Phatt (he has given me some ideas to try), recommended that I post the schematic here as there are many SS experts here that could help resolve my pedal problems. First I need to give credit to Torben and  kusi at FSB for the schematic and Sabrotone for the layout. This is a dumble style pedal similar to the ROG umble. The schematic is in a pdf form so I added the link to it, http://www.freestompboxes.org/download/file.php?id=1579. I have built the pedal following the schematic and layout. It works but not as I had hoped. My main problem is I'm good at reading schmatics but need help with modding them. The pedal has what I believe is called "ice pick" overtones when the drive or gain is turned up or when heavy picking, (far from the smooth overdrive I was expecting). I was expecting a bit more midrange control. Others compare it to "chewing tin foil". This sound compares to my MIM strat with Tex Mex style pickups which I changed because of the ice pick sound. If some one with experience could look over the schematic and offer suggestions I would greatly appreciate it!

Roly

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Re: I need help with howie style pedal.
« Reply #1 on: February 20, 2014, 07:39:28 AM »
Gotta be a member to download.

Could you post it here please?
If you say theory and practice don't agree you haven't applied enough theory.

phatt

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Re: I need help with howie style pedal.
« Reply #2 on: February 20, 2014, 08:36:34 AM »
Yeah Gets confusing try to cross reference between sites xP
I've added it here.
my first thought was slope resistor might be too large (R22)
Phil

sjturbo

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Re: I need help with howie style pedal.
« Reply #3 on: February 20, 2014, 09:21:56 AM »
Thanks Phatt! I was not sure how to set the link.

Loudthud

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Re: I need help with howie style pedal.
« Reply #4 on: February 20, 2014, 11:46:14 AM »
Thanks to phatt for posting the file here!

Some questions about your build:

1) Did you use J201s or some other JFET?
2) What is your Supply voltage? Have you tried any other?
3) How did you adjust all the trim pots? Have you tried tweeking the pots slightly, maybe a volt high or low from the "ideal"?
4) The slope resistor (R22) seems high, Can you install a trim pot there?
5) Regarding R32 (location F3), did you use 470 ohm or some other value?

sjturbo

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Re: I need help with howie style pedal.
« Reply #5 on: February 20, 2014, 12:23:29 PM »
Thanks for asking!
1) I used J201's.
2) I use a Dunlop "Brick" 9vdc/8vdc to power all my pedals.
3) All trim pots were adjusted to 4.5V. I have not tried any adjusting the input voltage. I believe that these are "cascaded" gain stages?, and I actually thought of cascading the voltage but I have no idea what that might achieve.
4) Installing a trim pot would be difficult but possible. I believe I might have a 50k or 100k I could try.
5) R32 = 470 ohm
6) Thanks very much!

sjturbo

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Re: I need help with howie style pedal.
« Reply #6 on: February 20, 2014, 04:43:40 PM »
100K Trim pot installed! Had a bit of time to tweak and settled in the area around 85K until I have more time. 68K seems to be a bit muffled. Certainly you both were correct, 150K is to high for my tastes. What I really need is someone to turn the pot while I play at different intensity to get a real feel.  What effect would reducing the bias voltage's have on the gain stages? When the drive or gain knobs are maxed out the gain is more than I would ever use. I do have the trim pot for the overdrive input VR2 set very low? Could this maybe be to low for the overdrive section? In my unknowing mind, could this mean the overdrive stages are trying to gain up a signal that is too weak?

Loudthud

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Re: I need help with howie style pedal.
« Reply #7 on: February 20, 2014, 08:17:16 PM »
What effect would reducing the bias voltage's have on the gain stages?
This thing has lots of stages and most have some tone shaping between stages. There are three sections. The first section, Q2, Q3 should preserve a fairly clean signal and just add low amounts of distortion. 4.5V or 5V would be good for those stages. In the OD section, anything goes. This section is where the Ice Pick tone probably comes from. Try tweeking VR3 high and VR4 low, or vice versa. You can't hurt anything, just try to get a pleasing tone without the Ice Pick treble. The third section around Q7 and Q4 will have to be a compromise to get good tone in both modes. You should probably stay close to 4.5V but try anything. VR7 gives a treble rolloff, use it in moderation to get rid of fizz. I suggest you just adjust the pots by ear, take notes and then measure and write down the voltages. It may take some time to find what you like.

sjturbo

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Re: I need help with howie style pedal.
« Reply #8 on: February 20, 2014, 08:39:55 PM »
Thanks much Loudthud! Sounds like plan. Tweaking is good when you can put all the pieces back! I think I may play with the bias voltage in the tone stack section also, I believe it has more gain than required. Interesting you mention the tone shaping on each stage.
The tone controls (T,B,M) all seem to interact. I still don't hear much difference in the 80's/90's switch. I would like to increase mids on one position of the switch. Would that just require a change in the rc network?
Again thanks for everyone's help!

phatt

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Re: I need help with howie style pedal.
« Reply #9 on: February 21, 2014, 11:56:29 PM »
Just simulated the first 2 stages and it's ho hum average :-X
but I'll tell you now that dumble tone stack is just way overrated.
I should know I've tested  most of the famous tone stacks in the last 20 years 8)

My advice;
R22 try around 50k
Remove C2
C4 and R17 does nothing except a slight 2dB loss below 1khZ. up to your ears?

This screen shot shows the difference between the given schematic "Yellow trace"
and above changes "Green trace"

This tone stack can only deliver about 12dB of tone change.
There are better ways likely delivering more than twice that control with less parts,,if you are interested?
As loud thud notes the next part could be anywhere but I'd get the front working first.
Phil.

Roly

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Re: I need help with howie style pedal.
« Reply #10 on: February 22, 2014, 12:15:48 AM »




{willya lookit all those furshlugger trim pots!   :duh   }
If you say theory and practice don't agree you haven't applied enough theory.

Loudthud

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Re: I need help with howie style pedal.
« Reply #11 on: February 22, 2014, 04:14:08 PM »
{willya lookit all those furshlugger trim pots!   :duh   }
It probably cost more for the trim pots than the JFETs. But the upside is the endless possibilities for tweeking. Nice to have one of those little plastic screwdrivers made for tweeking pots.  :)

sjturbo

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Re: I need help with howie style pedal.
« Reply #12 on: February 22, 2014, 04:47:27 PM »
It was hard to part with but I traded one furshlugger for all the trim pots;). And yes I can tweak all nite long:0 ?
Next- Back to reality, Phatt, taking your advice I really don't need a 2db  loss. So, I used another trim pot to dial in R22 to 50K, and removed C2, C4, and R17. Spousal unit is napping currently so I cannot try it out.
What's next?, stage 3 and 4 or 5,6? Twice the control would be nice on my next pedal which will likely be as soon as I can wrap this one up. Thanks again for the help and humor!

sjturbo

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Re: I need help with howie style pedal.
« Reply #13 on: February 23, 2014, 05:44:49 PM »
One step forward, two steps back. Modded to  Phatt's suggestions and biased overdrive stage fets to 5v (?) based on tone, sounded good and turned pedal volume up and poof! something went south. No sound unless turned all the way up and then just faint in the background sound. Will have to troubleshoot tomorrow.

sjturbo

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Re: I need help with howie style pedal.
« Reply #14 on: February 24, 2014, 08:06:20 PM »
Update! Found the problem. One of the fets had  a slight disconnection when measuring. I also returned the bias to ~4.5v. Played for about an hour just tweaking knobs. I will resume bias tweaks on the overdrive stage tomorrow. Oh, everything sounds very good except that when the Level or Drive are increased on the OD channel it sounds like I get noise like water flowing?
Thanks again!!