freestompboxes.org

analogguru wrote:

I believe much, but I can´t believe that this hand-painted pcb has been manufactured by Tesla Vrable, even when components look like old czech/russian production.

maybe somebody exchanged the PCB ?

This unit was sent to me for repair. The pcb quality looks similar to the one on Disco Freqs site. I don't believe they are the same unit as there are other differences.

We´ll see, maybe it´s the single supply version (LM 324) made with single op-amps.

It is a dual supply version with the battery snaps wired in parallel to an external DIN connector. The IC's are standard 741 pinouts with the DIP sockets extended to the board with leads. The board looks like it was designed for TO-5 packages. The circuit uses two (LP,HP) active filter sections mixed with the dry signal. I was surprised to see the low quality
PCB work in a commercial effect, but the unit sounded fine after repair.

I don't believe they are the same unit as there are other differences.

And which differences should there be ?
Compare the photos taken from the back (jacks) and you will see the same mistakes in the laquer....

IMHO it´s the same unit and the pcb not original.... this pcb was made with an "Edding 3000" or something like that.

analogguru

http://www.4shared.com/dir/4492636/1219 ... aring.html

Cool.... many thanks !!!

analogguru

I know… it is as far away as you can imagine from a boutique stompbox.

I bought this pedal recently and I love it. In a nutshell, it is just a (clever?) eq. The signal gets split in three components: dry, low and high. Low is everything below 85 Hz, high is everything above 6.5 kHz and dry the input signal.

Every knob controls how much of every component goes in the output signal. In other words, if all knobs are set to 0, there is no output. If low is set to 12:00, dry to 0 and high to 0 only everything below 85Hz pass through and so forth.

It sounds relatively straight forward. I wasn’t thinking of cloning the pedal. It is reasonably inexpensive and I am not sure it is worth the effort. I was intrigued by the functioning and was thinking more to reverse-engineering it. I would like to build a version with selectable frequencies and ideally with 2 channels.

The circuit uses 2 ICs with 2 op-amp each so it shouldn’t be that complicated.

According to the manual the filters are:

85Hz, 7-Pole Low-Pass Filter
6.5kHz, 6-Pole High-Pass Filter

Can someone point me in the right direction for designing the filters?

Thanks,
Silent Fly

check out don lancaster's active filter cookbook. good stuff in there, including 6pole filter designs.

OH NOOOO !!!!!

A MAX1044 there inside too.....
The rest seems to be nearly identical to the old version.
Today nobody would construct filters in that way....

And the corner frequency:
85 Hz for the bass part.... the lowest frequency a guitar produces is 82,5 Hz.....
6,5 kHz: guitar-speaker rolloff is about 3,5 kHz

The amplifier will be "happy" with this kind of overloading.

analogguru

analogguru wrote:OH NOOOO !!!!!

A MAX1044 there inside too.....
The rest seems to be nearly identical to the old version.
Today nobody would construct filters in that way....

And the corner frequency:
85 Hz for the bass part.... the lowest frequency a guitar produces is 82,5 Hz.....
6,5 kHz: guitar-speaker rolloff is about 3,5 kHz

The amplifier will be "happy" with this kind of overloading.

analogguru

Who says that the KO is for guitar only? (I am a bass player)

I run the pedal in a frequency analyser and it can easily go down to 10Hz... (not that I could actually hear anything a 10Hz, of course)

I tried it with my guitars: an Ibanez (a 335-like) and a MusicMan VanHalen and it works really well. I can, among the other things, manage to make my guitars sound very similar to a Stratocaster. But I agree, with guitar only, a MAX1044 looks a little bit unnecessary.

Silent Fly

But I agree, with guitar only, a MAX1044 looks a little bit unnecessary.

It is always unnecessary - only fashion.
Instead you can use two batteries in series, it will cost the same - cause with one battery the current consumption is doubled and a single battery will die faster. You won´t believe it, but the original used two 9V batteries.

analogguru

I have a red and black Attack Equaliser. Does this thread need the gutshots, or have I missed them?

Gutshots are always welcome.....

since we have only the schematic for one version, they are highly welcome to find out the differences to the other version.

analogguru

Some of you may already know it, but regarding the filter design, I managed to find this:
http://www.analog.com/Analog_Root/stati ... ilter.html

Silent Fly
---
P.S. Thanks to the admin for moving my original post. It makes much more sense here.

Silent--that link doesn't work as-is. Can you tell how you navigated to it?

Seems to me you could use a graphic or parametric EQ to do a similar thing, no?

As for the <85Hz and >6.5KHz stuff- Although guitar Fc is 82.5Hz, it's a gradual rolloff so there is still some freq content below 85Hz and vice-versa for 6.5KHz. The important issue is how it sounds and the -3db points only tell part of the story. (I know that's a response to an old comment.)

I've just finished one and the "Low" pot works great.
The "High" pot works acceptable on guitar, but on bass it has almost no effect...am I right or it's a problem of my clone?
I think that the 6.5kHz corner frequency it's too high for bass...I will try to halve it and to see how it will sound.

Great guts.......thanks

some more from old one???

cheers

Boris

analogguru wrote: Today nobody would construct filters in that way....

That looks similar to the multi-pole high pass filters you see in vintage guitar amps for minimizing LFO "thump" in a tremolo circuit. I agree that I don't understand why anyone would do it that way when they have a perfectly good op amp to implement an active filter with.

borislavgajic wrote:some more from old one???

Which one do you need?

I don't have the modern EHX pedal and the Tesla pedal, but I do have these:

Fabulous collection!

Have you tested them on bass? I am very curious if the treble pot has almost no use on bass or not, like in my clone...

gigelmargel wrote:

Fabulous collection!

Have you tested them on bass? I am very curious if the treble pot has almost no use on bass or not, like in my clone...

I test everything on bass, the treble pot gives more attack (and fret noise).

Maybe the cutoff frequency in your clone is too high?

IIRC, the Polish attack equalizers have cutoff frequencies at 300Hz for bass (LP) and 3000Hz for treble (HP).