freestompboxes.org

Hi there,

There is the schematic diagram corresponding the images previously posted by drbob1...Thank you, drbob1!!!!!!!!!!

Signal section: Power supply section: So, my best guess is that the gain and volume pots are of 500K each, and the bias pot somewhere in the range of 10 to 25K.

Anyone can suggest what kind of clipping diodes (the clear blue ones) are soldered in the board ??

Cheers,
Jose

Just got my replacement unit in and MAN, with a functioning gain pot this thing is a whole different animal. Big problem before was too much output, and nothing less than balls to the wall drive. Now it'll do a clean boost with just a bit of hair/warmth to a raging distortion. I played it in the shop with an Egnator Tweaker, and it would turn the clean channel into a higher gain channel than the dirt one, with the ability to still clean up and not lose treble when I backed off the volume of the guitar. Very cool! And kudos to Fryette for the customer support!

Oh yeah, one other problem with this pedal. For $119 from GC, it's going to be hard to source a transformer, tube and sockets, big caps and not lose money!

Hi drbob1,

Glad to read that your unit is working again !!!

It´s also interesting to know that a clean amp channel can be vary from have a little boost to convert it into a complete distorted one, merely by the twist of one knob.

This leads me to wonder again about what values ​​the potentiometers can have, and also to know what type are these mysterious pair of light blue diodes ... (Zener, perhaps?)

I'm not asking you to open again your unit (at least in the next few days... ), so I beg to any forum member that read this humble post, to participate to solve this puzzle.

PLEASE HELP ME TO ANALYZE THE PREVIOUS SCHEMATICS, BOYS...!!!!!!

Besides, I agree with you that it's impossible build a clone of this unit at the same retail price of a new one, if you have to buy all the individual components.

But if someone already has several parts buyed, or lives somewhere in the world with a huge custom fee (as it´s currently my situation), perhaps it´s not so weird try to build a clone of this pedal.

Finally, I think that another Fryette pedal named "Boostassio" must have many similarities with your SAS unit.



But is matter to wait to see the guts of one of these model...

Cheers,
Jose

I havent seen one of these, (not am i an expert & i stand to be corrected) but my best guess would be 500k for the volume & gain pots.
The EF86 will have a gain of more than 100 in this configuration (very rough estimate), so i think the clipping diodes are not zeners (or they would need to be in inverse series), i think they are small shottky diodes 1N5817 or similar which often have a blue body.
Vg1 for the EF86 is only 2.2V

With 300VDC & 100k anode resistor, from the svetlana EF86 curve

www.jogis-roehrenbude.de/Roehren.../Ef86/EF86_SV.pdf

we need to set the bias somewhere around 3.25VDC which gives an input voltage swing of +/- 0.75V peak.
As Bias is adjustable we need to go from 0V to around 6V, a 20k pot gives a range of 0V to 5.9V
Thats why i think shottky diodes are used here, to keep the EF86 input voltage within +/- 0.4V approx around the bias point.

shame about the op-amp infront of the tube.

the pentode circuit is pretty textbook.

Hi mozwell,

Thank you for your kind answer. I´m agree about the potentiometer values you reccomend.

The remaining question is about the clipping diodes as can be seen a "47" number stamped on them in the previous images posted at this topic, but the entire denomination is unknown...

Is there any Schottky barrier diodes named 1N xx47, 1N 47xx, or similar ?

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Hi diagrammatiks,

I´m not completely against to use an hybrid implementation mixing tubes, fets and opamps if we can extract and combine the best of any of them.

But I´m surprised to see that this unit is designed around basic building blocks:

The pentode section is, as you say, a classic tube gain stage designed by the book, the op amp driver is nothing than a MXR Distortion+, and the supply section is also straightforward.

Nevertheless, the high quality of pcb and materials we seen in the images, the reasonable retail price of this unit, and the efficient post sales service mentioned by the user (drbob1 in this case) deserves to be congratulated, I think.

Cheers,
Jose

ppluis0 wrote:Hi there,

There is the schematic diagram corresponding the images previously posted by drbob1...Thank you, drbob1!!!!!!!!!!

Cheers,
Jose

Big thanks Jose for the schem ! I will definitely try this one. Great sounds on Youtube:

Mat

diagrammatiks wrote:shame about the op-amp infront of the tube.

the pentode circuit is pretty textbook.

Without it, there would be no way to hit the tube any harder than your pickup's with the volume pot maxed.

The op amp is an easy source of clean gain with some EQ shaping to follow with a volume/gain pot to control how hard the second tube stage is hit, which is how the first tube stage and gain control of almost EVERY clipping tube amp functions - purely CLEAN amplification of input signal (with or without frequency shaping) followed by a volume pot, to control how hard to following tube(s) are clipped.

Liquids wrote:

diagrammatiks wrote:shame about the op-amp infront of the tube.

the pentode circuit is pretty textbook.

Without it, there would be no way to hit the tube any harder than your pickup's with the volume pot maxed.

The op amp is an easy source of clean gain with some EQ shaping to follow with a volume/gain pot to control how hard the second tube stage is hit, which is how the first tube stage and gain control of almost EVERY clipping tube amp functions - purely CLEAN amplification of input signal (with or without frequency shaping) followed by a volume pot, to control how hard to following tube(s) are clipped.

except there's a set of clipping diodes right at the op-amp output.

Hi mat,

Glad to read that you like this kind of distortion. The sound is like when an amp is at the edge to blow out...

I finally found that the couple of clipper diodes are BAT41 (since the number "41" can be seen in the previous images... )

If someone decide to build a clone, I think that all the values of components can be assumed as verified.

Cheers,
Jose

Does the EF86 pick up the mechanincal noise of turning it on and off? EF86's are usually super microphonic, so it makes me wonder how smart it is to put one in a stompbox?

I happen to have an EF86 tube in my parts collection somewhere, might have a go at building this circuit one day...


An EF86 is a small-signal Pentode tube as I'm sure you're all aware of, a Pentode typically has a much higher mu than triodes do, so I'd expect them to be more sensitive, or prone to, microphony...

When they're manufactured, they are usually tested to ensure that they meet all relevant specifications, and all tubes that don't pass are weeded-out, I guess it's a case of try-what-you-have and see what works for you....

They are quite known for their microfony so expect em to be........

And they are great V1 tubes in amps! The Vox AC15 for example is quite known for this

I think the original Vox AC30 Top Boost also used an EF86 in the top boost channel too....

Yes, pre '61 Voxes had a EF86 but were changed to ecc83 as they were too unreliable

diagrammatiks wrote: except there's a set of clipping diodes right at the op-amp output.

That's fair, and not to be literal, but you said op amp, not diodes...that said, those diodes could obviously be easily snipped by anyone. If rail-to-rail clipping ensued, gain could be re-configured for clean gain only.

To me, an EF86 as a V1 seems strange...it's clipping characteristics are more easily exploited when it is being driven by variable gain, rather than the first source of amplification...not that it can't have so much gain as to distort at the smallest of unamplified signals...but then you have no control.

The Z amps that use this apparently CAN clean up, which to me suggest that the overdrive tone is the sound of the EF86 amplifying mostly or completely clean, driving the phase inverter to a varying degree.

Some ampegs have preamp pentodes later in the circuit chain (i.e. after standard triode stages) so the 'characteristic' sound of driving a pentode can be heard more obviously.

DrNomis wrote:I happen to have an EF86 tube in my parts collection somewhere, might have a go at building this circuit one day...


An EF86 is a small-signal Pentode tube as I'm sure you're all aware of, a Pentode typically has a much higher mu than triodes do, so I'd expect them to be more sensitive, or prone to, microphony...

When they're manufactured, they are usually tested to ensure that they meet all relevant specifications, and all tubes that don't pass are weeded-out, I guess it's a case of try-what-you-have and see what works for you....

It should be noted that it's hard to separate a particular preamp pentode from being overly microphonic from the sheer amount of gain/amplification available.
Certainly some will be incredibly resistant to microphonics beyond their spec, others will go microphonic well under spec.
in a tube amp, a V1 triode is always going to be most sensitive, since the gain it creates is amplified exponentially, assuming amplification stages follow. The microphonic tendency of a tube that was unusably microphonic in the V1 spot can often do just fine as a V2 tube.
In a good design, using a pentode's full gain potential should be unnecessary...and microphonics can be controlled by simple re-biasing it to yield more reasonable gain levels. Following, if you make it the second or third pre-amp amplification tube/stage, microphonics should be little to no issue....or if nothing else, far less than if used as V1.

Liquids wrote:

diagrammatiks wrote: except there's a set of clipping diodes right at the op-amp output.

That's fair, and not to be literal, but you said op amp, not diodes...that said, those diodes could obviously be easily snipped by anyone. If rail-to-rail clipping ensued, gain could be re-configured for clean gain only.

To me, an EF86 as a V1 seems strange...it's clipping characteristics are more easily exploited when it is being driven by variable gain, rather than the first source of amplification...not that it can't have so much gain as to distort at the smallest of unamplified signals...but then you have no control.

The Z amps that use this apparently CAN clean up, which to me suggest that the overdrive tone is the sound of the EF86 amplifying mostly or completely clean, driving the phase inverter to a varying degree.

Some ampegs have preamp pentodes later in the circuit chain (i.e. after standard triode stages) so the 'characteristic' sound of driving a pentode can be heard more obviously.

well ya. Vox used the ef86 because it was a cheap way to drive el84s. A single ef86 into a pi was enough.

That meant that unless a pedal was plugged into the input there was no way to overdrive the pentode.

As far as the fryette pedals are concerned, I'd bet the other pedal the boostasio is a single ef86 stage.
the SAS is marketed as an overdrive/distortion pedal so the op-amp and clipping diodes make sense.

The thing is that I ran some numbers last night and it seems that if bat41s are used as the clipping diodes, the signal at the input of the pentode doesn't seem like it would be able to drive it into clipping.

ppluis0 wrote:Hi mat,

Glad to read that you like this kind of distortion. The sound is like when an amp is at the edge to blow out...

I finally found that the couple of clipper diodes are BAT41 (since the number "41" can be seen in the previous images... )

If someone decide to build a clone, I think that all the values of components can be assumed as verified.

Cheers,
Jose

Hi Jose,

I built a small combo (86-Special) amp with Dumble style V1(12AX7) + EF86 overdrive section going in a single EL84. When gain maxxed it sounds quite like the Fryette SAS pedal (almost like a germanium Fuzz Face). Here is a clip (just noodling with the guitar) of the amp (IIRR the gain was not at full on this clip):


I will try tomorrow to run trough the preamp of the small combo into a Marshall 2555 to see how it sounds.

mat