Help with buffer followed by Electra

[antonis]

Yes..
(strictly speaking, at one diode forward voltage drop above GND..)
&
Yes.. 
(except for buffer 'cause it's inherently set to unity..)

P.S.
First one stands for hard clipping configuration with diode pair connected to circuit GND..
There is a similar arrangement with diode pair connected to Vbias, which also represents AC ground due to filter cap.. In such an arrangement, filter cap blocks DC but it "leaks" to GND through voltage divider lower resistor so DC gain is then set by the ratio of feedback resistor and gain + lower divider ones..

[Gargaman]

I was not able to understand and resolve the diode switching issue, my time has come and so I decided to try to use them to distort on the feedback loop of the inverting amp.
It worked, switching manually on the breadboard. I tested with two pairs of diodes. I wanted to use also without diodes (as a clean boost).
Is it possible to use a spdt (on/off/on) for that, like diodes to ground on hard clipping?
tks


PS. I decided to leave the tone stack out since the midiscoop of BMP tone control was not good for the bass.

[idy]

On/off/on should work. But I think you need a double pole. One pair goes to the Opamp +input, the other goes to Vref.

If ithat second pair went to ground, one diode would be conducting when the opamp is "idling" at mid voltage. The other would never turn on (never get below 0.)

Or you put that pair after the 4.7uf  capacitor; there they can go to ground. I think the second way is more conventional. I haven't seen the other way done.

[iainpunk]

On/off/on should work. But I think you need a double pole. One pair goes to the Opamp +input, the other goes to Vref.

If ithat second pair went to ground, one diode would be conducting when the opamp is "idling" at mid voltage. The other would never turn on (never get below 0.)

Or you put that pair after the 4.7uf  capacitor; there they can go to ground. I think the second way is more conventional. I haven't seen the other way done.

no you don't need a double pole

Garagaman is clipping like in a tube screamer, but with an inverting stage, somewhat like a blues breaker, this gives hard clipping! nice
you can just use a no/off/on switch to chose between the diode pairs.

you can take out the 101 capacitor in the feedback loop of the first opamp since its shorted anyways, and after the transistor gain stage you have 2 resistors and a cap in series, you can leave out one of the resistors and replace the other with a 15k

cheers

[Gargaman]

Tks for the tips, Ian.
About the clipping switch I found this:



Will work? If so, what value the C7 cap should be to not affect the tone?

[antonis]

The higher the C7 value the more "transparent" the clipping effect..
(the less the stage gain in diode bypass mode forn on-ON-on switch, which isn't the case here..)

100nF to 1μF should be fine..
(check for Big Muff Π various versions..)

[iainpunk]

Tks for the tips, Ian.
About the clipping switch I found this:



Will work? If so, what value the C7 cap should be to not affect the tone?

that connection from the output of the gain stage to the middle lug would kill all gain, making it silent in your case, that should be left open.

the rest looks fine

cheers

[Gargaman]

Tks.

Tks for the tips, Ian.
About the clipping switch I found this:



Will work? If so, what value the C7 cap should be to not affect the tone?

that connection from the output of the gain stage to the middle lug would kill all gain, making it silent in your case, that should be left open.

the rest looks fine

cheers

With C7 where it is?
If so, when switch to the side 1 or 3, the cap will be series with a diode pair.
In the middle position, diodes and cap bypassed?
Right?
I'm having trouble to incorporate this to layout.
Just to make it clear, I have an ON OFF ON switch.





PS. Values on the layout may not be updated. For the cap we're talking about, I'm going with the values suggested by @antonis

[Gargaman]

..and after the transistor gain stage you have 2 resistors and a cap in series, you can leave out one of the resistors and replace the other with a 15k

won't this mess with the setup gain of the inverting?

Signal (AC) gain indeed is 4.68 (22k/4.7k)..

Maybe just taking the 10k out, since Antonis suggested it when there was diodes to ground on there?

[antonis]

Just to make it clear, I have an ON OFF ON switch.

I'm not able to post a schematic for the moment but you just haver to wire one leg of C7 to pin 6 (inverting input) and the other leg to switch middle lug..
Each of switch outer lug should be wired on Ge or Si diode pair respectively..

P.S.
It will also work with a SPDT ON-ON switch..

[Gargaman]

Working on it now, wish me luck.
Tks.



"Expect there to be 'serious design flaws..." 

[iainpunk]

Tks.

Tks for the tips, Ian.
About the clipping switch I found this:



Will work? If so, what value the C7 cap should be to not affect the tone?

that connection from the output of the gain stage to the middle lug would kill all gain, making it silent in your case, that should be left open.

the rest looks fine

cheers

With C7 where it is?
If so, when switch to the side 1 or 3, the cap will be series with a diode pair.
In the middle position, diodes and cap bypassed?
Right?

yes, right!
having that cap there in series prevents lower notes form getting clipped, this makes it less fuzzy and gives a bit more 'clean' bass, while still having distorted mids /higher notes, i recommend playing with that cap's value (or even adding a switch for more cap options!)
you can actually leave it out if you so desire, but for the original where you took it from its there to block DC, which isn't necessary with an opamp feedback loop im 95% of all cases

cheers

[Gargaman]

Made the board with the layout above, put it in a box, no sound. (not rocking before boxing damnation)
Bypass fine, led is (was) on when engaged. Voltages on the chip seems to be fine. Checked for shorts on pots.
Started to track the signal with audio probe and was going inside pin 3 but not coming through pin 1)
Meanwhile the led burnt.
Gonna take it out from the box and check for shorts on the board.

EDIT: Man, what a dumb. The layout don't have the feedback loop of the buffer and since I remove the little cap as suggested by Iainpunk, it's open. Gonna fix.

[Gargaman]

That's it!
Thanks for the tips.

[iainpunk]

how does it sound? is it as bass friendly as you hoped?

cheers

[Gargaman]

Sounds ok.
This  friend of mine asked a month ago if my fuzz face clone would sound good on bass. I tested and sounded bad. I sent him some Bazz Fuzz samples and he said was too much distorted and point me a Cream video as example of the sound he wanted. I searched Jack Bruce used Marshall amps so I gave a try to a Marshall Guvnor that I was screcthing. Bad idea. Sounded no good. Then I ended at this Electra sandwiched into a tl072.
He liked more the germamiun diodes pair distortion on low and high notes. The other pair is a led and a silicon but in the end clipping was very subtle than when I was breadboarding and planned. EDIT: I see why. I.didn't breadboard the cap (C7), maybe it made less distorted. On the breadboard it was very noticeable.
For my taset it loose brightness a bit when distorted.
One issue is that popping is occuring when engaged, despite it has the 1M5 resistor at the input. Maybe another cap is causing the pop?
Thanks again, mate

EDIT: the pop is much loudet at clean mode and Led+silicon mode; doenst pop on germaniun, at leaat not audible.

[mdcmdcmdc]

FWIW, the fairfield barbershop works really nicely on bass for that low/medium chugalugging overdriven bass amp vibe.