Ramble FX - Marvel Drive 1.0  [traced]

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Re: Ramble FX - Marvel Drive 1.0

Postby FuzzMonkey » 07 Jul 2016, 20:29

Nice work people. For me personally, I'd make the bright cap switchable. 100pf works well if you're using the 'High Treble' channel by itself but gets kind of lost when blending it with the 'Normal' channel. Maybe switchable between 100pf and 470pf depending on taste. My 2¢.

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Re: Ramble FX - Marvel Drive 1.0

Postby tiagojoy » 08 Jul 2016, 12:01

brejna wrote:Few mistakes: R17 and 18 are wrong, probably 'cause of copying, they should be 47R and also charge pump schematic is for TC1044 or 7660 not LT1054. If you want to use 1054 you need to lift pin 1. Also your vb and va are connected so decoupling is not existing and also there is no diode protection in 18v mode.

Cheers :)


This was failure time to change the names haha :lol:
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Re: Ramble FX - Marvel Drive 1.0

Postby J0K3RX » 08 Jul 2016, 20:28

Marvel bares a striking resemblance to this... :twisted:
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Re: Ramble FX - Marvel Drive 1.0

Postby FuzzMonkey » 09 Jul 2016, 09:28

J0K3RX wrote:Marvel bares a striking resemblance to this... :twisted:


It is based off the 1987 preamp.
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Re: Ramble FX - Marvel Drive 1.0

Postby bucksears » 28 Feb 2017, 13:36

brejna wrote:Few mistakes: R17 and 18 are wrong, probably 'cause of copying, they should be 47R and also charge pump schematic is for TC1044 or 7660 not LT1054. If you want to use 1054 you need to lift pin 1. Also your vb and va are connected so decoupling is not existing and also there is no diode protection in 18v mode.

Cheers :)


Resurrecting this one.
With these changes, is this last schem correct?
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Re: Ramble FX - Marvel Drive 1.0

Postby POTL » 09 Jun 2017, 05:03

Hello
Tell me why in podnyuyh circuits use trimming resistors instead of conventional resistors?
After all, you can calculate the value of the resistor using DMM
The reason in the spread of the parameters of the transistors or you can safely replace the trimmer resistor by an ordinary one and collect several instances?
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Re: Ramble FX - Marvel Drive 1.0

Postby plush » 09 Jun 2017, 09:49

POTL wrote:Hello
Tell me why in podnyuyh circuits use trimming resistors instead of conventional resistors?
After all, you can calculate the value of the resistor using DMM
The reason in the spread of the parameters of the transistors or you can safely replace the trimmer resistor by an ordinary one and collect several instances?


The reason is jfets (their inconsistency). It's easier to bias them with a dmm and a trimpot, than socketing multiple resistors to catch desirable drain voltage.
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Re: Ramble FX - Marvel Drive 1.0

Postby POTL » 18 Jun 2017, 22:02

One more question
I built this pedal on the development board, I set it up at 9 volts, when I connect the 18 volt circuit the circuit needs to biasing the transistors again

The original pedal allows you to switch between two voltages without tuning.
I feed on batteries.
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Re: Ramble FX - Marvel Drive 1.0

Postby FuzzMonkey » 18 Jun 2017, 23:26

POTL wrote:One more question
I built this pedal on the development board, I set it up at 9 volts, when I connect the 18 volt circuit the circuit needs to biasing the transistors again

The original pedal allows you to switch between two voltages without tuning.
I feed on batteries.


Carefully selected JFETs maybe? Biasing the JFETs at 4.5V (using a 9V power supply) won't necessarily mean they will automatically bias at 9V when using the 18V power supply.
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Re: Ramble FX - Marvel Drive 1.0

Postby POTL » 27 Jul 2017, 15:35

Hi
A question
This scheme has no input and output buffers, which are desirable for preserving the tone.
Tell me, how are things at this pedal with input and output impedances?
What are their sizes
Does it make sense to add buffers or input impedance is 1 megohm and the output does not exceed 10 kilo ohms
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Re: Ramble FX - Marvel Drive 1.0

Postby POTL » 20 Aug 2017, 23:30

Tell me about the fets matching
On what parameter to look, what data should be?
How can I select transistors for the mu-amp cascade?

I'm interested in switching from 9 to 18 volts
On my layout, the transistors work either 9 or 18 volts
Put those that were.
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Re: Ramble FX - Marvel Drive 1.0

Postby FuzzMonkey » 21 Aug 2017, 09:02

For a mu-amp, you don't have to worry about bias like you would with a regular jfet gain stage i.e. using trimpots etc. As long as the voltage doesn't exceed the maximum the jfet is rated for you can casily switch between 9V and 18V. The Catalinbread Dirty Little Secret Mk III is an excellent example of this.

I haven't done it but it is possible to find jfets that will bias at half voltage i.e. 4.5V when using a 9V power source with a fixed resistor of 'X' value. It means you don't have to use trimpots but it does mean you need a bunch of jfets to test to find right ones as jfets vary wildly. This always seem a waste to me especially ìf using 'hard to find' jfets in your design.

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Re: Ramble FX - Marvel Drive 1.0

Postby POTL » 21 Aug 2017, 14:15

FuzzMonkey wrote:For a mu-amp, you don't have to worry about bias like you would with a regular jfet gain stage i.e. using trimpots etc. As long as the voltage doesn't exceed the maximum the jfet is rated for you can casily switch between 9V and 18V. The Catalinbread Dirty Little Secret Mk III is an excellent example of this.

I haven't done it but it is possible to find jfets that will bias at half voltage i.e. 4.5V when using a 9V power source with a fixed resistor of 'X' value. It means you don't have to use trimpots but it does mean you need a bunch of jfets to test to find right ones as jfets vary wildly. This always seem a waste to me especially ìf using 'hard to find' jfets in your design.


thanks for the answer
Just today I was playing on my copy of the marvel drive and decided to run it on 18 volts
I had to adjust one trim.
The sound at 18 volts seemed more interesting (although the minuses in the form of strong noise were also there).
That's why I asked myself about the selection.
How to choose the right one? By cutoff? What should it be? 4.5 volts?
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Re: Ramble FX - Marvel Drive 1.0

Postby POTL » 21 Aug 2017, 21:21

Today Marvel Drive assembled and decided to warm it up with AMZ Mosfet Booster, there was a problem - the tuning of the first transistor was lost.
Solved the problem by installing a shunt resistor at the output of the booster (set it between the output capacitor and ground).
The question who does not work correctly is the AMZ circuit, since it does not have a shunt resistor at the output (for example, in ZVEX SHO or EQD Black Eye, it is either a normal resistor or a volume control).
Or is there something wrong with the input impedance of Marvel?
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Re: Ramble FX - Marvel Drive 1.0

Postby POTL » 06 Sep 2017, 03:26

Ripdivot wrote:
FuzzMonkey wrote:Using tiagojoy schematic above as reference, the version 2.2 changes are as follows:

C17 is now 330pf.

The power stage has two LPF stages running in parallel (47R resistor and a 220uf electrolytic cap). One filter feeds the trimpots of 'Normal' and 'Treble' channels; the other the Mu-amp section and trimpot of the final gain stage.

R12 is now 68K.

The second order LPF the follows the 100n cap is replaced by a third order LPF to create the 'Presence' control Note:This differs from that seen in the schematic above and represents the actual configuration used in the V2.2 pedal

R14 is 22k / C13 is 1n5; R15 is 22k / C14 is 2n2 and the extra LP stage is a 27k resistor and a 3n9 capacitor. The 3n9 cap is tied to ground via a 500kA pot wired as a variable resistor. The junction where the 27k resistor and 3n9 cap meet is the outlet for the 'Master Volume'.


Here are the revisions to the above schematic. Based on your text I think I have it correct but if not let me know what to change.


Are you sure that the circuit requires 2 power filters?
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Re: Ramble FX - Marvel Drive 1.0

Postby FuzzMonkey » 06 Sep 2017, 08:04

POTL wrote:
Ripdivot wrote:
FuzzMonkey wrote:Using tiagojoy schematic above as reference, the version 2.2 changes are as follows:

C17 is now 330pf.

The power stage has two LPF stages running in parallel (47R resistor and a 220uf electrolytic cap). One filter feeds the trimpots of 'Normal' and 'Treble' channels; the other the Mu-amp section and trimpot of the final gain stage.

R12 is now 68K.

The second order LPF the follows the 100n cap is replaced by a third order LPF to create the 'Presence' control Note:This differs from that seen in the schematic above and represents the actual configuration used in the V2.2 pedal

R14 is 22k / C13 is 1n5; R15 is 22k / C14 is 2n2 and the extra LP stage is a 27k resistor and a 3n9 capacitor. The 3n9 cap is tied to ground via a 500kA pot wired as a variable resistor. The junction where the 27k resistor and 3n9 cap meet is the outlet for the 'Master Volume'.


Here are the revisions to the above schematic. Based on your text I think I have it correct but if not let me know what to change.


Are you sure that the circuit requires 2 power filters?


Probably not but that's what it is built with. Just reporting the facts.
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Re: Ramble FX - Marvel Drive 1.0

Postby ct_anthony » 22 Jan 2018, 13:37

a little late to the party... but seems the best place to ask...

does anybody know the Vp/Idss of the used J201? I think Vp in relation to drain voltage is more interesting (harmonic content) than Idss...
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Re: Ramble FX - Marvel Drive 1.0

Postby mr coffee » 28 Jan 2018, 15:19

Hey Fuzzmonkey,

Is this what you are saying is correct?


Thanks,

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Re: Ramble FX - Marvel Drive 1.0

Postby FuzzMonkey » 30 Jan 2018, 07:14

mr coffee wrote:Hey Fuzzmonkey,

Is this what you are saying is correct?


Thanks,

mr coffee


Yes sir. You are correct. Nice work!
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