Hi everyone, this is my first post here on this great forum.
What I want to do is slightly modify my wampler pedal to make it more suitable for my needs, I want to feed line levels into it without the need for a reamp box, which is what I have used to do that so far.
I've traced the input circuit and there is a 1M resistor to ground which sets the input impedance, I would like to replace this resistor with 50K as I think that will make the input slightly less sensitive.
What I need to know is: Is my assumption correct (about making the input less sensitive)? And if I did swap the resistor I'm guessing I will also need to replace a capacitor so as not to affect an rc filter? If so I need a little help!
Is there anyone familiar with this particular pedal or is there anyone who has modified a guitar pedal to make it more suitable for line levels?
Any help / advice / opinions would be greatly appreciated
Thanks
What I want to do is slightly modify my wampler pedal to make it more suitable for my needs, I want to feed line levels into it without the need for a reamp box, which is what I have used to do that so far.
I've traced the input circuit and there is a 1M resistor to ground which sets the input impedance, I would like to replace this resistor with 50K as I think that will make the input slightly less sensitive.
What I need to know is: Is my assumption correct (about making the input less sensitive)? And if I did swap the resistor I'm guessing I will also need to replace a capacitor so as not to affect an rc filter? If so I need a little help!
Is there anyone familiar with this particular pedal or is there anyone who has modified a guitar pedal to make it more suitable for line levels?
Any help / advice / opinions would be greatly appreciated
Thanks
Is the device using opamp's?
If so then you can maybe change the value of the Feedback resistor to change the gain of the first stage.
Or if you change the value of the input resistor to a lower value such as 10K or something then you can use a series resistor with the input signal that feeds the 10k to ground.
As 10K series resistor will give you a 50% voltage reduction and a 1K will give you a 10% reduction of the input voltage feeding the device after the mod.
This is assuming that this is using a non-inverting opamp input stage as this is a typical configuration for a device that is design for plugging a High impedance source such as guitar directly into the unit.
The series resistor in conjunction with the resistor to ground will form a voltage divider and attenuate the input voltage.
This will allow you to not have to mess with the gain structure of the First stage as it may mess up any of the rest of the feedback controls as it is an echo unit, Correct?
I can also try this without changing the 1Meg resistor and see if that works First.
Again 100k will give you a 10% reduction and a 1Meg will give you 50%.
I hope this helps you.
jer 🙂
P.S. Just changing the input resistor to a lower value generally only changes the input impedance and doesn't change its sensitivity or gain.
This of course depends on the actual configuration of the input stage as well such as if there already is a series resistor with the input jack to the input of the gain stage with the 1meg resistor to ground then yes this can change the sensitivty.
If so then you can maybe change the value of the Feedback resistor to change the gain of the first stage.
Or if you change the value of the input resistor to a lower value such as 10K or something then you can use a series resistor with the input signal that feeds the 10k to ground.
As 10K series resistor will give you a 50% voltage reduction and a 1K will give you a 10% reduction of the input voltage feeding the device after the mod.
This is assuming that this is using a non-inverting opamp input stage as this is a typical configuration for a device that is design for plugging a High impedance source such as guitar directly into the unit.
The series resistor in conjunction with the resistor to ground will form a voltage divider and attenuate the input voltage.
This will allow you to not have to mess with the gain structure of the First stage as it may mess up any of the rest of the feedback controls as it is an echo unit, Correct?
I can also try this without changing the 1Meg resistor and see if that works First.
Again 100k will give you a 10% reduction and a 1Meg will give you 50%.
I hope this helps you.
jer 🙂
P.S. Just changing the input resistor to a lower value generally only changes the input impedance and doesn't change its sensitivity or gain.
This of course depends on the actual configuration of the input stage as well such as if there already is a series resistor with the input jack to the input of the gain stage with the 1meg resistor to ground then yes this can change the sensitivty.
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To drive the pedal with a line level signal, you need to install a pot to lower the input voltage or you will overdrive the input FET, or if you have a volume pedal use that in front of the Wampler.
Hi Gerald, thank you very much for the reply. I have done a bit more investigating of the circuit and have found the first stage is an inverting op amp (one half of a opa2134) with a gain of two. I have also found a basic schematic of the circuit which seems to be correct though not entirely complete.
This is the schematic: Wampler Faux Tape Echo
What I'm thinking of doing to start with is replacing r6 (1M) with a 560K resistor giving a gain of approx 1.
I am also considering changing the resisitors that set the input / output impedances. Currently they are 1M and 100K and I think for line level purposes it would be better to be 50K and 100ohms.
Most of these ideas are taken from this article: Boss DE-200 gain mod for use on keyboards - Gearslutz.com
Anyone with anyone with advice / ideas / interest please get involved!
This is the schematic: Wampler Faux Tape Echo
What I'm thinking of doing to start with is replacing r6 (1M) with a 560K resistor giving a gain of approx 1.
I am also considering changing the resisitors that set the input / output impedances. Currently they are 1M and 100K and I think for line level purposes it would be better to be 50K and 100ohms.
Most of these ideas are taken from this article: Boss DE-200 gain mod for use on keyboards - Gearslutz.com
Anyone with anyone with advice / ideas / interest please get involved!
Yes, I would even consider going with a gain of 1/3 to 1/2 by using a 220k to 470K in place of R6.
This is something you will have to try depending on the level of the signal you are applying to the input.
R1 is just there to discharge the input capacitor from any residual voltage that may still be on it when you unplug a device so that it doesn't cause a pop.
Or any extra voltage charge on it that it could be still there that is too high and could damage the next device you plug into it.
As most devices, But not all, have a DC blocking cap on their output connection.
When you say line level there are different standards.
Home equipment is set at -10dbv for a 0db VUmeter reading.
And music and pro mixers are much much higher at +4dbv for 0db VU meter reading.
Here is the Wiki on the actual line level standard,
Line level - Wikipedia, the free encyclopedia
You could go with that and/or add a 100k pot in series with the feedback resistor to find your optimum gain value and then measure it to find your final value to insert for R6.
Typically a guitar signal (My Strat) will hit about .8v to 1.2v peak if I hit the strings really hard.
And they are using a gain of 2 for the input stage.
So you can figure out very easily of how much gain you will need if you know what the voltage of your line level signal is.
I think I know what the delay chip is that the are using, as I had just discovered it not long ago but I forgot what the number is.
It is a really neat little all in one unit.
I think I even have found and saved the data sheet on it too.
I would guess that it is designed for approximately a 1Vrms to 1.5Vrms signal max in to the input of the chip.
I do know that the very hard to find Reticon SAD 1024 chips were in this range at 2Vp-p.
I still have 4 of those (had 6 but I can't seem to find 2 of them) that I have never used.
I have had them since the early 80's.
I will be attempting to see if they still work sometime soon. 😉
You can use lower values of the resistors as well as this will also lower the noise that is generated in the gain stage as well since it is an inverting type.
Just watch your gain structure.
I used to use only 1K's 10K's in those type of stages and 100K's if I need more gain for the feedback resistor in my custom fuzzbox's when I was building them.
Even though they had super super high gain they were very quiet and didn't hiss when the input was turned down.
Rarely did I ever use any 1Meg's except in the very first stage if I wanted an extreme amount of gain using a High impedance non-inverting input stage.
In this case you will be quite okay with lower values just don't exceed the Delay Chip's maximum input voltage, or else, as you know, clipping will occur and possibly damage the delay chip by overdriving it.
I know they are about $20 to $30 a pop!!!
It helps alot if you are using a scope too but a good DMM is just fine.
You are on the right track and let me know how it works out for you.
To make things really easy you may be able to get by with just a simple 10k trimmer pot in place of the 1Meg resistor R1 to ground as mentioned earlier.
Just make sure you tie the wiper of the trimmer pot to the input of capacitor C1 and the signal input directly to the top of the 10k pot.
No extra input capacitor is needed!
jer 🙂
This is something you will have to try depending on the level of the signal you are applying to the input.
R1 is just there to discharge the input capacitor from any residual voltage that may still be on it when you unplug a device so that it doesn't cause a pop.
Or any extra voltage charge on it that it could be still there that is too high and could damage the next device you plug into it.
As most devices, But not all, have a DC blocking cap on their output connection.
When you say line level there are different standards.
Home equipment is set at -10dbv for a 0db VUmeter reading.
And music and pro mixers are much much higher at +4dbv for 0db VU meter reading.
Here is the Wiki on the actual line level standard,
Line level - Wikipedia, the free encyclopedia
You could go with that and/or add a 100k pot in series with the feedback resistor to find your optimum gain value and then measure it to find your final value to insert for R6.
Typically a guitar signal (My Strat) will hit about .8v to 1.2v peak if I hit the strings really hard.
And they are using a gain of 2 for the input stage.
So you can figure out very easily of how much gain you will need if you know what the voltage of your line level signal is.
I think I know what the delay chip is that the are using, as I had just discovered it not long ago but I forgot what the number is.
It is a really neat little all in one unit.
I think I even have found and saved the data sheet on it too.
I would guess that it is designed for approximately a 1Vrms to 1.5Vrms signal max in to the input of the chip.
I do know that the very hard to find Reticon SAD 1024 chips were in this range at 2Vp-p.
I still have 4 of those (had 6 but I can't seem to find 2 of them) that I have never used.
I have had them since the early 80's.
I will be attempting to see if they still work sometime soon. 😉
You can use lower values of the resistors as well as this will also lower the noise that is generated in the gain stage as well since it is an inverting type.
Just watch your gain structure.
I used to use only 1K's 10K's in those type of stages and 100K's if I need more gain for the feedback resistor in my custom fuzzbox's when I was building them.
Even though they had super super high gain they were very quiet and didn't hiss when the input was turned down.
Rarely did I ever use any 1Meg's except in the very first stage if I wanted an extreme amount of gain using a High impedance non-inverting input stage.
In this case you will be quite okay with lower values just don't exceed the Delay Chip's maximum input voltage, or else, as you know, clipping will occur and possibly damage the delay chip by overdriving it.
I know they are about $20 to $30 a pop!!!
It helps alot if you are using a scope too but a good DMM is just fine.
You are on the right track and let me know how it works out for you.
To make things really easy you may be able to get by with just a simple 10k trimmer pot in place of the 1Meg resistor R1 to ground as mentioned earlier.
Just make sure you tie the wiper of the trimmer pot to the input of capacitor C1 and the signal input directly to the top of the 10k pot.
No extra input capacitor is needed!
jer 🙂
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Hi Gerald.
Thanks for taking the time to write a reply and offer some help. I just wanted to let you know what I've done and I'm hoping that maybe this thread may be of help to somebody some time as I have personally learnt so much from reading up on various forums. So what I have done is reduce the input gain from 2 down to 1 by replacing r6 (1M) with 560K. I have replaced r1 (1m) with 56K to reduce the input impedance. I also lifted r7 (22k) and inserted a switch there so now I have the choice of dry signal on / off, which is much better to use the effect in a send return loop. This has all worked perfectly and I can now connect my synth straight into the pedal and its not overloading and distorting the repeats! This is great as it means I no longer need the diy reamp box I was using and the pedal is now much more usable.
I should have explained before but what I use the pedal for is my dub sirens, I'm a dub reggae head, I have tried out (and still own) a ridiculous number of delays but the wampler is the one I have settled on for my creative needs in this area, it really is a brilliant delay.
I do however still have a couple of questions....
I've assumed r1 and c1 are forming a rc filter ( hope this is correct ) and by replacing the 1M with 56K I have calculated that will give a high pass filter with a corner frequency of 28.4Hz which I am happy with as I don't really want low bass going through the delay. What I need to know is: am I correct in my assumptions? and would it be better to use a higher value cap to get closer to the 1.6Hz corner frequency as it was originally?
Also when you mentioned having a gain of 1/3 to 1/2, I was wondering is this possible? I mean I did check the op amp was unity gain stable but I didn't realise you could go less than 1.
Thanks for the input
Ben
Thanks for taking the time to write a reply and offer some help. I just wanted to let you know what I've done and I'm hoping that maybe this thread may be of help to somebody some time as I have personally learnt so much from reading up on various forums. So what I have done is reduce the input gain from 2 down to 1 by replacing r6 (1M) with 560K. I have replaced r1 (1m) with 56K to reduce the input impedance. I also lifted r7 (22k) and inserted a switch there so now I have the choice of dry signal on / off, which is much better to use the effect in a send return loop. This has all worked perfectly and I can now connect my synth straight into the pedal and its not overloading and distorting the repeats! This is great as it means I no longer need the diy reamp box I was using and the pedal is now much more usable.
I should have explained before but what I use the pedal for is my dub sirens, I'm a dub reggae head, I have tried out (and still own) a ridiculous number of delays but the wampler is the one I have settled on for my creative needs in this area, it really is a brilliant delay.
I do however still have a couple of questions....
I've assumed r1 and c1 are forming a rc filter ( hope this is correct ) and by replacing the 1M with 56K I have calculated that will give a high pass filter with a corner frequency of 28.4Hz which I am happy with as I don't really want low bass going through the delay. What I need to know is: am I correct in my assumptions? and would it be better to use a higher value cap to get closer to the 1.6Hz corner frequency as it was originally?
Also when you mentioned having a gain of 1/3 to 1/2, I was wondering is this possible? I mean I did check the op amp was unity gain stable but I didn't realise you could go less than 1.
Thanks for the input
Ben
Excellent!!!
I am glad to hear of your results!!!
Come to think of it, I have a friend that I think has that pedal or one similar to it.
This will be good information if ever he will need me to modify it as well.
Yes, you will have to increase the value of the capacictor in order to get back down to the 1.6hz lower corner frequency limit.
How ever I don't think that it necessary though.
Also don't quote me, But I think that the lower frequency limit is calculated from the input series resistor R4 to the opamp's -input and the input capacitor C1.
I will have to look that up.
jer 🙂
P.S here is a screen shot from a Wiki on this,
High-pass filter - Wikipedia, the free encyclopedia
I am glad to hear of your results!!!
Come to think of it, I have a friend that I think has that pedal or one similar to it.
This will be good information if ever he will need me to modify it as well.
Yes, you will have to increase the value of the capacictor in order to get back down to the 1.6hz lower corner frequency limit.
How ever I don't think that it necessary though.
Also don't quote me, But I think that the lower frequency limit is calculated from the input series resistor R4 to the opamp's -input and the input capacitor C1.
I will have to look that up.
jer 🙂
P.S here is a screen shot from a Wiki on this,
High-pass filter - Wikipedia, the free encyclopedia
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Hi Gerald and anyone else reading this. I just wanted to say the project has been a success, thanks to Ger for contributing. I have modified and re-housed my Wampler delay along with my favourite reverb pedal so that now at gigs I have one box built instead of two pedals, reamp box, all the cables, power splitter etc. Anyway I have created a little gallery so you can have a look at the finished project along with my custom reggae siren box. Please take a look: Wampler mods - My Photo Gallery
Many thanks
Many thanks
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