Dry output?

gnasher1993 · #1 05-11-2009, 11:56 AM

Just a quick one...

I'm making an Overdrive pedal and I want to have a dry output as well as a wet output. How would I go about wiring this?
How about the tip and sleeve of the input jack wired to the tip and sleeve of the dry out jack. I'm assuming there's more to it than this so...help me out?

Thanks,

Gnasher1993

niftydog · #2 05-11-2009, 05:00 PM

That would work, but you'd have to be careful about what you connect to the dry output as it will affect the input impedance seen by your bass, which may cause a level drop or a loss of high end.

The alternative is to put the dry output after a buffer amp stage - this prevents the dry output from having any affect on the input impedance.

Does your pedal have a buffer? Is it true bypass? Do you want the dry output to be active all the time or only when the pedal is engaged?

Swimming Bird · #3 05-11-2009, 05:32 PM

+1, but buffer >> split or split >> buffer?

I suggest you find a schematic for a pedal that does what you're trying to do and get an idea off that. DOD FX92 is perfect if you can find the schematic, if that's what you want...

seanm · #4 05-11-2009, 05:33 PM

As long as the dry output is going to a different place than the wet output, say a second amp, you will be fine.

gnasher1993 · #5 05-12-2009, 05:22 AM

Quote:

Originally Posted by niftydog

That would work, but you'd have to be careful about what you connect to the dry output as it will affect the input impedance seen by your bass, which may cause a level drop or a loss of high end.

The alternative is to put the dry output after a buffer amp stage - this prevents the dry output from having any affect on the input impedance.

Does your pedal have a buffer? Is it true bypass? Do you want the dry output to be active all the time or only when the pedal is engaged?

You see, I'm doing something a bit different. The pedal contains an overdrive circuit (with boost) and a passive tone circuit. I want the tone circuit to be in use all the time so only the overdrive part is wired to be true bypass (that's what the stomp switch activates). I want a dry output to be in use all the time even without the drive. It doesn't need to be bypassed in any way. So...will my initial idea work for what I'm wanting?

Thanks

seanm · #6 05-12-2009, 10:26 AM

Quote:

Originally Posted by gnasher1993

You see, I'm doing something a bit different. The pedal contains an overdrive circuit (with boost) and a passive tone circuit. I want the tone circuit to be in use all the time so only the overdrive part is wired to be true bypass (that's what the stomp switch activates). I want a dry output to be in use all the time even without the drive. It doesn't need to be bypassed in any way. So...will my initial idea work for what I'm wanting?

Thanks

So they are both going to the same amp? Then, no, you have to have a buffer or you will get feedback when you engage the OD.

gnasher1993 · #7 05-12-2009, 11:03 AM

Will a simple op-amp do the job?

seanm · #8 05-12-2009, 02:45 PM

Quote:

Originally Posted by gnasher1993

Will a simple op-amp do the job?

Very well. Opamps are almost perfect buffers. A simple transistor would work too.

gnasher1993 · #9 05-12-2009, 03:34 PM

I don't have much experience with op-amps. I understand how they work but I'm not sure when it comes to different types etc. Could you offer any advice on a specific op-amp I could use and how I could wire it between input and output jacks? Any help would be greatly appreciated.

niftydog · #10 05-12-2009, 05:13 PM

Quote:

Originally Posted by gnasher1993

I want a dry output to be in use all the time even without the drive.

Ok, but just clear up one thing for me, does the tone circuit go to the dry output as well, or is it truly "dry"?

Quote:

Originally Posted by gnasher1993

Could you offer any advice on a specific op-amp I could use and how I could wire it between input and output jacks? Any help would be greatly appreciated.

There's lots of different types of op amp that will work just fine - are you using one in your distortion section? You could use another like it. Some common types: TL071, NE5534, LM741, LF351, LM308 etc.

Have a google for buffer amplifiers - there's stacks of info out there and you'll get better advice than us trying to cram everything you need to know into a forum post. The main decision you'll need to make is whether to make it inverting or non-inverting. Personally, I'd go non-inverting which allows you to easily set the input impedance with a single resistor.

So the input jack feeds straight into the input of the buffer amp, then the rest of the circuit gets tacked onto the output. The dry output can simply be tacked onto the output of the buffer as well.

Do you have a schematic of what you've got so far?

seanm · #11 05-12-2009, 09:38 PM

Quote:

Originally Posted by niftydog

Do you have a schematic of what you've got so far?

+1 That would help.

Jack Orman's AMZ site has the ultimate article on buffers: http://www.muzique.com/lab/buffers.htm

gnasher1993 · #12 05-13-2009, 04:56 AM

The schematic is on the computer at my dad's house. I'm there this weekend so I'll get it then.

I've been reading those articles that you guys gave me the links to and....

How about this... http://www.maplin.co.uk/Module.aspx?ModuleNo=2889

Wired like this... http://www.muzique.com/images/buff7.gif

I'm a complete amateur when it comes to op-amps but I think it's about time I learnt. I don't have to use all 8 pins do I?! Oh and would you say I should change the capacitance values of the schematic above?

Quote:

Originally Posted by niftydog

Ok, but just clear up one thing for me, does the tone circuit go to the dry output as well, or is it truly "dry"?

The dry signal is not affected by anything. It is truly dry. The Tone circuit is wired to the 'wet output' with the overdrive.

Quote:

Originally Posted by niftydog

So the input jack feeds straight into the input of the buffer amp, then the rest of the circuit gets tacked onto the output. The dry output can simply be tacked onto the output of the buffer as well.

Would a non-inverting op-amp buffer require power or is it passive? I'm assuming it's passive...

moose23 · #13 05-13-2009, 02:20 PM

The chip should be grand but you need -ve voltage which is gonna complicate things. You don't have to use all the pins on the chip. You will need to power it though as with most if not all opamps. Here's the pin out diagram:

Here's another nice op amp article:

http://talkingelectronics.com/projec.../OP-AMP-1.html

I'd say you're better off getting one of the ones listed above. Here's a pretty cheap german site for the chips(ic's) and pretty much every other thing you mihgt need in pedal/effect building.

http://www.musikding.de

seanm · #14 05-13-2009, 03:55 PM

That 741 is fine for a buffer.

You don't need a -Ve, but you *will* need a Vr. Jack's article mentions how to provide Vr. Basically Vr is 1/2 your voltage so that you can pretend that ground is V-.

niftydog · #15 05-13-2009, 05:08 PM

Quote:

Originally Posted by gnasher1993

How about this... Wired like this...

I don't have to use all 8 pins do I?! Oh and would you say I should change the capacitance values of the schematic above?

The dry signal is not affected by anything. It is truly dry. The Tone circuit is wired to the 'wet output' with the overdrive.

Would a non-inverting op-amp buffer require power or is it passive? I'm assuming it's passive...

741 will be fine, and yes, that schematic should work. You'll need to also utilise this bit to obtain Vr.

Nope, just use the pins that are shown in the schematic. Capacitance values - well, that's one of the things you'll have to work in with your current schematic, that's one reason why we need to see that as well.

Ok, so dry is completely dry - got ya.

The circuit is active - meaning it needs power. All op amps are active devices.

Quote:

Originally Posted by moose23

...you need -ve voltage...

Not necessarily, moose. Check out the link seanm gave and read about Vr and single supply op amp configurations.

gnasher1993 · #16 05-14-2009, 10:30 AM

Ok, just to let you know, capacitance values are sorted. I've spoken to a few people who have made effects loads in the past and we've sorted all that jazz out. But anyway, back to the buffer questions...

I'm going for the LM741 op-amp. What difference does it make by having the op-amp in a socket?

Going back to my previous post, what do I need to add to this to get what I want? http://www.muzique.com/images/buff7.gif

Everything else in the circuit is sorted, it's just the dry output 'problem' that I' struggling to get my head around. I could do with someone showing me a schematic of everything that I will need in only the 'dry out' part of the circuit. Will the schematic in the link above do the job? If not, what's missing?

Thanks again for all your help and persistence when faced with a nagging 16 year old

bongomania · #17 05-14-2009, 10:40 AM

Quote:

Originally Posted by gnasher1993

What difference does it make by having the op-amp in a socket?

That allows you to easily swap in different opamps, as long as they have the same pinout and similar power specs. Also sometimes when soldering IC's you may accidentally overheat and burn out part of the IC. By soldering in a socket instead, you never apply heat to the IC.

Quote:

Originally Posted by gnasher1993

it's just the dry output 'problem' that I' struggling to get my head around.

Once you've got the input buffered, it's easy as pie. Just connect the output of the buffer to the dry out jack and to the input of your effect circuit (presumably via the 3PDT footswitch).

gnasher1993 · #18 05-14-2009, 10:56 AM

Quote:

Originally Posted by bongomania

That allows you to easily swap in different opamps, as long as they have the same pinout and similar power specs. Also sometimes when soldering IC's you may accidentally overheat and burn out part of the IC. By soldering in a socket instead, you never apply heat to the IC.

Once you've got the input buffered, it's easy as pie. Just connect the output of the buffer to the dry out jack and to the input of your effect circuit (presumably via the 3PDT footswitch).

Thanks for clearing that up. I think a socket would look a little tidier on the circuit board so I'll go for that. Could anyone draw me a quick schematic of the buffer part of the circuit, that's all that's left to do now

niftydog · #19 05-14-2009, 05:24 PM

It's actually really easy.

See the two points labelled in red text "Vr" - wire those together and that's it.

Now, regarding capacitors - it is not the values we are interested in. To combine your distortion circuit and this new buffer circuit properly you should probably omit a capacitor or two - we can show you which one's to leave out, but it's hard to explain without a schematic to refer to.

The danger here is that you'll end up with a DC voltage at your dry output, or something equally undesirable.

gnasher1993 · #20 05-15-2009, 04:58 AM

Quote:

Originally Posted by niftydog

It's actually really easy.

See the two points labelled in red text "Vr" - wire those together and that's it.

Now, regarding capacitors - it is not the values we are interested in. To combine your distortion circuit and this new buffer circuit properly you should probably omit a capacitor or two - we can show you which one's to leave out, but it's hard to explain without a schematic to refer to.

The danger here is that you'll end up with a DC voltage at your dry output, or something equally undesirable.

Thanks alot, my Dad's picking me up at 3 'o' clock so I should have the schematic for you guys in 4 hours or so. Then hopefully we're done here

thanks again for your patience