ABC with volume or a Compressor

[pastorjustinb]

Hello all,
I'm new here...
I'm using multiple guitars and want to be able to switch em out of my effects chain without a huge volume/drive difference. I have a cheap Jay Turser Strat copy, a Martin D-41 with an aftermarket piezo under the saddle, and an old Guild.  There is a huge amount of difference in output with these guitars. I use the same chain and amp for all three... would a good compressor do the trick or should I be looking at a A/B/C with volume controls? (I'd also like LEDs and external power)

Any other suggestions... thoughts... ideas... 
thanks a lot.

[jimilee]

Don't know that anyone has a layout, but tone bone makes a great one for just such situations. I have heard bass bone or my bass and I love it

[pastorjustinb]

Thanks for the info!
Any idea if a compressor would accomplish close to the same goal. what difference could I anticipate... I have never had the opportunity to try a compressor...

[samhay]

The output from a single coil pickup is vastly hotter than from a passive piezo pickup in an acoustic. What's in the Guild? If either are passive (no on board preamp), your best bet may be to make/get a good acoustic preamp (it needs to have a very high impedance to play nice with the piezo; what are you using now?) for the Martin and Guild and then to run this into a simple AB channel selector with the Strat direct into the other channel.

[pastorjustinb]

Thanks for your input.
Sorry, the guild is one single-coil neck pickup...
I'm not currently using my effects loop.. I'm just running through my effects into my 30 watt 2 channel Mega.  I'll admit I'm set up like a noob LOL
My chain is currently as follows. Any of 3 guitars... Tuner, Moded Ibanes MS10, Bones Texal dual overdrive, JD original CryBaby, DanElectro Fish & Chips EQ, Line 6 EchoPark, MXR evh Phase 90, Fab Flanger, Volume Pedal, Amp. 

[samhay]

Ah OK - the Guild is an archtop then? Doesn't really matter if they all work through the rig you are using.
While I am quite fond of compressors, I don't think one will be your magic fix. I think that your want an active 3 channel ABC box.
What kind of pickup is in the Martin? If it is a ceramic piezo, then you probably want an input buffer (for this channel) with 5-10M input impedance. You can quite easily do this with a FET or FET op-amp, but it will be a little different to your average electric guitar preamp/buffer.

Edit - Where do you set/change the gain when you switch guitars? Is it on the amp?
Also, what kind of tuner is it and does it use a buffered bypass (does it still bypass without power)?

[pastorjustinb]

Thanks again.
Can't answer all you questions at the moment... but i can answer some...
Yes the Guild is an archtop... http://www.guitar-museum.com/uploads/guitar/112/350090965201-2.jpg (that's close) i'll get the exact info soon...
I don't often change guitars during a set because of the volume difference... I'll pick the one that fits the majority of the songs and use it.
When setting up... i'll pick a guitar and plug it in... if it's too loud i plug my chain into the other channel   then i'll adjust the volume on the amp to accommodate.
My tuner is a Behringer TU-300, if you need i'll check the power situation... not sure about the piezo though.... any way to tell?
thanks again
justin

[samhay]

No worries about the exact Guild model.
My guess is that the Behringer tuner is probably uses a buffered bypass. If this works ok with the Martin, then that makes life relatively easy.

I would go with something functionally like this - individual gain stages that can be independently switched on/off all feeding into an output buffer.

This is not especially elegant and the caps between stages and 100k resistor to ground may not be necessary - they were added to prevent switching pops. This has not been tested.

[pastorjustinb]

Sweet thanks... I'll have to learn to read this and start cracking   LOL

I noticed the "etc" at the bottom... I'll assume I can add additional channels?

Can I use multiple channels at the same time as well?
and LEDs?
thanks A LOT!!!!

this is awesome!!!!

[samhay]

You are correct - etc means keep adding channels as needed.
It should work fine with multiple channels going at one time. While this is a pretty simple idea, it has not been tested and I would suggest you try it on a breadboard first as a few of the components may be necessary and/or will need fine tuning. Let us know how it works.
The switches as marked are SPDT. If you use DPDTs then you can use the other side to turn on/off LEDs just like you would an effect indicator.

[pastorjustinb]

I've only ever moded a Fab echo and my Ibanez MS10... this would be my first build... Lots of noob questions... and is this right?
https://www.dropbox.com/s/3dt14e4d2043vph/AB_with_gain%20Marked.JPG

[samhay]

Everything labelled looks right to me. The circled op-amp is an output buffer. This is not absolutely requid but will make it play nice with whatever is conncted to it. Also, If you have three input stages then you will probably have a spare op-amp to make use of.

The other circled bit is the power supply filtering and bias voltage. Connect the +9V to the battery or DC jack AND the op-amps's V+ (usually pin 8 for a dual op-amp) Connect all the points labelled Vb together. The INs and OUT go to jack tips and jack sleaves a grounded.

Edi: I would replace the 100k resistors to ground with 1Ms.
If/once it plays nice on the breadboard then I guess you will need to think about a layout...

[pastorjustinb]

Noob is an understatement when it comes to me. Lol. Any particular op amp? I found one listed as low noise.. model ne5532.
Also I noticed there is a third output buffer... should this one be a separate op amp... or could I use 2 dual and have 3 in and one out.
I'm gonna pick up a bread board... definitely looks like it will make things easier.
I'm guessing that plain mono jacks will be fine.. no switches necessary in the jack?

Thanks again for sharing your knowledge... this is starting to look possible for even me to do!!!

[samhay]

You don't need a physically separate op-amp for the output buffer. All up, two doubles or one quad will be fine.
The 5532 is a great op-amp, BUT it does not have FET inputs and the input impedance is thus only about 300k. This may not play nice with your Martin. A safer bet would be TL072s (or TL074), but you might want to try both.

You typically use a stereo jack when you are using a battery. You could use one on the output jack if this were the case, so that it was only battery powered when plugged into the rest of your pedal board.

[pastorjustinb]

I think i have everything ordered or taken off an old TV...  I was wondering what the horizontal arrow to the top left of the pot means.

Also... without redoing any schematics, how simple would it be to add a tone control to each channel?

Time to sit and wait for my parts.... tick, tock, tick, tock......


justin

[samhay]

The arrows suggest (not very well standardised) that you should get more resistance (which will be more gain) as you turn the pot clockwise.

Depends on what you want the tone to do. You could put your favourite tone stack after each input stage, or a single tone stack before the output buffer after the switches.
The 1u caps will roll off some bass, but this should be inaudible and you may wish to decrease these quite a bit. You could put a smallish cap parallel to the gain pot that will roll off more treble as you increase the gain. That reminds me - if you need more gain, decrease the 10k resistor and vice versa. This is when the breadboard is your friend.

[pastorjustinb]

Thanks yet again... what i was thinking about was a single tone control per channel. I've looked around a little bit and it seems as though tone controls are connected to the volume control. Would the gain serve the same purpose on this contraption? (On a sound board gain and volume do not mean the same thing...
Also... What would the possibility be for me to connect a mic to one of these channels?... my brain won't stop thinking about where this could go...

Edit:

[samhay]

Ah, mission creep.
The 3 channels each have a gain stage that amplifies the signal. You can set the overall level/volume this way, or you could (but I wouldn't) add e.g. a standard volume pot after the output buffer.
I guess the tone control you added could go between the gain stage and the output buffer. It will work, but I don't know how well - experiments are fun though.
As for the microphone input. You could add one. Depending on the type of microphone, this might be a trivial add-on, or not. I think there have been some recent(ish) posts about mic inputs.

One of my acoustics has a Baggs passive iBeam in it. This played OK through one of my pedals with a similar input stage as shown in the schematic, but you will likely need a lot of gain to get it up to electric guitar levels.