blend

makepeace

I want to put a cheapy (http://cgi.ebay.com/Guitar-Transducer-Piezo-Under-Saddle-Pickup-Pick-Up-/120621403874?pt=Guitar_Accessories&hash=item1c15988ee2) piezo pickup in my archtop, along with the P-90 that it already has.

Whats the easiest way to blend the two pickups? Ideally I'd like to only have 2 pots: a master volume and a blend control (ie fully on: only magnetic pickup, fully off: only piezo pickup, range in between: combo between piezo and magnetic pickups). Either that or a pot for the magnetic volume and piezo volume. I understand that there will be a difference in the magnitiude of the output of the two pickups.. I could see which has the lower output, and attenuate the louder one?

Is there a way to do this all cheaply with passive components? There is the Artec Master Blender, but its pretty expensive and I don't have the need for aux outputs, tone controls, selector switches etc.

Thanks to anyone that can help! ?

MikeM

It might be worthwhile trying to get an acoustic preamp as well...

But blending can be done with a simple blend pot ?

http://www.stewmac.com/shop/Electronics,_pickups/Potentiometers/Blend_Pots.html

makepeace

ah thanks man. i saw that on stewmac a while back, but forgot about it. ?

yeah good idea about the preamp. will see how it sounds without it first.

djpauw

you don't really need a special pot... Any pot can do the trick (higher resistance = better), just solder one pickup to one of the side pins, the other pickup to the pin on the other side and use the centre pin as output.

That way you have a 50/50 split in the middle and more piezo to one side and more P90 to the other side.

I've done this a few times before albeit not with piezos and it always works a charm.

Cheers

DJ

AlanRatcliffe

Sorry - you have to use a specialised blender circuit. Piezo pickups need a very high input impedance (usually between 2 and 5 Megohm), while magnetic pickups only need a high (500K - max 1 Meg). Wire them together passively and the mags will completely overpower the piezo. Use a preamp on the piezo and it will then have a low Z output, which will overpower the relatively high mags. So you need a preamp for both - with different input impedances for each and the same output impedance, and then you can blend them.

djpauw

makes sense... My lack of pieze experience was showing hey? :-[

makepeace

Ah. So it is a complex beast.

What about if you used an attenuation circuit to match the output impedance of the mag and the piezo? Like this one:

(jacked off of wikipedia: http://en.wikipedia.org/wiki/Attenuator_%28electronics%29)

djpauw

in theory that could be done... I suppose you know how to work it out with the two-port parameters?

makepeace

no idea.. :-\

edit: yea found some equations on the net.

just need the impedance of the mag and piezo pickup.

although i was just reading about active buffer preamps for piezo pickups to avoid clipping. maybe this isn't possible. anyone with any experience care to shed some light?

AlanRatcliffe

The transients from a piezo are very fast and significantly higher amplitude than the average. So the headroom in any active circuit designed for piezos is very important AFAIC. Generally the higher quality the circuit, the better the tone.

I'm no EE, but I presume good rise time and slew rate specs are an advantage too - but then again, a slower rise time might help tame the transients without resorting to using a VCA for peak limiting, where IME, attack and decay times have to be faster than most circuits can handle.

I'm surprised that we don't see more high end valve preamps for piezos - I would think that the natural compression of valves would be tailor-made (or should that be Taylor-made? ?) for the application. Certainly I've had good results using high end valve mic preamps.

Vick

Dud, are you sure you are prepared to ditch the tone knob?
I have experiance with a prs se one and it sounded amazing,but the
Problim is you have to change channels or use pedals to change the tone
It duzint sound so bad,but it is...haha

makepeace

Thanks Alan. Although a lot of that went over my head. Maybe I better invest in one of those Artec jobbies.

To be honest I'm not too attached to the tone controls on most guitars I play.. This guitar is pretty bassy as is, and it gets very muddy when i fiddle. So I don't even use the tone control.