piezo/mic blending issues.. matching outputs and impedance problems!

[bass349]

Hey guys i recently bought a shure beta 57a on all the positive posts (thanks chris fitzgerald) in regards to blending that and the piezo. (sorry for the long post in advance, just want to get everything clear..)

I instantly had a few problems.. the output of the piezo is ridiculously louder than the mic. I made a simple home made line mixer (ala http://www.epanorama.net/circuits/linesum.html) that i have been attempting to mix the signals with.

My initial idea was to put the pickup straight into the preamp of my head (gk 700rbII, has a high enough input impedance i believe), then from the effects send blend that signal with the mic - which is running through a sansamp BDDI for some gain. Didn't work as well as i thought it would! It sounded OK, but the mic was BARELY in the mix, even with the BDDI at full gain.

I tried it the other way around (mic into GK preamp, pickup into BDDI), the mic sounded ok (the gain still seemed to be an issue) and the pickup didn't sound that great. I didn't expect it to, as i've read that the input impedance for the BDDI is too low for a piezo's output impedance.

So i tried blending the two before the head (mic into BDDI then to simple mixer, piezo pup straight in), then running that line straight into the preamp of my head. This would have several disadvantages, as i can only eq the piezo signal AFTER it has been mixed with the mic. Sounded ok, and i got some decent volume out of the mic, but when i soloed the pickup i realised it sounded HORRIBLE. like i was listening through a cheap radio speaker.

Soooo i started reading up on impedance matching (it hurts my head, i must admit). i believe that the little line mixer i built from the circuit i linked to above has no-where near the right impedance for the hi output piezo.

I'm looking for a low cost solution (aren't we all?). i've looked into the Dtar Solstice and the new Radial PZ preamp (which looks great!), but for the moment they're out of my budget. I found this little piezo/mic blender on ebay after googling. It's intended for acoustic guitars, but i'm wondering if it will work for my dillema. I realise that it's a cheap and probably crappy product, but i'm wondering if it's worth a crack.. i've emailed the guy about the eq frequencies and the impedance of both the piezo and mic inputs. This is the link to the product http://www.acousticpreamp.com/servle...E-BT-MC/Detail

I also found this little fellah http://personalpages.tds.net/~fdeck/bass/quickand.pdf
looks interesting. i'm probably gonna have a crack at building it this arvo if i get time.. it may help.

Also, i'm tempted to try changing the resistors on the simple mixer to see if that helps the matter. i don't claim to understand too much of this (ahh if any) but i think if put in some higher resistors (like a 1 meg), then that may fix the impedance problem?

Anyway, would love to hear any thoughts on this or from anyone who has attempted to do this before. I had no idea blending two signals would be such a problem!

Thanks in advance for your replies.

all the best,
Andy

[riimodar]

I use LR Baggs Mix Pro to blend pickup and microphone. This is a two channel preamp especially designed for this. I must say blending works well (although I do not like the unit overall) with any pickup and with any CONDENSER microphone, however it does not work well with SM 57. Unfortunately, SM 57 has extremely low output. I like SM 57 sound (mounted under tailpiece, bridge or fingerboard), however I think you will have this lo-output problem with SM 57 with most simple blenders, as most of them are designed for electret condensers which are more typically used to pick up double bass or guitar.

Of course it is possible to mix SM 57 using any all-purpose mix. Now there are lots of small all-purpose mixes available at low prices (e. g. 4 channel). They have the gain range (+60dB) required for dynamic mics. You will still need a bass preamp between the pickup and the mix, as the input impedance of the mix is low.

[Chris Fitzgerald]

The Beta 57, like most mics out there, won't be as loud as a good pickup though an amp because of feedback issues. I use mine to add some added ambience, air, and "wood" to the blended sound. It definitely helps to be able to EQ each source separately. I've used several external blenders successfully, the best being the Raven Labs blender (no longer made).

Has anyone tried using a small cheap mixer for this purpose? What's the impedance of the line inputs on most 2-4 channel mixers?

[bolo]

Originally Posted by bass349

... as i've read that the input impedance for the BDDI is too low for a piezo's output impedance.

Not trying to argue or confuse things, but my BDDI owner's manual says the input impedance is 1 Mohm, which depending on your p/u and who you talk to should be okay for most of today's piezo p/u's.

Your profile says "fishman pickup", and if it's the old BP-1oo, you're right, that p/u really seems to prefer 10 Mohm from what I've read.

[riimodar]

Sorry for one confusion - bass349 wrote about beta 57 while I referred to SM57. Beta has probably higher output.

Link input on mixers is typically between 10kO and 47kO.

In my experience, 1MO is usable for piezos, but still far from optimal. For most peizos, there is still quite a big difference if you hook the pickup to 1MO or 10MO. Realist being an exception (works with lower impedance inputs well). I have 1MO input on my multi-effect unit an also on my soundcard, so I can compare sound of my Shadow 650 pickup to 1MO and 10MO. The difference is easy to hear.

BTW all K&K preamps claim "only" 1MO input.

[bolo]

Originally Posted by riimodar

In my experience, 1MO is usable for piezos, but still far from optimal. For most peizos, there is still quite a big difference if you hook the pickup to 1MO or 10MO.

Yeah you're not the only one on TB that feels that way. Me, I hear a notable difference as you said w/ my Planet Wing, but a much more subtle difference w/ my Rev Solo. Depends on the pickup I reckon. Or maybe I'm all wet. YMMV of course.