Re: Update on preamp design for piezo pickup
- From: hill@xxxxxxxxxxx
- Date: 30 Dec 2006 16:23:52 -0800
tempus fugit wrote:
Finally got the pickup in the guitar and had some time to mess around with
preamp designs. A simple voltage follower works very well - clean and quiet,
even with a TL071. However, trying to add any gain at all turns the thing
into frying eggs. There is SO much noise. I also found, though, that any
extra gain isn't really needed; in fact, a gain of more than about 3
distorts the signal when I strum hard. I suppose it would be nice to get a
little more gain (2-3), but not at the expense of the noise that's added.
We'd need to see your actual circuit to comment properly. There are
lots of ways to add noise besides the opamp. What's more, as I'm sure
you know, the TL071, with en = 18nV at 1kHz, is _not_ among the quiet
JFET opamps. For example, the AD743 has 3.2nV/rt-Hz of noise at
100Hz, whereas the TL071 has 25nV of noise. Hey, that's a lot!
I also tried the JFET amp posted by J. Legris
(http://www.till.com/articles/GuitarPreamp/) but couldn't get it to work at all
with a J111, which is all I have handy. This was a bit of a disappointment,
because it has fairly small gain (although maybe too much at 10) and
should be fairly quiet, as the J111 has a fairly low noise figure.
Actually, J. Legris' J201 choice isn't that quiet either (i.e. 8nV at
500Hz at 100uA), and your J111 isn't much better at 9nV/rt-Hz (500Hz
and 100uA). But then, we don't have your circuit, to know if you're
making mistakes to overshadow these low-noise specs for these parts,
like too much cable capacitance creating en-w-Cin noise, or if perhaps
you're employing some enhancements to improve on the specs (e.g.,
operating at higher currents, keeping critical resistor values under
220 ohms,etc.).
BTW, the really low-noise discrete JFETs get down to well under 1nV.
As we point out in the extended low-noise discussion in AoE, you'll
want to select a JFET with larger area = higher input capacitance.
.
- Follow-Ups:
- Re: Update on preamp design for piezo pickup
- From: tempus fugit
- Re: Update on preamp design for piezo pickup
- References:
- Update on preamp design for piezo pickup
- From: tempus fugit
- Update on preamp design for piezo pickup
- Prev by Date: Re: job thing, maybe
- Next by Date: Re: Electric Chair
- Previous by thread: Re: Update on preamp design for piezo pickup
- Next by thread: Re: Update on preamp design for piezo pickup
- Index(es):
Relevant Pages
|
