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Digest of preamp construction articles.
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Newsgroups: alt.guitar
From: rstern@col.hp.com (Richard Stern)
Subject: Re: Building your own (ONBOARD PREAMP!)
Date: Tue, 29 Sep 1992 14:38:56 GMT
Organization: HP Colorado Springs Division
till@acid-rain.lucid.com (Don Tillman) writes:
>
> I personally don't like the sound of opamp-based preamp circuits. The
> noises and distortions they produce are annoying and umusical and when
> overdriven their clipping sounds very buzzy and recovery is ungraceful.
> For me a discrete FET circuit is the best way to go and, as a side effect,
> is only half the space (4 resistors, 1 fet, 1 cap, less wiring, add a cap
> and a pot if you need the gain adjustment).
Try this op-amp based pre-amp using the following circuit.
This is a design from Mike McTigue who has posted this a few times already.
Mike has this pre-amp in both of his electrics, I have it in 2 of my
electrics, and we've built them for friends who are very happy with them.
This circuit has no noticable noise or distortion, and a 9 volt battery
seems to last forever (none of us have had to replace one yet in 2+ years).
Please note that the purpose of this pre-amp is to act as a buffer between
the R of the volume pot and the C of the cable. I did modify one of mine
for gain, but I use it set to a gain of 1 almost all the time.
1M ohm 1M ohm
+9v---\/\/\/--------O-----\/\/\/---gnd
|
from |
pickup /
switch 500k \
| ohm / +9v
| \ |\ |
250k \ | 3 | \ |
vol / <------||----O-----|+ \|7
pot \ .1 uF | \
/ | u1 \_____o------\/\/\/----||----->
| 2 | / 6 | 50 1uF to
| o------|- / | ohms cable
gnd | | /|4 |
| |/ | |
| gnd |
| |
o-----------------o
u1 LT 1012 uPower op amp or other low noise low power op amp
(use a stereo jack to turn on/off the power)
Richard Stern
rstern@col.hp.com
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Newsgroups: alt.guitar
From: till@acid-rain.lucid.com (Don Tillman)
Subject: Re: Building your own (ONBOARD PREAMP!)
Organization: Lucid, Inc.
Date: 30 Sep 92 09:20:08
Date: Tue, 29 Sep 1992 14:38:56 GMT
From: rstern@col.hp.com (Richard Stern)
Organization: HP Colorado Springs Division
Try this op-amp based pre-amp using the following circuit.
(Umm, proper engineering practice requires you to decouple the 9v supply
and to bypass the lower 1Mohm resistor with a .1 uF (or so) cap,
especially if you're driving a load.)
The design you present is nearly identical to the "Guitar Handbook"
circuit that started this conversation, and suffers from the same
problems -- high feedback, bad feedback topology, ungraceful overload
and recovery, noise, and the signal has to go through a dozen non-linear
devices inside the chip before it gets out. Exactly the sort of thing
that gives solid-state amps a bad reputation!
Date: Mon, 28 Sep 1992 13:15:11 -0500
From: Kurt Taylor <kurt@istwok.ods.com>
Please post a schematic of your fet pre-amp. (I have tried many op-amp based
circuits with little success, unless you like BAD pre-amps :'))
Date: Tue, 29 Sep 92 10:34:54 -0400
From: tjs@godzilla.eecs.umich.edu (tim stanley)
You mention your preference for FET based pre-amps. Can you give me
any pointers to where I can lift a schematic of such a critter?
Date: Tue, 29 Sep 1992 07:55:32 GMT
From: chuck@spectrum.cs.unsw.oz.au (Mark Andrew Hawling)
Can you post one of your FET designs that you think is good.
Well okay. Here's a nice design from the "op-amps are for weenies"
school. Low distortion, low noise, low feedback, graceful overload,
simple, elegant, inexpensive, etc. This baby sings. It has a transfer
characteristic somewhat similiar to the first 12AX7 tube in a Fender
amp.
+------------------------+--- +9v
| |
< |
< 6.8k |
< |
| 5uF |
+----||----+--- out |
| | |
|-+ | |
in ---+----->| | |
| |-+ | |
| | | |
< 10M < 2.2k < 51k ---
< < < --- 10uF
< < < |
| | | |
+--------+----------+-------------+--- gnd
The FET is a 2N5457. The voltage gain is subtle, 3dB or so. You can
substitute another low-Vdss FET if you know what you're doing. Power
drain is about 0.5 mA, so a 9v batter will last a good long time. It
does start to sound a little grubby when the battery sinks below 7v.
It's also trivial to add a high-boost switch if you'd like; have it
shunt the 2.2k resistor with a 0.05 uF (adjust to taste) cap. Or shunt
the 2.2k resistor with a 10uF cap for more gain.
Obviously you want to wire it so it's powered off when the instrument
isn't plugged in -- it's far superior to use a switched jack instead of
the weenie approach of using the second connection of a stereo jack.
Also note that this design is easily phantom-powered, so you can even
get by without installing a battery.
-- Don
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Newsgroups: alt.guitar
From: till@acid-rain.lucid.com (Don Tillman)
Subject: Re: Building your own (ONBOARD PREAMP!)
Organization: Lucid, Inc.
Date: 7 Oct 92 16:06:03
From: db@seachg.uucp (David Bell)
Date: 5 Oct 92 12:38:06 GMT
Organization: Sea Change Corporation, Mississauga, Ontario, Canada
In article <TILL.92Sep30092008@acid-rain.lucid.com> till@lucid.com writes:
>
>Also note that this design is easily phantom-powered, so you can even
>get by without installing a battery.
>
Excuse my ignorance, but what exactly does this meen ?
"Phantom power", from the latin "phantasma potere" (powerful, but from no
apparent source), means that the output signal of a preamp and the supply
voltage to power it both run on the same wire.
This is possible without compromise due to a fluke in the circuit: you can
cut the circuit at drain of the FET, place the left half in the instrument,
place the right half in a powered box a cable away, and it'll work just
fine with just a hot lead and a ground lead.
This technique is used alot with condenser microphones, and many
professional mixing consoles offer phantom powered mic inputs -- inputs
with a resistor pull to a supply voltage. Those Radio Shaft PZM mics are
phantom powered f'rinstance.
-- Don
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Newsgroups: alt.guitar
From: mikem@col.hp.com (Mike McTigue)
Subject: Re: Building your own (ONBOARD PREAMP!)
Date: Mon, 5 Oct 1992 17:02:21 GMT
Organization: HP Colorado Springs Division
I'm the one who "designed" the LT1012 opamp circuit for a guitar
preamp. I refuse to get into a disscussion (flame war) on this
subject. Below I will state the reasons why I believe it is pefectly
fine for THIS application.
o High feedback is exactly what I want. I do not want this preamp
to color the signal AT ALL. I have a tube amp to do that and it
does that job very well. High feedback means it reproduces the input
*exactly*. If I want something to color the sound, it goes in my
effects.
o Yes you probably should bypass the 9v battery. Use a 10uf tantalum or
so.
o Overdrive recovery is not an issue for this preamp. The signal is
small and will never drive the output of the opamp anywhere near
the rails.
o What gives transistor amps a bad reputation is that they a) do not
color the sound the way people have come to like and b) they do
not saturate the same way as amps people have come to like.
In summary, if you want a preamp that colors your sound then definately
look into various fet preamps. The extent to which they color your sound
will depend on how linear they are and what their transient response
looks like. If however, you are already very happy with your sound but
would like a preamp that simply buffers your signal so it can drive a
capacitive cable without attenuating the high end, use a high feedback
opamp circuit with enough slew rate.
Mike M
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From: nm1@ukc.ac.uk (N.McBride)
Newsgroups: alt.guitar
Subject: Guitar-to-hifi box
Date: 30 Nov 92 10:55:13 GMT
Organization: Computing Lab, University of Kent at Canterbury, UK.
Someone asked for a circuit that will enable guitars or microphones
to be plugged into and aux input on a hifi, tape deck, ghetto
blaster etc. Here is one based on the 741 op amp (this can be replaced
with a better quality op amp)
The noce thing about this circuit is that it can be powered from a 9v
battery, is very cheap, and power consumption is very low so
the batery last for ages. (Connections are at o):
o--------------------o--------------------o 9v
| |
- |<--power rail(+)
| |R1 |
C1 - \ |
|| | | \ C2
o---||-----o------------------|+ \ +||-
|| | |op >------o---||----o
^ - |amp / | ||
| | |R2 o----|- / | ^
| - | |/| ___ | |
| | o -------|___|----o |
| | | | R3 |
Vin | - | Vout
| | R4| | | |
| | - |<--power rail(-) |
| | | + | |
v | C3===== | v
| | - |
o----------o-------------o------o--------------------o 0v
R1 = R2 = 220K C1 = 1uF (capacitor values
R3 = 100K C2 = 15uF aren't critical)
R4 = 100K C3 = 22uF
Gain of the circuit is set by R4. Gains of 2, 5, 10, 30 are given by
R4 = 100K, 24K, 11K or 3.3K respectively. Use the smallest gain that
you can get away with (2 is adequate for most things) as a high gain
will cause it to distort.
The op amp connections with pin numbers (viewed from above) are:
Out
9v |
| |
--o--o--o--o--
| 8 7 6 5 |
| | 741 op amp
| 1 2 3 4 |
--o--o--o--o--
| | |
-In | 0v
+In
I would recommend puting a switch an LED in between the power rails
so you know when it's on (and can turn it off!):
\
-----
| |Switch
|_____|
o o o
| |
| |
------------- | |
| 9v +|o---------o |
| cell | |
| -|o------o o--------o-----------o 9v
------------- | |
| -
| | | 510 ohms
| -
| |
| v LED
| |
o-------------o-----------o 0v
Cheers.
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From: whc2993@ritvax.isc.rit.edu
Newsgroups: rec.music.makers.guitar
Subject: Build a Tube Preamp etc.
Date: 15 Jan 93 20:49:50 GMT
Organization: Rochester Institute of Technology
The newest issue of Guitar Player has an article on how to build a tube preamp
for under $100. I wish I was good at electronics. Part of the preamp contains
a speaker simulator. I think some people asked about schematics for them and
you could probably extract the speaker simulator part from the schematic
provided.
Question: Can a tube preamp be used in front of a solid state combo amp or
would it mess up the sound because of the preamp in the combo? How about if the
tube preamp was plugged into the effect return of the combo, because I think
the effects sends are after the preamp.
Bill C.
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From: larryh@fawlty.lmc.com (Larry Huntley)
Newsgroups: rec.music.makers.guitar,alt.guitar
Subject: Re: Guitar Player's Stack in a box
Summary: Error in pre-amp schematic
Date: 27 Jan 93 03:10:41 GMT
Organization: Logic Modeling Corporation Beaverton, OR
In article <lm7u79INNqip@saltillo.cs.utexas.edu> borst@cs.utexas.edu (Christoph W. Borst) writes:
>
>If anyone has built Guitar Player's stack-in-a-box or something
>similar, I would like to know how good it sounded . . .
>
Sorry; I haven't built one, but I've looked at the schematic enough to
warn you that there is one (at least) error in the schematic as pub-
lished in the magazine (pg 94.)
At the right side of the schematic where the wiring is shown for the
polarity switch, S5, there is a mis-wire.
This is the way it's shown:
|
+------o
|
|
+---+--o This produces a dead short between the two complementary
| | outputs.
| |
| +--o
| |
| |
+------o
| |
| |
This is the way it should be:
|
+------o
|
|
| +--o
| |
| |
| +--o
| |
| |
+------o
| |
| |
I'm assuming that this is a typographic error; if you buy the parts
from PAIA they probably include a correct schematic. Since this was
off-board wiring, it was more likely to cause someone trouble than an
error in the area that is actually on the PCB.
- Larry Huntley
--
(larryh@lmc.com) | ".... and if that, that don't kill you
Logic Modeling Corporation | soon, the women will, down at the
Beaverton, OR | Spanish Moon." - Little Feat
From mcjimi@aol.com Sat Jan 14 13:52:47 1995
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From: mcjimi@aol.com (McJimi)
Newsgroups: rec.music.makers.guitar
Subject: amp kit catalog
Date: 11 Jan 1995 14:41:29 -0500
Organization: America Online, Inc. (1-800-827-6364)
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Sender: root@newsbf02.news.aol.com
Message-ID: <3f1c99$dku@newsbf02.news.aol.com>
Reply-To: mcjimi@aol.com (McJimi)
Copeland Electronics ( PO Box 931, West Sacremento, CA 95691 ) makes a 50
watt, all tube, Marshall style amp kit for about $250. ( including
transformers )
They also make a really cool "tube mod board" that lets you experiment
with a 12AX7 in all kinds of circuits-gain stages, cathode followers (
these don't add gain, but they do lower impedance. Cathode follwers are
often used just before the EQ circuits in many high gain, "British"
sounding amps), phase splitters, etc. All you have to do is simply plug in
various resistors and capacitors.
Copeland also makes a cap mod board that can filter out the ripple of up
to 800 volts. Great for quick design power supplies.
They don't yet make a tube preamp kit ( low weight, high voltage
(350-450 volts, 10-20 milliamps) transformer, 4 or 5 tube mod boards, cap
mod board, chassis, etc ), but they might if enough people write and ask
them to.
Another good thing about Copeland is that they don't seem to hype their
products like some other amp kit suppliers. They seem very
straightforward.
If you know of any other amp part/kit suppliers, please post the
addresses here and/or e-mail them to me. I'm having a hard time finding
transformers designed expressly for tube preamp use ( high voltage, low
current for B+, and DC voltage for tube hear ) I do NOT want to use big,
heavy, expansive amp transformers. Thanks.
McJimi
From mcjimi@aol.com Sat Jan 14 13:52:58 1995
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From: mcjimi@aol.com (McJimi)
Newsgroups: rec.music.makers.guitar
Subject: Re: amp kit catalog
Date: 12 Jan 1995 17:18:33 -0500
Organization: America Online, Inc. (1-800-827-6364)
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References: <3f1jb8$q0p@panix2.panix.com>
Reply-To: mcjimi@aol.com (McJimi)
Mr. Len Moskowitz wrote:
Telephone information doesn't have a listing for [Copeland Electronics].
Might you have a
phone number?
--
Sure do. 916-372-0275
McJimi
Len Moskowitz
From UKRR38A@prodigy.com Tue Jan 24 11:44:20 1995
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From: UKRR38A@prodigy.com (Joseph Pennisi)
Newsgroups: rec.music.makers.guitar
Subject: Re: speaker->line level out for Fender BandMaster?
Date: 24 Jan 1995 04:06:41 GMT
Organization: Prodigy Services Company 1-800-PRODIGY
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Is there any product to convert speaker level signal to
>line-level? I'd be willing to do the master volume mod if it didn't
add
>too much noise or devalue my equipment to much. Any hints?
Nick:
Go to your nearest authorized Fender dealer and grab a copy of the Fall
'94 issue of Fender Frontline (Steve Winwood on the cover), the promo
magazine that Fender puts out. On page 35 you will find an article
called "Master Your Amps" in which they show you a simple circuit: I
quote": "If your master amp has no Line Out but does have an External
Speaker Jack, you can use the simple circuit shown here to attenuate your
output to a workable line level."
Hope this helps.
Joe