> >"Kevin F." <fiduccia@dreamscape.com> wrote:
> >Thanks for replying. I need an input from a guitar, or dynamic mic, about
> >15k impedance.
> >Thanks,
> >Kev :-)
> >>>"Kevin F." <fiduccia@dreamscape.com> wrote:
> >>>Does anyone have a simple schematic for a preamp with bass and treble
> >>>controls, that uses 2-3 transistors?
> >>>Thanks,
> >>>Kev :-)
leonard@nospam.com wrote:
> Here is a good old preamp - can have 70db s/n.
> Old transister stuff...
So is this one. It's a phono preamp, but you can change it to a mic
preamp.
All you do is remove the 2.7 nF 10% and the .01 uF 10% capacitors and
use the 470k as the level control. The smaller the value, the lower the
gain.
RIAA Magnetic Phono Preamplifier (one channel shown)
ASCII Schematic by John Lundgren 8-22-98 rev 980822a
Magnetic Phono Input
+-----------------------( O )
| |
| |
| 22 uF =====
| 16 V -----
| + |
| 180K |
| +---/\/\/\-----+
| | |
| | |
| | -----
| | E / \ 62K
+--/\/\/\--)-----+----/ Q1 \-----+----/\/\/\--------+
| 220 ohm | | NPN | |
| | | | Approx |
| | +-----------+ | 1.75 VDC |
| | | | | |
| | \ | | |
| | 30K / 2.7 nF | | |
| | \ 10% ----- | |
| | / ----- | |
| | | | | |
| | | | | |
| | +-----------+ | |
| | | | | |
| | | .01 uF \ 470K | |
| | ----- 10% / | |
| | ----- \ | |
| | | / | |
| | | | | |
| | +-----------+------)------+ Approx |
| | | | 11 VDC |
| | | | |
| | ----- | |
| 1 K | 82 ohm E / \ | 10K |
+---/\/\/\-+---------/\/\/\-----/ Q2 \--+--/\/\/\---+
| | NPN | |
| | | |
|100 uF 6V | | |
| || + | | |
+---||-----+ | |
| || | |
| ----- |
| 4.7K E / \ |
+-------------/\/\/\-------+-----------/ Q3 \-------+
| | NPN |
| + | |
| 10 uF ----- |
| 25 V ===== |
| | |
| | || + |
+----> | <--------||------------+
| | || 220 uF |
| | 35VDC |
+------------------------( O ) |
| Output Jack |
| |
----- Ground +24VDC |
--- well filtered O
-
Legend: ) = No Connection
+ = Connection
> = Wire continues in direction of arrowhead
All resistors are 1/4 W 5% unless otherwise marked.
All capacitors are 16V or more. Observe polarity!
Note: This must be viewed with a monospaced
font such as Courier.
Parts List
Q1 2N5088 or 2N3904 NPN low noise audio transistor
Q2 2N3904 or 2N2222 or PN2222 NPN audio gen'l purp transistor
Q3 2N3904 or 2N2222 or PN2222 NPN audio gen'l purp transistor
This is a two transistor series shunt feedback circuit with an emitter
follower low impedance output stage to drive the amplifier. Notice
that this basic circuit has no volume control, so you should have a
level control on the following amplifier or mixer.
For High Fidelity, certain construction details should be observed.
For low noise, the 180K and 62K resistors should be metal film
resistors. For low hum, the common should only be grounded to the
external circuitry at one point to prevent ground loops. So the
shield of the input and output RCA jacks should be isolated from the
chassis if the chassis is metal. The Q1 transistor should be a low
noise type. The 2N3904 is spec'd for low noise, but the 2N5088 is a
better choice. To reduce the input impedance to the usual 47k that is
required for a magnetic phono cartridge, an 82K metal film resistor
should be put across the input jack. It is not shown here.
--
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Date: Mon, 23 Nov 1998 19:38:26 -0800
Original Subject: Re: Preamp help - preamp.gif (0/1)