AkitikA PAT-4 User manual

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PAT-4 PHONO PREAMP
REPLACEMENT (PAT4PPR)
ASSEMBLY MANUAL
© 2017 AkitikA, LLC
All rights reserved
Revision 1p08 January 25, 2017

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Table of Contents
Table of Contents ................................................................................................................ 2
Table of Figures .................................................................................................................. 2
Section 1: About This Manual ............................................................................................ 4
Who Should Attempt these Projects? ............................................................................. 4
Tools and Supplies You’ll Need ..................................................................................... 4
Recommended Solder ..................................................................................................... 5
Project Overview ............................................................................................................ 5
Important Safety Notes ................................................................................................... 5
Section 2: About the Phono Preamp Upgrade .................................................................... 6
Effects of the Modification ......................................................................................... 6
Prerequisites ................................................................................................................ 6
Building the PAT4PPR Circuit Boards....................................................................... 6
Component Order............................................................................................................ 7
Install the Resistors ......................................................................................................... 7
Prepare and Add Shielded Cables to the Inputs ........................................................ 10
Install the Mounting Brackets ................................................................................... 10
Preparing to Install the Assembled PAT4PPR Circuit Board ................................... 11
Drilling Mounting Holes in the PAT-4 Chassis ........................................................ 11
Connect the RCA Jacks ............................................................................................ 11
Move Power Wires ................................................................................................... 12
Move Selector Switch Wires .................................................................................... 13
Converting to Accept 5 high level inputs and 1 phono input ................................... 14
Inspection and Preliminary Reassembly ................................................................... 16
Final Sanity Checks .................................................................................................. 16
Prepare to Reconnect your PAT-4 to your Music System ........................................ 16
Record Playing Reminders ........................................................................................... 16
Gain Tweaks ................................................................................................................. 17
More Tweaks ................................................................................................................ 17
Schematics .................................................................................................................... 18
Specifications ................................................................................................................ 20
Appendix 1: The Toothpick Trick ................................................................................ 21
Appendix 2 - Preparing a Shielded Cable End ............................................................. 22
Appendix 3 - Resistor Color Code ................................................................................ 24
Table of Figures
Figure 1-Component side of the phono preamp PCB before loading ................................. 6
Figure 2-Installing resistors ................................................................................................ 7
Figure 3-Shielded cable installation (right channel shown here)...................................... 10
Figure 4-Use 6-32x1/4" screws to attach mounting brackets ........................................... 10
Figure 5-Locating the mounting holes .............................................................................. 11
Figure 6-locating the two added 9/64" mounting holes .................................................... 11
Figure 7-Connecting Left Channel input jack and 0.01 µF capacitor .............................. 12
Figure 8-Selector Switch wire identification .................................................................... 13
Figure 9-Back Panel Re-wiring ........................................................................................ 15

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Figure 10-Phono Preamp Schematic Page 1 ..................................................................... 18
Figure 11-Phono Preamp Schematic Page 2 ..................................................................... 19
Figure 12- Shield wire end prep completed (right channel) ............................................. 23
Figure 13-demonstrating the resistor color code .............................................................. 24

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Section 1: About This Manual
This manual gives the information you need to build and install the PAT-4 Phono Preamp
Replacement (and Upgrade), part number PAT4PPR, into your Dynaco PAT-4 Preamp.
As of this writing, the following other PAT-4 upgrades are available from
Updatemydynaco, a division of Akitika LLC:
 Blue Light Kit (BLUE)
 Line Amp Distortion Reducer (DRD4)
 Tone Control Switch (TCS)
 Electronically Regulated Power Supply (PAT4PWR)
 Line Stage Replacement Components (P4LSRC)
 Phono section upgrade (PAT4LP)
In my opinion, this kit, the PAT4PPR is preferable to the PAT4LP, even though the
PAT4PPR costs more. Why?
 The PAT4PPR kit is easier to build and install than the PAT4LP kit.
 The PAT4PPR kit has a tight layout with ground-planes and bypass capacitors
that give it great high-frequency stability and noise rejection.
 The PAT4PPR kit has a built-in second order high-pass filter that minimizes the
woofer wobble caused by record warp.
 The PAT4PPR kit has a built-in second-order lowpass filter that makes it much
less likely to pick up external signals like switching transients and radio stations.
 The PAT4PPR is installed much farther from the power supply, so picks up much
less of the stray hum fields inside the PAT-4. This makes it very quiet and free of
hum. The only hum you will pick up comes from the phono cables outside of the
PAT-4.
Note: the phono upgrade kit requires the PAT4PWR supply to be installed.
Who Should Attempt these Projects?
You can build this kit if you can:
1. solder (using normal rosin core solder and a soldering iron),
2. use simple hand tools like screwdrivers, wire cutters, and pliers, and
3. Read and follow directions.
It helps if you:
1. know a bit about electronics, or
2. have a friend who knows a bit about electronics
3. can get to YouTube to watch a few helpful videos about the assembly process (not
available as of this version of the manual)
Tools and Supplies You’ll Need
You’ll need the following tools:
1. flat blade screwdrivers for #4 and #6 screws, #2 Philips head screwdriver
2. a power drill with a 9/64” drill bit. A center punch is also helpful, as you will be
drilling two holes into the bottom of the PAT-4 Chassis.

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3. needle nose pliers (helpful, but not strictly necessary)
4. pencil type soldering iron of 25 to 50 Watts (no huge honking soldering guns or
blowtorches)
5. wire cutters and strippers
6. de-soldering tools (see the Appendix 1 and Appendix 2)
7. Magnifying glass, if you’re over 42!
8. A multi-meter for measuring Ohms and DC volts is handy, but not strictly
necessary
Recommended Solder
The kit must be assembled with 60/40 Rosin Core solder. The recommended diameter is
0.032 inches. Among many such sources of solder, I have used Radio Shack part number
64-009. It contains 8 oz. of solder, which is much more than you’ll need to assemble this
kit.
Project Overview
Broadly, the project consists of the following steps:
1. Building the PAT4PPR circuit board.
2. Adding two screw holes to the bottom of the chassis.
3. Transferring a few wires from the phono preamp section of the original preamp
circuit boards to the new phono preamp.
4. Fastening the new phono preamp in place and performing a few sanity checks.
5. Reassembling the preamp.
Important Safety Notes
By purchasing, using, or assembling this kit, you have agreed to hold AkitikA, LLC
harmless for any injuries you may receive in its assembly and/or use. To prevent injuries:
 Wear safety glasses when soldering to prevent eye injuries.
 Always unplug the power before working on the equipment.
 Large capacitors hold lots of energy for a long time. Before you put your hands
into the equipment:
o Pull the AC plug!
o Wait 1 full minute for the capacitors to discharge!
 Remove jewelry and rings from your hands and wrists, or anything that might
dangle into the amplifier.
 If working in the amplifier, keep one hand in your pocket, especially if you’re
near the power supply or power supply wires. This can prevent serious shocks.
 Build with a buddy nearby. If you’ve ignored all the previous advice, they can
dial 911 or get you to the hospital.

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Section 2: About the Phono Preamp Upgrade
Effects of the Modification
 The phono preamp will be at least 4 dB quieter than the stock preamp. Internally
generated hum will be reduced by much more than that.
 The phono equalization will be much more accurate, providing truer sound.
 You will change the wiring to provide 5 high level inputs and 1 phono input:
o The PHONO LOW input will be active, accepting a moving magnet
cartridge.
o Tape Head and Special inputs will be converted to accept high level inputs
 The preamp won’t clunk when you switch it in and out of the phono position.
 Your cartridge will see the correct loading impedance. The original PAT-4 design
used a form of feedback biasing that made its input impedance look inductive,
falling to 10K ohms or less at low frequencies. This kit presents an input
impedance that looks very much like 47 K Ohms in parallel with 220 pF across
the whole audio band.
Prerequisites
The PAT4PWR supply must be installed along with the phono preamp upgrade. The
reason is that the PAT4PWR supply generates a -17.5 Volt supply that is used to bias the
phono preamp in the PAT4PPR.
Building the PAT4PPR Circuit Boards
This section details the process of building the phono preamp circuit board. We start with
an overview on this page. The specifics you need to start building begin on the next page.
The bare PCB is shown in Figure 1.
Figure 1-Component side of the phono preamp PCB before loading

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Begin by carefully emptying the contents of the parts envelope into a broad soup bowl, as
shown below. In general, you’ll start with the components that lay closest to the board,
working your way towards the taller components. You will:
1. Install the resistors
2. Install the capacitors
3. Install the transistors
Component Order
You’ll notice that the component designations in the directions don’t go exactly in order.
We have grouped them so that all components with the same value appear together. This
makes assembly easier. You’ll find in the parts kit that similar parts, e.g. 3 1K resistors,
are typically (though not always) taped together.
Install the Resistors
In general, you install the resistors by placing the body on silk screen side of the board,
and the leads through the indicated holes. Bend the leads over on the back of the board to
keep the resistors from falling out until you solder them in place. Try to bend the leads in
a direction that won’t lead to solder bridges between traces that should remain
disconnected.
Figure 2-Installing resistors
We recommend the following procedure:
1. Insert all the resistors of the same value, e.g. R4 and R7.
2. Bend the leads as described above.
3. Solder the leads on the back of the board.
4. Clip the leads.
Track your progress by placing a check-mark in the done column as you install each
resistor. Check resistor values with a meter, or by reading the color code1. Orient the
1 See “Appendix 3 - Resistor Color Code” on page 24 to see how to read resistor color codes.

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resistor with the fat brown band on the right, then you can read both the Color Code
column and the resistor from left to right.
Here are two assembly hints:
1. Finding the components: The PC Board has two essentially identical layouts, one
for each channel:
a. Left channel along the top half of the PCB.
b. Right channel along the bottom half of the PCB
c. You’ll often find that pairs of identical resistor values are separated by 13.
For example:
i. R4 and R17, separated by 13, are both 158 Ohms.
ii. R4 and R17 are in essentially the same left to right position on the
PCB, with R4 in the left channel, and R17 in the right channel.
2. The resistor leads are spaced at 0.4”. If you have a lead bender, this will speed up
and neaten your assembly. A lead bender is not required.
Desig Value Marking Done☑
R4 158 Brown, green, white, black, brown □
R17 158 Brown, green, white, black, brown □
R2 1k Brown, black, black, brown, brown □
R3 1k Brown, black, black, brown, brown □
R10 1k Brown, black, black, brown, brown □
R14 1k Brown, black, black, brown, brown □
R16 1k Brown, black, black, brown, brown □
R23 1k Brown, black, black, brown, brown □
R1 22k Red, red, black, red, brown □
R15 22k Red, red, black, red, brown □
R13 27K Red, violet, black, red, brown □
R26 27K Red, violet, black, red, brown □
R5 30K1 Orange, black, brown, red, brown □
R18 30K1 Orange, black, brown, red, brown □
R6 3320 Orange, orange, red, brown, brown □
R7 3320 Orange, orange, red, brown, brown □
R19 3320 Orange, orange, red, brown, brown □
R20 3320 Orange, orange, red, brown, brown □
R11 47k5 Yellow, violet, green, red, brown □
R12 47k5 Yellow, violet, green, red, brown □
R24 47k5 Yellow, violet, green, red, brown □
R25 47k5 Yellow, violet, green, red, brown □
R8 5900 Green, white, black, brown, brown □
R21 5900 Green, white, black, brown, brown □
R9 75K0 Violet, green, black, red, brown □
R22 75K0 Violet, green, black, red, brown □

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Now you’ll install the non-polarized capacitors. We start with the smallest capacitors, and
work toward the larger capacitor values. These capacitors are not orientation sensitive.
Desig Value Marking Done☑
C12 100 pF 101, axial □
C25 100 pF 101, axial □
C5 220 pF 221, axial □
C18 220 pF 221, axial □
C6 680 pF 681, axial □
C19 680 pF 681, axial □
C13 2.7 nF 272, blue ceramic radial cap □
C26 2.7 nF 272, blue ceramic radial cap □
C2 10 nF 10nF1K0 □
C15 10 nF 10nF1K0 □
C1 47 nF 47n F 630 □
C14 47 nF 47n F 630 □
C10 0.1 µF µ1J100 □
C11 0.1 µF µ1J100 □
C23 0.1 µF µ1J100 □
C24 0.1 µF µ1J100 □
C3 0.33 µF 0.33J63 □
C4 0.33 µF 0.33J63 □
C16 0.33 µF 0.33J63 □
C17 0.33 µF 0.33J63 □
C9 3.3 µF 3.3k63 □
C22 3.3 µF 3.3k63 □
The following capacitors are electrolytic capacitors. The polarity is important. Be sure to
look at the polarity as marked on the silk screen, and make it agree with the capacitor
markings. Note that the 47 µF capacitor foot print doesn’t quite match the PCB, but it
installs reasonably well.
Desig Value Marking Done☑
C7 47 µF, 25V See the value column □
C20 47 µF, 25V See the value column □
C27 47 µF, 25V See the value column □
C8 1000 µF, 10V See the value column □
C21 1000 µF, 10 V See the value column □
Match the shape of the transistor body to the shape of the silk-screen. Leave about 3/8” of
space between the bottom of the transistor package and the PCB. Don’t get too much heat
onto the transistors.
Desig Value Marking Done☑
Q1 MPSA18, high gain NPN MPSA18 □
Q3 MPSA18, high gain NPN MPSA18 □
Q2 MPSA45, Darlington MPSA45 □
Q4 MPSA45, Darlington MPSA45 □

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Prepare and Add Shielded Cables to the Inputs
For lowest hum, you must use shielded cable between the PHONO LOW RCA Jacks and
the inputs on the PCB. Prepare two 4” lengths of shielded cable:
1. One for the right channel, using the red conductor and the drain wire.
2. One for the left channel, using the black conductor and the drain wire.
Details on the preparation of the shielded cables can be found in Appendix 2 - Preparing
a Shielded Cable End. Prepare both ends of both pieces of shielded cable now, as it will
make it much easier to later complete installation of the input wiring.
Figure 3-Shielded cable installation (right channel shown here)
Connect the wires as follows:
1. Right channel signal wire (red) to the eyelet labeled INRIGHT
2. Right channel drain wire (bare wire covered with added gray outer jacket) to the
eyelet labeled GNDRIGHT.
3. Left channel signal wire (black) to the eyelet labeled INLEFT
4. Left channel drain wire (bare wire covered with added gray outer jacket) to the
eyelet labeled GNDLEFT.
Double check that you have not reversed the ground and signal wires.
Install the Mounting Brackets
Use 6-32x1/4” sems screws to install mounting brackets as shown in Figure 4. Make sure
the brackets are straight before you tighten them.
Figure 4-Use 6-32x1/4" screws to attach mounting brackets

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Preparing to Install the Assembled PAT4PPR Circuit Board
1. Disconnect the PAT-4 from your music system.
2. Unplug the power cord and allow the preamp to sit for one minute before moving
on.
Caution: Be sure that the preamp power is unplugged! 120 VAC can be lethal! 240 VAC
can be lethal!
3. Remove the 4 screws that hold the cover in place, 2 on the left side and 2 on the
right side.
4. Lift the cover straight up and set it aside in a safe place.
Drilling Mounting Holes in the PAT-4 Chassis
You’ll need to add two 9/64” mounting holes to the PAT-4 chassis. 5/32” holes are also
ok, and may give you a bit more margin if you drill slips a bit. It’s a good idea to use a
center-punch to locate the centers of the two mounting holes. Without the center-punch,
the drill will tend to drift off the mark.
Figure 5-Locating the mounting holes
Locate the drill holes near the selector switch as follows:
1. The front mounting hole should be on a line with the front hole that holds the
cover. The center of the hole should be 0.250” from the inside lip of the chassis so
that the end of the bracket won’t bump into the lip of the chassis.
2. The rear mounting hole is also placed 0.25” from the inside lip of the chassis, but
it is located 3.400” behind the front mounting hole.
Figure 6-locating the two added 9/64" mounting holes
An easy way to locate the holes is to sit the PCB with mounting brackets (make sure
they’re on straight) in the intended location, then mark the hole locations with a pencil or
a center-punch.
Connect the RCA Jacks
Remove the PEC 555005. It is no longer needed. Please note that the PHONO HIGH and
PHONO CER jacks will no longer be active.
De-solder or cut any existing wires on the center terminals of either the right or left
channel PHONO LOW input jacks.

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Make the following connections between the shielded cables and the RCA jacks:
1. Right channel signal conductor (red) to center of right channel RCA jack.
2. Right channel ground conductor (drain wire covered with a bit of reserved gray
jacket insulation) to the ground lug of the right channel RCA jack.
3. Left channel signal conductor (black) to center of left channel RCA jack.
4. Left channel ground conductor (drain wire covered with a bit of reserved gray
jacket insulation) to the ground lug of the left channel RCA jack.
For both the right and left channels, connect a 0.01 µF 400 V capacitor between the
chassis ground lug and the RCA ground lug. Figure 7 shows this connection for the left
channel. The right channel is connected similarly. Note that the white wire shown
connects to the jack-field grounds (or the associated RCA jack lugs) and pin 5 of the
selector switch. Also note: your 0.01 µF cap may look different than the one pictured.
Figure 7-Connecting Left Channel input jack and 0.01 µF capacitor
Move Power Wires
At this point, +17.5 V, -17.5 Volt power and ground wires run from the PAT4PWR board
to the phono section of the original preamp PCBs. We will instead run those power wires
to the new PCB.
 Clip or de-solder the wires currently going to eyelets 3, 4, and 8 of the original
PCB closest to the front panel.
 Clip or de-solder the wires currently going to eyelets 3, 4, and 8 of the original
PCB closest to the rear panel.
 De-solder the far-ends of the wires just removed from their connections to the
PAT4PWR board. Clear the associated holes on the PAT4PWR board using your
preferred method (for example, the toothpick trick).
 Form a twisted pair from the supplied red and black 22 AWG wires. Connect:
o Red wire to the P17P5 eyelet of the PAT4PWR
o Black wire to the associated GND eyelet
o The other end of the Red wire to the POS17P5 eyelet of the new phono
preamp.
o The other end of the black wire to the PGND eyelet of the new phono
preamp.
 Connect a purple 22 AWG wire from the N17P5 eyelet of the PAT4PWR board to
the NEG17P5 eyelet of the new phono preamp.

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Move Selector Switch Wires
Figure 8-Selector Switch wire identification
Now we’ll move the selector switch wires to select the output of the new phono preamp
when the selector switch is in the PHONO position.
1. Identify the wire that connects to terminal 8 of the front deck of the selector
switch. De-solder the opposite end of that wire from its current location.
a. If your PAT-4 phono section was stock, that end was connected to the
center terminal of the right channel PHONO LOW RCA jack.
b. If your PAT-4 phono section was upgraded with the PAT4LP, that end
was connected to eyelet 5 of the front preamp PCB.
2. Re-attach the end of that wire to the OUTRIGHT eyelet of the new PCB. Cut it to
a reasonable length. Insert the wire from the solder side, and solder it on the
component side.
3. Identify the wire that connects to terminal 8 of the rear deck of the selector
switch. De-solder the opposite end of that wire from its current location.
a. If your PAT-4 phono section was stock, that end was connected to the
center terminal of the left channel PHONO LOW RCA jack.
b. If your PAT-4 phono section was upgraded with the PAT4LP, that end
was connected to eyelet 5 of the rear preamp PCB.
4. Re-attach that wire to the OUTLEFT eyelet of the new PCB. Cut it to a
reasonable length. Insert the wire from the solder side, and solder it on the
component side.

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Converting to Accept 5 high level inputs and 1 phono input
These modifications will give you 5 high level inputs and 1 phono input. After
performing these modifications, TAPE HEAD and SPECIAL will both accept normal
high level inputs.
Ground Changes, refer to Figure 9. Done

Desolder the ground wire from FRONT PC-16, eyelet 2. Cover the bare
portion with electrical tape, but leave it connected to the switch.

Desolder the ground wire from REAR PC-16, eyelet 2. Cover the bare
portion with electrical tape but leave it connected to the switch.

Remove the following ground wires at the rear panel:
a. Short Lug 2-3 to Short Lug 4-5
b. Short Lug 13-14 to Short Lug 15-16
Add the following ground wires at the rear panel:
a. Short Lug 4-5 to Short Lug 6-7
b. Short Lug 15-16 to Short Lug 17-18
Selector Switch Wiring Changes, refer to Figure 8. Done

Identify the wire that connects to terminal 5F of the front deck of the
selector switch. De-solder its far end (it will typically be connected to
eyelet 1 of the front PC-16).

Identify the wire that connects to terminal 2F of the front deck of the
selector switch. De-solder its far end (it will typically be connected to
eyelet 5 of the front PC-16).

Twist the above two wires together, solder, and tape the connection.
The effect of this is to connect together front-deck selector switch
terminals 2F and 5F.

Identify the wire that connects to terminal 5F of the rear deck of the
selector switch. De-solder its far end (it will typically be connected to
eyelet 1 of the rear PC-16).

Identify the wire that connects to terminal 2F of the rear deck of the
selector switch. De-solder its far end (it will typically be connected to
eyelet 5 of the rear PC-16).

Twist the above two wires together, solder, and tape the connection.
The effect of this is to connect together rear-deck selector switch
terminals 2F and 5F.


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Figure 9-Back Panel Re-wiring

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Inspection and Preliminary Reassembly
Inspect your work for good solder joints and freedom from solder bridges. Touch up any
questionable connections now.
Install the phono preamp adjacent to the selector switch using 6-32x1/4” screws and the
holes you drilled in an earlier step. You may have to finesse the existing wires on the
selector switch, but the new phono preamp PCB will slide in there nicely.
Final Sanity Checks
Here are a few last tests before you reconnect your PAT-4 to your music system. With
the top still off, plug in the AC mains. Turn on the power switch. Set your meter to DC
volts. Connect one lead of the meter to ground.
Be careful! These steps are performed with the power connected and
turned on!
Done

Done

The voltage on the NEG17P5 terminal of the new phono preamp should
measure between -17 and -18 Volts DC (with respect to ground).
 
The voltage on the POS17P5 terminal of the new phono preamp should
measure between 17 and 18 Volts DC (with respect to ground).
 
The voltage on eyelet 12 of both original preamp PCB’s should
measure between 36 and 40 volts DC (with respect to ground).
 
Prepare to Reconnect your PAT-4 to your Music System
 Turn off the power.
 Remove the AC plug from the wall socket.
 Replace the cover.
 Reinstall the four screws that hold the cover in place.
 Reinstall the PAT-4 to your music system.
 Notes:
o Use the PHONO LOW input for your turntable. The other two PHONO
inputs, PHONO HIGH and PHONO CER are disconnected.
o Given the 5 high-level and one phono wiring, then:
 The TAPE HEAD input is a high-level input
 The SPECIAL input is a high-level input
Record Playing Reminders
If it has been a while since you’ve played records here are a few hints that you may find
useful.
 The ground wire between the turntable and the ground screw on the back-panel of
the PAT-4 preamp must be connected to minimize the hum. Usually, that wire
runs loosely along with the RCA cords.
 Check your tracking force and anti-skating force. Re-balance your tone arm if it
has been a while.

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 Make sure that the grounding crown of the RCA plugs fit snugly around the
grounds of on the preamp inputs. A good connection is important for low noise
performance.
 Watch for acoustic feedback that can arise if the speakers are too close to the
turntable. Increasing the space between the speakers and the turntable will help.
 The signal to noise ratio (SNR) of a record isn’t what you’re used to with digital,
it’s less. Still, the music on the records mostly masks the noise, except in soft
portions, or if the record is worn or dirty.
 Is one channel out? Swap phono outputs and preamp inputs to get to the bottom of
the problem. This will let you figure out if it’s a turntable/cartridge problem or a
preamp problem.
 A frequent source of “one channel out” problems in the turntable/cartridge system
comes from bad connections between the wires in the head-shell and the phono
cartridge. The push-on connectors become flakey. If this is the issue, you can
often renew the connection by carefully rotating the push-on connector on the
cartridge’s input pin:
o Be careful not to bump the stylus or catilever.
o Hold the cartridge body in one hand.
o Rotate the push-on connectors around the input pin using needle nose
pliers. This will clean the crud, and also let you tell if the connections are
so loose as to also cause a problem.
 Need more information on your old turntable? Visit www.vinylengine.com . They
have an extensive collection of turntable service manuals.
 Why Vinyl? Because it seems to have a higher SAR (Soul to Annoying Artifacts
Ratio) than most digital.
Gain Tweaks
I think you’ll find that the phono preamp has just the right amount of gain for you, which
will put the PAT-4 volume control at a nice play when you play LP’s. However, if you
find that the phono preamp has too much gain for your setup (cartridge and power-amp),
you can drop it by up to 6 dB by increasing the value of both R4 and R17 to 300 Ohms.
Be sure to use a high-quality metal film resistor.
More Tweaks
The design is unique in that the collector resistor (R6 and R19) in the output stage can be
made as low as 1K Ohm (even lower, actually) with no other adjustments to the phono
preamp. However, you will need to change the power supply to assure that you have
adequate current available. The advantage of lowering this resistor is the availability of
more current to drive the feedback network, further lowering distortion below the already
low numbers.

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Schematics
Figure 10-Phono Preamp Schematic Page 1

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Figure 11-Phono Preamp Schematic Page 2

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Specifications
Frequency response – typically within a 0.5 dB error band between 20 Hz and 20 kHz,
with the exception that the response is -0.5 dB at 20 Hz in support of the high pass filter.
High Pass Filter (with respect to 1 kHz)
 -0.7 dB at 20 Hz
 -7.4 dB at 10 Hz
 -19 dB at 5 Hz
Low Pass Filter (with respect to 1 kHz)
 -0.5 dB at 20 kHz
 -4.4 dB at 100 kHz
 -10 dB at 500 kHz
 -22 dB at 1 MHz
Gain at 1 kHz – 33.4 dB
Distortion
 5 mV rms input at 1 kHz produces 230 mV RMS with only 2nd harmonic, which
is -87 dB (0.0044% distortion)
 10 mV rms input at 1 kHz produces 460 mV RMS with only 2nd harmonic, which
is -80 dB (0.01% distortion)
 40 mV rms input at 1 kHz produces 1.84 Volts RMS with just 0.044% distortion.
40 mV is probably 4 times as much as will ever come out of your phono cartridge.