Here are all infos details for the Caruso PreAmp.

As it seems not for everybody clear. we try to make it clear:

the caruso preamp is the essence of more than 20 years of cutterhead design, repair and work in the field of professional cutting equipment. somehow the distillate, the mother of all the cutting preamp processors.

it has ingrediences and combines many ideas of   minicut, vc200, neumann SAL74 with state of the art technolgy not available back in the days.

the idea was: keep it simple but hard to make it better. at the current stage it is universal , simple to build and can outbeat any commercial product if carefully build at very low cost.

it took countless hours and that means a lot of work and efford is spent and we are happy to share this info for free use in non commercial projects. all the schematics are licencend under copy left. and the minimum we ask is to keep your changes also public and mention the origin.

if you want to make money with our design. drop a line and talk to us.

otherwise we send cosmic energy to  make your cut sound worth than any 64kBs MP3.yeah.

but let’s start:

please read carefully. its easy to build.

you need to read and understand all that info here.


another version built into an old router case. low cost recycling version.


current Version: 3.0

since beginning 2016 there is only the new print 3_0 sent out.

the schmeatics is here:  caruso_schema_HW3_12_2016b

the partslist with lots of mouser ordering numbers: caruso_partslist_hw3_2016_2

old Version: 1.1

pdf: block schematics of the CarusoPreamp

how to build together the caruso board  for the caruso cutterhead:

-print out the  schematics: caruso_schema_HW3_12_2016b

– get all the parts. check the partslist. most parts are quite easy and you can a wide  range. for example you can use all 47uf, 25V elkos and it will work perfectly.

here is a new partslist for hw 3_0 version caruso_partslist_hw3_2016_2

here is a partslist V1.1  for mouser electronics.not complete yet. but helps as a start. dont put C401,R401 for the moment.

ATTENTION a few parts changed by october 27th. check the latest schematics.


-start with all the resistors. if the gain of your power amp is <26 dB (20 times amplification) increase R410 to 15k- 22k.samson servo300 has only a gain of 23 dB!

-the put the ic sockets. spend the money for high quality sockets!

– add the potis.

– solder in caps , start with the ceramic ones, then the bigger ones.

caruso preamp v1.1 3th edition

-then solder in all the  other parts.

the only parts which must be accurate are the resistors and caps in the riaa encoder, decoder.if you can afford it use 1% caps there. or order 10-20 pcs of the 47nF & 10nF and match for the best.

encoder side: C300,C318,R301,R305,R303,R315

decoder side: C702,C703,R701,R702,R703,R704

rest is not that important.

– make sure you have a +/-15 or +/- 18V power supply with 100-200 mA each side.


i measured with 5532 and SSM2017 around +/- 33mA at +/-15V  for one board so 100 mA is minimum required for for a stereo version

if you have all parts. you need 2-3 hours to sold everything together.

Power Supply:

you need a symetrical Power supply +/- 12,15V or 18V. i suggest +/- 15 Volt

a nice site which explains all is ken stone’s power supply. check.

easy to get. easy to build. use a transformer with 2x12V windings, a bridge rectifier, 2x2200uF Caps and LM7815,LM7915 regulators. thats it.

or buy a kit or working one. there are tons of products.  for example:

vellemann K8042

crazy audio Classic Power


connect as follow:

Caruso preamp connections


Board tests:

test the board without the opamps first.

check on J100 with a multimeter if you have connection between pin1 &2,Pin2&3 and Pin1&3. if you have connection between those pis. something is bad.

then put in the opamps and attach the board to the power supply.

make sure drive poti is fully open.FB Poti is fully close (counter clock wise)

FBmon is fully open.

feed  1kHz sinus tone 0.5-1V to the input. check the output on a scope or with a soundcard. check for different frequencies. if you close the riaa switch at 20kHz you should have plus 20 dB approx. your signal might already clip with 1 V depending on the voltage you run the preamp.

then feed 20-50mV on the FB input and check at R605 if you have a signal. if yes. all is ok. if not this section does not work. you should also have the signal at the FBmon output.

caution: if you make open loop tests. (that means without a cutterhead attached)

you wont have a propper RIAA curve. Bass will be way higher…. so dont worry this is part of the regulation loop.

if all works its time to test the preamps together with the amp.

i strongly suggest to use a dummy head for testing the whole system

here is the schematics for the dummy head we will produce soon. but its easy, you can build your own on the fly.

putting together the whole system:


if you have successfuly built the 2 preamps you have to complete the whole system.

you need :

1. a lathe that fits the caruso.

2. a caruso cutterhead

3. a cable to the cutterhead with db15 female connector

4. the rc network and 0.5-0.63A slow blow  fuse in series of each drive channel.

there will be a special protection card. but its not ready for sale yet. we work on it.




5. the preampboards in a box with a +/-15 Volt power supply

6. a decent power amplifier.  around 60-150 Watt is nice. voltage gain should be around 26 dB.

i did not found the ultimate amp. a good start are LM3886 based amplifiers.

or any other descrete bipolar or FET amp . check on the net. many projets out.

7. a dummy head for testing te system.

8. a scope will help or at least a metering software on your DAW.

9. a decent tonegenerator or createt testtones on your DAW



older stuff (V1.0 version and grampian heads)

V1.0 Version is sold out. All new boards are V1.1 and are yellow.

But the schematics is almost the same little bugs eliminated.

dimensions of the pcb: 160mm x 65 mm , approx 45 gr. without parts

the built preamp picture to download

pdf: Partslist for Version 1.0

pdf: Schematics for Version 1.0

Bugs: Board Version 1.0 has two  little bugs.

– 1. in the last outputstage you have to add 2 resistors.use same value for example 10k or 4k7. the cooper traces i already cut before shipping. so its basically just adding the 2 resistors. the one between the opamp pins you can use 0805 or 1206 smd resistors…

-2. you need to add a little bridge on the RIAA switch.

general remarks to building the boards:

there are a few parts you dont need at the moment. also it totally depends on the cutterhead you want to use. all values are given for sx74,sc99 for the moment. maybe later i add a table for the parts to adapt. at the moment figure out yourself whats best…

– C403 is twice on the schematics, but only once on the PCB. so C403 is the 3n3 cap. if you use SC99, neumann head or caruso start with 3n3 1% and maybe there will be a modification later for caruso. for grampian. dont put the C403 and make a bridge for R405

– C400,c402 can be both 47uF no problem. you can bypass them by 100nF mkp,mkt cap

– C403 (100pF) , R401 not needed for the moment. but the C403 (100pF) is anyway not on the PCB so just leave out R401. and you are fine.

-C405 needs to be adjusted for specific head. 3n3 is for sx68,sx74 or sc99 a good value to start

-C608,C609 should be tantalum for best performance

-C316 limits the high frequency. so you can open up your board if you like….

-R606 set gain for Feedback Preamp. 270 ohm is a good value for SX74,SX68. change if you need more or less gain.

R606    Gain [dB]
OPEN    0
4K7        10
1K1        20
330        30
100        40


Caruso and Grampian Head:

i just did a quick test on my test cutting yet.

i used a tone generator, a scope a multimeter an amp. no rc network for grampian is used.

so this is a very unapproved  adjustment, but it could work:

1. remove R606. Gain=0dB

2. 1/4 inch jack. Tip goes to F-terminal, Ring goes to S-Terminal on Grampian.

3. use a digital multimeter to measure across amp output .

4. feed  50 Hz adjust level to obtain 0.5 V across Head Drive. make sure RIAA is off = J109 is open…

5. measure voltage on FBMon (poti full up) i measured 1.511V

6. change frequency to 100 Hz

7. measure voltage on FBMon (poti full up) i measured 1.705V

8. change frequency to 200 Hz

9. measure voltage on FBMon (poti full up).  I measured 1.422V

10. increase FBpot approx 1.5-2 turns.(at 4 turn it started oscillating on my setup)

at 50 Hz voltage drops to 0.593V,100Hz=0.604V,200Hz=0.576V,300 Hz=0.536V

adjust FBlevel so you have close values for 30 Hz,50Hz, 100 Hz , 200 Hz, 300 Hz. you should manage to adjust within 0.5-1 dB. the goal is to linearise the low end…..

also good to monitor FBmon Output on a scope. if you apply too much feedback your head starts oscillating at very high frequencies and the coils will burn very fast. so take care…

you can also use a dB meter for that. even better.

also if you measure distortion you can lower it from to 3% to 0.4% at 100 Hz.


remember: the Grampian Head is not a real Feedback Cutterhead ! the feedback is more like a transformer that helps linearize in the low end….this is very important to know.



general setup of the preamps in the cutting system

1. you need a power supply +/- 15V or +/- 18V linear is best. check the net for schematics.

2. use the preamp with a decent power amp for example LM3886 is quite nice for power up to 65-100W

3. always use a correct RC network in series with the head.

for SX74,SC99 start with 2u2 and 4.7 ohms

4. always use some kind of protection in series with the head. simpelst solution is a 0.5-0.63A Fuse or better a protection card.

we will provide soon the ProtectionOne. An electronic Cutterhead Protection without Fuse and with Relais.


power consumption for each board. measured with HP3478A, 5th of july 2012

preamp board version1.0
all TL082 opamps (fet and low power)and IC601 not used.
11mA at +15V
11mA at -15V
preamp board v1.1
all NE5532 (bipolar and not low power) opamps and SSM2017 for IC601
33mA at +15V
33mA at -15V

preamp board v1.1
all NE5532 (bipolar and not low power) opamps and INA 126P for IC601
23mA at +15V
23mA at -15V


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