PRE CR (EQ, Dist preamp) by FEEDBACK [Pcb update]

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: lisa, Kent, Joe.

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

PRE CR (EQ, Dist preamp) by FEEDBACK [Pcb update]

Post by strat-1 » Tue Jun 14, 2016 7:36 am

UPDATE : PRE CR is back in stock with rev 1.2Pcb.
Nothing is changed in terms of sound, just updated the pot prints and rerureted the paths in such a way you don't need to cut the pots ear holders anymore.

www.feedbackmodules.com

ImageImage
Image

Dear modular enthusiast.

A small and affordable mixer was always part of the electronic musicians setup.
Most of the times electronic musicians were using small and affordable mixers mostly
because they needed just a few channels, it had to be portable and relatively cheap.
In the last four decades there were tons of small and affordable mixers designed,
built and sold by various manufacturers but only a few became classics and long time
favourites for their sound in the electronic musician community.

There are three vintage small mixers that are highly regarded for their specific sound.
The oldest one was a product of a famous japanese guitar pedal maker and was used in
the late seventies and in the eighties by many electronic musicians (like Tangerine Dream
and others). It was a six channel stereo mixer with tone control on each channel.
A compact and sturdy little workhorse.

The second is also the product of the same company but a more modern one.
It was sold in two versions, eight and sixteen channel versions. It had a plastic case and
looked a bit like a toy but it didn't matter because it was used and loved by techno artists
since the early nineties and it is still used and loved for the sound.

The third one was a product of a US company and it was extremely popular in different fields
(small studios, rehearsal rooms, television, broadcast, etc ). It was a true winner because it
was affordable but at the same time it was very durable (sturdy metal case) and had tons of
features and connection possibilities. It existed in 12 and 16 channel versions. After this
successful series the company released "improved" versions but as a general consensus
between musicians only this old first generation mixer has "that sound".
It was extensively used with a very high gain setting to make a specific distorted TB303
sound. It was also used to mix some albums that became classics (like Biosphere Substrata).

Many years we saw people asking for modules that replicates the sounds of channel strips
from these small mixers. Ourselves being users of these mixers we thought it would be a
great idea to offer to the modular community the three classic sounds.
So we started breadboarding the circuits and tried to identify where the specific sound
comes from and how to reproduce this in the most convenient way. After a while we
identified which were the relevant aspects and made the prototypes.
Some more technical tests followed by listening tests and now we have three
eurorack modules, each one replicating the audio qualities of the vintage classics.

PRE KM - this module emulates the good old sound of the late seventies and eighties mixer
PRE BX - this modules emulates the sound of the mini plastic mixer used by the techno
artists from the nineties on.
PRE CR - this modules emulates the sound of the high gain TB303 distortion.

They all sound great and their sound can change from slghtly coloured to extreme distortion
and colour depending on gain and tone control. We encourage you to experiment with
different sounds from bass to drums and noises. You will have some pleasant surprises.

Sound Demos :
- all the modifications in the sound are made only with the PRE unit.
- all the demos respect the formula : 2-3 measures original sound, increasing hi freq, increasing low freq, increasing gain, increasing hi freq etc.

https://soundcloud.com/strat1/pre-cr-3vco-arp
https://soundcloud.com/strat1/pre-cr-tb303
https://soundcloud.com/strat1/pre-cr-kick909
https://soundcloud.com/strat1/pre-cr-snare909
https://soundcloud.com/strat1/pre-cr-synthlead

There are 3 type of kits available :

KIT1 : 20EUR (2PCBs+frontPanel)
KIT2 : 30EUR (Pcbs+FP, + 2xRC4560 + BC550,BC560 Matched Transistors + Antilog POT 10KC)
KIT3 : 40EUR (Pcbs+FP, + 2xRC4560 + BC550,BC560 Matched Transistors + Antilog POT 10KC + 2X50KB POTS, 25KB POT, 2xMinijacks, 2xboard connectors, 3xCream Knobs)

COMPLETE MODULE : 70eur

KIT1

Image

KIT2 (includes 10KC ANTILOG POT)

Image

KIT3

Image
Image
You do not have the required permissions to view the files attached to this post.
Last edited by strat-1 on Wed Mar 20, 2019 5:11 am, edited 21 times in total.

User avatar
DomMorley
Super Deluxe Wiggler
Posts: 1153
Joined: Sat Mar 10, 2012 3:27 pm
Location: UK

Post by DomMorley » Tue Jun 14, 2016 7:53 am

A PRE CR Kit 3 please! PM'ing you now.
How I fill my days: www.dommorley.com

"Your head will collapse, but there's nothing in it..."

trumman
Learning to Wiggle
Posts: 21
Joined: Mon Feb 02, 2015 6:12 am

Post by trumman » Tue Jun 14, 2016 8:31 am

oh been thinking of adding some kind of pre-module for bringing my 303 into the modular, good timing :)

One kit 3 please!

euromorcego
Super Deluxe Wiggler
Posts: 2757
Joined: Sat Jan 18, 2014 6:22 am

Post by euromorcego » Tue Jun 14, 2016 12:34 pm

nice! :tu:

So do I understand correctly: this is the channel strips, there is no mixing involved? Is it an option to include a header on the back (for example from the switching connector of the output jack) to connect 2-3 of them to a mixer?

And would it be possible to use these to boost line level to modular? Maybe with a tweak in component values?

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Tue Jun 14, 2016 1:09 pm

euromorcego wrote:nice! :tu:

So do I understand correctly: this is the channel strips, there is no mixing involved? Is it an option to include a header on the back (for example from the switching connector of the output jack) to connect 2-3 of them to a mixer?

And would it be possible to use these to boost line level to modular? Maybe with a tweak in component values?
Yes. There is no mixer involved.
This will be an upcoming module, a stereo mixer with additional sockets on the back of module where you can connect any PRE you want. This first batch don't have an output socket on the back, I updated them after I ordered the PCBs, but a simple 2pin header can be soldered on the back. (like you said.)
And yes you can raise up the volume of your modular, they have a lot of gain, and a generous output.

This PRE series are not only for mixing, but for sound sculpting. Like I wrote in the main post, many of the thechno and electronica sounds were made with this type of mixer lines.

theartstrip
Learning to Wiggle
Posts: 9
Joined: Tue Jun 28, 2016 12:35 pm
Location: FR

Post by theartstrip » Tue Jun 28, 2016 12:40 pm

I'm interested in a full built module. PM

euromorcego
Super Deluxe Wiggler
Posts: 2757
Joined: Sat Jan 18, 2014 6:22 am

Post by euromorcego » Tue Jul 05, 2016 12:28 pm

strat-1 wrote: This will be an upcoming module, a stereo mixer with additional sockets on the back of module where you can connect any PRE you want.

[...]

And yes you can raise up the volume of your modular, they have a lot of gain, and a generous output.
To connect them to a mixer is good idea (so I can also connect multiple PRE if I want?). And how much gain do they have, I guess to amplify line signals, approx 20dB is needed (10x).

And one question: I assume the value of the antilog pot cannot be changed easily, like to 5kc. Thonk has these wityh a white indicator line, looks better than the usual plastic alpha.

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Tue Jul 05, 2016 9:54 pm

euromorcego wrote:
strat-1 wrote: This will be an upcoming module, a stereo mixer with additional sockets on the back of module where you can connect any PRE you want.

[...]

And yes you can raise up the volume of your modular, they have a lot of gain, and a generous output.
To connect them to a mixer is good idea (so I can also connect multiple PRE if I want?). And how much gain do they have, I guess to amplify line signals, approx 20dB is needed (10x).

And one question: I assume the value of the antilog pot cannot be changed easily, like to 5kc. Thonk has these wityh a white indicator line, looks better than the usual plastic alpha.
- Yes you can connect multiple PRE modules you want to a summing mixer.
- You can raise a standard laptop, mp3, keyboard output of 1V PP to almost 20v PP without distortion. This is with gain at a quarter and level at maximum.
- Original mixer have 5KC for gain, alpha doesn't have that values so we used 10KC. Both value works well.

tuukka.j
Learning to Wiggle
Posts: 46
Joined: Thu Jan 30, 2014 9:34 am

Post by tuukka.j » Wed Jul 20, 2016 6:21 am

If these are still available, I'm interested in 2 sets of KIT 2 plz.

ilovedrums247
Learning to Wiggle
Posts: 2
Joined: Wed Mar 06, 2013 5:46 pm

Post by ilovedrums247 » Wed Jul 20, 2016 8:22 am

strat-1
would love one of the CR kits..pm'ing now

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Thu Aug 04, 2016 4:01 am

UPDATE : PRE CR is updated to rev 1.1 boards, now available.
New files provided - build files including the manual 1.1 and photo zip with details of the build

Read the main post for complete details.

User avatar
Apola Kipso
Common Wiggler
Posts: 189
Joined: Tue Jun 10, 2014 4:10 am

Post by Apola Kipso » Wed Sep 14, 2016 4:16 pm

strat-1 wrote:UPDATE : PRE CR is updated to rev 1.1 boards, now available.
PM'd for 1 x KIT 3

User avatar
coolshirtdotjpg
Super Deluxe Wiggler
Posts: 1282
Joined: Wed May 06, 2015 4:13 pm
Location: Santa Cruz, California

Post by coolshirtdotjpg » Wed Sep 14, 2016 4:21 pm

I built a Pre-CR and absolutely love it. It is really amazing for distorting kick drums, or basically anything involving drums.
New video for my track
Opening The Portal

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Tue Dec 27, 2016 5:32 pm

UPDATE : I corrected a mistake in manual. The 50KB pots and 25KB pot were filled with the wrong color.

glitched01
Wiggling with Experience
Posts: 330
Joined: Wed Nov 03, 2010 5:16 pm
Location: US
Contact:

Post by glitched01 » Sat Mar 25, 2017 10:03 am

These look like some great projects.

Hey: How important is it to match transisor-pairs in this day and age? I've found that tolerances are usually quite close in trannies if you get a reel of them. What are some of the symptoms of not so well-matched transistors?

User avatar
fragletrollet
Wiggling with Experience
Posts: 478
Joined: Wed Dec 21, 2011 5:55 am
Location: Norge
Contact:

Post by fragletrollet » Sun Mar 26, 2017 5:03 am

Cool! So... Yamaha, Yamaha and what... peavey?

User avatar
synthetek
Wiggling with Experience
Posts: 438
Joined: Fri Jun 05, 2015 3:32 am
Location: Orange County, California
Contact:

Post by synthetek » Tue Mar 28, 2017 3:36 pm

fragletrollet wrote:Cool! So... Yamaha, Yamaha and what... peavey?
Boss , Boss & Mackie

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Thu Mar 30, 2017 2:49 am

glitched01 wrote:These look like some great projects.

Hey: How important is it to match transisor-pairs in this day and age? I've found that tolerances are usually quite close in trannies if you get a reel of them. What are some of the symptoms of not so well-matched transistors?
Try to buy at least 20pcs of each transistor and match them by hfe with
a regular multimeter. Your wave symmetry will not be good if there is a big hfe difference between the transistors.

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Sun Mar 25, 2018 4:51 am

UPDATE : I corrected the building manual for some typos.

cor909
Learning to Wiggle
Posts: 4
Joined: Tue Apr 14, 2015 11:42 am
Location: Ireland

Post by cor909 » Thu Aug 16, 2018 8:21 pm

Just finished building this and it was working perfectly for about an hour when all of a sudden the 10 ohm R24 resistor burned out. Replaced it thinking it was a bad component but same thing happened again instantly on power up. My soldering looks ok but I'm fairly new to this and haven't a clue where to go from here. Anyone got any ideas of what I could do to find out what is causing R24 to burn out?

Cheers

User avatar
synthetek
Wiggling with Experience
Posts: 438
Joined: Fri Jun 05, 2015 3:32 am
Location: Orange County, California
Contact:

Post by synthetek » Fri Aug 17, 2018 12:45 am

The 10r resistors by the power connector are usually the 1st thing to blow if you reverse power the module but it shouldn't have worked at all if you did that. Replace it and check for shorts between +V -V and GND on the power connector, Check the orientation of the diodes D5 , D6 and that they aren't blown. Also check the orientation of C16 & C17. After that pull out the 2 opamps and power it up and test the points on page 10 in the build manual. If you cant figure it out post some pics.

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Thu Oct 25, 2018 2:55 pm

UPDATE :

I attached a pdf file in the main post with output readings of each PRE type using a 1Vpp source at input.

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Mon Dec 24, 2018 8:40 am

[UPDATE] Updated with rev1.3 manual.

User avatar
strat-1
Wiggling with Experience
Posts: 490
Joined: Wed Jun 03, 2015 8:58 am
Location: Romania
Contact:

Post by strat-1 » Wed Mar 20, 2019 5:08 am

[UPDATE] : PRE CR is back in stock with rev 1.2Pcb.
Nothing is changed in terms of sound, just updated the pot prints and rerureted the paths in such a way you don't need to cut the pots ear holders anymore.

User avatar
jschussler
Common Wiggler
Posts: 247
Joined: Tue Sep 13, 2016 7:00 pm
Location: Seattle
Contact:

Post by jschussler » Sat Nov 16, 2019 1:10 am

I seem to be having build issues. I get 12v to the first diode, but then mv readings after that. Both + and -. I replaced the diode, no change. I've reflowed everything, no change. Not sure how to diagnose this.

Image
Image
Image
Image
Image
Image
Image
Image

Post Reply

Return to “Music Tech DIY”