How to build a Mixbuzz 500 step by step
« on: August 16, 2010, 07:19:43 AM »
Igor is known for his high quality projects. This one is even the top of the line. You get 9 pcb's (2 pcb's not in the picture) and the needed metalwork and screws. The quality is just spectacular. Strong thick pcb's, some with gold, nice layout, everything fits better than any other DIY( except other Igor stuff ) :) . Well this can become better than what is API standard today.

Also good news: 2 test pcb's are now delivered with the kit. So all people without a lunchbox can easely build some case for it. Later when you want more outboard the decision for a lunchbox will be easier. Just take it out of your home made box and place it in the lunchbox.
look at:

Igor started to draw another 500 module for Crush & Blend option, it is almost there.
If there are people interested to add C&B to MixBuzz500, as 3rd slot, it is easy.
BTW, stay tuned for MixBuzz1 (1RU with more options/flexibility).

Print & study:

This was the first schematic and since than some changes were done. Important to know is that in this schematic IC 2 & IC 6B is IC 11 on the PCB,  IC 6C & IC 6D is IC 10, IC 6A is IC 9.
Look further to the Zipped files for the correct schematic when you start building the your mixbuzz;msg=501417;topic=40493.0;sesc=ebd5ad916a79741f7331893140dfb1a6

Here you can see the result from Igor & Brizco:
« Last Edit: April 12, 2011, 04:32:44 PM by reanimatorstudio »

Re: How to build a Mixbuzz 500 step by step
« Reply #1 on: August 16, 2010, 10:07:40 AM »
Notes on component choices

1N4001 - 1N4007 all are the same except the voltage raiting

They all work. I don't recomand 1N4001. I usually buy 1N4004 or higher. I never take lower numbers in stock, don't see the point of them still existing
resistors: Use 1% metal film for precision, except R96, 98, 87, 89   R87/R98: 1/4W, 10%, closer value to calculated
All resistors except one 2k should be 1/4 watt. I have a lot of 1/2 watt resistors in stock so I will use them although I do not recommend it. They fit if you bend the wires very tight to the body of the resistor, 1/4Watt resistors are slightly easier to mount. Anyway the 10 Ohm resistor should be 1/4 watt. They also act as fuse and 1/2 watt doesn't give the protection needed. Order enough 20k (and 5K1) resistors, it is a good thing to match those on the little VCA boards as close as possible.

R4, R39 is ferrite bead or jumper: It's a great thing Igor implemented this use it when you are going to use a fast opamp with high GBW. You don't want RFI.
RS stocknumber 226-8191   Panasonic   EXCELDR35C  or RS stocknumber 226-8185  Panasonic EXCELSA35
Farnell Ordercode: 9526820    MURATA   BL01RN1A1D2B
Farnell:Ordercode: 9265252    MULTICOMP MCAB 035090-33

For each VCA, R6, R3, R100 on audio board can be different.
this compressor  can be build with DBX202X,  with 4xTHAT2181( A and C) or with 1xTHAT2181C.

DBX202X has internal resistors on inputs 8x10K,the input resistance should be skewed
by 1k25. Control port impedance is 832 Ohm. I.e. R6=3k74, R3=4k99, R100=909R.
202XT should be the same.

4xTHAT2181 A/B/C on VCA replacement board, input resistors are 4x20k,
and control port impedance is same as 202x, 832 Ohm.
I.e. R6=jumper (0R), R3=4k99, R100=909R.

1xTHAT2181C on VCA replacement board, the resistors on input board are R6=0R (jumper), R3=20k, R100=909R.
It is possible to lower C1 down to 22pF.


VCA's in the signal path: I'll go for 4 x THAT2180A. This is the most transparant and cleanest option.

Igor: 2181A+LME49710 combo should work great.
My personal opinion, 2181A don't worth additiional $3 per VCA, soundwise.
Neither it is tooooo sterile, no, it still has some VCA sound if you listen it
in hi-res monitoring setup, and the diffrence between perfectly adjusted
for minimum distortion A or B grade is almost negligible.
For me, quartet of 2181B after trimming sounds more "alive".
Anyway, it is just my opinion...
Paralleling VCA's does not lowers minimum possible distortion;
but, it increases the dynamic range, what is important IMHO.

Smooth transient response is matter of timing capacitor and PCB layout, as well.
I did not used tantalums here by this reason; one 0.47uf poly cap used for
all release settings except A, with a little rearranging the release switch if
you guys noticed. Time constants remains same, anyway.

Sidechain VCA's: Simplest and cheaper solution is THAT2180C, don't install SC_SYM trimpot and R33.
There's no need for A version VCA in sidechain.

the decoupling caps: should have a lead spacing from 2.5mm. I use 100nF

film capacitors for sidechain filters: regular, 5 or 5.08mm pitch, 50...63V . C5 and C7 the ones who need good quality.
c29 & C1/ C29 is not so critical I've put a 22pf ceramic, C1 I suggest a silver mica but 22pF could be OK. It really depends on your opamp. You can always try to lower the value as long you don't have any high frequency oscillation even above the audio range.
electrolytic caps: the ones under IC8 are 47 uF or  non-polarized 10uF. Farnell Ordercode: 1236690  MULTICOMP NP100V106M8X11.5

opamp/  IC11. NE5532, OPA2604. I'll take OPA2604. TL074 and TL072 are not so critical, although they come in different flavours.
I use TL074B in the side chain. For the side chain filter I take the cheapest ones (TL074). IC 9 should be a low noise opamp too, I'll try LME49710 or AD797. All the noise injected in the VCA's here will directly be on the output of the VCA's.

parts in audio path: C1, C2, C3, C4, C5, C6, C7, R3, R4, R5, R6, R100, IC11 are critical parts.

trimpots: you only need 4 bourns 5Ok multiturn
 (RV1) on audio PCB: changes threshold point... install 5k1 and forget.
Threshold trim (TR_TRM): changes threshold zero. Omit (install nothing) and forget!!!
(Or use side screw, 50k, 10(25) turns trimpot to change 0db threshold point @ratio=4).

line recievers/drivers: THAT1246, INA137 or SSM2143 (-6db line receiver) is the right choice.
1   THAT1246 /INA137P           IC1: some additional  RFI protection look at page 4 and page 5 fig 4 of :  . As suggested do this directly on the connector. The IC is protected against +48V on the input pins, so no worry there.

Igor: I avoided capacitors in soundpath at every possible places, to get
minimum unwanted sonic artefacts, thanx to these chips.
And, another thing. Try to feed 1khz 5V P-P squarewave into GSSL's output balancer,
sum the + and - output with pair of 2k resistors and 100R trimpot and adjust for less possible signal;
than, see on scope what you get here.
As well, GSSL output balancer does not likes when - is connected to ground.

These are the reasons why I used "balancing" chips.
INA137, DRV134, THAT1646, THAT1246, can be used in MixBuzz500.
Beware of SSM2142, it is not best line driver. However, SSM2143 can be used at the input.
1   THAT1646 /DRV134P           IC8: some protection against 48V and RFI is suggested in the date sheet. I would strongly recommand this modification for reliability:
look at page 9 of:

Sonically and measurement-wise, THAT1246 and INA137 more or less same.
Maybe, THAT bit cleaner.
I go with the THAT's, the datasheets give a better S/N ratio.

switches/pots: Lorlin and Bourns
Farnell Ordercode:  1550189  1M33T1B5M1QE
connectors:8 of each: 10-PIN DUAL RAW CONNECTOR, MALE AND FEMALE
12V relays: Coil resistance should be more than 500 Ohm. 90% of relays are within this spec.
    MULTICOMP HRS2H-S DC12V   Farnell Ordercode:  9480218  has got coil resistance of 720 ohm and Contact Material:Silver, Contact Plating:Gold
Each slot consumption according to Lunchbox specs should be less than 80mA.
It is better to spend these milliamperes to OPA2604 and quad/eight (DBX202X) VCA.
I recommend to use relays with more than 500 Ohm coil resistance.

« Last Edit: September 24, 2010, 06:15:34 PM by reanimatorstudio »

Re: How to build a Mixbuzz 500 step by step
« Reply #2 on: August 16, 2010, 10:41:47 AM »
Installing components

Look at those guys!!:

Solder with lead, put your solder iron slightly higher than normal, those are really thick pcb's !! Also the solder islands are due to the compactness rather small so a fine soldering tip is recomended.

look at the pcb so you can read the text.
L = left
R = right
A = above
U = under/underneath

For the audio boards:

0 ohm: small wire or resistor leg: R6 under the spot for the VCA's (DBX202X)and R4 & R39 if you don't use ferrite beads (I do). Only if you choose not to use the sidechain filter, you have to put a jumper at JP1. But I don't see why you would not choose for this great option.

First install the diodes: double check the polarity. It's the most common mistake!!!!
Then install the resistors:
Please measure before soldering, later it will be a pain in the a** to find a mistake here
on the LU you see a row of 6 resistors.
- Install 1k for top & bottom of row
- second 33k, the other 33k is AL of pcb
- third 10k, the other10k is A TL072
- fourth 3k3
- fifth 15k

R from this row you see 33R

1M: AR of pcb, R of TL072 you see R7 (1M).
10R: all resistors right from DBX202
49R99: R of detector
68R: A of PCB
750R: detector
909R: detector
4k99: R of ic11
5k1: R of detector, U pcb in RV1
5k6: R of TL074, RU TL074
6k8: RU TL074
12k: L of TL074, U TL074
13k: U TL074
20k: R of TLO72, A of TL072, ..........
47k: L of CTL connector
150k: A of dbx202, R of TL074, R of detector
R4, R39: ferrite bead

Then install the IC sockets.

install the small capacitors: start with the decoupling caps
next the ceramic 22pF caps A & U TL074
then the film caps, the smallest first

the connectors

trim pots

now the relais

last the electrolytic caps: please use the best you can get. This is the component that will age the quickest.
I've changed the ones under the line driver to Non polarity 10 uF as suggested in the application notes. Unfortunately good qualitycNon polars are hard to find.

Later you can put the IC's in the sockets. Push the VCA's in the sockets harder than you normaly would expect.
Crush and Blend option
SJ points. Mixbuzz done with thought it should be modular, and SJ points reserved for
C&B option. If there's no C&B, these points should be connected, like picture shows.

For little VCA boards:

resistors first: like I mentioned before I matched the resistors the best I can
IC sockets/ IC's: theoretically the VCA's should have the same temperature. You could thermically couple the VCA's. I'm not going to do this.
The control buffer op-amp: NE5534, LME49710 or AD797
Don't install the IC's yet.

For control boards:
Large one
first resistors, than 2 capacitors, than the connectors. You could wait with connector SC2 after installing the switches.
Than switches and pots: Before you install the Lorlins you have to cut the little plastic pin on each switch. I've installed an extra nut between the Lorlins and the metal frame. The nuts on the other side of the metal frame fall in the holes of the frontpanel. The switches now just come out of the frontpanel. Looks nice!
2   TBD   at least 1/2W     5%     R87, R98*
Depends on relay's coil resistance
R87=R98=(RREL/6). For the relais I choose, the coil resistance is 720 ohm so: 720/6= 120

LED: anode is round, cathode is flatten.
no print +/- for 5mm led's on PCB.

small board
sequence: resistors, IC socket, filmcaps, voltregulators, electrolytic caps,connectors
Power-3 pin connector on small pcb located at the back of front panel
should be connected to one of boards

1. Power for the small board with time constants/ratio etc. Does this come from the 3 points at the top of either audio PCB just above the sym trim pot?

Yes, take the power for small PCB from one of audio boards. 3 wires can be soldered directly,
or with use of Phoenix 2.54mm pitch screw terminals, or with use of 3-pin 2.54mm pitch Molex connector.

and don't forget to link the 3 point on the side of switch on off on if not the relay could not work and the unit stay in bypass
That's right Smiley
This jumper is for people who will use the unit in GSSL or Gyraf mode only,
but... just put a solder joint here to have both options.

Quote from: stereokillah on 16 July 2010, 01:44:31
a small trick with ribbon.

cut 4 parts about 20cm put your connector on it and after calibration just cut in the middle two of this to have 4 ribbon for assembled the unit .

Don't forget to put stoppers on switches at right positions Smiley
« Last Edit: April 23, 2011, 08:58:31 AM by reanimatorstudio »

Re: How to build a Mixbuzz 500 step by step
« Reply #3 on: August 16, 2010, 01:15:13 PM »
Installing the little VCA boards

Before installing the pcb's clean the pcb's, remove all flux (resin).
Don't install the VCA's yet.

Use thick wire, the holes are big enough. First solder 2 wires on little pcb. One next to CBP20 and one next to CBP22. Cut those wires at the upper side of the pcb, later it is going to be difficult. Leave the wires at the bottom long so later they will absorb heat when soldering the  pcb in place. Put the pcb in place. I've put something thin ( peace of tie-wrap) under the pcb that I'll remove later. now turn the audio board and solder the remaining wires, leaving a long peace of wire on this side (for absorbing heat later). Turn the board, push the VCA board in place and solder the wires on the upper side of the VCA boards. Don't heat to long. Remove the tie-wraps and turn the audio board once again.
Solder the 2 fist wires. Cut all wires
« Last Edit: September 10, 2010, 04:15:47 AM by reanimatorstudio »

Re: How to build a Mixbuzz 500 step by step
« Reply #4 on: August 24, 2010, 03:45:37 PM »

The card edge connectors for the little pcb's with the XLR's can be ordered from our member Volker [silent:arts]

Pin 1 of the XLRs is standard not connected to the circuit. With jumpers you can choose to connect it with case or ground.
If you make wire bridges for the power from one test pcb to the other do it at the backside otherwise they will run over the card edge connector.

Trimpot adjustment.
Adjust for minimum distortion with analyzer (audio) and 0mV dc offset (sidechain).
Don't have analyzer?
Sidechain RV1: adjust for 0.0 mV DC at IC11a, NE5532, pin1
Audio SYM: adjust for 0.0 mV DC at IC11b, NE5532, pin7

I've used opa 2604 and noticed there is a constant voltage drift on the output pins of IC11 esp. when the power is switched on. I suggest you wait 30 minutes before calibration. After 30 minutes the voltage drift is only 4mV. The OPA2604 have a temperature of about 45°C in the middle.

Some words about testing the unit.
easy way to do this is connect power supply to all boards
via 3-pin Molex connectors and use pair of same cable assembly's for audio.
I.e. take 5 of Molex 3-pin/2.54 pitch connectors,
MOLEX - 22-27-2031 #9731156
MOLEX - 22-01-2035 #1697895
MOLEX - 08-50-0032 #9773789

SOLDER 20-25cm wires to "crimp" pins;
Then, connect 3 of wire assembly's in parallel-this is for power supply.
Feed audio in/out via 2 wire assembly's left.

Ratio calibration.
My sidechain ratios were constant for all builds, about 2.1:1, 4.3:1 and 10.5:1.
Then, we go to audio, input signal is to let meter show 1-2 db GR, measuring output,
input signal 10 or 20 db more, measuring output.
Less R60 higher the ratio, more R60 lower the ratio.
I needed to change it to 33R only with DBX202X VCA.
/Yours 202x can differ/
However, there can be slight differences inside same batch of VCA's,
some adjustment may be needed.
I got to exactly 2,4,10 in 3 of MixBuzz500.
« Last Edit: April 23, 2011, 03:49:32 PM by reanimatorstudio »

Re: How to build a Mixbuzz 500 step by step
« Reply #5 on: September 09, 2010, 02:14:08 AM »
Being suspicious on ratio settings with SSL compressors in general

Some words about ratio.
I copypasted ratio switch exactly as it was on 4000' deck. This is the way it works,
like gain reduction on 33609 goes "more-right".

With a steady test tone input producing say 6-8dB or GR on the 2:1 ratio and selecting different ratios[ and not adjusting the threshold pot] the 2:1 setting still shows more GR than 4:1 which still shows more GR than 10:1
Yes, it done by way to keep same amount of compression at different ratios.
For me it seems....strange at least, BUT that's the way it goes in original comp.

Re: How to build a Mixbuzz 500 step by step
« Reply #6 on: September 10, 2010, 03:25:26 AM »
If for some reason you made a mistake, the PCB's have indicated ereas (doded lines). So you can find the section with the problem very fast.

I first installed 100k instead of 100 ohm for R60 on the control board. Result low output with a slight increase if I turned the Threshold down. Unit is sounding great now. Thanks again Igor!!

I tested my Mixbuzz 500 not assembled yet in the frame and with a DC power supply. You can limit the current (to 15mA) and save you from burning expencive IC's.
One disadvantage is that you can easily put the connectors for SC and CTL in the wrong position. I did it for a short moment. The current limiting on my power supply and the smart lay out saved me and nothing got damaged.
If you are testing one channel at a time, don't forget to connect the CTL-flatcable to the other channel too, otherwise the unit will stay in bypass (relais connected in series between both channels).
« Last Edit: May 09, 2011, 07:55:42 AM by reanimatorstudio »

Re: How to build a Mixbuzz 500 step by step
« Reply #7 on: May 09, 2011, 07:48:58 AM »
I thought I was doing a great job but I have to say mnats is the best!!;topicseen


Re: How to build a Mixbuzz 500 step by step
« Reply #8 on: October 25, 2011, 07:02:17 PM »
Massive thank you to this thread, it helped me a *lot* in building the mixbuzz 500.


Re: How to build a Mixbuzz 500 step by step
« Reply #9 on: November 07, 2011, 02:44:37 AM »
Yep. Thumbs up for Mnats and Reanimator!!!
(new site hopefully will be up in July)

Re: How to build a Mixbuzz 500 step by step
« Reply #10 on: December 29, 2017, 12:14:35 AM »
Hey does anyone have the correct standoff lengths available? about to start assembling my builds finally.


Related Topics

  Subject / Started by Replies Last post
How to build a stereo 2254c step by step

Started by reanimatorstudio « 1 2 » The Lab

27 Replies
Last post March 30, 2012, 04:16:22 AM
by khstudio
1 Replies
Last post February 12, 2019, 05:12:28 AM
by Khron
11 Replies
Last post January 04, 2020, 07:09:18 PM
by efinque
9 Replies
Last post January 20, 2020, 07:43:55 AM
by Cardinen