Rumblings from the Blacet Research design pit.
Having three LEDs on the front panel really helps in
understanding this module`s operation.
You will need three low current/ultra bight T1 LEDs, a 3.3K resistor and
Start by carefully drilling three 1/8" holes in the front panel to the right
of the A, B and C jacks. You can also drill a hole in the PCB to route the
LED wires through, for a neater mod.
You can use hot melt glue to mount the LEDs.
The LED anodes are commoned and connect to the +15V buss via a 3.K resistor.
The three cathode wires are actually soldered to the RN1 pins as these are
sturdier than the IC pins.
MIX3500 Assembly Photos
FD3120 Assembly Manual
for page 7 of the Manual, showing PCB to front panel mounting photos.
Pots will sometimes dry out. Depending on where they
are used, scratchy sounds can result. The pot has not "worn out" but the
lack of lubrication on the rotating parts causes jumps on the resistance
We have had good results with WD-40 applied to the small rotating nub at
the back of the pot. Don't just spray the pot, you'll end up with a huge mess.
Using the straw on the WD-40 can, spray briefly into a paper towel. Use the
small drop remaining on the straw tip and apply it to the nub. Rotate the
pot and blot up any excess WD-40 with a paper towel.
Push Button Switch Alert
This switch is the thru the front panel right angle switch
used on a lot of our modules.
On rare occassions, when using a bit too much solder, kit builders may
find that the solder may bulge up on the component side of the PCB and contact
the metal mounting ears. If both ears happen to contact the solder on each
pad, a short will result and the switch will not work. You can fix this by
gently prying each ear out just a bit with an xacto knife.
Maxim MAX365 IC Alert
Recently, the MAX365 has been hard to purchase, with
a long lead time and huge minimum order. Fortunately, the MAX362 is pretty
much the same component and will "drop in" to our designs with no problem
or loss of performance. You will be seeing these in most modules currently
A similar situation may occur with the MAX364 and these may be replaced
with the MAX361.
Hex Zone Reliability Alert
A few customers have experienced failure of op amp U3
and a blank display screen. Replacing the op amp returns operation to normal.
While we do not have a definite failure mechanism at this time, a likely
culprit is the high differential between +15 and -15 current draw (150:1).
Upon power down, due to the power supply filter caps, this can cause the +15
to draw down much quicker than the -15. The op amp may be sensitive to having
one supply turn off a long time before the other.
As a precaution, we are advising changing "CD" from 100uF to 1uF. "CD"
is on the lower side of the power connector.
MD2600 Scanner Mods
I was noticing that I kept using an attenuator when patching
the scanner. This was to keep the CV from causing the Scanner to go "out of
range", ie; no channel "on" at the top end.
The design of the Scanner is basically a CV level activated sequential
switch (as opposed to the nearly identical MD2650, which is a clock toggled
switch) with a "off-on-on-on-off" response. That last "off" was proving a
bit annoying in at least the patches I was using the scanner for.
The fix is to change R7 to 15K and R6 to 39.2K. With the Ref trimmer (RT1)
at full CCW (maximum voltage between steps), the scanner will stay on the
"C" channel even when the CV is at max. With the Scan knob fully CCW,
IN-A will come on at about 2.7V, IN-B at 5.4V and IN-C at 7.8V. You can turn
the Scan knob CW to start with IN-A "on" and thus have one channel on throughout
the CV range.
You can still turn RT1 CW and get the original response with an "off" at
the end, along with a narrower voltage range between steps.
A second mod greatly reduces the
transition noise between two of the steps. On the solder side of the PCB,
locate pins 1 and 3 of U2. Take a 10K resistor, bend one lead over, trim the
leads pretty short and solder them on to the two pads of U2.
This works because of the different impedance of pin 1 of the bar graph
display driver chip. The 100K pull up resistor SIP used allows a transition
state at 5V instead of the expected common and +15.
These mods are now included on the modules currently shipping with the
second mod done by using a 10K SIP.
Hex Zone Assembly Tips
A couple of things that might help and some photos:
1. Handle the LCD display as you would ICs as it is static sensitive. Also,
it has a protective film over the display area. Remove this only at final
assembly of the front panel. Clean the display area only if necessary with
a soft dry lint-free cloth such as a microfiber style commonly used for lenses
and eye glasses.
2. You can use the front panel as a jig to help mount the LEDs. Use the
back side of the panel and take care to protect the front side. Install the
two long screws into the panel on either side of the display cutout and secure
with kep nuts.
Place some spacing material under the panel so the LEDs will have space
to drop all the way through. Lay it flat and position the PCB and installed
LEDs over it. You will need a 3/4" piece of foam, etc to hold up the top side
of the PCB. Get the LEDs lined up in the FP holes and check the alighment
in both axis before soldering.
3. When installing the four angle brackets, they can be slid all the way
toward the rear of the boards. Be sure to install before mounting jack PCBs
on mother board.
4. Solder only the four corner pins mentioned on the 6 pin headers for
the jack PCBs. Solder the remaining pins after the front panel is attached.
This allows some play when mounting the panel.
5. You can do a preliminary function test before mounting the panel if
you first install the ICs. Power up the module and wait until the "Sequence
Mode" appears. Push the right arrow button, then the Play button. You should
see the 16 LEDs sequence.
Our handy production jig.
Don't forget to install the angle brackets before you mount the
Installing the LCD
Installing the switch PCB.
Installing the rotary encoder.
"Taming of the Q"
The DF 2420 Dual Filter has an awful lot of Q; more than
is reasonable for some folks. But who said the designer was "reasonable"!
The fix is very simple though. Just change R11 to 68K for the "A" channel
and R21 to 68K for the "B" channel. It will still self oscillate just fine
but at a point closer to the end of the pot travel.
Errata in SB2780/2790 Manual
A couple of minor bugs crept into the Parts Lists. These
will probably not cause any assembly errors. These include a couple ref des
errors on the power input filter caps (CA-CD), a missing reference to RT2
on the Mixer and wrong board and front panel part numbers on the 2790 (says
The corrected Parts Lists are below:
Errata in VCA2200 Manual
Please note that a line has been omitted in the "Options"
section. Please add the following step if you are doing this modification.
"Change R7 to 82K."
Service Tips for the Dark Star
This module has had excellent reliability An exception
is the last version, that used a "shrink DIP" 76477 and a less than well engineered
socket. The IC would tend to pop out of the socket, causing erratic operation.
There are two fixes: wrap a ty wrap around the IC and socket lengthwise
or solder the four corner pins to the socket while pressing down on the IC.
It is also possible to remove the socket and solder the IC directly to
the PCB, although this has to be done very carefully to avoid damage to the
for the Final Filtre and Time Machine
Based on repair records for these two modules, a likely culprit for problems
are the high frequency clock ICs in each module. These are the 13600s; U13
in the FF and U7 in the TM. We suggest that you try replacing these if your
module starts acting strange. See the FF note also immediately below.
FF2030 (Final Filtre) Long Term
Based on some long term testing being done here and by one of our customers
(thanks, JP!), there is evidence that changing R44 and R45 to 10K (from 5.6K)
will significantly improve the reliability of U13 (13600). Over the years,
this IC has shown failure in most units returned for repair.
If U13 is bad, the filter will not self oscillate or may have a noisy
spot as you rotate the frequency knob. Sometimes cycling the power will restore
IC function, but it may work only sporadically.
We are advising that you change the two resistors and replace U13.
Assembled units that shipped after Oct 2004 have already been modified.
If in doubt, check your board.
Overloading the Time Machine
When the audio input is too high, the TM cuts out. Reducing the input
level and waiting a few seconds restores normal operation. This applies to
no rev and rev A PCBs.
This problem is caused by the limited headroom of U4, the "front end"
anti alias switched cap filter, which is running off +/-7.5V supplies. This
results in a maximum input signal level of +/-7V (with input attenuator trimpot
The TM will happily run along with typical +/-5V signal levels, but if
you introduce amplification in your system prior to the TM, I would suggest
keeping an eye on the levels. You can adjust RT4 to allow larger input signals.
For example, positioning the trimmer at mid rotation, you could use signals
up to about +/-14V, which is around the limit of the op amps in the rest of
the system. This comes at the cost of 50% attenuation through the module.
Modules built at the factory have this trimmer set at about 70% rotation
which allows +/-10V signals.
The "cutting out" of the TM is not a typical symptom of overloading an
IC, but in this case, the LTC1063 disturbs the power rails and shuts down
both the +7.5V and -7.5V regulators! This causes the "crash" of the clock
driving the filters and the MN3005, which also use the +/-7.5V supplies.
This is annoying to say the least but can be fixed with one 1N4148 diode
(Dxx, shown below). Rev B boards include this mod.
The diode is connected between pin 14 of U6 (anode) and the +7.5V supply
(cathode/band). The right hand side of R26 can be used for the first connection
and a PCB feedthru can be used for the +7.5V. A bit of heatshrink will protect
Rev B PCBs have this change incorporated into the board.
Negative CVs into Time Machine
This applies to no rev versions of the PCB only.
The rev A and rev B versions have this change made to the board.
If the Delay CV mix goes more than about a volt negative,
the high frequency clock will stop and the delayed effect will stop working.
Removing the negative voltage source and cycling the power will restore normal
To fix this, locate R11 and unsolder the left side,
pulling up the resistor to about a 45 degree angle.
Clean out the vacant pad with a solder sucker and
insert one end of a 1K 5% resistor. Solder that end to the pad and lift up
the free end to mate with the free end of R11.
Take two 1N4148 diodes and connect one cathode to
the other's anode. Connect the unattached anode to the junction of the two
resistors above and solder the junction.
Place some heatshrink over the two diodes and solder
the unattached cathode to the feedthru just under the "2" in the silkscreen
"Q2". (This is common.)
Kit Assembly Tip: top 1/8" jack
The new Blacet Rack has less clearance for the top
and bottom front panel jacks. The bottom jack should have it's lower lug bent
upward a bit. This is covered in most of the assembly manuals.
The upper jack's "switch" contact tends to touch
the upper Blacet Rack rail. While this contact is not used in any of our
modules, mounting the module can be made a bit easier by mounting the jack
at 45 degrees or greater as shown below:
Existing modules can be modified simply by loosening the jack nut and
turning the jack. You should not have to modify the wiring except to make
sure nothing shorts out.
Newer runs of front panels have more clearance for these two jacks.
Final Filtre Rev A
"What changes have been made to the Final Filtre
and is it a good idea to attempt changes on older boards?"
Most of the changes involved making the gate circuit
more sensitive. This involves about 5 new components and these cannot be
added to the old board. (They would have to be built up on a bit of proto
or perf board.)
The three 150 pF anti alias and smoothing filter
caps (C1, C9, C10) have been changed to 100 pF. This results in a modest
increase in filter output level and possibly a small change in the sound
at the same Q setting.
R9 has been changed to 15K, resulting in more range
for the Frequency pot.
We also employed a different transistor pair for
the expo converter due to availability.
Blacet to Doepfer Power Connector
Some Blacet Modules will work on +/-12V and some Doepfer Modules will work
on +/-15V...Check the Doepfer Web site for voltage info.
Frac Rack/ Blacet Rack Standards
Paia invented the "Rack". We engineered a slightly different version to
meet our quality and delivery needs. Modules from Paia, Blacet and some of
Wiard's will fit in either rack. A typical front panel drawing is shown below
for making compatible DIY modules. Note that the maximum PCB height is 4.22"
to allow clearing the Blacet Rack mounting rails. Click on the drawing for
a much larger version.
To achieve the same "feel" as Blacet units, use
Panasonic Pots (Digi-Key P3T9503-ND), Rean knobs (Rean is out of business
2010) and jacks: Mouser 16PJ012 (old style), 161-3142M-E (new style), Digi-Key
CP1-3524N-ND (PCB mount).
Power input protection and filtering is highly
recommended for all modules! See below.
PS1 and PS2 are polyfuse resettable fuses available
in various mA ratings. A typical module with a 50 mA current draw would use
A power supply reversal causes the diodes to conduct, creating a short
circuit. That condition or a short on the PCB causes the polyfuses to heat
up and go into current limiting.