Some have expressed interest in how my Delta rebuild project progresses.
So, here's a summary of what's been done so far.

If interested, please come on along -- helpful comments, questions, and
suggestions always welcome. If you're not interested, please killfile now,
either on my name or on the subject keyphrase "Delta Rebuild Update" (I'll
always use that in the subject line).

==
Acquired console August 2004 based on its functions, flexibility, and
clean design for our main application: location live and location session
work, mainly acoustic.

Basic build quality seemed solid; best of all it was modular with lots of
room on the boards -- easy to work on.

Acquired PDF of schematic set. Ran off two sets of 20"x24" prints on the
big plain-paper printers at the local blueprint house. Started studying as
time allowed.

Cursory tests showed that everything worked; further tests indicated most
switches crunchy, but all faders in excellent health and only a few pots
were bad.

Ran 100 Hz through all channels to find bad switches (channel on, pan,
pfl, eq on, line, phase, etc -- mostly all bad).

Got 100+ new DPDT and 4PDT switches from Harmon. Good to know they still
carry full spares for this model. Talked to Frank and Rene there; nice,
helpful folks.

Replaced bad switches, retested. Switching now solid and silent. TB
function restored (another bad switch; but replaced electret TB capsule
anyway based on age).

Console used on a few sessions; intermittent phantom and PFL on some
channels. At first assumed switching but was perplexed as most had been
replaced. Instead, eventually concluded bad sockets on the master loom
(ribbon cable assembly called "loom" by Soundcraft). Most contacts pretty
relaxed on those 34 pin female connectors probably due to age; some were
so loose they just fell off the board connector once the hold-down levers
were released.

Master loom many months on back order. Rene finally said he'd just build
one. Next time I will probably get the $20 connector press and do my own.
An audio systems designer friend suggests hardwiring; probably a good idea
but mostly impractical; I'd rather just build a new loom every couple of
years.

New loom installed, all documented weird intermittent problems now seem
gone.

==

Added a 2-gang pot to RH master so as to provide variable monitor dim,
along with DPDT ON-OFF-ON toggle to provide switchable monitor dim,
normal, and mute functions via a switch. (a small 20K linear is what I had
in the parts box; an 50K log taper would likely be better.)

Added a momentary mono switch. Very handy.

It's convenient that these modules are built so that without too much
hassle the PC board can be removed from the metal frame. Made using the
drill press for switch and pot mounting holes much simpler.

Also added PS rail LEDs. One unsettling thing about this unit is that the
power supply shoebox has NO pilot lights, and there's nothing on the
console that glows if it's just idling. Aside from running a signal, you
have to press a channel "on" or PFL button to see if there's power; I
prefer to know at a glance that incoming voltages are present.

Located dim pot just above and to the right of the master faders (wiper
and one leg from each dim pot segment replaced R151 and R51 on RH master).
Mono and monitor switches nearby.

Did little paper strip labels and glued to panel, matching the finish and
lettering colors. Done with ink jet on plain paper; coated with artist's
fixative. Not a perfect visual match, but very close and easier in this
instance than some sort of press-on transfer.

==

After at first thinking it not possible, was finally able to break apart
the TB switches and remove the latching assemblies, then reassemble -- all
while the switch was still on the board. I prefer not to have a latching
TB switch -- much more comfortable to push-and-hold/immediate-release the
TB. Double-tapping a latching switch is annoying for TB.

==

Dropped in 2134s in the right and left hand master section. Outputs probed
for HF oscillation; everything seemed fine, though aux sections might have
some gunk. Replaced headphone jack (normalling jack in the control room
monitor circuit). Much improved sonics, even doing nothing else.

==

Looked at 1KHz square wave into mic inputs all the way through to program
outs. Initial sense of feeble LF now quite visible as downward tilt on
trailing edge of square wave. Got worse and worse the farther along in the
path. And the LF restriction seemed quite "hard" in that dialing in a few
dB of bass boost via EQ would mostly level out the slope, but the last
little bit always drooped, no matter what.

So, replaced coupling caps with much larger Panasonics and bypassed with
Wima films. Program summing amp input caps replaced with Black Gates.

No more LF loss. Squarewave nice and level all the way through. Top end
clean. Sounds relatively sweet even with a lot of top end dialed in. Not
exactly warm, but acceptably neutral. Way better than what it was (thin
with a layer of fuzziness).

==

Beware slip-on jumpers! A couple of the submasters were not passing
signal, or would cut in and out as the board was tapped. Brushed against
bus select jumper and signal came through loud and clear. Removed/inserted
several times to firm up connection. Might go ahead and hardwire these
jumpers. Places where aux send pre/post jumpers are used should be checked
as well.

==

Replaced insert (normalling) and line in jacks. Replaced mic XLRs on those
channels I'll use to supplement my outboard preamps. Those XLRs looked
pretty bad and didn't want to clean up. Might be okay, but would rather
not risk it.

==

Added EQ bypass switches to standard input modules where the EQ is
otherwise in the circuit all the time. Nice to have that option as the
kind of work we do does not require EQ a fair amount of the time.

==

Added mechanical coupler on master L/R program faders so that they
cross-track perfectly all the time, at least to the limits of the fader
electrical tolerances. This consisted of a precision drilling through the
plastic fader caps. Hole sized for a tight fit of a 1" 4-40 machine screw;
nut applied between the fader caps to provide mechanical support. Works
great! No more inadvertent L/R channel imbalances, minor as they typically
might be.

Actually, this is pretty important as we do the 3-fader mid-side decode,
and to work optimally the Side-minus and Side-plus signals need to stay
perfectly equal in their levels. Locking the master faders means one less
place to have to tweak for this.

Also, board fades are a lot easier.

==

Aux send 1 had 7 volts DC on the output!! New caps and input transistors
cured this.

==

Still to come..,

Replace main PS with new 18V International Power linear. Use original PS
as "hot backup", the two supplies wired together via diodes. Drop through
diodes will then put the main rails at 17.4V; the backup rails at 16.4V. I
assume I can get away with these slight voltage unders/overs.

Socket rest of ICs with machined sockets and add 0.1 decoupler caps to
each op amp supply rail throughout. Upgrade to handle "faster" chips. (47
pf in series with 100 ohms across op amp inputs, per Jim Williams.)

Investigate noise floor and find optimal gain staging. Dynamic range is
probably around 90-95 dB, but I'm only using 70 dB of that (0 dBFS at
A-D). Most likely can push the console 5-10 dB harder, but haven't wanted
to get into higher distortions. LED ladders on Delta match metering on
external recorders/converters quite closely. That is, 0 dBFS on an
external box is all LEDs lit on the Delta, both in and out.

==

Many thanks to Jim Williams, Scott Dorsey, Stephen Sank, Monte McGuire,
Paul Stamler, Phil Allison, and others who provided valuable advice in
recent months. This project would not have been possible without your help.

==

That's it for this update. Too long? Not enough?

Frank Stearns
Mobile Audio
--

Hello from Finland

Is this a Soundcraft Delta project?

If yes - i have a simple ( tested, too ) modification of how to foolproof
the lousy channel ON-switches so, that the channel NEVER goes silent (
unless you want it ) and you DON´T have to cut anything on the board.....


--
nuuska tm @ sci.fi - delete spaces
+358400 44 35 36



"Frank Stearns" kirjoitti
...
Some have expressed interest in how my Delta rebuild project progresses.
So, here's a summary of what's been done so far.

If interested, please come on along -- helpful comments, questions, and
suggestions always welcome. If you're not interested, please killfile now,
either on my name or on the subject keyphrase "Delta Rebuild Update" (I'll
always use that in the subject line).

==
Acquired console August 2004 based on its functions, flexibility, and
clean design for our main application: location live and location session
work, mainly acoustic.

Basic build quality seemed solid; best of all it was modular with lots of
room on the boards -- easy to work on.

Acquired PDF of schematic set. Ran off two sets of 20"x24" prints on the
big plain-paper printers at the local blueprint house. Started studying as
time allowed.

Cursory tests showed that everything worked; further tests indicated most
switches crunchy, but all faders in excellent health and only a few pots
were bad.

Ran 100 Hz through all channels to find bad switches (channel on, pan,
pfl, eq on, line, phase, etc -- mostly all bad).

Got 100+ new DPDT and 4PDT switches from Harmon. Good to know they still
carry full spares for this model. Talked to Frank and Rene there; nice,
helpful folks.

Replaced bad switches, retested. Switching now solid and silent. TB
function restored (another bad switch; but replaced electret TB capsule
anyway based on age).

Console used on a few sessions; intermittent phantom and PFL on some
channels. At first assumed switching but was perplexed as most had been
replaced. Instead, eventually concluded bad sockets on the master loom
(ribbon cable assembly called "loom" by Soundcraft). Most contacts pretty
relaxed on those 34 pin female connectors probably due to age; some were
so loose they just fell off the board connector once the hold-down levers
were released.

Master loom many months on back order. Rene finally said he'd just build
one. Next time I will probably get the $20 connector press and do my own.
An audio systems designer friend suggests hardwiring; probably a good idea
but mostly impractical; I'd rather just build a new loom every couple of
years.

New loom installed, all documented weird intermittent problems now seem
gone.

==

Added a 2-gang pot to RH master so as to provide variable monitor dim,
along with DPDT ON-OFF-ON toggle to provide switchable monitor dim,
normal, and mute functions via a switch. (a small 20K linear is what I had
in the parts box; an 50K log taper would likely be better.)

Added a momentary mono switch. Very handy.

It's convenient that these modules are built so that without too much
hassle the PC board can be removed from the metal frame. Made using the
drill press for switch and pot mounting holes much simpler.

Also added PS rail LEDs. One unsettling thing about this unit is that the
power supply shoebox has NO pilot lights, and there's nothing on the
console that glows if it's just idling. Aside from running a signal, you
have to press a channel "on" or PFL button to see if there's power; I
prefer to know at a glance that incoming voltages are present.

Located dim pot just above and to the right of the master faders (wiper
and one leg from each dim pot segment replaced R151 and R51 on RH master).
Mono and monitor switches nearby.

Did little paper strip labels and glued to panel, matching the finish and
lettering colors. Done with ink jet on plain paper; coated with artist's
fixative. Not a perfect visual match, but very close and easier in this
instance than some sort of press-on transfer.

==

After at first thinking it not possible, was finally able to break apart
the TB switches and remove the latching assemblies, then reassemble -- all
while the switch was still on the board. I prefer not to have a latching
TB switch -- much more comfortable to push-and-hold/immediate-release the
TB. Double-tapping a latching switch is annoying for TB.

==

Dropped in 2134s in the right and left hand master section. Outputs probed
for HF oscillation; everything seemed fine, though aux sections might have
some gunk. Replaced headphone jack (normalling jack in the control room
monitor circuit). Much improved sonics, even doing nothing else.

==

Looked at 1KHz square wave into mic inputs all the way through to program
outs. Initial sense of feeble LF now quite visible as downward tilt on
trailing edge of square wave. Got worse and worse the farther along in the
path. And the LF restriction seemed quite "hard" in that dialing in a few
dB of bass boost via EQ would mostly level out the slope, but the last
little bit always drooped, no matter what.

So, replaced coupling caps with much larger Panasonics and bypassed with
Wima films. Program summing amp input caps replaced with Black Gates.

No more LF loss. Squarewave nice and level all the way through. Top end
clean. Sounds relatively sweet even with a lot of top end dialed in. Not
exactly warm, but acceptably neutral. Way better than what it was (thin
with a layer of fuzziness).

==

Beware slip-on jumpers! A couple of the submasters were not passing
signal, or would cut in and out as the board was tapped. Brushed against
bus select jumper and signal came through loud and clear. Removed/inserted
several times to firm up connection. Might go ahead and hardwire these
jumpers. Places where aux send pre/post jumpers are used should be checked
as well.

==

Replaced insert (normalling) and line in jacks. Replaced mic XLRs on those
channels I'll use to supplement my outboard preamps. Those XLRs looked
pretty bad and didn't want to clean up. Might be okay, but would rather
not risk it.

==

Added EQ bypass switches to standard input modules where the EQ is
otherwise in the circuit all the time. Nice to have that option as the
kind of work we do does not require EQ a fair amount of the time.

==

Added mechanical coupler on master L/R program faders so that they
cross-track perfectly all the time, at least to the limits of the fader
electrical tolerances. This consisted of a precision drilling through the
plastic fader caps. Hole sized for a tight fit of a 1" 4-40 machine screw;
nut applied between the fader caps to provide mechanical support. Works
great! No more inadvertent L/R channel imbalances, minor as they typically
might be.

Actually, this is pretty important as we do the 3-fader mid-side decode,
and to work optimally the Side-minus and Side-plus signals need to stay
perfectly equal in their levels. Locking the master faders means one less
place to have to tweak for this.

Also, board fades are a lot easier.

==

Aux send 1 had 7 volts DC on the output!! New caps and input transistors
cured this.

==

Still to come..,

Replace main PS with new 18V International Power linear. Use original PS
as "hot backup", the two supplies wired together via diodes. Drop through
diodes will then put the main rails at 17.4V; the backup rails at 16.4V. I
assume I can get away with these slight voltage unders/overs.

Socket rest of ICs with machined sockets and add 0.1 decoupler caps to
each op amp supply rail throughout. Upgrade to handle "faster" chips. (47
pf in series with 100 ohms across op amp inputs, per Jim Williams.)

Investigate noise floor and find optimal gain staging. Dynamic range is
probably around 90-95 dB, but I'm only using 70 dB of that (0 dBFS at
A-D). Most likely can push the console 5-10 dB harder, but haven't wanted
to get into higher distortions. LED ladders on Delta match metering on
external recorders/converters quite closely. That is, 0 dBFS on an
external box is all LEDs lit on the Delta, both in and out.

==

Many thanks to Jim Williams, Scott Dorsey, Stephen Sank, Monte McGuire,
Paul Stamler, Phil Allison, and others who provided valuable advice in
recent months. This project would not have been possible without your
help.

==

That's it for this update. Too long? Not enough?

Frank Stearns
Mobile Audio
--
.

I have one too. Replace the worn switch. Inject a very small amount of
Stabilant 22A. Work the solution by pushing the switch. Now they will
last for at least 30 years. Did this to mine in 1995 and they all still
work like new.

Re-solder all the switch and pots and especially the jacks. They used a
thin flow solder so they commonly work loose.

Replace those **** alps faders with conductive plastic. I use TKD's.
These alps faders suck the air out of the mix. You can hear it by
reducing the input trim 10 db and the shove the fader all the way up.
Hear the improved clarity?

Replace the mono faders in the stereo module with a stereo one. They
are laser matched. Solves the miss match of two crap mono faders. Then
you can wire the mono fader up for variable mono outs.

Jim Williams
Audio Upgrades

Replace those **** alps faders with conductive plastic. I use TKD's.
These alps faders suck the air out of the mix. You can hear it by
reducing the input trim 10 db and the shove the fader all the way up.
Hear the improved clarity?


Jim Williams
Audio Upgrades

Are you saying that changing the faders to conductive plastic can make
an improvement to the sound "clarity" when the faders are sitting
stationary and all the way up, i.e. at 0 dB attenuation?

Would you happen to have any explanation of how this could happen?

Mark

In article .com,
"Mark" wrote:

Replace those **** alps faders with conductive plastic. I use TKD's.
These alps faders suck the air out of the mix. You can hear it by
reducing the input trim 10 db and the shove the fader all the way up.
Hear the improved clarity?


Jim Williams
Audio Upgrades

Are you saying that changing the faders to conductive plastic can make
an improvement to the sound "clarity" when the faders are sitting
stationary and all the way up, i.e. at 0 dB attenuation?

Would you happen to have any explanation of how this could happen?

Mark


No, he's saying the sound improves when the Alps faders are full up and not
attenuating the signal.

Frankly, I like the sound of the stock 200 Delta we've been using for live
electroacoustic concerts for the last decade. Sometime I will have to get the
hum out of the stereo output strip, though.

-Jay
--
x------- Jay Kadis ------- x---- Jay's Attic Studio ------x
x Lecturer, Audio Engineer x Dexter Records x
x CCRMA, Stanford University x http://www.offbeats.com/ x
x---------- http://ccrma.stanford.edu/~jay/ ------------x

This is a great thread - thanks Frank!

dave

In article writes:

Frankly, I like the sound of the stock 200 Delta we've been using for live
electroacoustic concerts for the last decade. Sometime I will have to get the
hum out of the stereo output strip, though.

If I could get the hum out of the stereo output of my Soundcraft 600,
I'd be a happy boy, and I'd be "quiet enough for digital."

Jim, any suggestions for teaching the 600 the words?

--
I'm really Mike Rivers )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

"Frank Stearns" wrote:

Master loom many months on back order. Rene finally said he'd just
build one. Next time I will probably get the $20 connector press and
do my own.

Wanna make one for me? I'm too klutzy.



Double-tapping a latching switch is annoying for TB.

Dangerous, too. Accidentally latching the TB has resulted in a
*cough* "critique" or two being overheard by the talent that I would
have preferred they not hear.



Looked at 1KHz square wave into mic inputs all the way through to
program outs. Initial sense of feeble LF now quite visible as
downward tilt on trailing edge of square wave. [...]
So, replaced coupling caps with much larger Panasonics and bypassed
with Wima films. Program summing amp input caps replaced with Black
Gates.

More details? Specific models/values/locations?



That's it for this update. Too long? Not enough?

Keep 'em coming!

--
"It CAN'T be too loud... some of the red lights aren't even on yet!"
- Lorin David Schultz
in the control room
making even bad news sound good

(Remove spamblock to reply)

"Lorin David Schultz" writes:

"Frank Stearns" wrote:

Master loom many months on back order. Rene finally said he'd just
build one. Next time I will probably get the $20 connector press and
do my own.

Wanna make one for me? I'm too klutzy.

Harmon only charged about $72 for the 16 input version (16 input positions
+ 4 subs + master), and then $24 or so for the smaller monitor loom that
runs across the subs, LR master, and then into the CR out/2 track return
jack block.

To make them I'll need to get the connector press, ribbon, and connectors,
probably $40-50 total. But then there's labor. You'd save money going
to Harmon.

Double-tapping a latching switch is annoying for TB.

Dangerous, too. Accidentally latching the TB has resulted in a
*cough* "critique" or two being overheard by the talent that I would
have preferred they not hear.

Yeeee-up. g


Looked at 1KHz square wave into mic inputs all the way through to
program outs. Initial sense of feeble LF now quite visible as
downward tilt on trailing edge of square wave. [...]
So, replaced coupling caps with much larger Panasonics and bypassed
with Wima films. Program summing amp input caps replaced with Black
Gates.

More details? Specific models/values/locations?

Oops. I lied, not Panasonics but Nichicon Muse series. 4x stock value
where possible, 2x in other places (most of the interstage couplers are 47
uF; took them up to 220 or at least 100; others where the stock value was
larger I took to 330 or 470 as space allowed). I elected to remove and
jumper the cap positions on the insert returns as I seldom use channel
inserts. (And when I do it's known gear.)

There was no room to put anything larger than the 1000 uf for the mix bus
summers, so I sprung for the Black Gates (at a whopping $4.50 each).

I had originally hoped to jumper many more caps but found more offsets
than expected, even when using an amp like the OP275, which maintains next
to zero offset even with large rail imbalances. Not sure exactly where the
offsets are coming from.

Jim Williams was kind enough to share his expertise and he gave some
really good ideas; do a search on his posts to this group on the various
Delta threads.

That's it for this update. Too long? Not enough?

Keep 'em coming!

Will do, as time allows (and as things prove out!!).

Frank Stearns
Mobile Audio
--