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The Poor Serbian Man's Optical Attenuator

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About the Author

Prodanovic Aleksandar and Slobodan Pavleski

"Zen Mod" Prodanovic
Aleksandar spends his time repairing home and pro electronics. He has been
making audio gadgets and pro systems for more than 20 of his 43 years but has no
formal education in electronics. Toobz are his love from a young age and he
blames “Papa” Pass’ influence for getting him started playing in the solid state
sandbox. "Spavleski" Slobodan Pavleski is an electronics engineer and his
professional bio is even longer than this article! He is 42 years old, audio and
music are his hobby and ZM sez: “One hell of an engineer!”

Related Links

Lightspeed
Attenuator a new passive preamp

Poor
Serbian Man Optical Volume Control

Silonex
LDRs for Lightspeed Attenuator

Optical
Volume Control Professional PCB

Kits

The Poor Serbian Man's Optical Attenuator

Prodanovic Aleksandar and Slobodan Pavleski
,

23rd October 2010

A gadget made by Spavleski & Zen Mod
Article scribed by Zen
Mod

You’re a Macho Man. You have all the gadgets which real Macho Guys absolutely
must have: A CD player, or even a transport with a separate DAC, and recently
you made a dedicated media PC, which is dead silent and as capable as HAL 9000!
You have nice and potent speakers too. Maybe you also have an ancient Black Disc
Spinner, but that's another issue. Or is it? It gives you even more
opportunities to later make another gadget, to amplify those tiny signals
randomly collected from black grooves...And you just finished making the best
amps money can buy, just because you’re lucky, you’re also potent, same as your
speakers, and you’re hanging with right Macho Bunch, at the right place,
diyAudio, sharing ideas and the newest tips on how to reach Audio
Nirvana.

As written above, you’re macho, and you like listening to your
music loud, and you also like to watch your fave Football or MotoGP, and
actually listening to them, not just staring at a moving picture. There is
nothing better than to hear bones cracking (Football) or the metal to asphalt
scream (MotoGP)! Wait a minute, you have a Wife, or even a Mom? And they aren’t
always in the mood for your torture of loud music every day? So, you really are
not so macho and you need a Volume Control. “gotcha!” – JB .

What is important in an Optical Volume Control ?

First, its name
must be written with Capital Letters. Second, it must be lossless, unlike those
MP3’s, which you hate even more than a Volume Control! Third, it must maintain
peaceful coexistence/cooperation with the preceding and following stages at the
same time. OK, except for the first, capital letters, the following two aren’t
easy tasks to achieve, so now we are going to have to get little more
technical...

Everyone here knows what a resistive divider is, so I have
no intention of teaching you that just to entertain you. In fact I’m pretty
lazy, so I’m typing all this just buying time until I really must paste some
schematics and pictures in here, and start to explain a few things. OK, now
here’s our first pic, a voltage divider:

Pic.
1

As you can see – that’s pic of a plain ole potentiometer. The
Optical Volume Control is however, not made physically of one resistor, with a
contact track exposed to a wiper, but from two variable resistors pictured as
this:

Pic.
2

These two variable pots are ganged in a way that, while the
series one is decreasing in value, the shunt one is increasing in value. To
complicate/or simplify things further, imagine that the pots are shaftless
(funny term, isn’t it?) and that these two resistors are light-dependent, or
better defined, their resistance is inversely proportional to amount of light to
which they are exposed. So the pic can look something like this:

Pic.
3

Assuming that we are still following the same law of
decrease/increase of series/shunt resistance, it looks that we have gained a
couple of things.

1. We have contactless variable resistance, which means
that we have succeeded in the first factor needed for losslessness, hehe...

2. We need a proper circuit to make these LEDs behave in the way we want
them to exactly. But number two actually has a hidden benefit. We must make some
unnecessarily complicated circuit blocks just to preserve the impression that we
are still Macho, doing things which our Chicks really aren’t able to understand.
The fact that they aren’t even slightly interested in understanding our toyz ‘n’
gamz isn’t part of the prospective of this clever document.

Luckily,
thanks to the kind people from the Pro Oriented Industry, who are pretty much
unaware of the existence of a bunch of wakoo people obsessed with using real
parts for something that is intended to make some funny noises called Music, we
have those nice and precious parts: LDRs, or Light Dependent Resistors. For
further info on other projects with these funny devices, including GeorgeHiFi’s
thread on the Lightspeed Attenuator, see the Links to the side of this article.
That boy started the entire Frenzy on Big DiyAudio.

But we boyz from
Serbian DiyA, had an idea how to ensure the good behavior of our tiny LDRs with
current sources, which must be of course, both adjustable and variable. For the
schematic look at “PCB01 Schematic” at the end of this document.

As you
can see, we decided to use the old fashioned approach, without the use of fancy
add-ons such as microprocessors etc. A pot is still the main adjusting part, but
this time we use the cheapest 2x10K linear one, and the audio signal is nowhere
near it. Its role is to handle variable voltages, which are steering adjustable
Current Sources.

For your convenience, the dedicated power supply
schematic is in upper left of schematic sheet. Of course both the PSU and the
steering circuit are on the same pcb, accidentally named as PCB01. The supply
schematic is pretty self explanatory. Center tapped or non CT transformer, a few
diodes, an LM317 as a 70mA CCS, and a few Zener diodes working as a reference
for the shunt Darlington on the output. Exact output voltage is the sum of Zener
voltages plus 2x the Vbe of Darlington (that’s 1V35). 15V is drawn on the
schematic, but who cares if we have 1V35 more...

So, now go back to the
exact LDR circuit schematic. If you’re looking at these pages on your ‘puter
screen, now is the time to either print these two schematics, or use two
screens. Do whatever you wish if you are not ready to jump back and forth,
reading text and looking at schematics. Here is what you will
discover:

-Q6, along with LED1 and VR1 form a reference voltage string,
with 3mA of current flowing through. We have available there two fine voltage
points, 2V5 on top of VR1, and ~ 2V more on top of LED1 .

-We are using a
reference voltage of 2V5 to inject it into our main Governor (Hasta La Vista -
ring a bell ?) Pot itself, so we have nice clean and steady DC voltage to play
with. Q3 is any small N type Darlington (or even two small signal diodes
connected in series if you’re a cheapskate ) and is nothing other than a
convenient voltage shifter. Using it there is to try to null TempCo of the same
type Darlingtons used as control elements in two main Current Sources (look
down) .

-So, we have clean and steady voltage (2V5 less two Vbe) on top
of Pot1. Now look at the vertical string starting from 15V, made of LEDS in 4
LDRs (OK7,5,3,1), closed jumper JMP01, and dedicated Current Source, CS made of
Q1 steered with voltage from POT01, cleverly cascoded (by Mighty ZM) with Q4.
That one, Q4, is biased from the previously mentioned voltage tap on top of
LED1. That vertical string is dedicated to series LDRs.

-I’m clever, so
I’ll paste the above paragraph here for the right vertical string, just changing
the appropriate part labels. So now look at the vertical string starting from
15V, made of LEDS in 4 LDRs (OK8,6,4,2), closed jumper JMP02, and dedicated
Current Source, CS made of Q2 (steered with voltage from POT02), cleverly
cascoded (by Mighty ZM) with Q5 . That one, Q5, is biased from the previously
mentioned voltage tap on top of LED1. That vertical string is dedicated to shunt
LDRs.

Idea is, with the main pot at zero (7 O’clock) position, minimum
current is flowing through the left series LDR LED string (on top of Q1) so the
mating LD Resistors have max resistance. At the same time, max current is
flowing through the right shunt LDR LED string (on top of Q2 ) so the mating LD
Resistors have minimum resistance. The result is that our poor tone signal is
attenuated maximally.

That crossed behavior is achieved with a crossed
connection of reference voltage to a two section of main pot, while the
reference voltage is connected to the “start” end of POT02, and it’s connected
to “end” end of POT01. Incidentally, at the 12 O’Clock position of the main pot
these two voltages coming on both wipers must be same. But we are clever, so we
introduce a “fake log law” inducing resistor in each section, R200 and R300.
That’s an old trick, to use a linear pot because the section matching of them is
better than with cheapskate class logs. Put a few resistors from wiper to ground
and Voila!, we have an Audiophool pot for pocket money, or we hope we do at
least .... where’s da :devil: smiley when a man needs it ?

OK, now look
again at Pic.3.
You see where the signal is coming in, where ground is, and
where the signal is coming out. Now, look at the Schematic of PSM LS. We have 4
(or just two, for stereo unbalanced, if you wish so) sections. The first one is
made of OK1 & OK2 (R-), the second one is made of OK3 & OK4 (R+), the
third one is made of OK5 & OK6 (L-), and the fourth one is made of OK7 &
OK8 (L+).

If you obtained your LDRs from me, use Series X and Shunt X as
a pair, where X is 1 to 4. So, Series 1 + Shunt 1, Series 2 + Shunt 2, Series 3
+ Shunt 3, Series 4 + Shunt 4. They’re matched with that in mind.

I
think that everything is clear regarding the points where the signal is coming
in, where Ground is, and where the signal is coming out. Just one note:
cleverly, on both the schematic and pcb itself, the audio ground isn’t connected
to any point of the steering circuit. My Fullrange Bro Spavleski, responsible
for those funny patchwork pcbs we made, even uses the top pcb layer as ground
for the steering circuit, without any ill effects.

The electrolytic caps
and block caps, connected in parallel with LDR LEDs, are there for cleaning up
any possible residual noise in the PSU. Use them or not, your choice, they
aren’t critical at all.

The P4-P11, 2M2 trimpots are there just in case
that the LDRs aren’t tightly matched. If you have tightly matched LDRs you don’t
need them at all. Later in this text I’ll explain a better cure, in case you
feel or measure that some section is slightly weaker than another.

We
will leave the Optical Volume circuit now, and look at the buffer schematic;
That’s the “PCB02 Schematic”, also on end of this document .

First – look
at the the buffer PSU schematic on the top left of the page, when oriented as
you’re used to looking at a page and still able to see letters .

Transformer
– its wisest to use common one for both Optical Volume and buffer circuits.
Whatever. While you’re free to use center tapped or not center tapped
transformer for Optical Volume circuit, here you must use a center tapped one,
because we need a two-leg supply, where we have both a positive and a negative
leg. Of course now, because the power grounds on two circuits/pcbs aren’t
connected through any other possible path – you can wire it for PCB01 in any of
previously mentioned ways, and for PCB02 you must connect the center tap where
it belongs .

The Reg itself, is pretty similar to the already explained
reg for Optical Volume. So it’s pretty straightforward; transformer, snubber
cap, Graetz diode bridge, electrolytics + solid caps filter for each leg, then
LM317 (100mA CCS for pos. leg), LM337 (100mA CCS for neg. leg), then an
interesting thing, a sort of common (for both legs) Zener reference string, made
of D5,D6,D7,Q1,D8,D9 and D10. The first three are a voltage reference for the
shunt darlington Q2, while the last three are voltage reference for the shunt
darlington Q3. Q1 is a little CCS for the Zener string, serving both halves,
upper and lower, and not being connected to ground.

OK, then we have a
string made of Q2 and Q3, and their emitters are connected to output ground,
while each Zener string half is finding their potential path/point via the
corresponding Darlington. Anyway, to cut the story short, and my pains in
explaining things on non-native, you’ll have a pretty low noise reg, with
5V1+0V65+5V1+1V3=13V15 on each output. Twice 5V1 is obviously from the two
Zeners, 0V65 is from conducting connected uni diode (1N4148) and 1V3 is 2Vbe of
the Darlington.

Stability vs. Time isn’t of much importance here, just
because once all parts reach their temperature equilibrium, the output voltage
is pretty stable. Conducting connected 1N4148, which have opposite TempCo to
Zeners is purely from habit here.

C5 & C6 are noise suppressors for
the Zener string. CX and CY are possible oscillation killers and tiniest noise
removers. Now I need rofl smilie, but I don’t have it handy .
C7,C8,C9,C10 - noise killers, what else ?

Now look lower on the
schematic. Pick the one you want of the 4 framed schematic parts, they’re
identical. Assuming that you’re looking at the farmost left, that’s nothing
other than a JC/Borbely (or Borbely/JC–who knows?) buffer stage, made of two
complementary Jfets. Unfortunately they’re the scarce Toshiba ones, but you’re
probably so eager to spend a few Greenies making the ultimate Macho Volume
Gizmo, that you already have them.

R1A: Usual
anti-oscillation/helper/niceplaceformylatestbestbrandofshinyresistor. R2A
defines the input impedance of the buffer, and at the same time conveniently
taking the gates of both Jfets to ground. Q1A & Q2A, they’re the workers
here. Ever see two Woodcutters working with a crosscut saw? They’re doing same
thing here, pushing and pulling (Got ya! a crosscut saw can be pulled only
) their common output, governed by the input signal on their common input. P1A
serves as a biasing device for both Jfets, while giving you a chance to adjust
the zero offset at the output, after the initial warm-up of these two funny Jfet
critters of course.

C4A & R4A , C3A & R5A are snubbers. C1A
&C2A are local decoupling, along with snubbers. R3A is there to clamp
outputs to ground, even when the outputs have no load. Well, one buffer
explained. You must believe me when I say that the other 3 are the same, just
differing in parts nomenclature and with the suffix B,C, or D instead of
A.

Before taking this writing (for me), and reading(for you) adventure
further, lets sum up a few things ...

The entire gadget is made of 4
volume blocks on PCB01, called PSM Optical Volume, and 4 buffer blocks on PCB02,
called PSM Buffer. We can use/combine them in several ways, and only you can
decide the best way to do it. Certainly the simplest way of combining them is a
pure balanced attenuator, buffered on the output, meaning that each of 4 volume
blocks/channels is buffered on the output.

OK, shall we power up the
bloody thing(s)? Naah, first we must be sure that you didn’t mess up a few
things regarding LDR orientation. Lets look at some nice pics, brought to you
courtesy of spavleski. See here:

Be
careful! The short (LED) legs are fragile. Even if you have a dot on the LDR
body, re-check the dot position with the diode tester on your DVM. The rest of
the picture is self–explanatory .

LDR’s are in opposite position in right
and left columns. Nota Bene: LDR’s are drawn as photo-transistors on our
schematic (now you’re saying before I can: “on end of document, PCB01
Schematic") But don’t worry, the LED’s are drawn the right way.

Its now
time to ask you – Did you wire that funny pot in this way?

Now
is also the time, assuming that you checked twice how the LDR’s are positioned
and soldered, and that you already soldered all the other parts (including those
funny PC-like jumpers JMP01 and JMP02). There is no need to mount any heatsink
now on IC1 and Q7, just check their temperature later with a finger. Warm is OK,
if hot then mount some small heatsink of any sort you have in your parts
drawer.

Ready for powering up PCB01? Do not connect the transformer leads
to PCB02. At this time we need it just for PCB01.
- remove JMP01 and
JMP02.
- turn main potentiometer to 12 clock.
- turn mains ON and check
PSU voltage. A convenient place for the black probe is any GND point (upper
ground plane - LSP1 point ), and for your red probe the upper pin of either
JMP01 and JMP02. You’re measuring PSU voltage through the LDR’s LED chain in
fact, but that's convenient to check LED’s orientation in same time. Expect
voltage of around 16V6. If you’re serious about programmed voltage, change one
of the 5V1 Zeners to a 3V9 one, and you’ll be in the 15V ballpark. If that’s the
case check few more things:

-Is LED1 shining? if yes, OK (it’s supposed
to shine )
-Check the voltage (ref to ground of course) on the middle leg of
Q3. It must be around 2V5.

Next, power down and connect a mA meter
between the pins of JMP01 with the main potentiometer still in a 12 O’clock
position. Then power up. The current is probably few mA. Turn the main pot
slowly clockwise, taking care that the current does not rise above 15mA. When
you are on max. position with the main pot (5 Clock), set the current to 15mA
with P1.

Now power down, remove the mA meter clips from JMP01, place a
jumper on it, place the mA clips on the JMP02 pins, and turn the main pot to 12
O’clock. Then power up and check the current. It must be in range of few mA.
Turn the main pot slowly anti-clockwise, taking care that the current does not
rise above 15mA. When you are on minimum position with the main pot (7 O’clock),
set the current to 15mA with P1. Power down, remove the mA meter clips and place
the bridge on JMP02. Bingo, you’re done with PCB01 for now.

Shall we
progress to PCB02 powering up now?

If you’re finished with that first
beer, don’t use another one .....
If you’re in for another mug of coffee, now is the time.

OK, you can
leave the transformer wires connected to PCB01, and you must connect them to
PCB02 now. You didn’t forgot to solder one tiny jumper, situated between the two
right most 100uF caps and right most 5V1 Zener did you? That jumper is for
connecting all ground-planes to actual ground .

There is one slight
omission in PCB02 ; you must solder a wire bridge between two bottom pads – look
at the picture – drawn as a yellow line. Its on the rev.B pcb, and we are going
to solve that mistake in later pcb issues. Then this note won’t be needed, along
with this pic:

You
don’t need heatsinks on LM’s and Darlingtons to start. Check later, as I
mentioned before. Warm is OK, but if hot mount any small heatsink you have. Pads
for buffer Jfets are oriented to ensure a face to pace position of little
critters. Feel free to put a small blob of thermal goo between them and tie them
with plastic wire tie or even small piece of heatshrink.

Power up da
thingie. Check positive and negative PSU rails with the black probe on ground
(mid point between two 2200uF caps is convenient place), and red probe to the
middle pin of BDX53C for the positive leg, and then red probe to middle leg of
BDX54C for the negative leg. If these two voltages are in the ballpark of 12V be
happy. Next check DC voltages across every 50R output trimpot. Its fine if you
see around 250-300 mV That’s the sign that both Jfets in each buffer are
conducting. While you are there, if everything is OK after 10min or so, put
black probe on ground, red probe on each ( one at a time) buffer output and
adjust DC offset to zero with the trimpot.

Now, you can power off your
new Semi-Macho gadget and think of what you really want to make. It’s sorta
complicated to describe the several possible variants, so I made few sketches
and I hope that things are clearer that way.

First – full blast .........
nope, just in case, I’ll start with simplest configuration:

It’s
pretty obvious that this configuration is for plain stereo attenuation – two
attenuator channels, two buffers. That means that each channel output is
buffered. It’s handy to have spare pair of outputs so you can add an additional
pair of RCA’s and feed them ditto from attenuator outputs, before the
buffers.

Next one is somewhat more complicated :

As
you can see, two attenuator sections and four buffers. That way each of the
stereo unbalanced channels is buffered on both the input and output. Same
thinking applicable as in the previous configuration, you can mount an
additional pair of RCAs and feed them pre-output buffers . You can also mount a
small 2-deck toggle switch on the front panel and bypass the input buffers
whenever you feel that’s wise in case that you have one source with enough
muscles to drive the LS directly, and other sources that are weaker in driving
capability. A toggle switch can be used to control a small relay, which will
usually have better contacts than the switch itself, so it’s beneficial to use a
relay as a bypass switch. You can steal a few dozens of mA for the relay from
the raw PSU before the PCB01 reg. Be creative and find these points, or for a
wiser/purist solution, make a small pcb with a tiny Graetz diode bridge and a
small electrolytic cap, and put an adequate resistor in line with the relay
coil. That way you’ll not pollute any part of the DC grid in the
gadget.

OK, the next one is the (in fact – almost) full blast
configuration. A fully balanced attenuator , buffered on output. Look at this:

The
picture is pretty self- explanatory, even without the text below

Now,
just one final teaser ...... This is what I call full blast!:

You
would need two PCB02 boards for that final configuration, and I firmly doubt
that anyone needs that, or has the time and will to make it.

Well, while
I’m in mood for writing, maybe I can write few words about some final tweaks
needed not so much for proper functioning of our PSM LS, but for peace of mind.
You’ll need a plain DVM (a ‘scope is even better) and any sort of signal
generator. It can be a proper siggene, it can be a tube oldie, it can be a test
CD, or a simple PC sine wave proggie output from sound card of crappiest PC you
have at home...

Now I’ll throw in some handy pictures here (courtesy of
spavleski) of several most convenient ways of wiring Da Thingie. First the most
complicated:

nice
place for two pictures. The first one is the crosscut saw in action .... Wood
Diy’ers understand this..

if
these two are like Jfet buffer then these must be analogous to a cascoded Jfets
buffer :

Of
course – you can make a mix of XLR/RCA connectors on both ends, input and
output, just like in this picture. And I presume that you must know how to wire
and mix these two if you’re willing to make gadget like this one:

Be
warned, this circuit isn’t any sort of balanced/unbalanced or
unbalanced/balanced converter. You can use it balanced in/unbalanced out (or
vice versa) but you must tie pins 1&3 on the empty XLR while using the
adjacent RCA. And yes, I just recently remembered the XLR pin outs, just in case
you recently forgot:

Pin 1 – Ground
Pin 2 – Positive Leg
Pin 3 –
Negative Leg

Now I can presume that you have decided which
arrangement is for you, that you read both the thread and this funny paper, that
you wired all needed wires between the transformer, both PCBs, input selector
(no, I can’t teach anyone how to wire the selector, hehe), and all input and
output connectors, so we are ready for the final procedure.

We need any
sort of signal generator, set for ~ 500Hz and a DVM on AC voltage or a ‘scope.
I’ll show block schematic for balanced stereo. If you’re using unbalanced
stereo, just cover half of the schematic with blank paper. (if you are reading
from a screen, tape paper on the screen hehe).

This
procedure is brought to all of us by Mighty spavleski .
OK – whazzat ?
Nothing other than a signal generator connected to ALL the
hot inputs in parallel. Obviously, all input grounds are tied together. That way
all 4 channels/sections are fed with the same signal. On right side, connect
your AC meter, (either the DVM on AC or a ‘scope) to ground and to one output
(HOT) at a time .

Step 1 – position main volume pot on 9 clock; measure
Out 1 & write down, measure Out 2 & write down, measure Out 3 &
write down, measure Out 4 & write down.
Step 2 - position main volume pot
on 12 clock; measure Out 1 & write down, measure Out 2 & write down,
measure Out 3 & write down, measure Out 4 & write down.
Step 3 -
position main volume pot on 3 clock; measure Out 1 & write down, measure Out
2 & write down, measure Out 3 & write down, measure Out 4 & write
down.
Step 4 - position main volume pot on 5 clock; measure Out 1 & write
down, measure Out 2 & write down, measure Out 3 & write down, measure
Out 4 & write down.

If you’re lucky, all values will be in 5% or even
smaller bracket. If not, you have one beautiful trick as a weapon tnx to my
clever engineer friend spavleski.

Lets say that 3 channels are pretty
equal in attenuation and that one is weaker. Lets say that the weaker channel is
channel No.2, intended for R channel, negative leg. If you look on the PCB01
schematic, you’ll see that the LDR responsible for that section is OK1 as series
LDR and OK2 as shunt LDR. That channel is weaker than the others IF shunt LDR
(OK2) consistently has a smaller resistance than needed. The way to cure that is
to steal some current flowing through it. Take a look at this:

I
already wrote previously that we are not going to mount these 8 trim pots on
PCB01. If you bought them in the meantime, you can curse me, or you can keep
them for something else funny, and curse me again.

So now we have a few
empty holes in that PCB, and they are a perfectly adequate place for soldering
two parallel 3mm red LEDs in parallel with our nasty behaving OK2. That way we
are stealing some current from it in the entire range of operation, not just in
some narrow area around the desired (listening volume) range, as is case with
parallel connected trimpots. This solution is certainly better. Of course you
can try for a start, curing it with just one red LED in parallel to OK2, and
repeat the procedure as needed. This time you need to just compare the “faulty”
channel with the nearest one. If needed, add another LED in parallel to first
one.

Now, if you’re using a ‘scope for this procedure, power up once
again that signal generator, position the main pot between 7 and 8 clock,
connect the ‘scope to any output, and fiddle with P3. The goal is to see just a
slight signal wobble on the screen, meaning that we choose a natural position
where we can just hear music singing through our new gadget. 7 is
zer/nada/zilch/mute, and around 8 is minimum. If you have just a DVM, perform
that part of procedure with a signal source connected to input and an amp &
speaker on the output when you finally place the PSM LS in your system.

Final notes – to achieve the same thermal conditions for all LDRs, we
prepared one nice 3mm hole ditto in center of LDR area. Look at these small pics
:

So
– I think that the technical part of this text is almost or completely finished.
I’ll add a BOM, in fact a list of parts, without a list of places where it is
both cheap and clever to buy them. I’m anyway from a different part of world
from most of you, and all the parts are probably easy enough for you to get at
the nearest Tobacco Store .....

Just few more facts:

Lowest input
impedance of LS itself is in range of 350 Ohms, at somewhere around the 9
O’clock position of the pot, while max is up to 35K near both extremes of the
pot. The input impedance of the buffer stage is pretty much the same as the
input gate(s) resistor, 220K, while output impedance is well in the range of 50
ohms.

Main BOM (Excel Spreadsheet)

Buffer Bill of Materials (Excel Spreadsheet)

PCB01
- PDF Download

PCB02
- PDF
Download

------------------------------------------------------------------

Comments on the article "The Poor
Serbian Man's Optical Attenuator"

23rd October 2010

Zen
Mod

diyAudio Member

Quote:

attentuator.......

diyAudio - diyAudio Articles

...... it's so fun - even Mighty ZM couldn't conceive it better

kudos
for at least triple grammar and spell check work ; you boyz are the best

P.S.
please - do not edit that announcement

my Papa is smarter than your Nelson !
clean
thread;
Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

23rd October 2010

VT67

diyAudio Member

Interesting device! Is
there a circuit board available for this?

Regards

VBITNGC Krell KSA-50 Krell KSA-100MkII

23rd October 2010

Zen
Mod

diyAudio Member

well - this article isn't
intended as any sort of advertising ..... but more as fun for boyz 'n' girlz
;

I don't have many threads in swap meet place , so you'll find -what you
need - easy

my Papa is smarter than your Nelson !
clean
thread;
Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

23rd October 2010

VT67

diyAudio Member

Thanks for the heads up, I
found what I needed.

Regards

VBITNGC Krell KSA-50 Krell KSA-100MkII

23rd October 2010

Blues

diyAudio Member

It's fugly complicated
Aleksandar!

Life simplified! Leap into the Warpspeed wormhole...
http://www.6moons.com/audioreviews/warpspeed/1.html

23rd October 2010

Salas

diyAudio Chief Moderator

Fugly cascode analogy pic,
naah, this would do it better.

23rd October 2010

TerryKing

diyAudio Member

This is a great idea. It
was also a great idea when Collins used it in their Broadcast Control Boards
(AKA Mixers) in 1968 when I was Chief Engineer of WALL in New York. Their
original units were plugged into a 7-pin tube socket and were housed in a metal
can about 1 inch high. They had incandescent bulbs run by the Pots on the
Control Board. Cool: 1 pot could control both channels of the stereo
board!

BUT they sometimes failed, and I designed new ones with those
really new solid state light thingies. Umm. oh, yeah.. LED's They only cost
about $4 apiece. I epoxied them on top of LDR's and put them back in those 7-pin
tube plugs. They matched better and were more stable than the original ones..

Hey, they may still be running today.. only 32 years later :-)

Regards, Terry King ..On the Red Sea at KAUST.edu.sa
[email-masked]
Newsletter: Red Sea News Community
Information: http://redseainfo.info/

23rd October 2010

Zen
Mod

diyAudio Member

yup
- this one is certainly looking as me - sitting on her shoulder

other
ones are certainly more cascode-like

my Papa is smarter than your Nelson !
clean
thread;
Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

23rd October 2010

spavleski

diyAudio Member

Dear
diyaudio friends,

I just want to underline that the whole idea comes
from who the else but "the fugly"
ZM mind. My sincere contribution was a bit on this Project by means of drawing
PCB's, schematics and giving comments. Anyhow, having made the prototype of this
gadget in balanced mode, my life has been changed, and my searching for the best
possible pre-amp finished.

With regards,
spavleski

PSMLS CookBook by ZM

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