question about yjm308 "grey" mod

[foreverman1022]

Hello to all,

I ran across this in one of the USENET newsgroups:

"Hello all,

The YJM308 from DOD, like the 250 Reissue is a great Overdrive Pedal, but
many
people still prefer or wish they could get their hands on an old GRAY DOD
250.

Most desire these over the yellows, re-issues and the newest YJM308 Yngwie
version.
However on EBAY the GRAY pedals go for as much as $300+ now.
Of course the grey version is the one most often associated with Yngwie
prior
to the release of the 308.

For my own personal use, I had a goal to both make a modern "Clone" and a
"Mojo" exact clone of the GRAY pedal using the newest YJM308 as the basis.
(I have also been working with some other folks this past year on guitar
related circuits, designs, modifications and products).

ANALOG MAN who is famous for his Ibanez TS9 to TS808 pedal mods worked
with me
on this project and was so impressed , he plans to soon offer these mods
to the
public.

http://www.analogman.com/

analogmike@[EMAIL PROTECTED]


While the YJM308 was an excellent pedal, it used some modern opamps
components
and subsequent EQ tweaking to match the tone of the older 250 pedals as
closely
as possible while trying to reduce noise.

Some people feel that while the YJM308 is excellent, it does not EXACTLY
match
the tone of the older grey pedals 100%.
The consensus seems to be the 308 has less low end, slightly more treble,
is a
bit thinner and "feels" different response-wise. It sounds great, but is
indeed
slightly different.

Many people love their 308 pedals, but would also still love to have a
"grey"
pedal in their collection for tonal variety.

With these mods, components are physically removed and substituted to
IDENTICALLY match the original specs of the grey DOD 250 pedals.
No emulating here... the pedal is converted into a copy of a grey DOD just
like
Analog Mike turns a TS9 into a clone of an old TS808.

We used the original DOD factory schematics from the 1970s and three (3)
grey
DOD pedals for reference.

Some of the modifications include:

Changing the stock 0.001uf input cap to 0.01uf improves low end and
exactly
matches original gray circuit design.
Stock YJM308 has some low end roll off.

A 25pf capaciter was added to the YJM308 circuit as an apparent "tweak" by
DOD
engineers to try and smooth the high end edginess of the 4558 chips to
adjust
them to sound like the older 741 circuits.
The 4558 being an "improved low noise dual replacement for the old 741"
has
more hi-frequency response to be toned down.
This small 25pf cap tweak is not needed with the change to a 1458 or 741
opamp,
nor was it a part of the original grey circuit.

A true purist will desire to clone the old Gray 250 by putting a single
741
opamp in this circuit and re-routing the pins in the existing dual opamp
pin
layout so it will work.

This is not needed if the Dual 1458 Opamp from Texas Instruments is used
since
the MC1458 has IDENTICAL specs as both the original LM741CN and UA741CP,
however a "mojo" mod will be available which is the ultimate in cloning
the old
grey pedals... it will put an old 741 single opamp into the slot.

TI even admits in it's literature the MC1458 is actually just two
UA741opamps
on a single IC... thus all the specs like Max Voltage gain, slew rate,
ramp,
recovery, bias are identical to the old UA741.
This is handy for use in this mod since the Dual 1458 and Dual 4558 share
the
same common 8 pin layout and make for an easy direct swap.

Again a purist may desire the original 741 opamp installed instead of the
1458
(Dual 741) but we are unable to hear any difference since the 1458 is
technically an authentic "Dual 741" opamp.
The mod is a cleaner wiring job with the 1458 since the YJM308 board
socket is
soldered to use a dual chip and the old 741 was only a single ship.
The "mojo" mod to a 741 chip requires some clipping, jumping and rerouting
of
pin assignments to make the 741 work in the dual 8 pin socket.
By contrast as mentioned above, the 1458 is a direct swap.
The overdrive circuit simply uses only 1/2 of the chip's dual 741 amps.

I compared this "Gray Mod" 308 to two (2) original Gray 250s I
have............... absolutely NO DIFFERENCE can be heard.
Analog Mike actually thought the mod possibly sounded a little better than
his
original grey pedal.
This could be due to the variations found in those older hand-wired
pedals.

Everything is the same... the better "tubey" feel and tone as compared to
the
slight transistory tone of the newer pedals.
There is slightly more noise but heh.... everybody using these Overdrives
with
a maxxed out Marshall already know they need a Noise Suppressor pedal
anyway.
And of course the original vintage greys are a bit noisy !!
The BOSS NS-2 is the suggested pedal for this purpose.

The perfect tone match to the much-sought-after "magical" Gray makes
sense.
After these mods, you actually have a 99.99% authentic "new" GRAY DOD 250
with
the identical cap and resistor values used in the old circuit, along with
the
"Dual 741" (1458) opamp with identical specs to the old 741 used in the
originals.
Go for the "MOJO" mod and be 100% authentic with the 741 if you desire."

Besides changing the opamp and input cap, what other components would need to be changed and to what?  Thanks in advance to anyone's response

[phillip]

Try building this instead:

http://fuzzcentral.tripod.com/liquid.html

I think you'll like it even more than the old Grey OD250  Pete Moore and a few others from here have built the Liquid and I've had nothing but positive feedback about it

Phillip

[petemoore]

Try building this instead:

http://fuzzcentral.tripod.com/liquid.html

I think you'll like it even more than the old Grey OD250  Pete Moore and a few others from here have built the Liquid and I've had nothing but positive feedback about it

Phillip

Yupp, the L.D. continually starts in the 'pole position', and very convincingly wins the races every time !!!
 Has very respectable S/N ratio [a 'quiet' pedal], grinds consistantly between 150-220 grit {built as shown], and has a more ... Liquid ... quality to the tone.

[tungngruv]

There is a gray OD 250 on Ebay now and the guy posted a pic of the inside. Doesn't look to magical but I'm sure it sounds killer! You know, I love how simple this design is yet it rocks so hard in front of an overdriven amp!! This design truly is a classic. Here's a pic that he posted;