Modding A Marshall 5005

[Superlizard]

Now, this isn't something I'd be interested in doing, but perhaps some of you who own one would be interested in this particular mod.

Buddy of mine on another board decided to change a few op-amps in his 5005 for better tone... not unlike modding a stompbox.

As he says:

I'm going to change out the op-amp in it. The original is a MC1458p. I've ordered a socket and a couple each RC4558p and TL072. Why a couple? Because I amp going to try stacking them too. I will try a pair of 4558s and will probably try a pair of 072s.

So I started with a pair of stacked 4558 chips. I decided to jump right into the stacked chips as I was going to have to solder all of these each time. In for a dime, in for a dollar. Laughing

Wow! Distortion is "more" and a bit smoother. Some more of that SS raspy-ness is gone. These op-amps (RC4558p) rolled off the highs. I can dime the treble tone control. Amp isn't overly bright. The down side is that the noise floor of the 4558's became apparent when I dimed the gain. The hiss turned to squeal. I upped a resistor inter-stage to try and tame it, but it really didn't help much.

On the the TL072s. These are a higher quality dual op amp. Now the treble is back. I can turn that down at the treble control though and it's great. The noise floor with these op-amps is much better. I returned that inter-stage resistor to it's original value. Now the amp has all kinds of gain and it's not as raspy as it was.

Very cool mod!!!

The chips are literally stacked one on top another and soldered together at the legs. This is something Dave Barber seems to have pioneered in the effects world. What you get is a lowering of input and output impedance from the parallel dual op-amps. In this case the amp got more drive and it smoothed the OD out a bit as well.

See the right side of this photo. This is the amp's PCB.

In retrospect I liked the tone of the 4558s better, but the noise issue was the determining factor.

 

[jimh]

Interesting..... I had'nt thought of stacking chips before. Might give this a go on some pedals.  I;ve got an old Boss Turbo Overdrive that I'd be happy to pull apart.

Cheers SL  :icon_thumright:

 

[Superlizard]

Interesting..... I had'nt thought of stacking chips before. Might give this a go on some pedals.  I;ve got an old Boss Turbo Overdrive that I'd be happy to pull apart.

Cheers SL  :icon_thumright:

Uh oh!  The mad scientist is concocting an uber-stomp... replete with 100 stacked op-amps!  :icon_jokercolor:

Cheers -

 

[jimh]

My op-amps go up to infinity!!!!

 

[mayfly]

My op-amps go up to infinity!!!!

but only in theory  :icon_biggrin:

 

[bigguspickus]

If those op amps are facing the same way, then by stacking & soldiering, you're effectively wiring them in parallel... only naughtier. :icon_smile:

 

[Cagey]

Indeed. Have to call it "Brokeback Marshall". "I wish I could quit you..."

 

[bonepickerx]

Tell your buddy to try an LM833N

Very good sounding OP-Amp. I use them in lots of mods (sounds great in a Stereo Memory Man). The 833 is between the 1458 and the 4558 in gain. It is also the lowest noise of all the 8 pin Dip Stereo Op-Amps, one would use in this type circut. The reason is not widely used is in most cases it costs double what the TLO-72, 1458 and the 4558 costs.

 

[mayfly]

Tell your buddy to try an LM833N

Very good sounding OP-Amp. I use them in lots of mods (sounds great in a Stereo Memory Man). The 833 is between the 1458 and the 4558 in gain. It is also the lowest noise of all the 8 pin Dip Stereo Op-Amps, one would use in this type circut. The reason is not widely used is in most cases it costs double what the TLO-72, 1458 and the 4558 costs.

Second for the LM833N  - besides the uber expensive Burr-Brown op amps, these are my favorite.

 

[Patrick from Davis]

The Burr Browns are not that expensive.  $2.61 vs $0.57 for the LM883N at Mouser.  A couple of side notes, the Burr Browns really do a job on a Tube screamer, and even though TI owns them, the ones I got still have the Burr Brown printing on the chips.

Mouser Links....

Burr Brown (now owned by TI) OPA2134
LM833N

Patrick

 

[Cagey]

The Burr Browns are not that expensive.  $2.61 vs $0.57 for the LM883N at Mouser.  A couple of side notes, the Burr Browns really do a job on a Tube screamer, and even though TI owns them, the ones I got still have the Burr Brown printing on the chips.

Mouser Links....

Burr Brown (now owned by TI) OPA2134
LM833N

Funny how rumor spreads, isn't it? The Burr-Browns are only considered "expensive" by OEMs who buy them by the bajillion. In their case, an $.08 cent premium on a part is outrageous; a $2.04 difference would be considered blatantly criminal. But, that's just because a million of anything is a lot. For your average Joe who's buying them one part at a time, they spend more on gas to go get the bloody thing than they do on the part itself. So, they're not expensive at all. But, somebody reads an article that quotes some industry "insider" saying the parts are "too expensive", and before you know it everybody thinks the same thing. Came from a good source, right?

 

[Superlizard]

Well that settles it then - one of youse has to do an op-amp Tone Test.  :laughing7:

 

[Cagey]

I don't need convincing about the Burr-Browns. I don't think anyone does. It's widely accepted that they're better parts. But, they're not "expensive" as is often cited as a reason to not use them. $2.57 for a high-end op-amp is nothing. I've paid more for low-grade fast-food hamburgers.

 

[mayfly]

Gentlemen,

I stand corrected on the Burr-Brown op amp price.

 

[Dan025]

i have always been surprised that a tone test like this hasn't been done on here.

i have a ts-7 that i took apart years ago and never put back together, i also have a super overdrive that i have grown tired of, i just need to work up the motivation to go mad scientist on them.

 

[bigguspickus]

I remember seeing an op-amp tone test somewhere a few years ago. They were using an ART Tube preamp, and I think, out of 5 or 6 tested, they said the Burr-Brown single op-amp chips sounded the best, though they had to wire 2 together side by side to replace the dual op-amp chip in the board.

 

[Superlizard]

I remember seeing an op-amp tone test somewhere a few years ago. They were using an ART Tube preamp, and I think, out of 5 or 6 tested, they said the Burr-Brown single op-amp chips sounded the best, though they had to wire 2 together side by side to replace the dual op-amp chip in the board.

  Interesting... I have 3 of those ART thingies.  Can't really complain about them, however... so no need to go warm up the iron.

But it's tempting.  LOL

 

[Patrick from Davis]

As far as the different chips in the Tube Screamer, some are warmer and some are not.  Really, it is quite hard to tell if you swap them out.  The easiest thing to hear is the increase or decrease in volume, but the tone is really the same.  The Burr Brown in a Tube screamer with a couple of other mods (the Landgraf mods) is also known as the Clay Jones Over Drive.  If you want to spend a lot on a tubescreamer copy, go ahead and try to find one.  The chips may be higher fidelity, but with that overdrive circuit (TS808), it is tough to tell a difference.  The Burr Brown lets you have a bit more meltdown area of overdrive.
Patrick