4558 question

[tcobretti]

I have a practice amp with an njm4558dd as the primary chip in the gain stage.  The amp sounds like crap so I was thinking about simple mods I might be able to do.

What's the difference between the 4558d and the 4558dd?  

I've tried mouser and google and can't find a way to compare them, so I thought somebody here might have some bright ideas.

Thanks,
travis

[niftydog]

one has one d and the other has two d's.

There's zero sonic difference between them.

[WGTP]

I've messed with quit a few op amps, and they don't sound different enough to make somthing that sounds like crap sound great. IMHO you need to look elsewhere for your soulution.  My PV Special uses 4558's sort of in a Distortion + configuration.  Good luck

[sir_modulus]

I'ts poor amp design. To prove this, shove some othe jelly bean Dual OA in place of the 4558. If the sound only very marginally improves, or stays the same (more likely), then look at the circuit that uses the OA, or the rest of the amp.

[Paul Marossy]

Yep. No such thing as a magic opamp...  :shock:

[tcobretti]

Thanks for the advice.   I was thinking that if the dd was higher gain maybe I'd try to d to mellow out the gain a little bit.

In the south we say, "you can't polish a turd,"  and I guess that applies to practice amps, too.

[sir_modulus]

Isn't the gain of an opamp set through resistors? In which case, maybe you can polish the turd (slight bit only) by tweaking the gain resistor (it most likely will be in te feedback loop, and in parallel with the diodes).

[Paul Marossy]

I believe that the "D" and "D" apply to the temperature rating of the IC chip, not the gain. And, as sir_modulus said, the gain is set by resistors and how the feedback loop is used.

[tcobretti]

A-Ha!  I'm clearly unfamiliar with opamps and wrongly thought they worked similarly to transistors.  I'll do some research and let you know if your suggestion pans out.

[ragtime8922]

Check the diodes comming off the opamp. When there is a set up with two diodes in parallel, placed in opposite directions, and one of the diodes is removed there is a very "test book" crap sound delivered. There isn't a huge chance of there being a bad diode but rather a bad connection, cold solder, etc...

[JHS]

What's the difference between the 4558d and the 4558dd?  


D=single shielded
DD= double shielded
DD only from JRC

JHS

[tcobretti]

Thanks JHS for the answer.

I compared the circuit to a TS and it seems to lack the diodes and a master volume. So, I am guessing,  as you crank the gain you're overdriving the both the second stage of the opamp and the power amp which creates a very square non-musical distortion.  I just went and soldered in some diodes where they would be on a tube screamer and have actually gotten a pretty cool sound out of it.  It reminds me very much of the mystery Billy Gibbons sound - that weird fuzzy tone he's used (occasionally) forever.  I have no idea what he uses, but this sounds similar to me.

[Steben]

Try some LED's instead of the "normal" diodes, you'll be amazed the change is less subtle than you would imagine (in the positive sense off course).