RC4558's in Furman Reverb unit

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buschfsu

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I have an RV1 furman reverb with eq and optical comp unit (50$ at guitarget used). that is noisy as hell. im going to replace the filter caps but don't know of a new low noise replacement for these TI RC4558's. Would the old NE5532 be suitable or is there something better????

this thing could be incredible if i can get rid of the frikin noise!!
 

adamasd

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4558s are not that noisy, or that bad, they have their uses. Get rid of the noise then worry about the opamps.
 

Gus

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The tube screamer is a circuit that uses 4558s

Now I have reworked a number of TSs over the years (starting in 95)
The TI 4558 has a different "sound" when over driven than a JRC4558 or a 5332 etc. Some people like the TI when overdriven(the vox valve tone used a TI). I have not noticed a noise problem with the TI 4558 vs the 5332 , that posted the TS only uses two opamp stages.

Now if you can find Walt Jungs audio op amp book there is a good section about noise with opamp circuits voltage and current noise.

Not knowing what the schematic looks like it would be guessing what would be best maybe a fet input would work better etc.
 

maxwall

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That unit has a real spring reverb inside and AC power transformer mounted near it .

I would try a external transformer approach - remove the internal one wire it distanced away from the circuit board and spring unit. easy. Maybe mount it in a small project box with a fuse, simple RFI suppression circuit and a extra safety ground that can be switched on/off - kinda of like a ground lift switch. Having a safety/chassis ground may help the noise a little.

The real spring and pickups are probably picking up RFI and generally
introduce noise into the audio path. Not much can be done with that design. its inherently noisey. sometimes the spring and its pickups can get RFI from other electronic equipment that gets near it. like in a studio rack for example.

try above before messing with IC's
 

mikep

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I wouldnt change anything. well, maybe the el-caps if they are old enough to need it.

IMO the RV-1 is a fantastic box. swapping the opamps probably won't ruin the magic but I suggest that you use it as-is for a while. noisy as hell? nah, its not like you run your reverb returns with the faders at zero. when you use it in a mix, at appropriate levels, the noise is not that bad. hitting it with the right levels also helps minimize noise. try a fast limiter in front (in addition to the built-in limiter).


mike
 

acrossen

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I had a noisy RV-1 and started off by recapping it. That didn't do much for it. I then swapped out all the 4558 opamps for NE5532s and voila - much quieter and overall better sound.
 

audioforge

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you can find much more mods here:
http://edanders.home.comcast.net/diy/rv1_mod.txt

hope this will keep busy a bit more than just swap the ICs...
let us know how your unit improved....
:wink: audioforge
 

leigh

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Old thread, but seems a good place to add this:

I was troubleshooting a Sound Workshop spring reverb, trying to reduce hum and buzz on the output signal.

The Sound Workshop (242) uses the RC4558 as its recovery amp. I tried some chip swaps, including the 5532. The 5532 had a much lower output signal (lower in overall level). That seems odd, doesn't it? This circuit is supplying 15V bipolar power to the chips, so it's not like the 5532 was underpowered.

I wound up putting in an MC33078 instead, and it had the same signal level as the original circuit, plus a lower level of hum, so it was a definite improvement. I may, however, be getting some audible oscillation on one of the channels now... so further investigation is underway.

Leigh
 

PRR

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Opamp gain is the resistors; gain-drop means something is wrong.

Hum and buzz is NOT the opamps but the power supply. Take it out in a field (far from all AC power) with a couple 15V batteries, there will be no hum.

Fix the problem. It's not the chips.

 

leigh

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PRR said:
Opamp gain is the resistors; gain-drop means something is wrong.

Agreed! Which is why I said it seemed odd - not the expected behavior of an opamp.

Unless... there was some idiosyncratic thing I was overlooking, and, with the 5532, the only candidate I found for that would be the diode limiters on the input. Hard to believe that the output from a spring reverb pan would be swinging higher than 0.6V, but maybe... I'll take a look on the scope. With healthy signal, the multimeter was reading about 0.2V (RMS of course) coming off the pan, going into the recovery amp. So maybe I should check the scope to see the peaks. But, again, this is not likely the issue.


PRR said:
Hum and buzz is NOT the opamps but the power supply. Take it out in a field (far from all AC power) with a couple 15V batteries, there will be no hum.

Fix the problem. It's not the chips.

In this case, the chips are socketed, and it was quick to try out a few options. Swapping out power bypass caps will take further dissassembly and, of course, soldering. So I was checking for a quick fix. This box may or may not justify further digging, it's just a matter of balancing priorities and available time.

Also, in this case, swapping the chips DID make a difference. Because I don't like to trust my ears' "memory", even when making a relatively quick chip swap, I made recordings before and after. The new chip is an improvement, perhaps due to a higher Supply Voltage Rejection Ratio. (The MC33078 is rated at 105dB typical for that spec. The RC4558 lists that spec as a supply-voltage sensitivity, of 30 microV output/V input typical, which if I'm not mistaken translates to a ratio of about 90dB.)

This recording was made from the output of the spring reverb into a line input (on a Zoom H2 recorder). The WAV files were dumped into the computer, then gained up 48 dB. First you hear the output with the RC4558 (stock) recovery amp, and then with the MC33078 replacement:

http://www.leighm.dreamhosters.com/tapeop/comparison_RC4558_then_MC33078.wav

Anyways, that's the full report up to this point. I may dig into cleaning it up more, or just roll with it as-is.

Leigh
 

abbey road d enfer

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leigh said:
PRR said:
Opamp gain is the resistors; gain-drop means something is wrong.

Agreed! Which is why I said it seemed odd - not the expected behavior of an opamp.

Unless... there was some idiosyncratic thing I was overlooking, and, with the 5532, the only candidate I found for that would be the diode limiters on the input.
Not very likely. Anyway, due to voltage NFB, the opamp's inputs see only a minimal fraction of the input voltage. I would tend to think an oscillation would be the culprit.
 

Gus

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Something that can fool you is the socket contact to leads.  If you changed the chips and the circuit sounded better you might have just cleaned the socket contact by removing the original chip.  Did you reinstall the original chips?  Did you look at the leads to see if they were oxidized etc.

Sometimes removing a chip from a socket and reinstalling it with cleaned leads "fixes" issues
 

leigh

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Gus said:
Something that can fool you is the socket contact to leads.  If you changed the chips and the circuit sounded better you might have just cleaned the socket contact by removing the original chip.  Did you reinstall the original chips?  Did you look at the leads to see if they were oxidized etc.

Sometimes removing a chip from a socket and reinstalling it with cleaned leads "fixes" issues

Good point, for sure. I did take a look for oxidation, but I could look closer.

However, that sound clip I posted was made *after* a couple different swaps, so it did get a chance to get its leads cleaned through pulling and replacing.
 

leigh

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PRR said:
Hum and buzz is NOT the opamps but the power supply.

Ha! It of course came back to this... the spring reverb "recovery" opamps are on the far end of the circuit board from the power supply... and, contrary to my assumptions, there were no local bypass caps in place to clean up the power for those opamps. So, there was 12" of circuit board trace between the power supply's voltage regulator and the opamps, and that was it for power conditioning.

I had seen a bunch of small ceramic caps around the recovery opamps, and assumed that they were bypasses (again, I'm doing this work without a schematic). Not a fair assumption, I guess.

Adding 0.1uF caps to the rails cleaned everything up.

Leigh
 

Blondino

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Hi guys,
I don't know if this threads still up, but I was looking to replace a couple of potentiometer for my RV1 that are just noisy and uncleanable. I know witch value are the pot but seems like I can't find the brand or the series trough the pot number. I don't care about the brand, but I would like to swipe it with something that fir the PCB. Anyone knows what kind of pot are those?

and weird question: you think is possible to find the spring inside? I was thinking to build a second unit from scratch.
Thanks
 

hodad

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Finding an exact match for a pot that was made 30 or 40 years ago is not always easy. Do some careful measurement (shaft diameter, shaft length, lead spacing, diameter of the body of the pot) and see if you can find something that is very close in size and specs to what you're looking for. It's possible too that a picture or two might help you to find the mfr.--someone here might recognize the pot even if they're not familiar with the Furman unit.
 
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