SS Amp Reverb Driver ?

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PB2

PB2

Member
Joined 2004
linkedin.com/in/petebasel
I've been working on several small SS amps with reverb and one uses the NJM4558 OP
amp or similar to drive the reverb. The NJM4558 has weak output drive and will do 13Vp
into 2K loads or 6.5 mA (42 mW):
https://www.njr.com/electronic_device/PDF/NJM4558_E.pdf

Found a Peavey and a Fender that use the NJM4560 that does 10 Vp into 400 ohm loads
or 25 mA (120 mW):
https://www.mouser.com/datasheet/2/294/NJM4560_E-365030.pdf

I wonder if anyone has tried the high current NJM4556A that can do +/-70mA into 150
ohm loads (375 mW), seems that it would be a big improvement:
https://www.njr.com/electronic_device/PDF/NJM4556A_E.pdf

Seems that most amps with a 12AT7 driver do about 1W into the tank, and the NJM4556A
comes close, the dual OP amp could be paralleled for nearly the same power. Seems a
150 to 200 ohm reverb tank would work best with it.

Anyone tried the NJM4556 OP amp?
 
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JMFahey

JMFahey

Member
Joined 2009
I wouldn´t diss Dick Dale by any means,**specially** on his Reverb sound.

Currently nobody really cares bout Reverb, it´s just a secondary effect, so puny 42mW out of a single generic OpAmp "seems" to be fine, BUT if you can drive them hard (nearing 1W) sound becomes GLORIOUS.

Serious amps such as some Yamaha, Roland, Lab series, etc. used a transistor BOOSTED Op Amp and now we´re talking.

Absolute best Reverb EVER I heard or built was a project by SSGuitar member PHATT, he designed one with an Op Amp driving heatsinked TO220 transistors, fed from +/- 35V rails, absolutely bone crushing Reverb.
 
PB2

PB2

Member
Joined 2004
linkedin.com/in/petebasel
Right, if it has reverb it should work reasonably well.
My son has a Fender Deville mostly tube amp but the reverb driver is from memory a
TL072, far too weak IMO.
I looked it over when one output tube was red plating and he also commented that the
reverb didn't seem to work. I think it was just very weak.

We have a small Peavey Backstage 50 with weak reverb, and the Ibanez TB25R also has
weak reverb. So, I do think that there is something to using puny OP amps.

We also have a Peavey Bandit 112 that I'm recapping right now and it has an OP amp with
a transistor booster on the reverb. I expect that it will do better than the others.
 
P

Printer2

Member
Joined 2010
I have a number of single coil reverb units from Yamaha organs. The drive coil is 3 ohms resistive ana 100 ohms R out. I still have work to do on it but I drove it from a chip amp and boosted the return with a mu amp and source follower. I will need to try it at a higher voltage, just used 12V to see if it would work. The only real different thing I did was to take the signal from the volume control (BF Champ styled circuit) and returned the signal to the cathode of the second stage triode. In this way I do not muck up the gain of the Champ with a pair of mixing resistors. I was thinking it of a relatively painless way to add reverb (without a pedal) to an existing simple amp.
 
PRR

PRR

Member
Joined 2003
Paid Member
JMFahey said:
I wouldn´t diss Dick Dale by any means,**specially** on his Reverb sound.
....an Op Amp driving heatsinked TO220 transistors, fed from +/- 35V rails, absolutely bone crushing Reverb.
Click to expand...

I don't think I dissed Mr Dale. But his tone is rare, near unique. 99 and 44/100% of guitarists don't need that much wetness.

+/-35V might be worked more conveniently with the speaker-amp chips, LM3668 etc. While over-kill for 150 Ohms the simplicity is appealing. Some could be worked near +/-10V for big power in 8 Ohm nominal tanks (which are to be favored because so many Fender etc TUBE amps used low-Z tanks so are easy to find). There's also 12-14V auto-sound amps.
 
PB2

PB2

Member
Joined 2004
linkedin.com/in/petebasel
Printer2 said:
I have a number of single coil reverb units from Yamaha organs. The drive coil is 3 ohms resistive ana 100 ohms R out. I still have work to do on it but I drove it from a chip amp and boosted the return with a mu amp and source follower. I will need to try it at a higher voltage, just used 12V to see if it would work. The only real different thing I did was to take the signal from the volume control (BF Champ styled circuit) and returned the signal to the cathode of the second stage triode. In this way I do not muck up the gain of the Champ with a pair of mixing resistors. I was thinking it of a relatively painless way to add reverb (without a pedal) to an existing simple amp.
Click to expand...

If you believe Rod's discussion about current drive you could use both halves of an NJM4556A with 150 ohms in series with each output. That is about as simple as it gets,
of course most of the power goes into the resistors and I'm not sure if it would be enough drive.
 
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PB2

PB2

Member
Joined 2004
linkedin.com/in/petebasel
I have two broken tanks:
One from a small Fender PR225 SS amp with 26 ohm DCR input and open output.

Another that looks like a very old large Accutronics 2 spring type, this also has 180 ohm
DCR input and an open output. Not sure what it came out of.

Perhaps the very fine wire for the higher Z output is more prone to breakage.

Here's a link to the Accutronics site but it seems to use flash which is no longer supported:
Untitled Document
 
P

Printer2

Member
Joined 2010
PB2 said:
If you believe Rod's discussion about current drive you could use both halves of an NJM4556A with 150 ohms in series with each output. That is about as simple as it gets,
of course most of the power goes into the resistors and I'm not sure if it would be enough drive.
Click to expand...
If I were starting from scratch I might pick a few up but I will probably cobble something together with all the crap I have. I am not a drippy kind of guy, I do like some to sweeten up the sound though. At some point I would need a delay unit to go with it. I will have to have to put an effects loop in an amp to accommodate them and tremolo. The driving I was not too concerned of, I was thinking of trying a switched amplifier next. The power from a smaller SMPS. I have acquired too many of them also. The thing I want to really work out is the recovery and feeding it back into the cathode circuit. Measure what is needed and set the goals from there. I just had a bunch of stuff laying around and did a quick test and have no idea what the signal levels were. I really need to reset up my test bench.
 
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