I have a Blues Jr B-138490. This has the worst reverb I've ever heard. It's been to a repair shop twice. It just barely has any reverb. You can turn the control from 0 to 10 with no noticeable change. The reverb is there but super weak. Shop said input and output reversed. No change from 1st time I took it in. Not ever going to that shop again.
Looking at it, the circuit looks straight forward, with one dual op amp. What I propose is replacing the accutronic's tank with an MOD 8EB2C1B, and since there is only the one op amp I propose to replace it. My questions:
1. Best op amp to use
2. Source to buy the op amp I am going to put a socket in so I can try different IC's with ease.
Looking at it, the circuit looks straight forward, with one dual op amp. What I propose is replacing the accutronic's tank with an MOD 8EB2C1B, and since there is only the one op amp I propose to replace it. My questions:
1. Best op amp to use
2. Source to buy the op amp I am going to put a socket in so I can try different IC's with ease.
Which op amp is in there right now? Just trying to figure out which version Blues Jr you have. If it's TL072 earlier version or a 4560 later version. The earlier one had a pretty bad way of routing the reverb around the circuit. There is also a "bright cap" across the reverb pot which I suspect is a reason most people find it a tinny sounding reverb when the pot is on low setting.
A TLO72 is currently installed. Yes C26 will affect the tone of reverb, but that is not the problem. The problem is the reverb acts like it's on the lowest setting no matter where the reverb knob is set. I thought about changing the TLO72 to something else, but in this circuit I don't think it matters much.
Yes, I also wonder which version.
Has it got the correct tank and is it working correctly. That is where I would start.
Should be a 28055 tank.
Has it got the correct tank and is it working correctly. That is where I would start.
Should be a 28055 tank.
I 've already ordered an new delay line. I went with a MOD instead of the Accutronics. Since the OP Amp and the delay line are the major components, I decided to start with the delay line. As long as I have it opened up, I'm thinking of replacing the TLO72. This isn't a complicated circuit. It could be a discrete component, but I doubt it and the is no sign of heat or a leaking cap.
The MOD tank is a good choice---it's better than the Accutronics. An OPA2134 would be an upgrade from the TL072---its specs are definitely much better; whether or not it is audible is open to debate, but for a coupla $$, why not?
The TL072 is the best choice for this amplifier. They either work or they don't.
It is not Hi Fi so don't waste you money and time.
It is not Hi Fi so don't waste you money and time.
I disagree; particularly in the reverb recovery circuit. The OPA2134 will be significantly QUIETER (~7db) than the TL072. A hissy reverb is annoying.
Yes, this is to be expected fromt the datasheet numbers. Both have FET inputs, so the voltage noise is the dominant hiss contributor.
I would also opine that the value of resistor R40 in the BJ's reverb recovery circuit is an order of magnitude too high---it should be ~ 1KΩ, not 10K. This is also contributing to the reverb's poor performance.
He's not saying it hisses. It is super weak. Any good opamp will fix that, IF it is the opamp. When that does not work, the pot is a good next bet. After that it comes to signal-tracing.
To be fair doesnt it totally depend on what the source impedance presented to the OP amp input?
I.e. from the little I know, A high Z input would actually be better off with a jFET input lamp, such as the TL071/2, or LF351/3, and noise wouldn't be improved with the use if a BJT type like the NE5532. Whether it's worth the OPA is anyones guess. Its something i have never bothered to do with my amp, most the hiss comes from the valves anyway!
But I do wonder, it sounds like you may have a bypass cap gone bad on a PSu rail supplying the OP amps, or other excess load on a single rail.
Maybe a dead regulator IC? Or a dead OP amp, that would also draw excess current or load something upstream
I.e. from the little I know, A high Z input would actually be better off with a jFET input lamp, such as the TL071/2, or LF351/3, and noise wouldn't be improved with the use if a BJT type like the NE5532. Whether it's worth the OPA is anyones guess. Its something i have never bothered to do with my amp, most the hiss comes from the valves anyway!
But I do wonder, it sounds like you may have a bypass cap gone bad on a PSu rail supplying the OP amps, or other excess load on a single rail.
Maybe a dead regulator IC? Or a dead OP amp, that would also draw excess current or load something upstream
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It happend to me once. The foam spring protector was still in the reverb tank.
Removed it and voila... Reverb.
But it can be somenthing different to.
Send the signal towards the springs in to another amp.
Is it loud enough? Then that part is probably ok.
Connect the signal towards the springs to the connector carying the output of the springs.
Place a potmeter of 47K lin in between.
Set the pot to max and slowly turn it.
Is it stil ok?
Check with another reverb can.
Removed it and voila... Reverb.
But it can be somenthing different to.
Send the signal towards the springs in to another amp.
Is it loud enough? Then that part is probably ok.
Connect the signal towards the springs to the connector carying the output of the springs.
Place a potmeter of 47K lin in between.
Set the pot to max and slowly turn it.
Is it stil ok?
Check with another reverb can.
I owned a Blues Jr. for a very short while. I didn't bond with it, but the stock reverb was anything but weak - it was the opposite! All usable reverb settings were right around zero on the dial. Turn the reverb knob beyond 2 or 3, and you were in surf city - far too much reverb for any kind of music I play.
So I actually modded my Blues Jr. to reduce the amount of reverb, so that more of the reverb knob's range was usable.
It's been a few years now and I no longer remember exactly what I did - most likely I changed the value of the reverb mix resistor.
Oh yeah, I don't recall any audible hiss from the reverb. But I don't play as loudly as many guitarists do, so it's possible that hiss is a problem if you turn up loud enough.
-Gnobuddy
If you have one of the "green board" reverbs in your Blues Jr., here's a mod that will improve it:
Billm Audio >> Improving Green Board Reverb
Billm Audio >> Improving Green Board Reverb
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