What can be expected by replacing the TL072 op amp in the Rebote 2.0 and 2.5 delays? I've heard of people using the OPA2132P or JRC4558D. I also noticed there's a OPA2134. What are the result from changing it out?
if it has the same pinout... it will work i guess... might slightly change the tone?, the worst that can happen is that it doesnt work :P
I thought I read something about it cleaning up the repeats?
in the mad prof deep blue delay, an OP275 is used instead if i remember right.
cheers,
lohstah
Quote from: gnugear on March 01, 2009, 03:12:12 AM
I thought I read something about it cleaning up the repeats?
Where?
I don't see how it would clean up the repeats honestly... the repeats being dirty are just part of the pt239x sound... especially the longer the delay. It's decently clean around 250-300ms or so. The opamp is just buffering/slightly boosting the signal (along with rolling off high end) and providing a mixing platform.
Ah, thanks Brian. With that in mind, do you know which op amps would roll off less high end? I actually like brighter repeats (think Deluxe Memory Man) and most of my pedals usign the PT239x chip are darker.
Quote from: gnugear on March 01, 2009, 12:57:37 PM
Ah, thanks Brian. With that in mind, do you know which op amps would roll off less high end? I actually like brighter repeats (think Deluxe Memory Man) and most of my pedals usign the PT239x chip are darker.
The Rebote is filtered so that it sounds more like an analogue delay. You can make be brighter sounding overall by tinkering with the filtering capacitors on the output of the chip.
What I would do is compare the Schematic of the rebote with the datasheet. On the data sheet they show you some of the common applications of the circuit and even include schematics of how the company that make the chip recommend you use it. What I would do is look at the capacitors used on the data sheet and then look at those used on the rebote. Then just split the difference.
It is very unlikely there is anything in the data sheet in regards to getting a lo-fi or analogue sounding delay, as those things arent really a concern with a chip that was intended to be used in karaoke machines!
Quote from: gnugear on March 01, 2009, 12:57:37 PM
Ah, thanks Brian. With that in mind, do you know which op amps would roll off less high end? I actually like brighter repeats (think Deluxe Memory Man) and most of my pedals usign the PT239x chip are darker.
as stated above, it really isn't the opamps that are making it darker. It is the caps going to ground around the last opamps (Low pass filters) for the most part. Keep in mind though - the reason they are doing this is to keep down the noise... the brighter you make it the noisier it will be. Take away all the low pass filters and you'll hear alot of yucky digital-ness in the echoes as well as noise.
bw
Can someone give me a link to the schem/schems? Cant find it, thanks.
Is Google broken? Try rebote schematic and PT2399 datasheet
Hi
the JRC4558D is almost a dead dinosaur. Almost anything else will be quieter.
Use something more modern.
cheers
The ne5532 also works well in this pedal and is certainly good enough for guitar.
cheers
Hi
the NE5532 is a great op-amp for many applications (eg.g tubescreamer). It is VERY quiet.
However, the input impedance is quite low.
It's too early in the morning for me to work out whether this will cause volume loss in the Rebote. (I *think* it will, because the first stage uses a 510k input resistor, which will form a voltage divider with the 5532's 100k input impedance.)
If there is a loss, you could increase the feedback resistor in the first stage to 1M to compensate.
cheers
I have used an OPA2604 in the Echobase and Magnus and the result was a better signal to noise ratio.