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2006-02-24 by doktazaus
Hi, I'm new to this group... Does anyone know the procedure to turn up the level of the reverb send and turn down the return level? Looks like it will involve changing out some resistors. This is supposed to reduce the noise in the reverb circuit. Also, can anyone advise on the usefulness of changing out all of the lm301's on the 4-2 board and replacing with high slew rate chips? Thanks in advance for any help... s
2006-02-25 by Michael Bacich
Also, can anyone advise on the usefulness of changing
out all of the lm301's on the 4-2 board and replacing with high slew rate chips?
2006-02-28 by stephen schoener
On Feb 24, 2006, at 4:24 PM, "doktazaus" <schoener@...> wrote:Also, can anyone advise on the usefulness of changingout all of the lm301's on the 4-2 board and replacing with high slew rate chips?You can't simply swap LM301's in an ARP 2600 with any other type of opamp. The circuits all depend on the LM301's non-frequency-compensated characteristics. If you really want to try other opamps, you will have to do some redesign in each of the circuits that use the amp, and the requirements would be a bit different for each circuit. For the most part, it usually just means removing the compensation cap associated with each opamp (at pin 1 and pin 8), particularly when they're used as audio opamps, as they are on board 4-2. If you wish to try it and see if it seems to improve the audio quality, you might try it first at A25, which is the summing amp for the mixer that sends signals to the main outputs. If you hear some discernable improvement, then it might be worthwhile doing it elsewhere, too (A26, A27, A29, A30, and A31), again, always removing the cap found at pin 1 and 8. I would probably try using TLO71 or TLO81 opamps in those spots, because the pinout is the same, and they are know for their low noise in audio apps. However, you may be disappointed to find that replacing the amps with low-noise, high-slew amps may not make much difference to your ears. That has been my experience with opamp replacements that I have tried in other gear. Noise is usually more circuit desugn issue than a opamp selection issue. Please do let us know what happens if you try it.Regarding the reverb, you could try decreasing the value of R273 on the 4-2 board. It (in conjunction with various other parts) determines the gain of the reverb spring driver. Right now, it's 100K -- you could roughly double the gain by replacing with a 47K (or by simply paralelling another 100K resistor across it). This may or may not give you the desired result -- it may cause audible distortion or unwanted artifacts in the reverb, but it's probably worth a try. I would not go much lower than 47K, however. As far as reducing the reverb return gain, all you need to do is turn down the two reverb sliders on the front panel. They are essentially reverb return level pots. If you want to permanently reduce the reverb return gain, you could increase the value of R288. It's now 2.2Meg, and replacing it with a 1 Meg would roughly reduce the return gain by about half. Personally, I'd probably keep the return gain as it is, which would allow for even more dramatic reverb effects, with your increased reverb spring drive.Michael Bacich
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2006-02-28 by Antoine Deschênes
That's a trick with a lot of equipment I think. You can do the same with a Kawai K5 to get an acceptable output level and less noise (Specs are ~ -52dB SNR) stephen schoener a \ufffdcrit :
> FYI, I did change R173 on the 4-2 board from 100k to 47k and the > reverb is much louder with much less noise. Not bad... Thanks for > the help! > > s