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jcsifu
Copper Member
USA
47 Posts |
 Posted - 08/05/2009 : 20:55:09
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So I just acquired through a gift, an Ibanez GE-601 that has a lot of noise that is hiss. I can't find a schematic or any other info on it anywhere to try to figure it out. My plan of action so far would be to just replace all the polarized caps. Anyone have any advice or quiet mod info for this old pedal?
thanx for any clues,
jc
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/05/2009 : 22:00:23
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| Replacing the opamps will usually yield a reduction in the noise. Can't see from the pics what sort they are? |
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jcsifu
Copper Member
USA
47 Posts |
Posted - 08/06/2009 : 05:48:49
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Ok, it's a MC1458p. I've been looking for subs, but it is becoming obvious that I have no clue as to what I'm looking for. Should I be looking for high speed or high fedelity or something different? I have seen these perameters reffered to in my search.
I'm unable to load the data sheet, but this is the site with the specs.
Thanks Laurie,
jc
http://pdf1.alldatasheet.com/datasheet-pdf/view/27232/TI/MC1458P.html |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/06/2009 : 07:16:33
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| This is a standard dual op-amp configuration. Swapping for a low noise/high fidelity type should improve things dramatically. If it was me I'd try the old standard - OPA2134PA. Solder in some sockets (if they will fit) and try the OPA2134PA. If that doesn't chage things (unlikely), maybe try some JRC4558's. |
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jcsifu
Copper Member
USA
47 Posts |
Posted - 08/06/2009 : 08:24:21
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Ok, sounds easy enough. How did you know what to look for in the specs to decide it's replacement? I think I have a half tube of OPA2134PA already from a "minimum" order that I bought back in April but forgot what I was going to do with them.
Anywho....
thanks once again!
jc |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/06/2009 : 08:53:23
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quote:
Originally posted by jcsifu
How did you know what to look for in the specs to decide it's replacement?
Years of experience grasshopper 
All joking aside, this is what I did:
1) Checked the spec sheet of the MC1458P to ensure it had standard pin-out configuration.
2) Recalled the opamp that many people use as a hi-fi replacement in pedals - the OPA is very commonly used to reduce noise in compressors and graphic EQs. Many commercial modders use them, and I have used them myself a few times to get lower noise.
3) Wrote the post above 
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jcsifu
Copper Member
USA
47 Posts |
Posted - 08/07/2009 : 01:18:20
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So I looked up a lot of chips and, if I'm getting this right, found the OP275 to look like another good replacement for lower noise. I am looking at the slew rates and the OP275 is higher than the OPA2134PA by 2 V/ms. I'm asking as the tube I have is not the OPA2134PA, but the OP275. Am I wrong about this, or would this be a good replacement as well?
jc
quote:
Originally posted by Laurie
quote:
Originally posted by jcsifu
How did you know what to look for in the specs to decide it's replacement?
Years of experience grasshopper
All joking aside, this is what I did:
1) Checked the spec sheet of the MC1458P to ensure it had standard pin-out configuration.
2) Recalled the opamp that many people use as a hi-fi replacement in pedals - the OPA is very commonly used to reduce noise in compressors and graphic EQs. Many commercial modders use them, and I have used them myself a few times to get lower noise.
3) Wrote the post above
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Edited by - jcsifu on 08/07/2009 01:19:42 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/07/2009 : 01:36:52
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Sonically the OP275 looks very good - quite similar to the OPA. The one alarm bell is the supply voltage - the OP275 has a minimum of +/-4.5V which is right on the limit for a 9V supply. The OPA has +/-2.5V miunimum supply.
I'd say give it a go. It should work from 9V, and if it doesn't all it will do is be noisy and distort (or not work at all).
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jcsifu
Copper Member
USA
47 Posts |
Posted - 08/07/2009 : 02:31:02
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Ok, I think I see. Your saying that the opa is more "forgiving" of supply voltage variances (min) than the op...right?
jc
quote:
Originally posted by Laurie
Sonically the OP275 looks very good - quite similar to the OPA. The one alarm bell is the supply voltage - the OP275 has a minimum of +/-4.5V which is right on the limit for a 9V supply. The OPA has +/-2.5V miunimum supply.
I'd say give it a go. It should work from 9V, and if it doesn't all it will do is be noisy and distort (or not work at all).
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/07/2009 : 03:02:37
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quote:
Originally posted by jcsifu
Ok, I think I see. Your saying that the opa is more "forgiving" of supply voltage variances (min) than the op...right?
jc
quote:
Originally posted by Laurie
Sonically the OP275 looks very good - quite similar to the OPA. The one alarm bell is the supply voltage - the OP275 has a minimum of +/-4.5V which is right on the limit for a 9V supply. The OPA has +/-2.5V miunimum supply.
I'd say give it a go. It should work from 9V, and if it doesn't all it will do is be noisy and distort (or not work at all).
Not "forgiving" - the OP275 is almost out of specification at 9VDC. |
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jcsifu
Copper Member
USA
47 Posts |
Posted - 08/07/2009 : 04:43:55
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Got it.
thanks for your time and wisdom! |
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jcsifu
Copper Member
USA
47 Posts |
Posted - 08/13/2009 : 08:15:58
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Just to follow up on this one, I replaced the op-amps the OPA2134PA, also changed the electrolytic caps to new ones, all of which were 4.7Uf or larger. I have less hiss, but I now have a hum that I believe to be a grounding issue. It is not really noticeable at room level, but is very pronounced at stage levels. Also, by tapping on my guitars volume knob at higher volumes it would make a similar noise to a microphonic tube, not the squeal part, just sort of like it would feedback if it was much worse. This was true on a well grounded humbucker loaded guitar as well as my strat. It was of course way worse with the strat, positions 1,3,5 were very noisy even for single coils. I will post pics of everything tomorrow. Anyone want to take a stab at suggestions for troubleshooting starting points? Much thanks for any takers!
jc |
Edited by - jcsifu on 08/13/2009 08:17:01 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/13/2009 : 13:58:07
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quote:
Originally posted by jcsifu
Just to follow up on this one, I replaced the op-amps the OPA2134PA, also changed the electrolytic caps to new ones, all of which were 4.7Uf or larger. I have less hiss, but I now have a hum that I believe to be a grounding issue. It is not really noticeable at room level, but is very pronounced at stage levels. Also, by tapping on my guitars volume knob at higher volumes it would make a similar noise to a microphonic tube, not the squeal part, just sort of like it would feedback if it was much worse. This was true on a well grounded humbucker loaded guitar as well as my strat. It was of course way worse with the strat, positions 1,3,5 were very noisy even for single coils. I will post pics of everything tomorrow. Anyone want to take a stab at suggestions for troubleshooting starting points? Much thanks for any takers!
jc
First thought (apologies for being a bit blunt) - did you get all the wiring back the same way it was? Is there a wire stressed/broken because of the work?
If it all looks OK... I've noticed that the OPA chips can be a little wierd with noise. I used them initially in the design for one of my "lauriepedals" (the LM-10) but they were "strange" when it came to noise. I swapped back to the JRC4558D and that fixed everything...
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jcsifu
Copper Member
USA
47 Posts |
Posted - 08/13/2009 : 16:26:36
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I tried the 4558 chip to no avail. As for your broken wire question, that is exactly what happened. Old wires are delicate....new lesson learned! I first noticed that the battery clip ground wire was not attached, this was previously existing and not my doing, but I attached it to the input jack ground lug. Then I noticed a loose ground wire coming from the output jack but not attached anywhere. After looking around, I located a solder point that had a small amount of wire buried in the solder. It matched the loose wire and it is marked BLA. just like the other ground. I attached the loose wire to it. It is the top BLK. point in the pic, the one next to the two 10Uf electrolytics. The next thing I tried was to put a 100 ohm resister inline with the 9v source, that is the red shrink tube coming from the point marked ORA. (orange). I was going to try a cap to ground there as well, this was my first idea to filter the 9v source. So, I'm not really sure if I attached the ground wire back correctly, but I'm pretty sure based on the priviously mentioned observations. I can find no schematics anywhere for this pedal either. In my limited knowledge, there is no reason I should have this hum. I should add, the hum is increased drastically as the level slider is increased and also when decreased. I was wanting to use this pedal as a clean boost, but even as I write this I am laughing at the notion of "clean boost"...not right now it isn't! Anyway, look forward to your suggestions.
jc
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 08/13/2009 : 17:04:13
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| Has to be grounding somewhere somehow... |
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jcsifu
Copper Member
USA
47 Posts |
Posted - 08/13/2009 : 17:08:55
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I know...that's what is so maddening about it. I can't see anything that would make sense.
quote:
Originally posted by Laurie
Has to be grounding somewhere somehow...
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Topic |
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Ibanez GE-601 noise issue
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