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Topic: Question about mod chips |
Steven Paris
From:
Los Angeles
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Posted 6 Jun 2017 11:22 pm |
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| Jack Stoner wrote: |
| I replaced the op-amp chips in my NV400, that had the Peavey factory tone mod installed but NO op-amp updates. Made no difference at all. On the other hand replacing them in a 1000 or 112 made a significant (plus) difference. |
The "factory tone mod" DID include an opamp upgrade, from RC4558s to OPA2604s, as well as the capacitor and resistor value changes. The OPA2604s were a definite improvement over the RC4558s. The later Ken Fox improvement to OPA2134s was also an improvement, but not as noticeable a change as the 2604s were to the 4558s. The NV112 used RC4560s, which are only maybe slightly better than the RC4558s.
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Emmons & Peavey |
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ajm
From:
Los Angeles
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Posted 8 Jun 2017 7:49 am
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Just a note: When you talk about replacing the ICs, it is important to detail what ICs you are replacing, and what you are replacing them with.
It can make a noticeable difference.
More than a few years ago I decided to try this experiment with an old Carvin XV112E that I use for six string. It had the 4558s in it, I think five ICs total, which means several stages of op amps for EQ, reverb drive, buffering, etc. None of the op amps stages are used to generate distortion.
I ordered some OPA2604s since they were the hot ticket here on the forum at that time. FWIW, in my case and my application, it sounded like someone threw a blanket over the amp.
I then ordered some OPA2227s. Figuring they would be brighter, and looking at the schematic, I replaced a few stages in the signal path with these, keeping the OPA2604s in a few key spots. Much better. And better than the stock 4558s.
This science project convinced me that all of this op amp replacement nonsense was not nonsense. It can make a difference, both in a good and bad way if you're not careful.
If you have an amp, and just want to do a real quick and dirty experiment, try replacing the stock op amps with OPA2604s (if you have any laying around).
Note that we are talking steel here, which is clean playing. The stages in my Carvin use tubes for distortion, and do not use the op amps to generate distortion. If you replace op amps in stages that are used to generate distortion, you're on your own. Some people say it makes a difference, some not. There are videos on YT about this, a couple done by Briam Wampler and Visual Sound. |
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Tommy Boswell
From:
Virginia, USA
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Posted 8 Jun 2017 12:58 pm
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| The mod kit that Ken Fox sent me came with a diagram of my amp board with clear markings to show which chips to replace, and which direction they should be inserted. Getting them in place without bending the contacts was a little tricky, but doable if you're careful. My Reno 400 sounds 100% better! |
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Steven Paris
From:
Los Angeles
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Posted 8 Jun 2017 8:05 pm
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| ajm wrote: |
| Just a note: When you talk about replacing the ICs, it is important to detail what ICs you are replacing, and what you are replacing them with. It can make a noticeable difference. More than a few years ago I decided to try this experiment with an old Carvin XV112E that I use for six string. It had the 4558s in it, I think five ICs total, ........I ordered some OPA2604s since they were the hot ticket here on the forum at that time. FWIW, in my case and my application, it sounded like someone threw a blanket over the amp. I then ordered some OPA2227s. Figuring they would be brighter, and looking at the schematic, I replaced a few stages in the signal path with these, keeping the OPA2604s in a few key spots. Much better. And better than the stock 4558s. This science project convinced me that all of this op amp replacement nonsense was not nonsense. It can make a difference, both in a good and bad way if you're not careful. |
I looked at the Carvin XV112 schematic---it does NOT show any IC power pin bypass caps---bad; this is poor design. The OPA2604s are ~15 times faster than the old RC4558s, and about 11 times faster than the OPA2227s. I think perhaps they were oscillating, or on the edge of it, when you swapped them in. An IC that fast (slew rate of 25v/uSec) DEFINITELY needs to have power supply bypass caps to avoid oscillation. Some amps already have this--a Peavey Nashville 400, for instance, has them right next to the power pins on every IC (except the + pin on the reverb driver, but that's another story), so it is prime for an IC upgrade. It would be wise to check for these bypass caps in any amplifier one intends to IC-upgrade.
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Emmons & Peavey |
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Steven Paris
From:
Los Angeles
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Posted 8 Jun 2017 11:47 pm
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| Ken Fox wrote: |
| I never used the tantalums listed from Mouser. My own kits were comprised of caps from Mouser and another supplier of caps from the internet (that is where the tantalums and electrolytics were purchased). |
Thanks for the parts list posting!! (I had it somewhere but misplaced it). I have also been wondering about the other caps that are in the NV400 signal path; for instance coupling caps C19-20-21. They sure LOOK like ceramics---are they? Seems ripe for a polypropylene replacement.[/b]
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Emmons & Peavey |
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Ken Fox
From:
Nashville GA USA
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Posted 9 Jun 2017 7:01 am
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Ken Fox
From:
Nashville GA USA
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Posted 9 Jun 2017 7:04 am
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| Not sure about those caps, Steve |
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ajm
From:
Los Angeles
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Posted 9 Jun 2017 12:16 pm
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Ken: Steven had two posts about caps, one right after the other.
One post was on decoupling caps for the ICs.
The other was for caps in the signal path.
Which of Steven's posts are you addressing?
And FWIW, Steven appears to be correct on the decoupling caps for the N400.
They are not exactly right next to the pins (like they would be in the perfect world), bit they are fairly close to the ICs.
They are shown on the schematic for 3-4 ICs, but not all (like the reverb ICs, which matches what Steven said).
They are listed as 0.05 uf.
I could try to add them to my Carvin, but at this point I have other things on the agenda that take precedence.
I like the way that the amp is sounding.
And FWIW, I have had OPA2604s in a couple of spots for several years and the amp seems to be OK with it.
But some day, if I get time, or get bored............. |
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Ken Fox
From:
Nashville GA USA
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Posted 10 Jun 2017 6:48 am
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| coupling caps C19-20-21 |
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