ADA Depot - A Forum To Support Users of ADA Amplification Gear
Let's Get Technical => Schematics & Modifications (mods) => Topic started by: peoriashows on August 07, 2018, 10:17:15 AM
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Has anyone seen this detailed MP-1 rebuild from Lydian.ca? If so, what are your thoughts? He suggests that the TL072 op-amp is a bad choice for the noise mod and would create more noise. He also added some main board component swaps. Most interesting was changing U17 to an MC33079.
http://www.lydian.ca/ada-mp-1-rebuild/
He seems to be knowledgeable, but a bit presumptuous when acknowledging ADA Depot. I hate it when I see people criticizing you guys as though it's some sort of competition when it comes to who has better ideas for a mod. The people on this board have been overwhelmingly the most helpful and supportive group in the world when it comes to mutual love of a product.
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Well we don't use a TL072 but a OPA2604 and only for U4. I did try to replace other opamps with "better opamps" but it sounded too hifi.
Tube board mods, I already do these way before he "figured" it out, he uses the same caps as I do but bigger and there's no need to do this. So nothing new at all.
The best thing he does is great, I quote;
"The pre-eq buffer feedback loop needs to be changed to filter out more hiss. This is done by changing C66 near opamp U18 from 150pf to 33nf"
Well if you change the C66 to 33nF you get a first order filter starting at 1kHz (going down 6dB/octave) so yes it will filter out the noise but also high frequencies. I don't think he even knows why that cap is there and I can tell it's NOT for noise reduction. Same deal he explains in step 5, BTW it is not U17 but U11 he's talking about.
Now on the other hand there are better opamps for the tone section, I personally use an LT1058 in my MP-1's.Never tried the MC33079 but I did try the OPA4134 but I liked the LT better. That comes down to taste. I also replaced all the caps in the tone section. Same values but 1% types.
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I'm confused. The noise mod on the Depot does call for replacing 3 op-amps with TL072.
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That's a real old one, there's a also a new one. We should delete the old one, Rnolan or Dante can you do that? I see too many mp-1's were U9 is replaced with a TL072, it should keep the original LF412 which is actually a comparator and not an opamp.
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Hey MJMP, Dante has the access to change those flies, I don't :facepalm: .@ Date can you liaise with MJMP and get this done please ASAP
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How recently was this change made? I'm pretty sure I swapped for the TL072's on at least two of my MP-1's.
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...I did try to replace other opamps with "better opamps" but it sounded too hifi.
Did you try an LM833? I happen to have a few of those lying around. Never thought to put one in before. They're considered very good audio op-amps, though.
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Well the LM833 is actually nothing special IMO, but I never tried in an MP-1. Could be good sounding in certain places, who knows.