I am refurbishing my brother's 2 ADA MP-2s starting off by performing the noise mod on them to clear up some power issues likely related to bad caps. We will see what comes after that as there are likely other issues with them.
I have been fixing his aging 1990's audio gear as a hobby. Recently fixed his Event Tria Triamp and his Carvin Quad X-Amp.
Content here is great. Hoping I can contribute somehow.
Hey Gregg, welcome to the depot (again lol). Well your brother is a lucky guy to have you doing this stuff for him :thumb-up: .
One issue that has just come up again for someone is R913. It may be a major contributor to the noise?? The test point to ground/chassis needs to be 190v or less, it's typically around 187v when normal. If it's more than 190v replace R913 (on PCB just under V2).
Hi Gregg,
Welcome to the Depot :wave:
Quote from: rnolan on December 29, 2023, 09:03:32 PM
Hey Gregg, welcome to the depot (again lol). Well your brother is a lucky guy to have you doing this stuff for him :thumb-up: .
One issue that has just come up again for someone is R913. It may be a major contributor to the noise?? The test point to ground/chassis needs to be 190v or less, it's typically around 187v when normal. If it's more than 190v replace R913 (on PCB just under V2).
R913 240k ohms 1% @ 1/2 watt is in my DigiKey cart along with the noise mod caps. Seemed like a good thing to replace while I am in there. Appreciate the confirmation.
Cool, the other one to check while you are in there is R611 for noise gate chatter see attached pdf :wave:
Welcome to the Depot Gregg!!
Quote from: rnolan on December 31, 2023, 07:11:03 PM
Cool, the other one to check while you are in there is R611 for noise gate chatter see attached pdf :wave:
Thanks... I would have missed that one. Am waiting for the units to show up to verify that the capacitors I plan to order will fit.
Finding a 4700uf @ 35V capacitor from a reputable source that will fit into the unit seems challenging. Everything else seems to have plenty of availability. Given how bad the capacitor supply chain is these days, I won't order from anywhere other than DigiKey, Mouser, Newark, etc. eBay, Amazon and AliExpress are off limits to me.
Since you are doing a total revamp, the other thing (apart from the memory battery and tubes) that goes over time is the display. It gets fainter and harder to see/read so you may want to replace those while you are at it. https://adadepot.com/index.php?topic=1824.0 (https://adadepot.com/index.php?topic=1824.0)
Tube choice is obviously very subjective, I use the New Sensor Mullard Long Plate re-issues in all my MP-2s.
R913 was at 3 mega ohms and the HV at 237VDC. Pulled all the parts and now waiting for DigiKey to ship.
I don't know if folks know about it here but low melt solder made getting the big caps out super easy. You can find info about it on YouTube and Google.
247 Solder 247-REMALLOY4.5 SMT Removal Alloy 4.5ft https://a.co/d/g7NIE9d
Gregg
Hey Gregg, wow that's quite high (237VDC) and would have been making the MP-2 quite noisy (or even worse https://adadepot.com/index.php?topic=2985.msg32527#msg32527 (https://adadepot.com/index.php?topic=2985.msg32527#msg32527)). I suspect changing it and getting the HV back under 190VDC will be the biggest improvement albeit the caps etc. will also help. Thanks for the tip re removal alloy (I didn't know it existed, what a great idea :thumb-up: ), the big caps are probably the hardest part of the MP-2 noise mod/fix. :wave:
Other than the large caps which I knew would be challenging, everything else came out with standard desoldering tools: braid/wick and a Hakko FR-301 (https://hakkousa.com/products/desoldering/desoldering-tools/fr-301-portable-desoldering-tool.html)
I was surprised to find flux in spots on the board. Since my brother is the only owner and it has never been touched by anyone but me, it must have been from the factory which is surprising to me.
Gregg
Here are some images of what I am working on:
(https://www.dropbox.com/scl/fi/qog4wc8zvmiz8ksdsleq7/IMG_1468.jpeg?rlkey=iq4dvbyrx6i9l00wvvf82yq30&dl=0)
(https://www.dropbox.com/scl/fi/9851iibocxw63yfgby1pg/IMG_1487.jpeg?rlkey=d75r2k3aiqhclxxs5sat1vuo3&dl=0)
(https://www.dropbox.com/scl/fi/c3acp8ln14434esmfpmp8/IMG_1488.jpeg?rlkey=6a1q3t24pyh5xj3n2bzvmh013&dl=0)
(https://www.dropbox.com/scl/fi/3ubpmnmu32giqhwsy7do5/IMG_1477.jpeg?rlkey=tse3wsv7pmz3qn4wax1t2z7mm&dl=0)
Hey Gregg, cool :thumb-up: I see you worked out attaching the images. When you click on them, you'll see what I meant by careful with the image dimensions etc. as they become hard to see in the forum screen (needing to do a bit of scrolling).