Why don't you start by replacing the fuses with SR Black fuses and see if it makes a big improvement before you invest bigger dollars?
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Unless someone knows a tech who has a tried-and-true proven mod for that particular piece, I would stay away from it. Replacing parts with more expensive parts may not yield the results you're looking for. You have a tube preamp, how about rolling the tubes for starters? I'm sure you could get some good recommendations here or from Andy at Vintage Tube Services.
I agree with lak and chauro. Manley makes great equipment. Just letting someone upgrade your already well thought out and built piece of equipment is risky! Try a fuse and tube rolling First! Save your $ for the "Real Deal" I have a Steelhead and am just finding out how good it is after nine (9) yrs. Take your time. Enjoy what you have. It's part of our Journey. Best Wishes.
Agree with chayro on this. I would have offered to do the technical work if you knew exactly what needed to be replaced. We could always look at upgrading any electrolytic caps, but this is minor. All the wiring and board lay-out on this preamp is already very good, unless you want to look at putting in OCC copper chassis wire. The hard part comes with replacing the film/foil signal capacitors. Since it's a tube amp, a lot of the capacitor choice has to do with voicing the preamp and you could make the preamp better or worse depending on what you replace. I actually have a lot of experience with solid-state preamps and have a good idea of what works and what doesn't.
1 The Jumbo Shrimp main voltage fuse is a 600 ma slo blo. If you don’t find improvement (or very little) you can return the Synergistic Research Black fuse.
2 You have three tube types to manipulate, 12AT7, 5670 and the 7044.
3 Your output stage capacitors are MIT/Multicap 30uf x 2 total.
I’d proceed in this order one step at a time.
The fuse can make a very noticeable improvement in some components. It’s worth a try.
Fuses are not part of the active, tone producing circuits in any amp, and are simply designed to allow current to pass through them and fail immediately if necessary to save the circuits from frying. Although SR fuses have a cult following with astonishing claims of transforming the tone quality of amps, I've tested these (SR Black) and found these claims to be nonsense, even while providing the weeks of break-in (!). In fact, after my little comparison to the Littlefuse (and other generally stock fuses) products I've used for years, I discovered an SR Black had been left in my amp for months, which I replaced with the original Littlefuse with zero change in tone. Try asking anybody how these little graphene enhanced seriously overpriced tiny wire devices actually work (magically coat the electrons with Special Sauce?) and prepare for scorn. The SR business model seems to be "money paid equals results experienced" even when the products are laughably unnecessary.
celtic66, you might check with Manley, providing your serial number, to see if there are any factory upgrades.
Otherwise, if you'd like to experiment I'd agree with trying a few different tubes. I don't have experience with expensive fuses so cannot comment on those.
Of course one might ask what sort of improvements you hope to achieve before thinking about changing anything.
I believe in your question you were requesting suggestions of who in the industry modifies the Manley Shrimp, or maybe both regarding technicians and types of mods. If you haven't already, I would contact Manley. I would think they would be able to refer you to repair and/or modification services/providers. Why not pose the question to the AG community of those owning the Manley Shrimp; what internal component modification they may have benefited from.
Also I found both repair and mod services for Manley products by an individual named Ben Jacoby. I have included the company address below.
Fuse directionality in AC circuits is technically irrelevant, and perceived changes in sound from reversing a fuse are likely imagined. Some think changing the direction meant you cleaned the fuse contacts and are hearing the results of that, but if the fuse worked before being reversed that's also very unlikely, although cleaning any contacts is generally a good idea. Like washing your hands after meeting a politician.
You might, w_g, want to look at some other threads, where the person measured the fuse's output (I have no idea what thread it's on) and found that he could determine the correct direction.
And while your experience is unique to you, it's absurd to say that everyone else is imagining things. Some of us, who have been professional audio writers, know different. Why it didn't demonstrate an improvement is one of those things that seem to only happen to those who are dismissive of the experience of hundreds of other users. I can hear the difference in my PS Audio Power Plant between different brands of fuses, and can pinpoint exactly what is happening in the music - IF the recording used is not overly manipulated and is natural. Voices are the easiest way to demonstrate the improvements to me - as well as acquaintances who are not audiophiles. And it's not due to cleaning the fuse contact, that much I can say with certainty.
I can't deny your experience, but my ability to hear is quite good, good enough for me to have written for a couple of magazines and been the editor for another one. There are just as many people who are inclined to toss 'snake oil' comments about a product as there are ones who believe the product's demonstrated - and repeatable - results. We're probably the same people who think AC outlets make a difference...
Fuse directionality in AC circuits is technically irrelevant, and perceived changes in sound from reversing a fuse are likely imagined. Some think changing the direction meant you cleaned the fuse contacts and are hearing the results of that, but if the fuse worked before being reversed that’s also very unlikely, although cleaning any contacts is generally a good idea. Like washing your hands after meeting a politician.
There are many perfectly good reasons why some people have bad results with some tweaks. Historically it has happened for everything from the Tice Clock to Mpingo disc to expensive cables, silver holographic foil, the Intelligent Chip, the VPI brick and many other controversial things, like fuses. If you like I’ll list the reasons. I’ll give you a hint. One of them is that the person is so committed to his belief that the thing can’t possibly work he has psyched himself out. But just going by the testimony I read on the fuse threads on this forum alone, not even counting all the discussions on fuse directionality on other forums, the positive results outweigh the negative ones by, what, gotta be 20 to 1. The reasonable thing to do, it seems to me, would be to throw away the negative results as outliers.
As you well know this fuse topic has been covered numerous times on this and other open discussion forums. As geofkait noted the ratio is usually quite high in favor of listeners with a positive response. I do believe that some people can have such a negative bias and expectation of "no difference heard" that they’d never admit to any sonic improvement. Bias can and does work in both directions. I’ve heard fuses make a + difference in various systems and multiple components over the years. I remember very similar debates regarding power cables in the past, not so much anymore. My well meaning suggestion to celtic 66 is hey, just give them a try and see what you think.
The "positive results" mentioned have been somewhat skewed by the relentless commercial promotion of SR fuses by a few very motivated posters, who by themselves make up a large percentage of the "testimony" in the primary SR fuse thread. When I posted the simple question asking if anybody had a reasonable explanation of why these fuses work (the Athletic Supporters of SR stuff seemed likely to know the answer), it became clear there was simply nobody who has a clue about why Quantum Tunnelling or Graphene dust in a fuse would make any difference. My tests showed it doesn't, but then I didn't pay anything for my test samples.
Modifications to the Manley Jumbo Shrimp should be very easy to do to because the main circuit board is on it’s side allowing you to access both sides of the printed circuit board. Don’t be shy to buy a solder gun and an auto-ranging multi-meter then watch YouTube "how to" videos to learn how to solder. I started modifying my own components a couple of years ago with no experience and now Parts Connexion and SonicCraft know me by name.
Start by upgrading the capacitors. Jupiter capacitors and Clarity Cap MR should yield very good improvements for a relatively low budget. Teflon caps are expensive but well worth the cost especially when using them to bypass power supply electrolytic caps (.22uf VCaps make a big improvement to the power supply).