Come with me this time as I repair and review a beautiful Musical Fidelity AMS35i class-A integrated amplifier.
Welcome back, everyone. I know this will make quite a few people happy – another article about many people’s favourite brand, Musical Fidelity. I’ll go one better, with the baby amplifier from arguably Musical Fidelity’s greatest product line of recent years, the Antony Michaelson Series.
Musical Fidelity calls it the AMS Series. That’s right, the Antony Michaelson Series, Series. Hmm. Anyway, this one is the Musical Fidelity AMS35i, a pure class-A integrated amplifier of considerable heft.
I don’t think it’s a secret that MF is a guilty pleasure of mine too. There’s something about the styling, mechanical build quality and general performance of some of their gear that is almost mythical. Unfortunately, there are some MF design issues and parts choices that are mythical for the wrong reasons and let down this otherwise lovely AMS35i.
First, though, have you seen the AMS50 or AMS100 amplifiers from the AMS series?! You need to, the AMS100 for example is a 100kg monster, surely one of the largest, heaviest class-A power amplifiers ever made, a true end-game amplifier.
Do any of my readers own one..? Have any of my readers owned or even heard one? Want me to look at it for you..?! Let me know in the comments below.
Musical Fidelity AMS35i Specifications
Courtesy of Musical Fidelity
- Power output: 35 Watts per channel into 8 Ohms (15.5 dBW)
- THD(+ noise): <0.014% typical
- Signal-to-Noise Ratio: >96dB
- Frequency Response: +0, –0.1dB, 10Hz to 20kHz
- 4x RCA Phono Line Level
- 1x Line level XLR Balanced
- Dimensions – WxHxD (mm): 483 x 148 x 475
- Weight (unpacked/packed): 28.3 kg / 33 kg
Features & Analysis
Perhaps most importantly, the AMS35i is a class-A amplifier, meaning it operates at full power all of the time. The output stage draws full power and the heatsinks dissipate full power from the moment you turn it on, to the moment you turn it off.
Full power here means 310 Watts drawn from the wall, so you’ll need good ventilation and for the amplifier to be situated in free space. You’ll also need to turn it off when you are not listening to it. Remember – heat kills electronics.
The Musical Fidelity AMS35i is an integrated amplifier, so it has a built-in line-level preamplifier and multiple inputs. The preamp is basic, a simple op-amp circuit, so you’ll be better served by a good separate preamp, but this will get you by, with line-level sources. There’s one pair of balanced inputs, but the amplifier is not internally balanced end to end, so this input is mostly for show I’m afraid.
The output stage utilises the rather unfortunately named STD03 devices, another Sanken Darlington pair that Musical Fidelity just seems to love. The problem is, these Darlington pair devices are not the most robust devices being an integrated two-transistor package and finding and matching new ones, should it be needed, will be a big problem at some point. My tip – stock up on these devices if you have equipment that uses them.
The Musical Fidelity AMS35i is a dual mono design, meaning it is essentially two power amplifiers in one box. This is achieved with two transformers as we see above. Again though, and as Musical Fidelity does, there are a ton of Jamicon and cheap film caps here.
Is this really good enough in an amplifier that retailed for close to $10,000 AUD? No, it’s not. This example also exhibited some pretty ordinary circuit board kludges, as you’ll see if you watch the video:
This Musical Fidelity AMS35i had a couple of issues: It kept blowing fuses and the fuse holders and fuses were overheating. There’s a little to unpack here but basically, the amplifier is slightly under-designed in terms of the power supply, an effort to save money, but not a great plan.
The diode bridges are small and were inadequately torqued and thermally bonded to the chassis in this example. Additionally, the fuse holders are of poor quality and inadequately soldered into place using lead-free solder. The spring tension of the blades holding the fuses in place is low, leading to excessive contact resistance.
So there’s heat from the diode bridges, heat from the voltage drop across the fuses assemblies causing them to dissipate heat. Add lead-free solder into the mix which is a disaster really in terms of metallurgy and throw in a high-standing current draw from the class-A design and you have a recipe for the area to get hot.
This unit had been repaired previously, but the issues I’ve mentioned had not been addressed or resolved. Heavier fuses had been installed, but that’s not the solution. I decided needed to remove the entire board, a slight pain in the bum, and make some substantial improvements. That way I could minimise the chances of this happening again for the owner.
After installing new fuse holders and fuses, reworking the affected areas of the board, improving the soldering, replacing a couple of caps and servicing her, this Musical Fidelity AMS35i ran beautifully once again, much to the relief of her lovely owner.
I think it’s fair to say that this is a good result and the right way to fix a problem such as this. In terms of further improvement, we could certainly replace all the cheap electrolytic capacitors in this amplifier. I would also install a few improvements of my own, which I know significantly improve performance.
In terms of performance, I had a good listen to her in the shop, as I do all equipment that comes in for work, and the Musical Fidelity AMS35i sounded really lovely, in a smaller, more beautiful way than say a beefier power amplifier might.
The AMS35i sounds warm, clean, punchy and rhythmic, certainly possing plenty of drive for most regular speakers. You also get what you can really only get with lots of class-A power and my business name points to this if you’ve ever wondered – that certain liquid sonic quality that seems to only come from class-A equipment.
This amplifier would be well suited to someone with efficient speakers, in a smaller room, wanting really excellent performance. I’d suggest investing a little bit in overhauling and improving an amplifier like this AMS35i because the bones are there as you can see. She just needs a little fettling to really bring out the best in her, like so much Musical Fidelity equipment does. Maybe I’m just fussy..!
As always folks, thank you for stopping by and sincerely hope you enjoyed this one. If You’d like me to give your Musical Fidelity AMS35i a little TLC, or maybe take a look at your AMS50 or AMS100, don’t hesitate to let me know. They can be improved, that I can assure you. I work on most MF gear, and I’m always happy to do so.
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Thanks and I’ll see you again soon.