Hi everyone! One of my customers sent me a particularly nice GFA-555 MKI to be refurbished. It’s never been tampered with, and has very few scratches on the case… just beautiful. So I thought I would take lots of pictures along the way as I refurbish it, and show you the latest iteration of my GFA-555 rebuild process. This is the full monty upgrade package including the Hoppe’s Brain soft-start power supply board, with all sound quality and reliability improvements. $975 in total.
Exciting news! Hoppe’s Brain power supply boards for the GFA-555 are here!
These boards feature a number of improvements over the stock arrangement with the old-style chassis-mount components:
- Soft-start circuit reduces stress on components like switches and capacitors.
- Reduced hum, buzz and noise from the amplifier’s speaker outputs.
- Capacitance upgrade from 4×15,000uF to 4×22,000uF.
- Earth-loop breaker with diode clamp safety shunt.
- Amp is converted to a 3-wire, earth-grounded chassis appliance, for safety and better noise rejection.
- Surge protection MOV
- Snubber capacitors across AC side of bridge rectifiers
- Compact layout. Overall wiring lengths reduced, fewer mechanical connections, and a much cleaner internal layout.
Hey folks, I hope this will be useful to anyone attempting to clean an ALPS sliding listen/record selector switch like those used in the Adcom GFP-555 and GFP-565. These are common in many brands of preamps and receivers.
It’s an “Earth loop breaker”; A common method of providing some resistive isolation between star ground and chassis, lowering noise in an amplifier. I designed it for the GFA-555, but it will also work in many amps.
My sincerest apologies; My communications have been terribly slow, and my turn-around time for refurbished equipment is getting out of hand. I have customers waiting up to four months for their equipment, and that’s no good. I wouldn’t want to wait that long!
I never anticipated such a level of interest! Many thanks to all of my customers; it’s a pleasure to help you build your music systems, and I love hearing people’s comments after they get their gear back.
I like to say “YES!” to everyone’s projects, but I have taken on more work than I can possibly keep up with. I am buried in emails, and it’s getting hard to find time to work at the bench. Things are snow-balling on me.
It’s a good problem to have. It means I’m succeeding, but I won’t be for long if I don’t limit the scope of what I do.
Adcom GFA-535 owners; Has it always bugged you, how the right channel of your amp buzzes through your speakers more than the left channel? Yeah, me too. The buzz is a buzz-kill… so I killed the buzz! With this thing I made.
Now, the GFA-535 is a legendary little amplifier, deserving plenty of buzz, but it’s too bad so much of it comes out the speakers. Oddly, the GFA-535’s bigger sibling—the GFA-545—using the exact same amplifier boards as the 535, is nearly silent as a stone. What’s going on?
Improved power supply boards for Adcom GFA-535 and GFA-545!
The Adcom GFP-750 preamp was designed as a companion piece to the GFA-5802, with matching aesthetics. It’s a MOSFET based, single-ended Class-A preamp designed by Nelson Pass. Conceptually, it’s similar to the Pass Aleph P and the ‘Bride of Son of Zen’ DIY project.
Here’s a custom GFA-555 I built for Mark in Michigan. This is a fully dual-mono conversion with all the tweaks. Each channel has its own, dedicated 500VA transformer, for 1000VA in total, replacing the single, 850VA stock unit.
Hi Everyone, it’s been a long time since my last blog entry. I’ve been so busy refurbishing amps and preamps! My wait times are getting a little long, but that’s a good problem to have. Customer emails were getting hard to track, so I’ve implemented Freshdesk, a cloud-based helpdesk ticketing system. (No affiliation.) Highly recommended! I can set due dates and track status, how long since I last contacted someone, etc… It’s reduced my own stress and improved my customer service. My queue may be long, but my customers are kept well informed.