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 4×27,000uF. Nearly double!
• 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.

Continue reading Introducing the Hoppe’s Brain Adcom GFA-555 soft-start power supply

OK, this tiny circuit board is just too cute!

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.

Continue reading Earth loop-breaker boards

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?

Continue reading Killing the buzz in the Adcom GFA-535. New power supply boards!

Improved power supply boards for Adcom GFA-535 and GFA-545!

Continue reading Nifty power supply circuit 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.

Continue reading ADCOM GFP-750 upgrade

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.

Continue reading A custom super-high-current GFA-555 Dual-mono upgrade

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.

Continue reading Quick update, November 2016

Even better! I made a few revisions to the original boards, and I can now say that these are better quality boards than the originals! These have plated through-holes for a more solid solder connection, and greater pad strength. They are also less affected by heat cycling. Even with poor soldering, a plated through-hole is extremely reliable.

Continue reading Adcom GFA-565 replacement boards Revision 2!