Powering Infinity RS 4.5's with Hafler amps

I have a pair of vintage (amp killers) Infinity RS 4.5’s which are well above my pay grade. I’m trying (on a small budget) to acquire amplification to drive them (Bi-amped) safely. Therefore I’ve been searching the used market. I’ve been offered an opportunity to purchase a pair of Haflers (9180 & 8270) along with a 945 pre-amp, all for $850. I have also been exposed to an opportunity to purchase some Adcoms (545ii’s). I don’t want to make a big mistake by purchasing something that isn’t up to the task. I’m dying to hear these speakers and would appreciate some counsel from you good folks. Thanks, in advance!

I don’t have any experience with the Haflers, but the Adcoms will drive the Infinities.

If I’m not mistaken, I think Nelson Pass was involved with the Adcom amps. His designs would ensure enough current.

The Adcom amps were slightly grainy as I recall. Nelson Pass designed the GFA-555 and is the sweet spot in the Adcom line. I had a Hafler preamp and amp in college for a short time. David Hafler was with Dynaco for some time and ventured out on his own with value oriented kit amplifiers. They were a good value in their day, but I’d steer clear of them today. They sound coarse to my ear. I changed from Hafler to GAS Son of Ampzilla with no regrets. Replaced the DH-101 preamp with an AGI 511a, again no regrets. Toyed with an early PS Audio phono preamp as well. Blew away the Hafler, IMO a better match at your price point would be Forte amplification. Built like a Brick Sh**-House. The Forte Model 3 is 200 WPC and a little sweeter sounding while still having an open and detailed sound. Another option is the Forte Model 4a, 50 WPC class A all the way. The Fortes have a robust power supply and don’t shy away from low impedance loads.
Partnered with Threshold preamps you can’t go wrong for vintage amps with these. The Forte preamps are just so-so IMO.

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From what I’m seeing, the Forte amps might be out of my current price range? I do prefer to bi-amp these speakers. I’m wondering (since I do own an Adcom pre-amp), If I should buy one of this guy’s Adcom 545ii’s for the top sections and search for a GFA 555 to drive my bottom ends? It would certainly look nicer to have matching equipment but I wasn’t sure if the Adcoms would support the 2-3ohm dips?

I believe you are cutting your self short with the Adcom 545’s, IMHO. Just a thought, and a totally different direction, have you considered the PS Audio S300 used? One may just do the trick.

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Agree there are many alternative options to consider, but if you want to stay with the Adcom/Halfer line, here are some considerations-

I can’t speak to the newer Halfer amps you referenced, however, used to help my dad build DH200/500 amps as a kid & I’ve owned both Adcom 545 & 555 as a young adult.

Both are great foundation points on a budget. With a few tweaks you can vastly improve their soundstage and remove much of the graininess/harshness @weedeewop referenced

Nelson has posted several options on DIYAudio, or if you prefer not to do it, Musical Concepts / Musical Design offers upgrades depending on the level you wish to take them.