Finemet FM-ATVR1 + Intact Audio Nickel 28-step Autoformer Volume Control

Finemet FM-ATVR1 AVC

I wired this Finemet Autoformer Volume Control (AVC) from Japan for a friend of a friend in 2018. Inserted between the output of my preamp and amp or as a passive attenuator for line level sources (CD/DAC, FM Tuner, etc), I noticed the fine qualities an AVC could offer. It definitely sounds better than a passive preamp employing a volume control or resistive ladder attenuator because an autoformer turns voltage into current whereas in the latter, voltage is merely dissipated as heat. IMHO, this is why passive volume control/ladder attenuators sound mellow but lack dynamics; and short cables are required, because of their inherent high output impedance.

Due to many other projects I had lined up, I kept the AVC idea in the back burner. Besides, the cost of a pair of these Finemet FM-ATVR1 AVC was, and still is, staggering!

Five years later, the owner got tired of the dual switching arrangement. So I rewired and rehoused the Finemet AVC pair, Redboy-style. 😉

Testing the rewired/rehoused Finemet FM-ATVR1 AVC

Sinatra via FM-ATVR1

Hank Mobley via FM-ATVR1

Intact Audio 28-step Nickel AVC

This unit which contains a pair of Intact Audio 28-step Ni-AVCs was also sent for repairs due to a couple of broken connections giving me an opportunity to compare them!

Intact Audio Nickel AVC with a 2 pole, 24 step ELMA rotary switch, after repair!

Finemet vs. Nickel

They're both very nice BUT different!

Back in the 90s, I found the amorphous Tamura F500X series output transformer series to be more extended in the frequency extremes but just a tad cold in the mids compared to the nickel F700X series. When I finally got a taste of Noguchi Finemet OPTs (now Gtrans), which is an amorphous type core, I was surprised that I enjoyed it a lot. Considering their diminutive size, they had ample bass extension, top end + very nice mids!

The exemplary performance at the frequency extremes was all there using the Finemet FM-ATVR1 AVC! But for some reason, the midrange warmth I've come to associate with my FM6WS output transformers and FM-MCT1 MC step up wasn't as prominent. In fact, when used in conjunction with the FM-MCT1 doing MC step up duty, the midrange thins out a bit for my taste. To offset this phenomenon, I have to replace the FM-MCT1 with either the Tamura TKS83 or Altec 4722 to achieve the tonal balance I prefer.

After several months of extensive listening comparisons between the Finemet and the Nickel, I decided that I need a pair of dave slagle's 28-step Ni-AVCs as additional tools to enjoy music. They possess the tonality I cherish in my nickel/permalloy Tamura F7002s in my SE2A3 amp and Tango NY15Ss in my SE300B mono blocks.

Under $10 Chinese 2x24 vs. over $100 Swiss Elma 2x24 position switch

Even if the unit I repaired was equipped with an ELMA + fancy OFHC wiring, I couldn't justify the expense. So I started with the cheap Chinese clone above + silicone insulated 24 gauge tinned stranded wire from Amazon. Honestly, I can't hear a difference between my budget build vs. the boutique parts version I repaired. 

Wiring a pair of AVCs may seem daunting. However, once the input and output legs of the AVC as well as their corresponding taps in the rotary switch are identified, wiring becomes routine. But admittedly, it's still a tedious task! Since my rotary switch only has 24 steps, 4 taps from the 28-step AVC were left unused. I chose to skip the first 4 even numbered taps from full attenuation.   

Because of the relatively low input Z of autoformers, they require sources with low Z out - at least 1k Ohms or lower*. My RCA derived octal phono and the Lar mod Shure M65 don't work with AVCs. But my Loctal EAR834P had no problems driving it because of its 7N7 (loctal equivalent of the 6SN7) cathode follower + 1uf output cap. The standalone octal based tube phono preamps that are featured in my AVC videos are forthcoming uploads.

For more technical info about autoformers, visit Intact Audio's FAQs.

*Addendum: A veteran DIYer internet friend has successfully used source components with a 3k Ohm output Z. Perhaps my 1k Ohm guesstimate errs on the conservative side.

AVCs work great with digital sources! Even better with a non-oversampling tube output DAC + line transformer "filtering" as in the above video.  

Compared to my Intact Audio Ni plate choke loaded 76 line preamp, the Intact Audio Ni-AVC presents more lower level detail and will come across as more accurate to those who consider "organic" a coloration instead of a virtue. At the moment, I'm revisiting the transformer coupled line preamp topology I wrote about in Sound Practices decades ago. That + this Ni-AVC is a combination well worth exploring too. Stay tuned!