Power Amplifier Reviews

by Kevin OBrien on January 3, 2022


With so many new high end reference cans on the horizon or already shipping for 2022, how are we going to test and evaluate them all properly? I have it figured out, pick up a headphone amplifier that is as versatile as is it is good looking. I'm talking about an amplifier that can be right at home with a pair of Audeze LCD-XC and still power HiFiMAN Susvara well enough to make them sing. Hmmm? That's not an easy task for any amp now that you mention it.

If you're out of Poland and your name is Ferrum Audio, you don't have anything to worry about because this is exactly what you've been busy coming up with for the past two years. But honestly, how can one amp possibly fit all these flagship headphone models under one roof?  I am calling BS. Well I'll be damned, it turns out you can do just that. If you have flexibility with gain settings along with multiple connection options, from inputs to outputs, you're all set. That's where Ferrum comes in again.

Ferrum started out of a need from its parent company, HEM, to come up with a headphone-specific line-up of audio gear that could compete with the 'high end' gear but keep the prices closer to reality. HEM makes Mytek gear for the 2-channel world. HEM makes Ferrum gear for the headphone world. Problem solved.

Here comes Ferrum OOR mated to Ferrum HYPSOS to save the day. This pairing can power any headphone currently on the market (electrostats excluded obviously) with ease and do it with versatility in mind. The OOR + HYPSOS Stack is how versatility will be measured going forward. I know, that's a bold statement. Read on and see what we mean...

Let's begin by talking a bit about OOR. There is a single set of RCA and XLR inputs and outputs on the rear panel along with the volume control bypass switch and the power input connections. One power input is specifically designed to be used with HYPSOS and is called 'Ferrum Link'. The other power input is a 2.5mm x 5.5mm female DC barrel connector (use this if you want to try a YFS LPS with your OOR). You can use OOR as a stand-alone preamp if you so desire by implementing the outputs on the rear panel. OOR can bypass its volume control as well if you already have that covered elsewhere (like in your DAC). Working your way around OOR, there's a set of headphone outputs, one balanced 4-pin and one 1/4" (6.3 mm) single-ended, located on the front panel. Input (RCA, Stand-By, XLR) and gain selection (Low, Standard, High) are handled on the front panel as well. This is one handy and versatile amplifier.

HYPSOS is Ferrum's answer to multi-rail linear power supplies. This particular power supply is a linear / switching 'hybrid' design of sorts. It's not a linear or a switcher. Interesting. It definitely mates well with OOR and that is its ultimate purpose but it can be used to power all sorts of HiFi devices. HYPSOS comes pre-programmed from the factory with a multitude of device settings (Voltage and Current output settings). Select your device from the menu on the front panel OLED display, and you're ready to go. The front panel shows your device output voltage, current, and power output in Watts. Very cool! HYPSOS can output 5V up to 30V at a max of 6 Amps of current output ( 80 Watts max output -> W= (V x i) ). We must say, that all sounds pretty slick.

So anyway, how does it sound? It sounds great! The Ferrum Stack looks and feels like it should be clinical when judging a book by its cover. It's a solid state amp after all. As it turns out, OOR sounds more like a good tube amp than a solid state amp. This sounds crazy but it's true. We were able to test with our Audeze LCD-5 and HiFiMAN Susvara. These are two of the most difficult loads to drive on the market currently. The Ferrum Stack made quick work of the Susvara in 'high gain' mode. The Ferrum Stack made the LCD-5 sound incredible in 'standard gain' mode. There was never any hint of harshness or brightness at all but the presentation was ultra-detailed and bass was tight. Everything was spot on. WOW! Impressive. We have to hand it to Ferrum here. 

Keep in mind the Ferrum Stack is fully balanced, even when using the single-ended inputs. The Stack converts all incoming signals to balanced, if they are not already, and then does its thing. OOR outputs 8 Watts into 60 Ohms via the XLR inputs and outputs 2 Watts into 60 Ohms via the RCA inputs. Not bad at all for a little 10 pound stack of gear with a 8.5"W x 8"D x 4.5"H footprint. This is impressive. If you're on a budget, you can purchase OOR by itself and then partner it up with HYPSOS later on. This is a smart way to go financially if money is tight. After all, this hobby isn't cheap. We tested OOR on its own and it does sound good but it doesn't 'wow us' like it does when mated to HYPSOS. If you can swing it, pick up the entire stack at once. You will be rewarded. We were SO impressed with OOR, we became dealers. YFS is an authorized Ferrum Audio dealer.

US Distribution for Ferrum Audio (VANA Ltd.) is out of NYC which is nice and convenient. It gets old sending money overseas when placing orders. The standard factory warranty is 2 years from date of purchase and defects are handled in NYC. What's not to love?

Thank you for spending your time with us and reading our review. Contact us for pricing and availability. Let us know if you have any questions or concerns.

Until next time..



by Kevin OBrien and Mike OBrien on 07/07/2011


I was wondering how the Quicksilver Audio Silver 60 monoblocks compared to my prized YFS modified McIntosh Labs MC75 monoblocks from circa 1960's era. Is this a fair comparison or are these two sets of monoblocks just not even in the same league? Is there really a worthy successor to the MC75 monos with a modified power supply? I will be using my reference Von Schweikert Audio VR-5 Hovland Special Edition speakers which are nominally rated at 4 ohms. One point to note is that both the MC75 and the Silver60 have 4 AND 8 ohm taps. I will be using the 4 ohm taps.

First, let's talk a little bit about what YFS did to the MC75 power supplies. The original power supply in the MC75 in the 1960's was unique for its time in it's use of a voltage doubler. In stock form the power supply has been known to break into motor boating as the B+ filter capacitors deteriorate. On the other hand, many MC75's are still operating today with no issues. To maintain physical layout, we chose to reform the original electrolytic capacitors since the original units had relatively low leakage. The second step was to replace the entire power supply with modern design using Panasonic TSHC series electrolytics and ultra fast recovery rectifiers. As it turned out, the sound was outstanding with the original components so we went no further.

At YFS we understand that the MC75 is a pure classic but can be taken to the next level with modern components and matched vacuum tubes. Basic electronic components have come a long way in 40+ years so it makes sense that an inherently sound topology can be improved by simple component substitution. No modifications were made to component values or the basic topology. We loaded the MC75 with matched Sylvania NOS 6550 output tubes and matched section (transconductance matched to 5%) NOS GE twin triodes (12AU7, 12BH7, and12AZ7). We also added a power switch, replaced the stock power cord, increased bias supply capacitance, replaced all signal capacitors with modern polypropylenes, and substituted metal film resistors in critical places to reduce noise. We also replaced the speaker output terminal strips and the RCA input jack.

In the Quicksilver Silver60 monoblocks we are using the popular SED 6550's for a tube compliment. Although the power ratings are not equal, 60 watts for the QS and 75 watts for the Mac, I feel we are close enough to do a fairly legit comparison. Check out the Quicksilver website. This is the only way to buy Mike Sanders' creations.

I played a few of my favorite albums on the Silver60 monos after they were run in for over 200 hours. I have to say that these monos sound pretty nice. We all know by now that Mike Sanders has a real handle on amp design and his designs are respected among the audiophile community. He doesn't even have to advertise for crying out loud. So, how do these puppies sound compared to the MC75's you ask? I thought the S60's sounded great! Great slam and resolution with a nice midrange but still PLENTY of detail. This is what you would expect from a quality set of monos.

I then switched back to the MC75's. I noticed just a bit better midrange and slightly more warmth but with all the detail still intact. Although both sets of monos sounded great, the MC75's just had that Mac magic that I just cannot seem to find anywhere else in a monoblock. Keep in mind we're talking about monoblocks under the $6,000/ pair range here. I am sure you can do better by spending more money but how much better, I'm not entirely sure.

So, if you're in the market for a pair of monoblocks do not hesitate to give the Silver60's a try. They have that Quicksilver signature sound that is nice and holographic while keeping that sweet tubey midrange sound intact that we tube-lovers enjoy. Can I reiterate that these babies really reveal a TON of detail when using the 6550 output tube. If you prefer a bit warmer sound, go with the EL34 output tube. You can also try a KT88 for a little more power output and that signature KT88 sound. The best part is that the S60's will not break the bank but still provide great audiophile performance. I know these are discontinued at this point but if you can find a pair used, JUST BUY THEM! Yup, I said it. DO IT!


Associated Equipment for this Review:

  • Von Schweikert VR-5 HSE (Hovland Special Edition) Speakers
  • Quicksilver tubed Linsestage
  • EE Minimax DAC Bolder Cables Level 1 Modified
  • IBM Laptop with Foobar 2000 Digital Audio Source
  • Theta Digital Carmen II CD Transport
  • EE Minimax Phono Stage
  • VPI Scoutmaster Turntable with VPI Zephyr Cartridge
  • Equitech/ PS Audio Balanced Power Conditioners
  • YFS Custom Cables & Interconnects
  • YFS Custom Room Treatment
  • Herbies Audio Lab Dampening Devices and Tube Dampers




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