Review: VTL Stereo Deluxe 90/90 power amplifier

 

A year or two into my audio journey, I was in college when an friend replaced his heavily modified McIntosh 240 amplifier with a set of VTL Compact 100 Monoblocks.  Our little audio community were a little disappointed since this change also meant the removal of his Quad ESL-63s.  These electrostatics were replaced by a big ol' pair of UREI 813 dynamic speakers, using the Alnico version of the Altec 604.  But, to be fair, the Quads - without a subwoofer, weren't the best for rocking out.  Understandable to us 20-somethings.

Along with the amplifiers came the VTL book, something that he loaned to me.  At the time I didn't know too much about circuits so I read David Manley's words with much interest.  I was a poor college student at the time and was firmly stuck in the (then) more affordable world of vintage gear.  Dynaco was more my speed with the PAS-3X and the Mark IVs being in my system at the time.  Owning new tube gear was just out of my means.  

I'll hit the fast forward button on my life.  So many years later my interest in modifying or building my own tube or solid-state gear has declined.  Some of it is cost, why make a tube amp when there are so many reasonably priced units out there?  And a lot of it is patience and my close up vision isn't what it used to be.  The idea of staring at a circuit board or a snake pit of wires hour after hour no longer holds the same interest.  It is so much easier to buy something, and at such a reasonable price, this used VTL Stereo Deluxe 90/90 power amplifier was a must buy when I saw it on Audiogon,

 

Okay, what is the VTL 90/90?  It is a 90WPC - their claim, not mine - tube amplifier using a pair of 6550s (or KT88s or KT90s) and a pair of 12AT7s per channel.  No tube rectification, no B+ regulation, and no power supply choke.  Instead they use a large amount of capacitance to get the B+ ripple down.  The output tubes are also connected in Ultralinear, which means the screen grids of the output tubes are connected to taps on the output transformer primary.  Bias is relatively low, only 35mA per tube, meaning heavy class B operation.   The output iron is of note - being made by Mercury Magnetics - which are known for high quality.

This is not really the way I would build an amplifier.  I prefer, at least philosophically, pentode output stage and some type of regulation for the screens and the input stage.

Physically speaking the VTL is not as imposing as my Sonic Frontiers SFS-50.  The SFS just looks better built with the meter, larger chassis, and bigger output transformers.  It also has a trick cascoded differential 6922 input stage, and well, lots of regulation going on.  The VTL, on the other hand, has a Mullard 5-20 type circuit with a parallel 12AT7 input tube and a long-tail phase splitter (with no current sink) afterwards.

So, you are already asking after that long introduction, how does the VTL sound?  I'll try to keep this short. I will be comparing directly against the Sonic Frontiers SFS-50.

A quick note on tubes:  I used vintage three-hole Tung Sol 6550s and GE labeled (made by Lansdale) 12AT7s for the VTL.  Not the pictured tubes which came with the amplifier.  The SFS-50  amplifier used the same output tubes and Tungsram ECC88s. 

The VTL has a big bold and dynamic sound.  This is a fun amp to listen to!  Bass, something the company was known for, has a deftness that a lot of solid-state amplifiers could only dream about.  How is this possible?  I don't know given the lower output impedance of silicon based amplification.  The Sonic Frontiers, however, seems to best the VTL in the very lowest bass notes.  I suppose that makes sense with the bigger output iron and all that regulation. 

 

What surprised me the most about the VTL 90/90 is how natural it sounds.  The character of the amplifier is the same from top-to-bottom.  It's just an easy amplifier to listen to.  The SFS-50, on the other hand, is more neutral.  When it comes to detail the Sonic Frontiers is the clear winner, but that, as I will mention later, this comes at a cost.

Soundstaging?  The VTL is w-i-d-e and deep.  Vocals, like in The Ubiquitous Mr. Lovegrove by The Dead Can Dance has real presence and body.  This is a real treat, as was my American copy of Pink Floyd's Dark Side of the Moon.

So where does this amplifier fail?  This is a thorny question and one that drives into the pros and cons of this hobby.. It is a matter of detail.  I love detail but I can also be actively annoyed by excessive amounts of it because lesser recordings sound, well, bad.

The Sonic Frontiers, with its 6922 front end, has so more detail.  Like the sound of the hands striking the aforementioned Dead Can Dance song.  It really breaks down the recording into more component parts that the VTL amplifier.  The VTL blurs this detail - only by a bit - but is also a touch more engaging.

What amplifier do I prefer?  It's a matter of taste.  The VTL is just enjoyable, sounding more like a powerful Dynaco amplifier.  The Sonic Frontiers is better for those days I want to eek out more detail and hear the best that my system can do in a purely audio geek sense.

  

System:

Rega P8 turntable with Rega Ania Pro MC cartridge 

to a Denon AU-S1 step-up transformer

to Cardas Neutral Reference interconnects

to an Audio Research SP-8 (with a mix of vintage Mullurd and Amperex tubes)

to Cardas Iridium interconnects

to the amplifier(s) being tested here

to Cardas Iridium speaker cables

to KEF R500 loudspeakers 

 

Review: Denon AU-S1 step up transformer

 

Moving back to a low output moving coil has been a real eye-opener.  Yes I had experience with the venerable Denon DL-103R mounted on a rather sketchy VPI HW19 Mark III with a Rega RB300.  But, at least with that system from long ago, I never quite cottoned to the sound I was getting.  I wanted more.  Luckily I found it (some time later!) with the Rega Planar 8 with a Rega Ania Pro MC cartridge.  This combination has quickly become my favorite analog reproducer so far.

My MC step-up transformer is the popular Cinemag 1254 which did its job quite admirably.  Nonetheless I had a nagging thought I could do better here.  Would a passive device, especially something made of wound wire actually make a difference?  I had to find out.  So I read and read some more, trying to find an affordable venue to follow.  I thought of buying some Lundahl transformers and DIYing my own case.  Or I could have gotten anything else, including an active device to give me that additional gain needed for the low 350 micro volt output of the Ania Pro.

Several searches on Ebay and I saw a Denon AU-S1 unit for sale.  It looked extremely well built, more so than my Cinemag "transformers on a box" look.  But finding information on the Denon was, to be blunt, extremely difficult.  It was designed for Denon's once top-of-the-line cartridge, the DL-S1 that cost a princely $1000 way back in 1996.  The transformers themselves are mounted horizontally in the case with padding to reduce vibration.  How much this would work in real life is questionable.

After several audio philosophical discussions a friend, I decided to take the risk on purchasing the AU-S1.  It was the idea that something like this would be of the highest quality given the amount of time and research that a company like Denon can do.  There was only way to find out.  Thankfully the Japanese seller was very quick and I received the transformer(s) in only three days.  The AU-S1 weighs _alot_ for such a small thing.  Build quality was extremely good with gold-plated RCA jacks and (oddly enough) separate grounding lugs for each channel.

 I took out the Cinemags and put the Denon in its place.  Turning the volume up I was immediately taken aback by the amount of hum I was getting out of the speakers.  Moving the AU-S1 around and I was able to get some reduction in noise but still I wasn't happy about it.  It wasn't until I touched my fingers to the left RCA outside jack and then to the ground lug that the hum completely disappeared.  It's the nature of the Rega turntable output connection which doesnt have a separate ground wire.   To circumvent this grounding issue I took a length of solid-core bare wire and wrapped it several times around the left RCA outside lug with one end plugged into the ground lug of the AU-S1.  After that I was hum free!

Well, dear readers, that was a lot of introduction for something that was ultimately bought as an experiment.  How does it sound?  Read on.

Initial impressions were good - solid bass, a "cleaner" view of the soundstage, and just better air. Several records later and a listening session with my audiophile friend and I can say the Denon AU-S1 was a worthwhile upgrade.   

Does it surpass the Cinemags?  Yes.

The Denon reproduces the space around instruments better - such as the horns on Lonnie Liston Smith's Visions of a New World.  This gives the impression of more body and weight.  

And speaking of body, the bass is terrific.  It feels like an extra octave is being recovered - not bloated - but detailed with depth and slap.  Something that was really apparent on Brian Bennet's Voyage album as the excellent bass player provides the space age groove.

Soundstaging is deeper and wider than before.  An example of this is the beautiful Dead Can Dance album Into the Labyrinth.  The second song, "The Ubiquitous Mr Lovegrove," has a moment where the drum shifts left and right, now well detailed beyond the edges of my KEF speakers.  A true demo disc moment.

Overall there seems to be less grain than before.  Why?  I have no idea.  The purity of the copper?  The padding reducing microphonics?  The quality of the transformer windings?  Your guess is as good as mine but the clarity is higher than before and that's all that matters.  Finesse would be a fine word to discuss these SUTs, and given their roughly $700USD price they are a good bang for the buck.  Perhaps, when funds permit, I'll try something more expensive.

Denon AU-S1 Step-up Transformer Specifications
- Ratio: 1:13
- Frequency range: 10Hz-80kHz
- Size: W150 x H70 x D175mm
- Weight: 7.1 pounds

Review: Monoprice MHP-839 headphones

(image from Google)

Having never spent more than a $79 on a pair, I'm a admitted headphone cheapskate.  For work, I'm a longtime user of the budget Sennheiser HD-201, while for home use, the Grado SR60s get the nod.  At heart I will remain a speaker guy since the visceral gut impact of something like the UREI 813As just can't be matched even by the finest headphones.  But for listening to MP3s at my desk or while doing late night mixdowns of my amateur synth music, it's hard to beat the sonic solitude of a pair of headphones.

When I finally decided to give up the Sennheiser HD-201s, a good audiophile friend recommended the Monoprice MHP-839s.  He's a longtime Sennheiser HD-600 user, but commented that the Monoprice headphones were quite enjoyable with a nice overall sound for the price.  I ordered my pair from Amazon - hey, free shipping! - and got them a few days later.

After a few hours of break-in, I found the Monoprice headphones to be quite decent.  The lowest bass goes quite deep with more impact and slam than the old HD-201s.  They also have a richer midrange, making the Sennheisers sound a bit nasal and hollow.  Perhaps the Monoprices are a tad congested - for example, sounding like a doped paper woofer than something like Kevlar.  Their biggest failing is in the treble.  My middle-aged ears don't quite hear the higher frequencies like they used to, but even I could hear a steep roll-off here.  This isn't a big deal for MP3 sources or anything that was recorded a little on the hot side - like many Synth or Dance mixes, but could be a deal breaker for the serious audiophile.  With their open back design, I prefer the Grado SR60s - they have a clarity that is hard to beat for the price - but such a design wouldn't work for my workplace.

As far as design, the Monoprice headphones aren't quite as comfortable as the Sennheisers.  I notice my ears getting hotter quicker.  I have a fairly large noggin though, so perhaps I'm stretching the band pretty hard.  Compared to the HD-201s, the background noise of a busy office is muted more with the Monoprices.  This is good if you require noise suppression like I do - programming takes concentration.

Construction quality is good - these headphones are built with heavy-duty plastic.  The two different lengths of supplied cords are a nice touch.