Tubes in phono amplification and RIAA de-emphasis
The final goal in phono stage design stands in two pillars. First is to invert the RIAA curve in order to get a flat response out of the recording and the second is to amplify the vanishingly low signal generated by the cartridge to an adequate level for the preamplifier to receive.
In 1954 the Recording Industry Association of America established a universal recording format (RIAA equalization), which compressed the low frequencies during the record cutting and allowed for longer duration of LP’s with lower distortion. This compression must be inverted during playback in order to get a flat response and it is obvious that the closer the de-emphasis is to the original compression scheme the more “high fidelity” the play back itself will be.
The second point that a phono stage must achieve is to amplify the magnetic cartridge’s electrical signal so that it can be properly handled by any given amplifier. When it comes to moving magnet carts, the output signal is usually somewhere between 2 and 5 mV, which it may not look as much but it is enormous when compared to the low output moving coil (LOMC) designs who range about ten times less at 0.2 to 0.5 mV.
Here comes the hard part. When a phono stage is called to get the MC’s signal to a line level, similar to a CD or radio output the lower the current produced by the cartridge the more the noise.
A normal person would ask, why use the MC’s if the current produced is so low, thus so hard to amplify without significant noise? The answer is simple, they tend to sound better! Is it worth going for a MC? Sure is!
There are several ways of getting the job done for the RIAA de-emphasis as for the amplification. Usually the equalization is achieved with a passive way, by using resistors and capacitors to invert the original compression but other designs also apply, such as L-C-R and passive-active ones. The necessary gain can be achieved with all active gain stages (usually solid state for the lower MC’s) or hybrid (solid state+ tubes). Another way is to use step up transformers between the LOMC and the phono, typical of the tube phono stages with only MM level active gain. Due to the inherent higher noise floor of the tube designs, the former is the way to go for most of the designers, such as Lamm, Allnic, Ypsilon to name a few.
Most designers, but not all.
Designer Andreas Hatziminas of New Valve Order went the hard way. He created a tube-only phono capable of managing LOMC without the use of SUT’s. This is no joke design, the original NVO II phono utilizes no less than 23 valves, while the “smaller” brother reviewed here has 13. Still quite a lot of tubes, and comparing the NVO with a “normal” tube phono which would necessitate two double triodes to get the job done. Why all these tubes are needed? Simple, to get the RIAA curve right and to get, from an all-tube design, low operation noise while boosting the signal to the necessary level. The SPA one will provide 50 dB of gain for MM’s but more importantly a more than sufficient 60 dB of gain for MC’s. All this with a declared S/N of better than -80 dB for a nominal 2 mV MM and still a respectable -60 dB for a 0.3 mV MC input. These may not be on par with some solid state designs but remember folks, we are talking a tube-only phono stage.
Matching the cartridge with the phono is also crucial. NVO’s idea is that simpler is better so they opted for external jacks loaded with resistive values. No tiny hidden dip switches or knobs. Some might find this rather primitive but, speaking with the designer, he insisted on this as being very important sound-wise. My review sample came with two pairs, one for MM’s and one at 100 Ohms which is many audiophile’s choice for MC’s. Additional loadings can be supplied at request.
The same basic (some might call it utilitarian) design philosophy can be found in the front panel of the SPA one. Just two switches, one to turn it on and the other to select the gain for MM or MC, both of these have LED indicators. Graphics and case work are simple and no power cord is provided.
I guess the NVO one will not play music for your eyes, so what about music for your ears?
I must admit that I’m deep into classical music, but in order to get the picture right I often like to start with jazz. An all-time favorite is the album that Dave Brubeck dedicated to his wife, For Iola (Concord Jazz records). This is a later live Brubeck record, meaning that none of the original members of the quartet played in it. His son Chris is actually on the bass with Randy Jones on the drums and the exceptional Bill Smith on the clarinet. Brubeck was in his mid sixties when he performed for this session and you can tell by the mature sound he manages to pull out of compositions such as “Thank you”, “For Iola” and “Summer song”. Passed is the time when his piano tried to “steal” the crowds, on this live record he lets all the soloists breathe freely to perform at their best. Piano notes are always there and the SPA one lets them out with ease, tonal purity and perfect pin point imaging while the clarinet feels vibrant, transmitting those palpable emotions typical of the woodwind instruments. Yes, tubes and Jazz are made one for the other. Brubeck knew not only how to compose but also how to re-arrange a classic masterpiece such as “I hear a rhapsody” by Fragos and Baker. The clarinet creates a mystical introduction to the more famous melody and the SPA one clearly shows what the “magic midrange” of tube amplification is all about. In fact it transmits a free air movement that holds no boundaries and almost feels like that the notes hit me in waves coming from a few feet away.
Sometimes the simplest things are the hardest to achieve and this could not be more true for piano music. A long pure tone produced by a pianist is probably the most common sound that can be produced by an instrument and just about everyone living in the western world can recognize it. Just about everyone can tell if something is wrong, even if most would not know where to attribute this “feeling”. And when it comes to pure, long tones of exceptional emotional impact the work that comes to mind is Gymnopedies by Erik Satie. Listening to the Italian born, French adopted Aldo Ciccolini, a true maestro of the French composers, playing those few, pale notes of the first Gympnopedie (EMI), highlighted not only the life-like sound of the SPA one, but also the low operational noise. Between every stroke I could hear nothing but the slightest whisper coming from my system. Part of the merit should be assigned at the external battery unit of my ASR Emitter along with the highly polished shibata tip of the Audio Technica AT-20SLa, but still, inserting a tube phono in the chain is usually synonymous with a higher noise floor. Speaking with the man behind the NVO one, I was told that the earliest tube in the amplification chain is not the usual 12AX7 but the ultra low noise 6C45P. As Ciccolini went on I realized that there was no grain, edge or other artifact that could spoil my session. This was turning out to be a very relaxing experience and went on for another 2 LP’s of the same pianist/ composer.
A couple of days later, the mood was right for some full-scale orchestras. I was missing a clear view of the frequency extension of the NVO phono stage, so I opted for the big guns tulips, Johannes Brahms Doppelkonzert, opus 102, with Schneiderhan on the violin, Starker on the cello and Berlin’s Radio Symphonic Orchestra conducted by Ferenc Fricsay (DGG). When it comes to bass slam, my recipe is quite simple. Garrard 401 with a SAEC 308 Long version tonearm and Denon 103 R loaded with the 100 Ohm jacks provided with the phono.
Two things immediately hit me. Ok, maybe one hit me and one missed me. What was missing was some “body” down in the lower frequencies. I was not getting that loaded representation I am used to, when playing my old ASR basis battery-powered phono. It was as if I was sitting not in the fifth row of the concert hall but rather at the 15th row. The impact of the full-scale orchestra was still impressive but not that shocking as this record portrays it. At the same time, moving a few rows back helped in the overall image of the orchestra. What hit me, and became more and more evident by time, was the ability of the SPA one to control the lower frequencies. Less for more, I would say. Less in quantity but more in handling. That little something that was missing probably helped the mid-low frequencies to be clearer, allowing me to see the exact three-dimensional setting of the Berlin Orchestra.
Orchestral works are an excellent test for low-level detail retrieval. Naturally, you cannot miss the cello talking to the violin, but what about the flutes, oboes and the bassoons? Brahms used wind instruments heavily, and if there is a common problem in tube phono stages and amplifiers in general, it is that they fail to discern one from the other when the “tutti” hits. This was not the case of the SPA one. Brahms’ Doppelkonzert never managed to put the phono into crisis. Even when the entire orchestra was demanding a piece of the phono’s clarity, the notes came out crisp and natural.
During the last couple of months I had the chance to listen to the New Valve Order SPA one phono stage extensively. And while I was writing my conclusions it struck me that this phono is truly a “New Valve Order”. With its 13 tubes, it manages what solid state phono stages do, meaning that it amplifies the signal at adequate levels while staying very close to the RIAA de-emphasis curve, and at the same time remains on the low side of noise with either MM or MC carts. On top of that, I got a very pleasant reproduction with no edges that left me focusing on my music, all thanks to the amazing all valve design. Yes, some SS designs will get you slightly deeper and heavier bass extension, but they will not provide the same sensations when listening to voices, wind instruments or piano music. That’s the magic of tubes.
–by Dr. Panagiotis Karavitis
- Amplifier: ASR emitter I HD with external Akku
- Phono stage: ASR basis
- Speakers: ATC SCM 40, speaker cables by VanDamme
- Turntable: Garrard 401
- Tonearm: AudioTechnica 1100 Straight, silver wired
- Audio Technica tonearm cable
- Ccartridge: Audio Technica 20 SLa
- 2nd tonearm: SAEC 308 Long, SAEC cables, cartridge: Denon 103 R
NVO SPA one Specifications
Gain MC: 60dB
Frequency response: 20Hz – 200kHz within 0.5dB of RIAA curve
Total harmonic distortion: less than 0.05% in MC mode
less than 0.005% in MM mode
Signal to noise ratio: better than -60db @ 0.3mV MC input
better than -80db @ 2mV MM input
Minimum recommended input for MC: 0.2mV
Input load : MC / 1000 ohms
MM/ 100000 ohms
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About the Author
Dr. Panagiotis Karavitis is a medical doctor and published researcher working in ophthalmology, in Athens, Greece. A DJ early in life, he is a classical music aficionado and vinyl enthusiast. You can find out more on our new Contributors page.