Dave Denyer: The Reel-to-Reel Rambler

Following the sad passing of ‘the god of open reel tape’ Tim de Paravicini (pictured right) in late 2020, Ken Kessler penned a couple of guest blogs on Tim’s life and work: “I’m sorting that for Paul McCartney” and “He worked on machines for three Beatles”, which proved hugely popular. There probably wasn’t an open-reel deck ever devised that Tim hadn’t examined, inside-and-out, domestic or professional. So, in another conversation with Ken Kessler, I found myself wondering about Tim’s decks of choice…  turns out that Tim’s default machine on the road was the semi-obscure Denon DH-710F. Over to Ken to tell us why.

Ken Kessler: Dave (Denyer, aka the R2R rambler) dropped by my place for a listening session and heard, for the first time away from a hi-fi show, a Denon DH-710F machine, just like the one Tim schlepped around the world – fully-serviced but unlike Tim’s mine is bog-standard. Whenever there was a show where EAR-Yoshino was exhibiting, Tim’s DH-710F would have pride of place, along with other oddities like a true 4-channel (i.e. quadraphonic) Sony deck.

It didn’t take much for Dave to be blown away by the Denon – which is all the more remarkable since he owns a few magnificent tape decks himself, and also he knew the tapes we were playing. The scariest part of this is that Dave was still dazzled by what he heard, despite my particular Denon not having been modified as per Tim’s machine.

As Dave made me aware, it’s a privilege to own any DH-710F, which my investigations suggest were not imported into the UK, the bulk staying in Japan or selling in the USA. Indeed, nearly every Denon open-reel deck that I’ve seen turn up online, as well as the related DH-510 and DH-610 models, has been offered from Japan or the USA, though recently a UK vendor was selling one for £7,500. Yes, they’re fetching that kind of a sum, if not more … and it’s invariably because the reel-to-reel underground knows it as “Tim de Paravicini’s Favourite Tape Deck.”

Combing through various sources, including Denon’s own superb website’s historical pages, I learned that the DH-710F was announced in April 1976 for 439,000 yen. In today’s money, that’s still £4,500 – less than you’d pay now for a mint example, but placing it firmly in the high-end. While I have yet to find a definitive listing of all the open-reel decks offered that could play both ½-track and ¼-track tapes, the DH-710F had this capability, like the Technics RS1500 and the Otari MX-5050. Unfortunately (for me), and unlike those machines, Denon provided only two speeds, 7.5ips and 15ips, so my 3.75ips tapes can’t be played on it, which is a pity: I would love to hear how they sound compared to playing them on the G36.

Denon’s own description is of a “full-fledged high-performance open-reel deck developed for audiophiles.” Tape handling is marvellous, thanks to its three-motor, direct-drive, two-capstan transport system, with electronic tension AC servo. On a machine this old, the latter sometimes has a mind of its own, e.g. slowing way down when rewinding a 10in spool so much such that it stops with the last couple of meters of tape still on the feeder spool. No big deal, but I thought you should know.

As the photos (below) show, the DH-701F is two-chassis affair, with the pre-amplifier in a separate enclosure. This can be positioned below, as I have it, or on top in studio fashion. There are fittings for hinged lids, which I do not own, but this suggests that Denon expected professional users to schlep it around. The electronics are divided into two identical sections truly separating the channels; umbilical chords connect the two, so it would be easy to try the Denon with one of the new after-market tape preamps, such as the all-valve model from Doshi, the Evolution Tape Preamplifier.

With power on/off, the transport controls, speed selector, cueing lever, counter and track select (a button on the heads cover) being the only operational elements on the transport section, everything else is found on the pre-amplifier panels. It’s worth noting here that the Denon has one of the easiest tape feeds I’ve experienced, as straightforward a path as that of the Revox G36, and the antithesis of the Technics RS1500 or those big-ass Studers with so many tensioners and rollers that you need a map to load a tape. Thanks to a symmetrical layout and two tension arms, Denon was able to design it to be as close to a straight line as possible.

In addition to the most obviously-required record and playback level controls – all mirrored for the two channels with nothing shared and “L” and “R” in the fascias’ upper right hand corner to denote which is which – the preamp units feature in their left-most segment two toggle switches to select record mode and monitor “Input”, “PB” for playback, and Bias. To the right of the toggles is the button to set Peak or VU for the analogue meters. The only variants between the top (left) and bottom (right) panels is that the latter houses the headphone socket for monitoring via cans.

Next come the VU meters with peak maximum indication +3dB, followed by stacked rotary controls for continuously variable bias and equalisation adjustment, so you can optimise the Denon to match the characteristics of whatever tape formula you prefer. Then there are three rotaries in a row for playback level, with a line and click-stop at 2 o’clock for median output levels (set to 0VU, 0.775V), then the separate record level controls for line in and microphone. Lastly are the button for mic attenuation by 12dB and a socket for ¼in mic jacks.

Denon went all-out with this machine, which Tim once told me was the state-of-the-art semi-pro or domestic deck of its day. The direct-drive, 2-capstan, servo-assisted transport employed a magnetic recording/reproducing system for speed detection, along with a sub-capstan coupled to the capstan motor shaft and an inelastic belt. Denon devised this to eliminate tape tension or large load fluctuations at start-up. This graced the DH-710 with a specification of wow-and-flutter of <0.02% WRMS 15ips. Further ensuring the safety of the tape, all contact was made with special guide rollers, save for the head contact, and the DH-710 featured a one-way air damper to prevent excessive tension; this is one machine that is super-smooth at the start.

Newly-developed record and play Sendust alloy heads made by Denon, with 2.1mm track width, ensured excellent S/N during playback, specified as >66dB for maximum recording level (514 pwb/mm) and >58dB for standard recording level (200 pwb/mm). Maximum output level of the recording amplifier was been set at >30dB @ 1kHz, above the standard level, to match professional equipment. Boldly, Denon stated that “distortion due to saturation of the recording amplifier will not be recorded – almost never.”

As uncluttered as the Denon DH-710F looks, it was brimming with hidden features, and I discover something new each time I fire it up. One safety design was the reel motor shaft rotation detection mechanism. This prevents accidental tape damage if you press the play button during fast forward or rewind, as playback will not start. This was designed so that playback and recording cannot commence until the tape motion has stopped. When the tape finishes running, the photoelectric tape end sensor automatically stops the mechanism.

Then there are the specifications, which also attest to the deck’s greatness – even without Tim’s tinkering. The frequency response was stated as 30Hz-30kHz ±2dB for 15ips and 20Hz-20kHz ±2dB for 7.5ips. EQ was NAB standard, and channel separation was >55dB (2track @ 1kHz). With Scotch 206, the Denon’s total harmonic distortion was <0.5% @ 1kHz. On a practical level, the shelf on which you might place it would need to support 27kg for the transport and 8.5kg for the amplifier, while the former occupied 505x420x310mm (WHD) and the latter 490x180x330mm (WHD).

In use, the Denon is a delight, and it is my dedicated deck for high-speed ¼- and ½-track NAB tapes when I have visitors calling. Again, threading tape is a no-brainer, and I cannot fault the sound. It is warm, open, transparent, and with bass so deep that it gives the Wilson Sasha DAWs a work-out. Sadly, Tim passed away before carrying out two threats, to modify my Denon DH-710F and my Technics RS1500, so I can only imagine how either deck could sound even better than they do, but Tim was never to be underestimated.

Tim’s declaration was that his modifications to both decks would render them flat to beyond audibility, any phase anomalies would be corrected, non-essential circuitry would be bypassed, and other tweaks and delights that I knew were not hyperbole. After all, I own a Revox G36 long ago blessed by Tim, and it’s the only one out of my ten decks which gives the Denon a serious run for the money. To choose between the two if I could only keep one would be torment.

As for choosing which deck to use with which tapes, that is one of those delicious challenges which I imagine is the sort of conundrum facing someone who owns a bevy of Ferraris, a few dozen Rolexes, or a substantially full wine cellar. The only serious concern with the Revox G36 – luckily for me I have the ¼-track 3.75ips/7.5ips version, not the 2-track, so it handles 98% of my tapes – is the heat it generates thanks to its tube count, while its age means I only use it for special occasions. The Denon, on the other hand, suggests the need for less cossetting treatment. As for the others, the Nagra IV-S is 2-track-only. The Pioneer RT-707 only handles 7in-spools. Same for my TEAC X3 or the TASCAM 22-2. Tough choices, someone has to do it.

While I doubt I will ever find the optional remote, let alone the fitted covers, my Denon DH-710F will stay where it is until it’s my time to see Tim again. He will say, finger pointing at my chest, “I told you so.” And I will gladly concur.

After working as Assistant Editor for the short-lived Stereo – The Magazine, Ken Kessler joined Hi-Fi News & Record Review in 1983, where he still serves, latterly as Senior Contributor. He writes a monthly column for SoundStage and contributes as well to online magazines Tone and Copper. A collector of old hi-fi components with a passion for the history of audio, Ken is the author of Quad: The Closest Approach, McIntosh… For The Love Of Music, and Audio Research – Making the Music Glow, and is co-author of Sound Bites: 50 Years of Hi-Fi News and KEF: 50 Years of Innovation In Sound. He is currently working on another four audio histories.