Category Archives: Recorders

Hi-End Hifi Upgrades for the Revox B77 / PR99 Reel to Reel Decks

The Los Angeles and Orange County Audio Society site hosts an interesting paper describing a step by step procedure for upgrading the B77 and PR99 Revox models for higher playback quality. The document is a work by Arian Jansen of Sonorus Audio. We talked about Sonorus Audio’s
ATR10 tube reel to reel deck here

The modified machine becomes a playback-only device, addressing hi-end hifi listening, however it is possible to preserve recording functionality by applying only part of the modifications.

The guide contains DIY instruction to perform:

  1. doubling operating speed up to 15 IPS, for lower speed models (US residents only, due to 60Hz power-supply requirement)
  2. conversion from NAB to IEC EQ
  3. upgrading the output capacitors to higher specs components
  4. removing from signal path the components (a couple of transistors) required for auto-muting, used to suppress audio output during ff/rew operations.

Visit the Los Angeles and Orange County Audio Society site here and the document in pdf format here.



Even more reel to reel decks: J-corder !

After Revox-based Sonorus ATR10 (discussed here) and TASCAM-based UHA-HQ series (here) let’s now give a look at the J-corder brand by Jeff Jacobs.  Most readers will immediately recognize the unmistakable headblock plate in the picture below: J-corder specializes in customizing and upgrading the RS-1500/1506/1520 Technics series.

J-corder reel to reel decks

J-corder reel to reel decks

These models are ideal listening devices for analog mastering studios or hi-end home hifi. The recording section is not removed, like with UHA-HQ models (and unlike Sonorus ATR10, which is a REPRO machine).

Cosmetic rework is simply beautiful: materials used for finish range from wood to carbon fibre, to kevlar.

Rather than focusing on upgrading the electronics, as other companies do, J-corder specializes in several customization options on the headblock, in collaboration with John French from  JRF Magnetics (we talked about JRF Magnetics here).

The headblock upgrade options:

  •  Three Head Option: eliminate the 2/4 head switch and have the machine converted to a fixed two-track or four-track configuration for best performance in specific applications.
  • Four Head with external Playback Option: an additional playback head with its own separate wiring for direct  stereo output. Maximum minimalism on the signal path here: ideal for external tube preamps.
  • Autoreverse modification for RS-1700: transform the recording/erase autoreverse heads into a unidirectional 2-track recording section, for increasing recording quality. Playback is still autoreverse.

Special machined headblock plates in Aluminum or Brass are available for the options above. Here is a nice picture of one of these new parts for the RS-15xx Isolated Loop dual roller transport. Note that the slot for the 2T/4T original switch is not present (see options above).

J-corder aluminium headblock plate

J-corder aluminium headblock plate

J-corder offers also a rebuilding service for your own machine:

  1. Completely disassemble the machine
  2. Replace brakes and springs
  3. Replace bearings if needed
  4. Hardwire in the heavy-duty power cord
  5. Resurface and laser align all heads
  6. Clean and lube all switches, pots and controls
  7. Treat all connecting posts with “Deoxit” rejuvenator and protector for better electrical connections
  8. Reassemble and recalibrate the machine with ATR tape

Visit J-corder web site here.

More reel to reel decks: United Home Audio !

I’ve recently talked about the ATR10 in this page. This time it’s turn of United Home Audio HQ series.

UHA reel to reels

UHA-HQ decks

UHA-HQ decks are based on recent TASCAM reel to reel units, with modified electronics, heads, power transformers and parts, depending on model. They are compatibile with prerecorded tapes included in the Tape Project catalog, discussed here.

We’re talking about machines intended to perform at their best for esoteric hifi listening. However it’s interesting to note that they can record as well, unlike the more common REPRO units often used as hi-end playback devices.

Here is a summary of UHA-HQ models (and for each one, a note describing the main improvement over the previous one).

  •  Phase 5 – new playback preamp
  •  Phase 6 – new UHA-HQ playback head
  •  Phase 7 – new UHA-HQ recording head
  •  Phase 8 – audiophile toroidal power supply – new playback and recording preamps
  •  Phase 9 – new esoterics caps on play and rec boards, nearly DC-coupled signal path

(complete details about differences are available at UHA site).

Features (some depend on model):

  •  Tape: 1/4”
  •  Reels: up to 10 1/2”
  •  Heads: half-track, capable of record and playback
  •  Speeds: 7 1/2 and 15 IPS – 19 cm/s and 38 cm/s
  •  EQ: NAB and IEC
  •  Servo-controlled tape tension
  •  Sealed bearings on the idlers
  •  XLR and/or RCA inputs and outputs – selectable RCA output of +6db or +12db

Visit the UHA-HQ series page at UHA site.

Sonorus Audio ATR10 Vacuum Tube Reel to Reel

Sonorus Audio produces the ATR 10, a reel to reel deck based on the chassis from the Revox PR99 . The ATR10 is a 1/4” REPRO machine (playback only, no recording) for hi-end music listening.


Sonorus Audio ATR10 Vacuum Tube Reel to Reel

Electronically regulated tape tension,  dual EQ (NAB and IEC), wire remote controlling and Library Wind (FF controlled speed to prepare tape for storage) are all new functionalities.

Sonorus builds the tape transport with original mechanical components from Revox/Studer. Internal electronics have been redesigned to use parts currently in production. The playback board is completely new, featuring a vacuum tube preamp section.

Frequency response:

  • 15ips: 18Hz – 23kHz (+2/-3dB)
  • 7.5ips: 14Hz – 20kHz (+2/-3dB)

Signal-to-noise ratios: RMS, ASA-A weighted,  +6dBVU (510nWb/m)

  • NAB (7.5ips): 73dB
  • NAB (15ips): 71dB
  • IEC (7.5ips): 71dB
  • IEC (15ips): 73dB

Distortion: THD measured at 1kHz

  • 15ips, 0dBVU: <0.15%
  • 15ips, +6dBVU: <0.5%
  • 15ips, +13dBVU: <3%

Tape tension: Electronically regulated. Tested with 10.5” (26.5cm) reels.

  • Supply reel side: 0.45N +/-0.05N
  • Take-up reel side: 0.60N +/-0.05N

Visit Sonorus Audio site here, or direct-download the brochure and the user manual.

Upgrading Tape Recorder’s Electronics: Tube Preamps

An interesting way of modifying an open reel deck is to take the direct output from the playback head and route it to an external, higher quality, preamp bypassing the internal one.

Bottlehead, located near Seattle, produces hand-made dedicated tube repro preamps.These units are intended for 2 track systems.

Their top end model, Tube Repro, features:

  • XLR-balanced outputs +4dB
  • RCA-unbalanced outputs +10dB
  • CCIR  EQ
  • NAB EQ

Different custom EQ curves available on demand.

Bottlehead Repro

Bottlehead Repro

Another model, the Eros Tape Head Preamp, is available as a kit. To my knowledge this is the only tube repro kit available on the market as of 2012.

Eros Preamp

Eros Preamp

Bottlehead also sells upgraded replacements for mechanical parts along the tape path (Otari and Technics decks)
Visit their site here and head to the Reel To Reel section.

Fostex, 3M, MCI Manuals mantains a terrific collection of scanned open reel manuals. Files are hosted on RapidShare. also sells ORGINAL HARDCOPIES for some models/brands at their site.

  • View Fostex manuals here.
  • View 3M manuals here.
  • View MCI manuals here.



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Ampex, Otari, Tascam Manuals mantains a terrific collection of scanned open reel manuals. Files are hosted on RapidShare. also sells ORGINAL HARDCOPIES for some models/brands at their site.

  • View Ampex manuals here.
  • View Otari manuals here.
  • View Tascam manuals here.

Studer/Revox: Technical Papers Including User and Service Manuals

FTP area at swiss Studer site containing:

  • user manuals
  • service manuals
  • brochures
  • technical info

for Studer and Revox open reel recorders.

Access the Studer documents here.

Access the Revox documents here.

Please don’t abuse of site bandwidth.

Reel2reel Frequency Responses

A wonderful page showing frequency graphs formany r2r machines, by Jack Endino.

Visit the frequency graphs page here.