Review: Threshold FET Nine Preamplifier

Category: Preamps

The FET Nine from Thereshold as well as the FET Ten were the last of the Nelson Pass designed preamps to emerge from the original Threshold Company co-founded by Nelson Pass.

The Fet 9 is a high end preamp of extraordinary build and sonics. This preamp has few peers in the lofty world of high end. It competes quite well with preamps from Krell,Levinson,Klyne and Coda.

This preamp has provisions for three line inputs, plus an absolutely stellar phono section and can accommodate two tape units as well.

Blessed with an outboard power supply to keep any transformer interaction away from the preamp.

The phono section can bet set up for Moving Magnet and Moving Coil and the appropriate loading values can be set as well.

One look at the interior of this preamp with its gold circuit boards and wiring layout, immediately makes the statement that this is a no nonsense preamplifier. The build quality with its thick front face plate to its all steel chassis puts this in rare company indeed.

Dual channel, non-Inverting, field effect transistor preamplifier designed to provide gain and equalization for all moving and stationary coil "magnetic" cartridges and conntrol and routing functions for high level signals. Gain, impedance, and capacitive cartridge loading characteristics are internally selected.

Three high level inputs are provided plus record and monitoring for two recorders. Front panel controls provide program selection, record signal routing, monitor signal selection, channel balance, and audio level.

Phonograph Cartridge Section:


Impedance loading variable in increments
between 22 Ohms and 47,000 Ohms
Capacitive loading variable in increments between 50 picoFarads and 1,000 picoFarads. Gain factor selectable at 40 dB or 60 dB.

RIAA Equalization:

Passive and active topology computer designed to 0.025% accuracy. Selected precision components used in construction hold deviation to within 0.25 dB of model.

Distortion: No greater than 0.02% @ 1 volt stage output.

Noise: No greater than - 80 dB referenced to (1 millivolt input @ 1,000 Hz.)

Crosstalk: No greater than - 70 dB @ 20,000 Hz with 1,000 Ohm source.

High Level Section Frequency Response:

Virtually flat within a bandwidth having - 3 dB points at 1.5 Hz and 125,000 Hz.

Distortion: No greater than 0.02% @ 3 volts RMS out 20 Hz through 20,000 Hz into 10,000 Ohms

Crosstalk: No greater than - 75 dB @ 20,000 Hz with 1,000 Ohm source.

Noise: No greater than -100 dBA referenced to 1 volt input.

Input Impedance: 25,000 Ohms.

Output impedance: 100 Ohms. Maximum output swing: 20 volts peak-to-peak.

Gain: +20 dB

Dimensions & Weight

Dimensions: 19" wide, 1.75" high (add .25" for feet), 6.5" deep (rear surface of faceplate to end of connectors). Approxiimate weight: 4.5 pounds.

Power Source Module

5.125" wide, 1.75" high (add .25" for feet), 6" deep. Approximate weight: 2.5 pounds.

Music Used For Evaluation:

LP Playback:

Bob James - Hands Down (Columbia FC 38067)
Hiroshima - Self Titled - (Arista MFSL1-525)
John Coltrane - Blue Train - (Blue Note BST 81577)
Wes Montgomery - Bumpin' - (Verve V6-8625)
Rickie Lee Jones - Self Titled - (Warner BSK 3296)
Wynton Marsalis - Live Blues Alley - (Columbia PC2-40675)
Eric Gale - Forecast - (KUDU Records KU 11)(CTI Records)
Kenny Burrell & Grover Washington Jr - (Blue Note BT 85106)
Earl Klugh - Finger Painting - (Blue Note MFSL 1-025)
Larry Carlton - Friends - (Warner 23834-1)
Sadao Watanabe - Autumn Blow - (Inner City IC 6064)
Doobie Brothers - Minute by Minute - (Warner BSK 3193)
Santana - Zebop - (Columbia FC37158)
Pat Metheny Group - American Garage - (ECM 1-1155)
Frederick Fennel - Cleveland Symphonic Winds - (Telarc 5038)
Paul Desmond/Jim Hall - Complete Recordings - Mosaic(MR6-120)
Time Out - Dave Brubeck Quartet (Columbia CS 8192)
Paul Desmond - Self Titled (Artist House AH - 2)
Ahmad Jamal - But Not For Me - Argo LPS 628
Bill Evans - At The Montreux Jazz Festival - Verve V6-8762
Bill Evans - At Montreux II - CTI 6004
Sunken Cathedral - American Gramophone - AG 361
No Bass Hit - Concord Jazz Label - CJ-97
Oscar Peterson - Night Train - Verve V-6 8538
Gerry Mulligan Reunion Chet Baket - Pacific Jazz ST 90061

Compact Discs Playback:

Ben Webster At The Renaissance (Contemporary Records OJCCD-390-2)
The Royal Ballet Gala Performances (Classic Compact Discs CDSCD 6065)
Jurassic Park Motion Picture Soundtrack (MCAD 10859)
We Get Requests - The Oscar Peterson Trio (Verve 810047-2)
You Won't Forget Me - Shirley Horn (Verve 847482-2)
On Every Street - Dire Straits (Warner Brothers 26680-2)
Trio Jeepy - Branford Marsalis (Columbia CK44199)
Paris Jazz Concert - Louis Armstrong (RTE 1001-2)
Braveheart Motion Picture Soundtrack - London Symphony Orchestra (London LC0171)
Patriot Games Motion Picture Soundtrack (RCA 07863 66051-2)
Highlights From The Plugged Nickel - Miles Davis (Columbia CK 67377)
Private Investigations Best Of Dire Straits (HDCD) - Dire Straits (Warner Bros 49891-2)
Straight Up - Bob James Trio (Warner Bros 945956-2)
Land Of Giants - McCoy Tyner (Telarc 83576)
New York Reunion - McCoy Tyner (Chesky 5173324)
Gladiator Motion Picture Soundtrack(Decca 2894670942)
Copland - Appalachian Spring (Telarc CD 80078)
Frederick Fennell - Holst Suites (Telarc 80038)
Tchaikovsky - 1812 Overture (Telarc 80041)
John Williams - American Journey (Sony 89364)
Bizet - Carmen (Telarc 80048)
Live At Sweet Basil - McCoy Tyner Trio (Evidence ECD 22106-2)

The Threshold FET nine is a unified preamplifier system containing both moving coil/moving magnet phonograph cartridge gain stages and high level control stages in a single, single rack height chassis with external power supply. All gain stages of the FET nine are operated in the pure class A mode.

The cartridge gain stage of the FET nine employs the same basic topology as the FET ten/pc. However, the extravagance of space and component expense implicit in production of parallel stage elements has been dispensed with. This allows the FET nine to exhibit the musical transparency of the FET ten in essentially half the physical size and with minimal amounts of measured noise and distortion.

The moving coil/moving magnet cartridge preamplification of the FET nine is provided by a single stage whose gain and loading characteristics are internally adjusted to the requirements of the carrtridge in use. The input of this stage is specifically designed to exhibit no source/load interaction and assures that subtle colorations will not be added to the character of the selected cartridge.

An exact inverse to the RIAA recording curve is achieved through a combination of passive and active equalization, This de-emphasis circuit is designed to a computer model accurate within 0.025% deviation, Production of the circuit as realized in the FET nine employs individually selected precision tolerance components, This assures that phase and amplitude relationships within the music signal of an analog disc recording are accurately maintained during playback, As a result the cartridge gain stage of the FET nine reproduces all characteristics of the cartridge in use with precise linearity,

In addition to the phonograph cartridge input deescribed above the FET nine provides three high level inputs plus record and monitor facilities for two associated tape recorders, This allows for connection and control of up to six pieces of ancillary equipment.

The high level gain stages of the FET nine include cascoded MOS-FETs, The cascode circuitry employed suppresses voltage variations and maintains operating linearity of the MOS-FETs at an optimum level while holding distortion to tiny percentages with simple, direct gain paths, Careful selection of internal operating impedances assures that all equipment will be appropriately loaded without the use of "buffer" amplifiers between the primary signal sources and the connected recorders, This places the recorders a step closer to the original source and assures that the recorded signal will not be subject to subtle degradation,

Biasing of all signal carrying gain devices in the FET nine is performed outside the signal path
by precision monolithic J-FET constant current sources. These shield the active components in audio path isolating them from modulation effects during transient supply demands. This provides a substantial dynamic capability and assures that the full potential of source equipment and material is effortlessly realized

The FET nine is powered from an external power supply module which is identical to those used for the FET ten system, The supply utilizes a large transformer followed by forty-two hundred microFarads capacitance provided by computer-grade capacitors, This smoothing of the supply voltage is then followed two discrete class A voltage regulators, The supply rail regulation of this design in conjunction with extensive film capacitor bypass and the extremely high power supply rejection ratio built into the gain topologies insures no interaction between either of the gain stages or the outside power environment. This preserves the neutrality of the FET nine gain stages by their complete isolation from any fluctuations that may occur in their power sources.

In its day the FET Nine was a clear cut Class A reviewed product in the audio press. And remaind to this day one of the highly sought after full featured preamps with on board phono section. If your looking for a preamp of this caliber the FET Nine just could be your forever preamp. I have used this preamp with a wide variety of power amps and have yet to find an instance where the FET Nine did not excel.

In the realm of previously owned preamps this should be on anyones very short list to acquire. The FET Nine does not come along all the frequently and the usually sell in the $750.00 to $900.00 price levels depending on condition and if the unit has original box and manual. When one considers the used value for a preamp of this quality, it becomes a literal no brainer to acquire. Highly recommended by this jaded audiophile.

Associated gear
Click to view my Virtual System

Similar products
Krell, Levinson, Threshold, Spectral, etc
I had one, I think it was the 9e, with upgraded power supply. Very good sounding for a solid stage unit. And the phono stage was excellent.

Unfortunately, the capacitors in mine began leaking fluid and I threw it out. This is a very old piece of gear at this point.
Viridian, couldn't you just replace the caps?
The stuff leaked all over the inside of the preamp. I am positive that someone could've cleaned it up and replaced the caps, but it was many, many moons ago. I had not learned to DIY yet, and was too broke to afford bench time with a tech, so I dumpstered it. I think that, if one buys gear that is this old, one must consider the cost of these types of replacements into the purchase price. Kind of like buying an old car, or house. Then again, It's fun to learn DIY and old gear can be the gateway into this enjoyable corner of the hobby.
The FET Nine was released 1987. Average service life on this unit is an average of 25 years. After that time the caps should be replaced. However in my experience I have never seen caps leak in any Threshold product. This is not to disparage Viridian about his unit. But over the many years in this hobby and having damn near owned all the Threshold products at one time or another, which includes amps as well, have never encountered leaking caps. I'll research this further. Just beause I have not encountered this problem does not mean it doesn't exists. However this is one fine preamp and the signature is all that could be asked for. More to follow.
Not to disparage Ferrari. Just a question, how do you know that average service life is an average of 25 years? Was the figure provided by Threshold, probably not, as they went out of business less than 25 years after the release of the preamp? Or is this a poll of all of the end users? If so, they missed me and the service life of mine would decrease the figure ever so slightly.

And please, understand, I make no claims about the marque or model other than to relate my own experience with one unit, which I assure you happened.
Ferrari ,

I have a fet9/E, no manual and I'm trying to obtain info on the phono setup, output impedance etc, do you know the difference's between fet9 and the fet 9 E ...

Not to jump in, but since you are not getting an answer, I believe that the only difference is that the e version has an upgraded power supply. While I don't know the output impedance, and hopefully others will jump in with this info, it is low enough to drive pretty much anything, as is typical of the Threshold designs.
I've had several Threshold FET Series preamps thta all worked hasslefree unlike offerings from Levinson and Krell.
I would recommend without hesitation, as I did a couple of months ago to a friend, any of those preamps.
Service life can be assumed by the parts used and the conditions in which the unit is operated. Electrolytic caps are the first to go and since yours leaked, you probably got a defective batch. Did you have the preamp sitting on top or a class A amplifier where it operated at high temps by chance?