The Vintage Amp Threshold Museum

    The Beginning:  The Threshold Corp. was founded by Nelson Pass and Rene Besne in 1975 and the first product was the 800A Cascode Amplifier. Most of the devices in the output stage are current followers also known as a current mirror.  This amp had a cooling fan and large VU meters on the front panel.
 
 

Model Stasis I

The Model Stasis I employed a unique circuit topology that was filed for patent as the Stasis Technology.
 

Cascode Series
These amps included the CAS 1, CAS 2, 400A and model 4000.

                                    Model 400A                                                                             Model 4000

    The 400a was released soon after the 800A as a smaller version of similar circuit configuration.  With external heat sinks this unit was capable of handling 100 W/ch into 8 ohms with distortion less than .1%.  This unit was also the first to use LED RMS and Peak meters. The NS 10 pre amp was also released during this time.

    The 4000 was manufactured from 1978 to 1980.  200 w/ch. The 4000 was a popular amp during the same time as the 400a.  It uses the peak and RMS LED display placed in a nice machined dress plate.  Good at driving hard loads.  This 200 W/ch is pleasant to listen to, but lacks the bandwidth of more modern amplifiers.  This amp is best known for its tube like quality.

The CAS 1 and CAS 2 which were smaller, used an internal heat sink chassis and produced 75 W/ch and 100 W/ch.

Things to be aware of:  The most common components to fail are the power switch and the 2W 1K ohm resistors on the Front End Circuit.  The output devices are no longer available, but Vintage amp can replace all of them with a newer components.  This amp is easily updated with larger main capacitors.
 

Stasis Series

                                                    Stasis 3                                                                                                 SA 3 Series II Optical Bias

    The Stasis 2 and 3 were manufactured concurrently in the early 1980's.  Both used the same output configuration.  The Stasis 3 offers 100 W/ch into 8 ohms.  The Stasis 2 was rated at 200W/ch.  The Stasis 3 is the same dimension as the 400a.    The SL 10 pre amp was released to production with this line of products.

    Many of these units had poor thermal tracking ability.  Thus, many were biased too cool to fully take advantage of  Class A operation.  Vintage Amp can modify the bias circuit and replace the main capacitors for improved performance.  Also available are upgraded components like: IXYS rectifier diodes, Blackgate caps, Cardas Binding posts, high quality copper power supply wire and Mills resistors for use on the Emitters of the output devices.

Series I
    The series I products consisted of the early S 500, S 300 and S 150 amplifiers.  These Amplifiers have grey tops and say "Overall Feedback Free" on the dress panel.  These units are overdue for new main caps to offer the performance they should.
The  Fet 1 and Fet II preamps were introduced at this time.  These units are overdue for capacitors.  Very good perfomance is possible from the JFET design of these models.

Series II

    The line consisted of the SA 3, (50 W/ch class A), the  SA 2 mono block (100 W/ch class A mono block,  and SA 1, (160 W/ch class A mono.  The S500, S300 and S200 rounded out the line in A/B models.  At his time the Fet 9, Fet10h, and Fet10p were in production.
Many early Series I and Series II units were upgraded to optical bias in the late 1980s and to E-line status in the early 1990s.  E-line upgrades can be improved with some modifications to the gain card, call for details.  Main caps and IXYS rectifiers bring added performance in dynamics and the bass performance.
The SA 3 was the 50 W/ch class A model.   This amp is one of my favorites.  Very smooth sound, more detail than earlier models and very good thermal stability.
 

                                                            SA 12  E-line                                                                                            SA 4 E-line
 

E-line
    This popular line of amplifiers was the result of years of research and testing of Stasis circuit improvement.  I believe this amp represents the maximum performance that can be obtained by using bi-polar devices in this famous patented circuit design of Nelson Pass.  Several engineers, including Eric Lauchli of Coda worked on the amplifier circuit while Rene Besne designed the particularly sculpted look of these products.  This amp was manufactured at the peak of Thresholds profitability.  The line consisted of many models as well as the introduction of the DAC 1e.

    This was a period of much growth and transision for the company.  The company was producing the Phantom Acoustic Shadow, Webber Wire, and began the Forte line with the Forte 1, followed by the model 1a and model 3 amplifiers a year or so later.
The Forte line was later moved from simple bi-polar circuits to the IGBT of the model 4 and model 6.  This provided a spring board into the design the T200, T400 and T800.

Fet 9E, Fet 10HE and Fet 10PE  Phono Stage
    Although Threshold may have not been best noted for preamps, none can say this is not a sharp looking unit.  It offered many cartridge loading options and parallel fets on each gain card.  In addition, the gain cards are placed in parallel further lowering the noise floor.  Attention to detail is impeccable by any standard of build quaility.

T-line
    The T series of products began with the T 2 preamp, the T 50 and T 100 amplifiers.  It was perceived at Threshold that a new approach was necessary to continue with out Nelson Pass.  The products developed at this time are the work of Mikael Bladilaius, Mike Jaynes and Wayne Coburn.  The T2 was developed as a balanced preamplifier with Remote Control.  The T 3, remote control preamp followed as a scaled down version with similiar circuits.
    The T 200 and T 400 were released shortly after the T 2 and employed the ultimate in IGBT technology with completely isolated and regulated Front End Circuit power supply circuitry.

                                        FET 10 PE                                                                                    T2 Preamp

 

T 800 D

    This amplifier is a testament to the hard work of engineers who strive to the absolute best that can be achieved.  This is the culmination of the entire T series of products.  The design of the T 800 is based on the technology obtained in production of the T 200.  When the T 800 is used with the T2 in a balanced configuration the signal is completely balanced all the way to the speaker.
 

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