Discuss the stuff that makes your ears bleed.

Moderators: Slowy, Capt. Black

I couldn't count the number of times I have heard people telling other people that The Jansen Bassman 50 was an exact copy of a Fender as if it were a fact .
This has now become an urban myth and I thought it was way past time it was dispelled so I asked our tech the question as he was the man who designed it here is his reply

To settle the matter of whether the JANSEN BASSMAN was a copy of a FENDER

The front panel was a copy. The chassis was also copied to some degree. I'm not sure which model was copied.
We modelled our cast knobs similar to the Fender ones but with a J instead of an F. But that is about all.

There are 26 FENDER amps which were called BASSMAN. Most use a simple paraphase phase splitter going straight to the grids of the power tubes.
Jansen uses a split load phase splitter followed by an inverting buffer on each phase. Totally, a different topology.

The FENDER company went to a silver face around 1970 and I remember Bruce ordering panels in the silver with Ken Wilson who was sales manager.(Ken remarried and with his new wife Cath Newhook started Stringed Instrument Company.)

The circuitry is much better than FENDER in the output tube drive department.

JANSEN uses an extra tube in the driver stage ECC82 so that the output tube drive signal is much cleaner and has enough voltage to fully drive the output tubes.
This means there is an extra 30dB gain, which can be used for overdrive if the rear master gain is turned up.
FENDER uses an extra tube (6 tubes) in some models with one tube as a mixer with unity gain.

With the JANSEN BASSMAN Series...
I set the gain for a sensitivity of 20 mV, which all reasonable guitars easily put out, and more.
The front panel volume is then set to around 30% for full output.
The tone controls use a tapped pot 350K tapped at 70K for the treble which gives cut as well as boost.
This gives you a warm tone if you want it. Fender amps have normal untapped pots.
The power and output transformers are a size or two bigger for more bass power without distortion.
We used a single secondary transformer initially but this led to power drop when the screen supply was lowering with full signal as screen current increased.
In 1970 we added a secondary to stiffen the screen supply so that the tubes did not run hot with no signal. This improved tube life and output efficiency.

Fender uses tapped primary windings for the screens (ultralinear screen supply) in some models and a 2,200 or 10,000 ohm dropper resistors or a choke for the screen supplies in their amps with the result of shorter tube life and more heat. This is where the Jansen amplifiers are superior.

Later modifications included a phase lag network on the splitter tube V3 to improve high frequency stability and less negative feedback to make the amp have more gain and "valve" sound. There were several changes as time went on. Tagstrips gave way to the DB1 printed circuit board and then to a board with a top cover plate.

From what I hear, the JANSEN BASSMAN 50 series is incomparable to other amps of this basic type for sound quality.

Jansen made valve amps such as the 12/100, 12/60, 8/FORTY, 6/Thirty Twin, 6/Forty Twin and others, which were very popular.

Fender told us not to use the BASSMAN name so we changed it to BASS as that name could not be registered.

I hope this settles the question for you all.

John Veldwijk
Technical Manager
email john@jansen.co.nz