Jansen 50 Bassman Amplifier

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nzsimon
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Re: Jansen 50 Bassman Amplifier

Post by nzsimon » Mon Oct 13, 2008 8:59 am

the real facts just for those that are intereseted in this sort of thing :D direct from the guy who designed them

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
believe nothing you hear and only half of what you see J.R.R Tolkien
Director of Jansen http://www.jansen.co.nz

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john
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Re: Jansen 50 Bassman Amplifier

Post by john » Mon Oct 13, 2008 12:47 pm

Great Informative post John( Grim repair man?) C/o Simon , :)
I totally have thought it was a copy for years.

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Re: Jansen 50 Bassman Amplifier

Post by beagle » Mon Oct 13, 2008 7:32 pm

Yeah that's great Simon .... v cool 8)
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Re: Jansen 50 Bassman Amplifier

Post by model.citizen » Tue Oct 14, 2008 6:45 am

yeah cheers, very informative post. i also love the number of oddities and prototypes that were made, one of my early Bassman 50 heads was a prototype with a solid-state preamp and tube power...weird. or the 6/35 that was covered with white tolex painted black (apparently at the time black tolex couldn't be sourced).

agreed tho, in good condition they have a nicer tone overall than the Fender, plus there's the added bonus of being a bit of Kiwi history :)
i like rickenbackers. and fridges.

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Re: Jansen 50 Bassman Amplifier

Post by foal30 » Tue Oct 14, 2008 9:49 am

this thread is a microcosm of why this website is good.
Steve for Parliament!

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Re: Jansen 50 Bassman Amplifier

Post by john » Tue Oct 14, 2008 11:12 am

foal30 wrote:this thread is a microcosm of why this website is good.
your just saying that cos you started this thread :mrgreen:

foal30 wrote:Steve for Parliament!
LOL . I don;t want to start hating him

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Re: Jansen 50 Bassman Amplifier

Post by foal30 » Tue Oct 14, 2008 11:16 am

starting means little hombre, pretty much everyone has turned up here.
team contribution and all that.

and that red upholstery seals it. beyond cool.

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Re: Jansen 50 Bassman Amplifier

Post by john » Tue Oct 14, 2008 11:21 am

I know , I know.
Just stirring , you are right though ....

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Re: Jansen 50 Bassman Amplifier

Post by beagle » Thu Oct 16, 2008 2:02 pm

foal30 wrote:this thread is a microcosm of why this website is good.
Steve for Parliament!
My country needs me... there's no denying it! ;-)
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Re: Jansen 50 Bassman Amplifier

Post by foal30 » Fri Oct 17, 2008 7:49 pm

for sure.
anyone who thinks they would do a worse job than the current bunch populating the house (on both sides) should be in hospital or prison.
it's reported badly too, it's like we got to copy America, no we don't.
some of the news is beyond the pale and the reporters bias is paraded like a badge of honor.


um,

look Fretless J, flats, Sadowsky Pre-Amp is a smokin through this amp. it pushes it into fart zone fairly quickly so some restraint required but on some blues and a lot of walking lines it is PRIME NEWS.

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Re: Jansen 50 Bassman Amplifier

Post by ryla » Mon Oct 20, 2008 6:59 pm

the Jansen Gladiator was good too - had a couple of those running 15" peavey black widows - had my ric-o-sound splitter plugged into my rickenbacker with each signal to each Gladiator.

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Re: Jansen 50 Bassman Amplifier

Post by Crazykiwi » Fri Oct 24, 2008 10:22 am

foal30 wrote:what school? if your from Christchurch you know how important this question is old boy!
Lincoln High School, mate :) I missed out on being chocolate weaten beaten at one of the posh places.
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Re: Jansen 50 Bassman Amplifier

Post by nzbassplayer » Sun Oct 26, 2008 9:00 pm

My first ampilifier. may have to do a revisit.

heh, first amp Jansen 50, lastest amp Markbass F1.

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Re: Jansen 50 Bassman Amplifier

Post by foal30 » Mon Jan 26, 2009 12:07 pm

well enjoying recording with this amp,Ashdown 15/10, flatwound strung Fenders.
warm warm warm

go the 15's for added body.

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Re: Jansen 50 Bassman Amplifier

Post by beagle » Mon Jan 26, 2009 6:50 pm

Good to hear it's all going well. 8) Any chance you can upload a snippet so I can hear how it sounds?
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