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Post subject: jumper channels?
Posted: Tue Jan 26, 2010 11:29 am
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I'm sure this has been a topic before, but i dont seem to get my head around that search-function, so please forgive me for asking again:

what difference in sound does it bring to jumper the channes on a bassman combo?
i dont use the break up from the amp, which seems to be one of the reasons to jumper.
then I read that the channels are already internally jumpered, so using a cable you actually lose some of the low-end?

any suggestions/ experiences/ technical facts?

thanx!


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Posted: Tue Jan 26, 2010 2:39 pm
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The channels in a Bassman are not jumpered. At least they're not according to the reissue and the 5F6A schematic. Jumpering allows you to mix the bright and normal channels to the power amp via the volume controls. I think most people just use the bright channel though.


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Posted: Tue Jan 26, 2010 9:01 pm
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That's an interesting scenario. The input grids of both channels share the same dual triode, so they also share the same cathode bias circuit and plate voltage supply. I suppose, if you ran both halves of that tube, at the same time you would experience a tonal change and some distortion, due to a slight voltage drop. The loss of low end would probably be determined by which channel input jacks you double up on, because of the series resistance at the input jacks and the signal loss from the jumper cable. At any rate, phase cancellation isn't a concern with this amp, like a Deluxe or Twin Reverb. A neat thing about this design is the interaction of the unused channels volume control on the channel being used. The input signals of both channels are combined following this first gain stage. That's what I guess folks mean by the internal jumpering. Seems like a neat way to experiment with tonal possibilities. Art

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Posted: Thu Jan 28, 2010 10:56 am
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I just spend a few hours dwelling on th econvcept of jumpering and hence played around with my bassman for a few hours.
heres what i found:
1) the 2 channels are internally conected in some way: only plugged into the normal channel, i can actually turn down that volume, but bring the signal to considerabe volume by turning up the bright volume.
2) merely connecting the two channels changes the sound, even if the second channels volume is completely down. what this means: when the guitar goes into the normal channel I (with that volume on say 4), the sound gets somewhat more middier when a conection is made from normal input II to bright input I. in a slight way the fenderish hollow-quality gets some kind of marshally low-mid-meat to it.

these two discoveries leave me somewhat puzzled, as I dont understand the technical stuff that goes on behind them. is there any "official" infosheet on this concept?


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Posted: Tue Feb 09, 2010 1:25 pm
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The term for doing this is called "double channeling" and the reason to do it is as you folks have described.
It will change the tone of the amp and allow you to use both sets of volume and tone controls.

This has been done as long as Fender has made double channel amps.

I remember it being described to me back in 1969.

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Posted: Tue Mar 16, 2010 11:47 am
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ok I now went back to my bassman combo and after long experimentation found that (for my ears) using one channel only sounds better. as I use loads of pedals, i dont need the amps distortion and the less compression the better, therefore using only the normal channel gives me headroom than using both together.

by the way: any suggestion sto make the amp go louder before breaking up?


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Posted: Tue Mar 16, 2010 11:47 am
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ok I now went back to my bassman combo and after long experimentation found that (for my ears) using one channel only sounds better. as I use loads of pedals, i dont need the amps distortion and the less compression the better, therefore using only the normal channel gives me headroom than using both together.

by the way: any suggestions to make the amp go louder before breaking up?


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Posted: Mon Mar 22, 2010 1:40 pm
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The same amp louder before breakup- Maybe change the pre-amp tubes from 12AX7s to 12AT7s. Those a re a lower output preamp tube and the may make the amp sound cleaner, but there really is only so much volume that yu will get out of a 50 watt amp.

If you really want loud and clean in a vinatage amp - get a Twin Reverb!

85 to 130 watts of pure tube volume through two twelves!
That amp will kick out some loud and clean volume.

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Posted: Thu Apr 01, 2010 4:32 pm
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BCbassman wrote:
If you really want loud and clean in a vinatage amp - get a Twin Reverb!

85 to 130 watts of pure tube volume through two twelves!
That amp will kick out some loud and clean volume.


Indeed they are and indeed they will!

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