new bass preamp

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new bass preamp

Postby Bryan James on Tue Apr 11, 2006 3:42 pm

Hey all, just finnished this last night.
iIt's a two channel preamp bassed of the second channel of the ampeg svt.
Sounds pretty cool, but won't get to test it at volume till tomorrow night (just ran it into a small power amp i had at the house last night, and since it was 1am and the wife was sleeping, didn't really get to turn it up).

The chassis is an old watchgaurd firewall that I got from work that we pulled out of service.
http://www.james-gang.org/jca/2bpa
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Postby marshman on Wed Apr 12, 2006 12:04 am

Looks cool. I also have a few ideas for a bass pre in a rack.

Were ya able to get the little LED stuff to still work? That'd be pretty schnazzy, blinken-lights dancin' to the tunage somehow...
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Postby ozsubrosa on Wed Apr 12, 2006 12:47 am

Very neat, Bryan. I wish I could do that kindof thing. Schems and dias give me a headache so I've never tried but that looks the biz.

Oz
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Postby Bryan James on Wed Apr 12, 2006 3:05 pm

marshman wrote:Were ya able to get the little LED stuff to still work? That'd be pretty schnazzy, blinken-lights dancin' to the tunage somehow...


not yet. the board for the LED's is all surface mount LED's, and welp I decided to wait on that.

I do want to adventualy set them up, use the load and traffic meters as DB meters. but really wanted to get it just finnished.
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Postby marshman on Wed Apr 12, 2006 5:38 pm

If ya could get 'em to spell schtuff while you were playin' that'd be a real hoot..."Eat at Joe's"..."Buy war Bonds!!"..."Nice breaths"...

Or, on a practical note, integrate your tuner and use that LCDs for that.
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Postby Bryan James on Wed Apr 12, 2006 8:31 pm

marshman wrote:Or, on a practical note, integrate your tuner and use that LCDs for that.


you know the tunner idea isn't to bad, other then that steel is a pain to cut on the chassis.
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Postby Bryan James on Mon May 01, 2006 4:23 pm

here's a pic of everything setup in my living room for testing.
http://www.james-gang.org/~bjames/setup.JPG

the preamp in in the rack uptop with a compressor, and the amp under it is a 100watt tube head with kt88's.

It's definatly going to take a little getting used to, after years of playing through my 100 watt plexi clone it's nice to have a lot of clean head room.
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Postby ozsubrosa on Wed May 03, 2006 12:59 am

Nice power amp, Bryan. Is that a Hammond transformer? Does a 100W KT88 amp come up a lot cleaner than 6550 or about the same?

Oz
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Postby marshman on Wed May 03, 2006 2:44 am

Since we're on the topic of bass preamps, how do you guys feel about bi-amping and crossovers? I have a real nice biamped cab and decent SS head, but would like to get a good preamp to run with my Mesa 295 power unit. Are crossovers easy to get/integrate into pre designs? Anybody played with this stuff?
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Postby Bryan James on Wed May 03, 2006 3:15 pm

ozsubrosa wrote:Nice power amp, Bryan. Is that a Hammond transformer? Does a 100W KT88 amp come up a lot cleaner than 6550 or about the same?

Oz


haven't tried 6550's yet. so really can't compair yet. In my 1959 clone that I was using I did some mods to the bright channel and then swapped the el84's for 6l6gc. Though I like the tone I was getting there was no headroom, and didn't relize how much crunch I had going till switching. thursday night is band practice, so should get some more pics and sound clips

and yep those are big hammond trannies. the OT is 1650R. I do have a 1650T I might replace it with.
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Postby ozsubrosa on Wed May 03, 2006 11:40 pm

In my 1959 clone that I was using I did some mods to the bright channel and then swapped the el84's for 6l6gc


Sorry Bryan, just wanted to check. Did you swap out EL84s or EL34s? I have a Marshall/CMI 100W Lead/Bass that is pretty much the 1959 Superlead/bass circuit. Personally, I like the EL34s but I do recognize that they break up a bit and it might not be every bass player's cuppa. If you did a EL34/6L6 swap, what did you find the tone difference to be? Apols if I got it wrong and EL84s were the starting point; I'm not really much good on schems and the like; they give me headaches :)

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Postby Bryan James on Thu May 04, 2006 3:39 pm

ozsubrosa wrote:
Sorry Bryan, just wanted to check. Did you swap out EL84s or EL34s?
Oz


sorry my fault, it was el34's for 6l6gc. not el84's.

it gave me a little more head room in the amp, and brighten the tone up. though I did prefer the sound of the el34's, but with the 6l6gc could get a cleaner tone up to about 6 or 7 on the volume knob, where as with the el34's. but could get noticably louder with the 6l6gc then el34
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Postby gypsy moth on Thu May 04, 2006 4:20 pm

oz, I didn't notice much when switching from old svet 6550's to new C 88's.
a tech told me that is because the only difference (in that brand) is the glass.
JJ 88s didn't make a big diference either, although to be fair I haven't got a lot of playing time on them, and the time between switching (and other slight changes to the amp) muddles this all up. but keep in mind that a few more watts doesn't make much of an audible difference volume wise.
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Postby Bryan James on Thu May 04, 2006 6:53 pm

gypsy moth wrote: but keep in mind that a few more watts doesn't make much of an audible difference volume wise.


very correct but wone thing switching tubes does do, depending on the tube swap is change your bias setting, and if you can set your grid from having -36 to -40 volts it will increase the amount of signal you can put on the output tubes before the output tubes distort, this does give a little bit more head room to play i with, which I did find important, Of course a better switch would of been a more efficant speakers and a better cab. but hey we do things that are with in our price range
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Postby gypsy moth on Thu May 04, 2006 8:00 pm

I'm not smart enough to set my bias myself, but each tube will have a different draw, so if you are after clean headroom it is quite important to get it set.

I should note that the amp I am referring to runs 700+ volts at the plate, so the big tubes are required. a typical designed for el34's circuit is going to be around 450 plate volts, so the 88's may not be breathing hard even at maximum settings, and the difference may be far more discernible in something else than in this amp.

this is guesswork, without a proper understanding of theory, but it may explain why 50 watt marshall guitar players consider 6550's sterile and need pedals, while I find my (and other noteworthy players ) 200 anything but sterile for guitar.
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