Anyone built a bass amp?

[rawnster]

Seeing that bass is really my first instrument, I'd love to build a bass amp. I'm currently using an older Ashdown EVO head and 4x10 Hartke cab. Great sounding rig. But I often think about trying my hand and building something like an old Ampeg SVT, or something similar. Nothing like big, round, thumping low end.

[RJ Guitars]

A good one to look at is the sunn 200s...

http://sunn.ampage.org/site/schematics/200s2.jpg

Great sounding 2 x kt88 amp! And I would imagine with a little experimenting the 6AN8 could be eliminated.

Do you know what kind of voltage they are throwing at those KT-88's? I assume that you want the voltage cranked up to keep the sound clean.

thanks,

rj

[M Fowler]

From another post by Cliff. https://tubeamparchive.com/viewtopic.ph ... 7&start=45

With the numbers you mentioned I was thinking KT88 too. They love about 500-550V plate voltage and you can play around with the screen voltage to get different sounds. I dropped the screen down to something like 300V (520V B+) on a SE KT88 build and loved the results (high gain amp topology). For a clean amp you'd definitely want a higher screen voltage like you spec'ed. Probably would be a very unique sounding Dumble-style build.

[RJ Guitars]

From another post by Cliff. https://tubeamparchive.com/viewtopic.ph ... 7&start=45

With the numbers you mentioned I was thinking KT88 too. They love about 500-550V plate voltage and you can play around with the screen voltage to get different sounds. I dropped the screen down to something like 300V (520V B+) on a SE KT88 build and loved the results (high gain amp topology). For a clean amp you'd definitely want a higher screen voltage like you spec'ed. Probably would be a very unique sounding Dumble-style build.

I was thinking about using an Edcor tranny that has 340-0-340 on the secondaries which would probably come in just under 500 on the KT-88 plates. Thanks for the help on that.

As far as the voltage to the preamp tubes, do you run them hotter as well? I was thinking of using a Bassman ish preamp circuit. It would seem that I'd need some big resistors in the dropping string to bring the voltage down on those plates.

rj

[Zippy]

I was thinking of using a Bassman ish preamp circuit.

Blackface or tweed? Why? What style bass playing are you hoping to serve? I don't know that the frequency response of either Bassman tone stack delivers the tone shaping that modern bass players need.

It would seem that I'd need some big resistors in the dropping string to bring the voltage down on those plates.

Time to do that math problem you've been avoiding, RJ.

[Cliff Schecht]

For bass preamps I would think you would want a high B+ on those 12AX7's for max headroom. In that post I made above I dropped the crap out of the screens and the preamp to get a lot of dynamics out of the preamp when distorting (i.e. touch sensitivity) but I think for bass you would want a lot o f headroom, wide frequency response and a versatile EQ. TMB controls I think are usually enough if you stick it after the preamp for max effect.

For the dropping resistors, you'll be using something above 1k from the plate to screen to drop it under 500V. IIRC the KT88 doesn't draw a lot of screen current for its power level. For the rest of the preamp you'll probably be using values in the 1k to 2.2k range to drop the preamp values. I'm sure we can help you with the math if you aren't up to it, it doesn't take but a few minutes and a simple hand calculator to run the numbers..

[M Fowler]

In my case I was thinking of Bass amp for guitar.

In the old days that was all I ran, pedals in front and pair of closed back 12's.

Mark

[KellyBass]

I think you've brought up a good point regarding the versatility (or lack of) of the FMV tone stack for modern bass. I do know that a very popular bass preamp, the Alembic f2b is based on a blackface showman. In fact, I believe that David Gilmour relies heavily on a f2b in his guitar rack and I still plan to build one someday. That being said, I do believe there are better tone stacks for bass out there. I played a SVT for years and it's unique mid control and the way it handles the mids is it's key. Another one that sounded amazing was the Hiwatt, which I think used a cathode follower bax style stack (correct me if I'm wrong). The hiwatt followed the sound city bass amp that also sounded very good.

I really like bass amps that are fairly flat in the eq. I hate any mid scoop and I hate having to boost mids. It never sounds right boosted. Isn't the FMV stack noted for a lot of mid scoop?

Nowaday, I'm playing an ashdown abm and love it. I love the "in between the knobs" sliders...but mine is set basically flat. The real magic of bass comes from the fingers...and an amp that doesn't cover up what's happening on the instrument. Otherwise, The bass might as well be a midi trigger.

[RJ Guitars]

Blackface or tweed? Why? What style bass playing are you hoping to serve? I don't know that the frequency response of either Bassman tone stack delivers the tone shaping that modern bass players need.

Well actually I am borrowing a page from the Stevie Ray Vaughn Play book... much like Mr. Fowler I was considering using my super clean bass amp for a guitar with the 2nd thought that when I'm tired of it I would give it to my brother in law who has been asking me to build him a tube bass amp for many moons now. The brother in law in question is more of an ancient bass player than a modern one so it might work out nicely.

Somewhat more seriously, what about the Rocket tone stack? That is really where I was headed since most of the Rocket preamp is borrowed from the Bassman.

Time to do that math problem you've been avoiding, RJ.

... how about a 36K, 18K, 18K and then I'll measure the voltages and guess again?

rj

[RJ Guitars]

I borrowed a note from Cliff Schecht from another post that was relevant and interesting...

Using really large dropping resistors can help to make a preamp stage more touch sensitive. As you play harder and more current is drawn, the plate voltages drop and you get more distortion. Play softer and the plate voltages shift up and you can get a (relatively) clean sound. The dropping resistors in the Express are relatively large too which I think helps to achieve the huge dynamic range the amp has...

Tell me if this makes sense. In designing a guitar amp it's kinda like you get two for one with large value dropping resistors. A reduction in voltage to brown the sound a bit and then this touch sensitivity that Cliff defines. On the other hand for our Bass amp, keep the dropping string values smaller and you get preserve the cleans.

*Has anyone ever put dropping string resistors on a rotary switch to get the Brown face / Black face / Silver face options?

rj


*Zippy will demand that I owe him design credit and a bag of exotic coffee beans since he drew this on the white board for me about 6 months back

[Zippy]

Somewhat more seriously, what about the Rocket tone stack? That is really where I was headed since most of the Rocket preamp is borrowed from the Bassman.

Ah, so we are talkin' 5F6A... I dunno, RJ. That amp never really made a statement as a bass amp - and consider also the instruments of the period... That's why I was asking about what kind of bass you were thinking about. If you are to design a bass amp and use it as a guitar amp, well, just go with a Big Clean Power Amp with whatever preamp you prefer for toneshaping and color.

Time to do that math problem you've been avoiding, RJ.

... how about a 36K, 18K, 18K and then I'll measure the voltages and guess again?

rj

I love you, man.

Iterate ad nauseum, ad infinitum - do it 'til ya do it right.

[jaysg]

Modern basses...the Sadowsky and Aguilar built-in pre-amps that a lot of guys use ARE the blackface fender stack. It's a very successful design. If I was going to build a dual channel preamp, I'd go Fender on one side and the Baxandall/Ampeg on the other. That's lots of flexibilty.

[mlp-mx6]

I'm wanting to build a bass amp as well. I have a NOS Stancor power xfmr that will put out about 470V @ 550ma. Would this be enough to drive 6 6L6s? Or would you recommend something else?

Thanks folks!
Michael

[KellyBass]

Modern basses...the Sadowsky and Aguilar built-in pre-amps that a lot of guys use ARE the blackface fender stack. It's a very successful design. If I was going to build a dual channel preamp, I'd go Fender on one side and the Baxandall/Ampeg on the other. That's lots of flexibilty.

I'm with you! That would really be a cool setup!

[Cliff Schecht]

I'm wanting to build a bass amp as well. I have a NOS Stancor power xfmr that will put out about 470V @ 550ma. Would this be enough to drive 6 6L6s? Or would you recommend something else?

Thanks folks!
Michael

That will work just fine. Gonna be a beast!