Mello cello(anyone build a bass amp?)

[jeff]

I got a phone call the other day from someone wanting me to build him an amp. Great I thought. Only problem is he's a cello player looking for a cello amp. I'd love to do it but not sure what would work with a cello. Maybe a Bass amp? Anyone got schematics for a good bass amp? The cello is tuned lower than a guitar so I'd probally need a different OT than what I'd use for guitar. Think ultralinear tran would be better? I was thinking this for the transformer. http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=P-T1650T
It's a 120W ultra linear 1900 primary.
If I use four 6L6's what's a good voltage for a 1900 primary? Probally want a SS rect too.


I never built a bass amp much less a cello amp.
Any suggestions.

[Frankenamp]

What's he/she using as a pickup? Piezo, Fishman? What's the musical style?

Here's an interesting bass amp;

http://hiwatt.org/Schematics/OxPre.gif

And a 100 watt EL 34 section:

http://hiwatt.org/Schematics/DR_100wOutput.gif

[bluesbear]

I once had to modify an old Epiphone Electar with strange 4 pin tubes... for a sitar! I feel for you! I'd have liked to build that one from scratch. I think it would be great. Oh, well, the next time I'm asked to build a sitar amp...
I'd go for a clean bass amp sound, maybe a single channel 5F6a with 6550's. Volume, treble, mid, bass, and presence, nothing else. I'd think you'd want warm with no OD, almost an acoustic amp.
Good luck. This one actually sounds like fun.
Dave

[jeff]

What's he/she using as a pickup? Piezo, Fishman?

I'm not quite sure yet. What considerations should be made for each type of pickup?

Thanks for the schematics.

I'd think you'd want warm with no OD, almost an acoustic amp.

That's what I'm thinking. Are the ultralinear with screen tap transformers more suited to this? I think I need to use this transformer vs a standard guitar transformer because, being a cello it's tuned lower. This Xfmr goes to 30Hz vs 70Hz.

I've never used a UL Xfmr. Is it basically the same but you wire the taps to the screens or is it a whole different animal requiering a different circuit?

 You suggested a 5F6a circuit, could I use the UL Xfmr in that circuit with the taps to the screens or should I ignore the taps and wire it like a 5F6a using this Xfmr for the low end responce?

[firemedic]

"What considerations should be made for each type of pickup?"

A piezo pickup has ultra-high impedance, like 10M, that range. That's why it can sound thin going into a regular guitar amp. You'll need to match or buffer the input impedance accordingly.

[Willabe]

A piezo pickup has ultra-high impedance, like 10M, that range. That's why it can sound thin going into a regular guitar amp. You'll need to match or buffer the input impedance accordingly.

You can use a 10M for the input grid return R.


        Brad

[PRR]

Jazz cello works good on 1972 Fender Twin.

There's many ways to play cello... you need to hear the act before you think.

[bluesbear]

I'm not what you'd call an expert with UL but every one I've heard seemed cold and harsh. Depending on the volume level needed, I'd guess a 5F6a with 6L6's for a large venue. If it's for a smaller, more intimate setting, maybe fixed bias 6V6's would do the trick. Even that's fairly loud. That's basically my guitar amp and I had to change it to a 5Y3 rectifier and cathode bias to help bring down the wattage a bit.
I think a cello would respond best to a guitar amp voiced somewhere between a guitar amp and a bass amp. It's such a warm, expressive instrument, almost like a human voice.
Dave

[jeff]

Jazz cello works good on 1972 Fender Twin.

There's many ways to play cello... you need to hear the act before you think.

The guy who's interested in me building him an amp says he's the cello player from the Smashing Pumpkins so that's the sound he's into. Maybe he really is "that guy", maybe he's not, it doesn't matter to me. I'm not star struck and don't care "who" this guy is, I'm only concerned with - Here's a dude who needs an amp and I want to build that amp.

 What I think I'm gonna do is build a power section into a chassis that is to become his amp and build an outboard preamp. I'll wire the outboard preamp with different preamp topologies and lot's of switches to change caps, resistors, tone stacks, etc. to tune in the sound he wants then go back and install those values into his chassis. This way I can have him over to play with it.
"Do you like this?"
"yeah but it needs a bit more..."
"How's this(click)"
"OK, but a little less...."
"How's this(click)"
"Good"
"Ok I have it wired up for you and give you a call when it's done"

Kinda like going to the eye doctor but for your ears "Better, or worse...... better, or worse"(anyone who wears glasses knows what I'm talking about)

OK so heres the plan. I want to start with the power section from a Twin. This way I can add/remove two power tubes and switch the secondary tap for his power needs. I'd rather build it a little bigger and be able to drop it than build it a little smaller and have to get new Xfmrs.
 I see what you're saying about 6V6s being loud enough, but to keep it clean I'm thinking a 50W amp turned down to 20W would be cleaner than a 20W amp cranked. I think most bass amps are more powerful than guitar amps playing together not to be louder but to stay cleaner. I don't know???

A) Do you think I should use the UL transformer wired without the taps, only because it has a lower freqency responce? I'm not sure a standard guitar Xfmr would cut it for cello.

B) Since this tran does have the UL taps. Can I wire it without the taps like a standard Twin and add a switch that uses/disconnects the taps with all other things equal?(bias, voltage, etc.) To see which he prefers. Or are ULs set up differently?

and C) This Xfmr has a 1K9 secondary and a Twin has a 2K is this OK? Do I need to adjust anything?

This is my first build for someone else. I've built many guitar amps for myself that sound great and I think I'm now ready to build and sell an amp. I just want this to be a good experience and give him something he's happy with. (I'm getting my feet wet in uncharted territory, but it's time to sink or swim. Sure wish he need a guitar amp, I can build the hell out of those.......)

[xm52]

The 135W Fender Twin Reverb used ultalinear taps. Very loud clean amp. My choice would be an Ampeg B15. A small amp like the B15 can hold it's own for smaller venues, especially if an extension cab with a second 15" speaker is added. If the band has PA support, the size of the amp doesn't really matter, as it is just used for on stage monitoring.

Check out the amps that standup bass players use. High impedance piezo pickups or a mic are often employed. Some upright players use a preamp with an adjustable high pass filter to remove the thump that you get when a string is plucked.  Here is a low cost example (http://personalpages.tds.net/~fdeck/bass/hpfpre.htm).

Here is a B-15N schematic:

[nateflanigan]

Edcor has some nice looking ul ot's that are quite reasonably priced.  The Sunn/dynaco power section might be nice as well, it uses kt88's and sounds gigantic and not at all harsh or sterile.  In another thread about UL's I started someone mentioned that the choke values are really different than what you'd use in a "normal" power stage.

http://www.el34world.com/Forum/index.php?topic=11589.msg108851#msg108851

[PRR]

> says he's the cello player from the Smashing Pumpkins

Eric should know by now what amps work or don't-work for him.

It may not matter to the amp. As a craftsman, be wary of confused customers.

> I'm not sure a standard guitar Xfmr would cut it for cello.

It will, until you get into BIG loudspeakers.

Drop-tuned guitar is similar to cello.

I suspect, in all non-orchestral work, the cellist doesn't boom that bottom octave too much. When s/he does, it's for woody stringy overtones.

UL connection is, IMHO, for music reproduction, not music creation. Yes, it can go either/every which way.

[PRR]

Hasty unscientific comparison: Yo-Yo Ma playing Bach in small studio, Clapton playing Layla in live concert.