Big bass amp

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Big bass amp

Postby elbinster » Tue Sep 21, 2010 4:25 pm

Ok, after bragging to my friends about how awesome tube amps were, one asked me to build him a head for a bass cabinet he has, and I'm starting my research into what I'll need to do.

I've read that to get the best sound, you want an amp that runs the speaker to the red line (the cabinet says it's rated to 300W rms), but a 300W bass amp seems a bit ridiculous to me. I've found a few schematics, and think a sextet of 6550 or kt88 would be more than enough (though not very likely to hit 300W), and I might cut it back down to a quad.

Before I dive into the deep end, does anyone here have any suggestions? Any suggestions as to websites i should read or avoid? The schematic I'd like to use as a starting point I found on the Weber Speakers website, but simply buying a kit might be too expensive. I'd also like to put in the standard bells and whistles like EQ, overdrive, presence, maybe reverb...

My guess is that finding iron for a 300W bass amp is going to be the most annoying part.
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Re: Big bass amp

Postby ChrisAlbertson » Tue Sep 21, 2010 5:16 pm

elbinster wrote:Ok, after bragging to my friends about how awesome tube amps were, one asked me to build him a head for a bass cabinet he has, and I'm starting my research into what I'll need to do........
My guess is that finding iron for a 300W bass amp is going to be the most annoying part.


This is a HUGE project. Don't think about tubes first. They are pocket change, peanut parts. The killer component that you need is an output transformer that works down to at last 40 Hz and delivers the power you need. You will need to be looking at HiFi transformers as guitar amps don't do 40 Hz. This assumes stanadrd four sting bass. Maybe your buddy's lowest string is lower than the normal "D"

An OPT that can do 100W will cost about $100. Hamond makes some larger ones buit I'd not go over 100W

You can build a 100W amp and then if more power is required build more amps. Each amp powers it's own set of speaker in the cab

It does not cost much more and it is good to have an amp you can lift. You can feed any number of power amps with one preamp
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Postby dhuebert » Wed Sep 22, 2010 7:20 am

My Hammertone BFA makes 156 watts RMS into 5 ohms and uses Hammond transformers and 4 KT88s. The KT88s are a little small for this application and I would go for KT90s or KT100s if I built another of these.

http://www.diytube.com/phpBB2/viewtopic ... fa&start=0

I was looking at the schematics and there is a change to the preamplifier: I replaced the input resistor and cap with a 10 meg resistor. This was done to make it compatible with piezo pick-ups on acoustic bases, it works nicely.

Don
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Postby ChrisAlbertson » Wed Sep 22, 2010 8:48 am

dhuebert wrote:My Hammertone BFA makes 156 watts RMS into 5 ohms and uses Hammond transformers and 4 KT88s. The KT88s are a little small for this application and I would go for KT90s or KT100s if I built another of these.
Don


I had to look it up. Are you using the 1650T for output? Hammond rates them for 120W but I think that is from 20Hz up so by not using the lowest octave you can safely at 156W Is this right?

What cab is used and can this keep up with an aggressive live drummer?

I ask because I have an interest in bass too but I always figured that a 100W bass amp was just a big .

EDIT: Sorry, just read it's an 8x10 cab. So you do get a lot of sound of of this. I think doubling the number of speakers is the same as doubling the watts. so what you have is like a 300W amp on a 4x10.
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Re: Big bass amp

Postby elbinster » Wed Sep 22, 2010 10:52 am

ChrisAlbertson wrote:You can build a 100W amp and then if more power is required build more amps. Each amp powers it's own set of speaker in the cab


This seems like a nice and sane idea to me. I saw that Hammond makes the 1650W (280W), which, at $282 +28lb of shipping is where I started to say 'this is ridiculous'.

I might start by focusing on the preamp alone and make sure that part is solid before jumping into the power amp. The cabinet itself lists a single 15" 4 ohm 300W driver tucked inside of a folded horn. I should probably find out how loud it is with the 100W guitar amp he already has before deciding it needs more power than that.

dhuebert wrote:I was looking at the schematics and there is a change to the preamplifier: I replaced the input resistor and cap with a 10 meg resistor. This was done to make it compatible with piezo pick-ups on acoustic bases, it works nicely.


I've read through the different BFA topics here, and I believe one on diyaudio, and I think bass players coming in to use the 'house amp' should be floored. If it can double as a house amp, I should have no ambitions beyond that. As long as the folded horn does its job, I can probably settle for 100W-150W

Not being much of a bass player, I've noticed plenty of amps with a 'hi' and 'low' input channels for active pickups, I was unaware of pizeo pickups. Is one high, one low input and a switchable overdrive channel good on the input side? I don't like the idea of having to plug into a separate drive channel.

Any bass players out there have any adjustments they wish they could make to their amp?
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Re: Big bass amp

Postby ChrisAlbertson » Wed Sep 22, 2010 2:40 pm

elbinster wrote:
ChrisAlbertson wrote:You can build a 100W amp and then if more power is required build more amps. Each amp powers it's own set of speaker in the cab


This seems like a nice and sane idea to me. I saw that Hammond makes the 1650W (280W), which, at $282 +28lb of shipping is where I started to say 'this is ridiculous'....


I looked at that transformers too. I have a pair of older Infinity speakers from the 70's that need a minimum or 100W each, 200W would be better. But a 200WPC stereo tube amp is just nuts that "BFA" looks to be the practical limit, after that go with solid state power sections

BTW the best place to buy Hammond parts is STF Electronics. For example they have the 1650W for $227 and free shipping.
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Re: Big bass amp

Postby elbinster » Wed Sep 22, 2010 3:28 pm

ChrisAlbertson wrote:BTW the best place to buy Hammond parts is STF Electronics. For example they have the 1650W for $227 and free shipping.


Free shipping on that behemoth? I am tempted...

If I had all the time and money I needed (and if all the parts were still available), I'd build this: https://taweber.powweb.com/store/ab200_schem.jpg.

But as it is, I'll build a nice preamp and if he's serious about having a tube-powered bass amp for this cabinet, a BFA-sized power amp will be my target.
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Postby Hotsauce » Wed Sep 22, 2010 5:27 pm

Why do you need that much power?

Can't you use a lower power amp and mic the cab to the PA system?

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Postby dhuebert » Wed Sep 22, 2010 6:28 pm

Lots to think about here.

Go to your local music store and lift an Ampeg SVT and ask yourself if that is what you want to drag from gig to gig. They are HUGE and HEAVY. But 300 watts RMS for them what want it.

The BFA is hooked to an Ampeg 8x10, it fills the venue with warm rich bass sounds and keeps up nicely with the loudest bands.

The output transformer runs cool and nobody has noticed a low-end rolloff yet. The power transformer OTOH runs very hot, in the neighborhood of 60C! (140F) No meltdowns yet although it has used up a couple of tube sets. First Sovtek KT88s and lately a set of JJs. The power goes down and down until someone complains and then I swap in new tubes and voila back to full power.

A high input impedance(10 meg) is necessary for piezo pickups and doesn't hurt normal pickups so I just have the one input.

Bass players I've talked to don't like having their basses folded back through the stage monitors. They are intended for vocals and I'm told crappy for bass.

One of the nice things about the Times Changed High and Lonesome Club

http://www.highandlonesomeclub.ca/

is that the bass cabinet is right behind the player and coincidentally if the bass player can hear himself on stage then the volume is usually right for the audience.

Don
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Postby elbinster » Wed Sep 22, 2010 7:49 pm

I certainly doubt I would need a full 300W out, but like I said, I read somewhere that you'll get the best sound out of a speaker that is driven to its breaking point (I quickly abandoned the 300W goal though). Recently I've been using my GSG as a guitar's power amp, and at a whopping ~2W, it is still uncomfortably loud. Probably not enough to keep up with a band in a crowded room full of screaming fans (if that ever happens (lol) )

Plus our ears aren't nearly as sensitive to low frequencies, so you tend to have to bump the power up a bit so you can feel it. I'm thinking 100W-150W would be more than enough to keep a bass player happy.
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Re: Big bass amp

Postby Gasman » Wed Oct 13, 2010 6:44 pm

There is a reason that bass players use high wattage rigs. It's because of the much higher amount of energy needed to push bass frequencies. A low E on a 4 string bass is 40Hz and the low B on a 5 or 6 string is 23Hz. You need some muscle to drive those. Quite frankly, anything less than 200 watts is useless unless you are playing in the studio or the tiniest of venues. You are gong to need at least one, possibly two transformers that weigh as much as an anvil.

I'm not sure that I would even try using an amp smaller than 300 watts to drive an 8 x 10 cab. If you are going to make a tube amp of that power, then you are going to end up with something the size and weight of an SVT. With a cabinet that already weighs 150 lbs., why worry about the weight of the amp?

As for what this bass player would like in a tube amp? I'd like lighter weight, but unless you can change the laws of physics, that ain't going to happen. I'd also like it to come with a lifetime supply of Belgian beer.

Let me know if you work out that last one.
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Postby ChrisAlbertson » Wed Oct 13, 2010 7:55 pm

Hotsauce wrote:Why do you need that much power?

Can't you use a lower power amp and mic the cab to the PA system?

John C.


The PA will typically not do bass frequencies. Just look at the typical PA speaker and you can see that it is not going to do 40Hz or lower. at wall shaking volume levels. bass player need to keep up, volume wise with a big kick drum that a drummer might have.

Almost every bass player is using solid state power amps. Many have tube preamps but 1,000W is not unreasonable for a bass amp and a 1KW tube amps is near insane. (unless it's for radio frequency)
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Postby EWBrown » Thu Oct 14, 2010 5:43 pm

The Karlson design speaker cabs are very efficient at lower frequencies, and if anything, they seem to extend the speaker's lower freq response.

These are a "cast iron beast" to build, as they take some fancy cutting and calculations, but they sound great (I have another posting about these on this forum). A 12-inch speaker-sized karlson cab is about 30-32 inches high, and is relatively heavy for its dimensions, but it is a flyweight as compared to a huge 8X10 cab. I use a Pyle PYM 1298 driver, which is basically a rebranded Eminance Kappa-12, and with just a few watts, it will rattle the rafters in my house, and with a couple hundred watts, it probgably could cause SPL-induced internal injuries (I refer to these cabs and drivers as my "sonic weapons). The Pyle (and Eminence) drivers are very efficient, and a few watts will go a long way with these. [:)

Also a good idea to use separate amp "head" and speaker cab, more flexibility, and with fewer hernias and sore backs ;) (lol)

Just another crazy thought...

/ed B
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Re: Big bass amp

Postby Ty_Bower » Thu Oct 14, 2010 5:57 pm

elbinster wrote:I've found a few schematics, and think a sextet of 6550 or kt88 would be more than enough (though not very likely to hit 300W)


Ampeg doesn't agree with you. (666)

http://www.ampeg.com/products/classic/svtcl/index.html
"It's a different experience; the noise occlusion, crisp, clear sound, and defined powerful bass. Strong bass does not corrupt the higher frequencies, giving a very different overall feel of the sound, one that is, in my opinion, quite unique."
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Postby ChrisAlbertson » Thu Oct 14, 2010 7:47 pm

EWBrown wrote:The Karlson design speaker cabs are very efficient at lower frequencies, and if anything, they seem to extend the speaker's lower freq response.

/ed B


I had to look this up. Yes I can see why, kind of like using a folded horn for a bass reflex port.

But my question is if you have really used this style speaker for bass guitar.

My fear with these kinds of tuned cabinets is they might resonate and sound "boomy" especially with bass lines that tend to be single lines of notes.
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