Commission for a small bass amp

[mlp-mx6]

Folks,

I am (probably) being commissioned to build a small bass amp. Say 15-20W for someone to play their upright bass through. I'm planning to order one of the small David Allen chassis (Vibro Champ-size). Would any of you suggest a particular circuit? It will be easy enough to build the Bassman 20 circuit in there. Would a Bax-style tone circuit work better? Would you suggest a small Ampeg circuit?

I welcome all recommendations.

Thanks,
Michael

[Structo]

15-20 watts doesn't sound like enough power for a bass amp.

Bass usually takes a higher output because you want a lot of headroom in the amp.
In other words, you don't really want it to distort when turned up.

I do know that when in a band with other guitarists that have 50 watt tube amps, that the bass usually requires at least double that wattage or even higher (like 300) because the guitar amps will exceed the 50 watts if they are turned up beyond the onset of clipping.

Now if this is a small jazz combo type band, then it may be ok but I think if it were me I would want at least 50 watts on hand.

[Alexo]

I think an Ampeg B-15 clone sounds like what you're looking for. Plenty of schematics on the web, and there's no bass player out there who wouldn't be glad to have one.


But +1 on Structo's comments, you can eat up 20 watts pretty quickly with a bass. you could use 6550's, or a quad of 6L6's for a little more oomph, and it doesn't hurt to over-spec the transformers, but unfortunately, these changes significantly raise the space requirements and the price.

[mlp-mx6]

Thanks, gents. I raised the same concern re: power needs to the customer. This is for a small bluegrass ensemble, and he just wants additional "stage fill" from this amp with a line out to go to the PA. I am overspec-ing the power to at least use 2 6L6s.

I will consult with the customer and see where we go.

Again, thanks.
Michael

[Andy Le Blanc]

A++ for a B-15. I jam once a week with folk/ acoustic bunch and the bass
player uses a B-15, nice circuit, very usable tone, you should sneak in as
many watts as you can with a prudent tranny and power tube selection.
But try to keep the pre as close to a B-15 as you can. The portaflex box
is very lovely sounding too, You can run a B-15 on a 300w inverter and car battery if your in a pickle.

[briane]

yeah, I've built a few bass amps for the locals around here.

15 watts - probably cant event hear it. The guys I built 50 watters for (what they requested) say its not enough. Now I only do 100 watt and 300 watt versions. Cant stand complaints.

If its auxilirary to a PA, still go with 50 watts. I suspect el34 would be better than 6l6 for bass though. Dont do the 7027. You need that extra current.

Built the b15, b25, sunn 100s, etc... their ok, but for a real bass amp (or more specifically a better one) go with a marshall 1986, add a master vol, LNFB, and a PICF, and your bassist will be really happy. Thats the circuit I am using now, and the reviews have been amazing (ps, my master is 500kA, with 20k to ground). I have a real SVT sitting around, and the tonal comparison of this to it is almost exactly the same.

[Structo]

Yes, definitely a 2 x 6L6 or 2 x EL34 amp.

[UR12]

Most bluegrass players I know only mike the upright through the PA and maybe a little in the monitors. What kind of pickup is he using for his upright or is he using a mike? I would think for a bluegrass group who ALL play acoustic instruments 20 watts would probably be plenty. It wouldn't hurt to do a B15 as they sound awesome and he can always turn it down.

[wscrane]

This may not be of interest but there is a dude in Australia (ESP) that sells nice transistor diy boards. I've used a 100W board called a P3a a few times to repair/refurbish old Polytone Minibrutes with good results.

Also... there are two reasons bass amps require more power than guitar amps. One is that bass speakers are by nature less efficient -- a consequence of the lower resonance. For a specific example, suppose you have a 15W guitar amp with a Eminence Legend 102 (98dB) and you want to make a comparable power bass amp using a Legend BP102 (92dB). To make up the 6dB you need 4x the power. The other thing is that bass players like clean, so its good to have another factor of 2 for headroom. Which brings the grand total to 120W.

One trick to get some free low end power is to double up on the number of speakers. For example you could probably get away with a 15W bass amp if you used an 8x10 SVT cab.

[mcrracer]

This may not be of interest but there is a dude in Australia (ESP) that sells nice transistor diy boards. I've used a 100W board called a P3a a few times to repair/refurbish old Polytone Minibrutes with good results.

Also... there are two reasons bass amps require more power than guitar amps. One is that bass speakers are by nature less efficient -- a consequence of the lower resonance. For a specific example, suppose you have a 15W guitar amp with a Eminence Legend 102 (98dB) and you want to make a comparable power bass amp using a Legend BP102 (92dB). To make up the 6dB you need 4x the power. The other thing is that bass players like clean, so its good to have another factor of 2 for headroom. Which brings the grand total to 120W.

One trick to get some free low end power is to double up on the number of speakers. For example you could probably get away with a 15W bass amp if you used an 8x10 SVT cab.

I guess as a bass player of over 35 years experience I need to speak up now. Not necessarily true.The right bass speakers operated in a properly designed cab are easily as efficient as guitar speakers , if not more. The BP102 is not a good bass driver. It is better suited as a subwoofer driver. I use custom designed cabs which use one Eminence Deltalite II 10 inch speaker. One cab is smaller for practice and small gigs about 30 pounds, the larger one , still with only one 10 inch driver and a bank of 6 piezos, about 24" X 24" X 24" about 40 pounds will play any place I have needed it. 50 watts through it is LOUD. I had until recently a 300 watt power amp SS with a tube pre. I never went past 2 on the controls. A high efficiency cab just does not need a lot of power.I no longer gig much because I am now disabled so I sold the amp rig. I kept the speakers. Most of us, bassists, do like good clean power. I have used tube amps but generally always went back to SS, For the same tone and power you would need a 300 watt tube bass amp. They sound great , but you need two good men and a boy to carry it.It really depends on the tone the player is looking for. 50 watts of tube power through the right cab could give him all that he needs. He is not playing in a rock band . Remember they play these in many situations with NO amplification Many DB players that I know use one of the new generation of pocket sized SS amps. Once you have used a 5 to 10 pound amp that you can just throw in a gig bag, that also has the power and tone you need, it is real hard to go lug a 50 to 75 pound monstrosity around any longer.
Now for guitar Tubes are it. I don't really play guitar , I just enjoy building tube amps and it is something my health still allows me to do. I can't work any longer so building amps keeps me sane. Just a bass players perspective.

[Structo]

Yes that was my other thought after I had posted is that a lot of bassists seem to favor solid state amps.

You could build a very simple preamp and power amp that would be very clean unless you want the tube warmth.

I think as most of us are six stringers we were coming from that view point and maybe incorrectly.

[mcrracer]

It's cool Tom...Some of my best friends are six stringers! and that is why I am here. I always loved the tube sound even for bass.

[KT66]

I am really enjoying this thread because I am mulling over some ideas to build a bass amp. +1 on the B-15 idea, a number of bass players I have talked to really like that amp. I would go SS on the recto though and beef up the PS filtering. You mentioned that your customer wants a line out, so I thought I should mention that the Fender Tonemaster OT (#026478) has a low level +3dB output tap that might be usefull for that, as well as 4,8,and 16 ohm taps. Angela stocks this and I think CE does too.

Does anybody have a source for the coil in the midrange control of the SVT ? Or an alternative to having that in the circuit ?

[benoit]

Folks,

I am (probably) being commissioned to build a small bass amp. Say 15-20W for someone to play their upright bass through. I'm planning to order one of the small David Allen chassis (Vibro Champ-size). Would any of you suggest a particular circuit? It will be easy enough to build the Bassman 20 circuit in there. Would a Bax-style tone circuit work better? Would you suggest a small Ampeg circuit?

I welcome all recommendations.

Thanks,
Michael

It seems like you've already been steered in another direction, but as a bassman 20 owner, I have to say, DON'T build one. Mediocre sound at best.

[Kregg]

I love the tone of Fliptops, as well as SVT's. I use a SWR 15" with a horn and I get along just fine with it for a practice amp. However, if I played a fiddle bass live, I think I'd build a head based on the B-15. As for the cabinet I'd take some creative liberty and build a down firing speaker with a front firing horn mounted on top of a beautifully finished cabinet.
Maybe I'll build one after I finish my Express cab and the Gemini II build.