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SirPoonga 15th February 2005 03:56 PM

Building a bass amp and speaker (cont...)
 
Hello folks. I decided to move a conversation here as this seems a better place to discuss this than diystompboxes.com.

The start of the conversation:
http://www.diystompboxes.com/sboxfor...ic.php?t=29755

---copy and pasted from another forum where I summed up my project --
To sum up. I've been looking to make an amp because I have to have a project. I figured it would be a fun project.

There's basically three things to make a amp
Preamp
Power Amp
Speaker Cabinet

For bass this is tougher than guitar I have found out. There are alot more DIY resources for guitar.

Preamp:
Acoustic Control 360 Bass Preamp and Fuzz Unit
http://www.lynx.bc.ca/~jc/pedals360.html
http://www.moosapotamus.com/360+/360+.htm

Flipster
http://runoffgroove.com/flipster.html

Speaker Cabinet:
You know the drill here, find a driver you like, plug the values into WinIDS, tweak, build. I think am choosing the Eminence Delta 12LF. I am going to just make a 1x12 for my needs.

I save the power amp for last.
This is the toughest part to find anything with power to drive bass. This is the part that why you see so many DIY guitar amps but very few bass amps.

If you read the thread I linked at diystompboxes.com you can catch up on what's going on. found (with help) the right transformer on ebay which for me is the toughest part. I plan on using the LM4780 kit from
http://www.chipamp.com/lm4780.shtml
That chip is bassically two LM3886 chips.
http://www.national.com/pf/LM/LM3886.html
Read the datasheet and AN-1192 app note.
What I am going to do is take the two LM4780 assemblies that come in the kit and brige them. That should effectively be the 200W setup from the AN-1192 doc.
Right now I am looking at how to provide enough power and the right power to that circuit.

I think what I am going to end up with is make a speaker cabinet. Then I might rack mount the power amp and preamp seperate. That way I can try seperate preamps. Otherwise I'd wire a preamp bypass jack and stick the flipster in with the power amp.

--------


I am currently on the takes of figuring out to build the power amp part. The transformer I need is going to be on the way shortly. I am still debating to do the LM4780 kit form chipamp or do 4 LM3886's as the AN-1911 doc points out. I am leaning towards the two LM4780 boards since I would just have to bridge those.
I've just started searching here because I've noticed this has been discussed before and I see there are pcb designs for bridged lm4780s :)

So the purpose of this thread would be to discuss all parts of my idea to make a bass amp. From speaker selection to preamp to power amp.

Right now, as it sits, I am thinking Flipster preamp, bridged LM4780 power amp, single Eminence Delta 12FL in a 3.5cu ft vented box tuned to 40ishHz. Will go 4x12 in future if needed, but since I just play around with friends right now this is all I should need.
I might do the 360 preamp also in the near future. So would it be best to build the flipster in with power amp enclosure and make a preamp bypass jack or seperate the rpeamp from the amp completely?

Brett 15th February 2005 04:50 PM

Couple of quick comments from a bassist.
- 200W isn't much for a live rig and a 1x12 isn't going to fill much space, compete with a drum kit and guitars etc on stage. You need headroom and the ability to move significantly more air then a guitar rig can to sound as loud. I have a JBL 15, and a 2x12+horn that I use individually or together depending on the tone required and the size of the room. My amp is 2x500 and sometimes it's been too small. Try competing with 2 100W Marshall 8x10. One of Bill Fitzmaurice's Tuba 24 small horns might be the go for the cab.
- Not real confident of the longevity of the chip amps under stage abuse. The only place I've used them is in a triamp rig, running the horn driver on the top end. Others may have more experience with them and be able to be more definitive.
- flat response to 40Hz is not always a benefit on stage. Can muddy up everything. Many people are happy with 4x10's etc which seldom have much below 80Hz.
- at first glance the flipster looks like it's going to run out of headroom (especially with an active bass) and give a dirty tone, but not be real flexible. With a 9V supply it's obviously been engineered with a stompbox approach, lower than I would use. Some of my active basses use an 18V internal supply (and some 24 and 60V external) and the difference with 9V is clearly audible.

For simplicity, build the pre amd power in the one box as a 'head', if you build both. You can add whatever jacking pre out/ power in etc you like. A 'combo' is too inflexible imo. Personally I would suggest building the pre and buying a decent PA amp new or secondhand for the power.

Go to one of the bass forums and see what people are using and emulate that in terms of specs.

SirPoonga 15th February 2005 04:57 PM

One thing I can not find info here on is how would one bridge the two boards that comes with the chipamp.com kit?

SirPoonga 15th February 2005 05:05 PM

FYI, this isn't for stage use. I'm new to playing bass. This will be for the living room and/or jamming with friends during happy hour at the local bar :)

Brett 15th February 2005 05:40 PM

Quote:

Originally posted by SirPoonga
FYI, this isn't for stage use. I'm new to playing bass. This will be for the living room and/or jamming with friends during happy hour at the local bar :)
That will be enough then.

I've read the diystompboxes thread, and the one on talkbass, if you're after cheap, then buy something secondhand. Building is one offs is ALWAYS more expensive than you think (20 years of DIY and commercial experience) and has zero resale value.

Buy something secondhand and invest your time, money and effort in a teacher and practice.

R.G. 15th February 2005 05:54 PM

One of the ideas in that earlier thread was an incremental amp: a 30-50W power amp driving one matched speaker. You substitute quantity for power by making as many as you need. That way you can realistically get to kilowatts for stage if you need them.

The LM3886 and its ilk on a flat back heat sink with its power transformer do a great job of this.

SirPoonga 15th February 2005 05:54 PM

I wish there was an edit here :)
I see your point about the 9v. Ok, the Acoustic 360+ schematic says takes 25V. The power amp takes 28V. What would happen if I ran the 360 circuit off the same 28V? Or would it be wise to just diode down the voltage for that circuit?

I'm open to either preamp. I like how they sound from the sound samples.

The other question comes up based on your reply is the comment about chip amps longevity on stage. What would you use, a tube amp then? And DIY amps (or kits) out there that will work for bass?

I want to try to make this almost completely a DIY project. Not to save money or anything like that. I just want to commercial instead.

SirPoonga 15th February 2005 06:11 PM

I like that idea RG has too. For me that approach would make possibly sense in the future.

I have to look back at the modular idea on how to "add on" another setup.

"- flat response to 40Hz is not always a benefit on stage. Can muddy up everything. Many people are happy with 4x10's etc which seldom have much below 80Hz."

I was thinking about this too. That's what EQs are for, right?

SirPoonga 15th February 2005 06:12 PM

Errr, this is why I am not fond of moderated forums.

Change "I want to try to make this almost completely a DIY project. Not to save money or anything like that. I just want to commercial instead."
to
"I want to try to make this almost completely a DIY project. Not to save money or anything like that. I know I could just do commercial for a decent price instead."

What I wrote before made sense in my mind before. Now that I re-read it after some time has passed....

Brett 15th February 2005 06:22 PM

Quote:

Originally posted by SirPoonga
I see your point about the 9v. Ok, the Acoustic 360+ schematic says takes 25V. The power amp takes 28V. What would happen if I ran the 360 circuit off the same 28V? Or would it be wise to just diode down the voltage for that circuit?
Just drop the voltage from the poweramp; a series resistor and cap would do fine. One of the links you provided showed the idle current of the Acoustic pre. Use ohms law to figure out the resistor. May work fine on 28V, didn't look closely enough to check.
Quote:

I'm open to either preamp. I like how they sound from the sound samples.
Never heard a soundsample sound like the real thing. Too many variables. The Acoustic is well regarded amongst some circles so it should be fine.
Quote:

The other question comes up based on your reply is the comment about chip amps longevity on stage. What would you use, a tube amp then? And DIY amps (or kits) out there that will work for bass?
No tube amp without a roadie to move it for me. Too heavy.
There are lots of high power SS amp designs out there.
Currently I use a Perreaux poweramp, but I can't say what's in the new one as it's a design someone else owns that's being made commercially.

Build what you're suggesting now with the chip amps. Build it as small and light as possible and leave space to add a crossover in. That way later you can add other cab(s) into a multiple/flexible rig depending on where you're playing, using other outboard larger poweramps for the lower end and the chipamps for the lighter loaded higher frequency stuff.
Quote:

I want to try to make this almost completely a DIY project. Not to save money or anything like that. I just want to commercial instead.
If you build a rig over time as I suggested, then I strongly advise to go with a big PA amp for the larger one. They're too cheap even new to stuff around with building one and put your time effort and money into building a few boxes (speaker) and add some tonal flexibility etc into the preamp. This'll give you bigger dividends than spending time building high power amps.

Not so sure about the small incremental approach RG is suggesting. Your 1x12 powered by 7480's and a 500Wer with a decent 1x15 and a small horn either passive or driven by a 3886 would be a decent rig and flexible. Just take the 1x12 to practice/jam and the full outfit to perform in a bigger club. At the local hotel I play at, they have a new and quite good PA. I take a preamp, small amp and my old 2x10 with Ampegs for my own monitoring and DI into the house system.
Note: when you're building, add a good DI and a tuner output.

Also look later at the pickups and onboard preamps on the basses themselves. Pickups are the biggest affect for $ spent in basses.

You also asked earlier
One thing I can not find info here on is how would one bridge the two boards that comes with the chipamp.com kit?
It's in the Nat Semi app note (#1192?).


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