Bass Guitar Amp Build Question

Hi all,

Been considering building a bass amp head recently and have an idea how I would do it - basically just wanted to run it past you guys and see if it's "a thing".

Can I just buy a switching power supply like this: 65V 500W Digital Power Dual-Voltage PSU Audio AMP Switching Power Supply Board 741722937198 | eBay

... and then use that to power a mono amplifier like this: IRS2092S 500W Mono Channel Digital Amplifier Class D HIFI Power Amp Board Part 8852074359094 | eBay

Add a preamp, and I'm just about there. Could that work? Has anyone done just this? What else is there to consider? :)

Regards,

James
 
Bigger Watts means smaller Speaker.

Bigger watts also means more dynamics without letting that "D" amp get anywhere near clipping.

I have one of those TI TPS3255 EVB boards running from a 48 volt 600 watt power supply that's turned up to 52 volts. I can rattle the bolts loose in the speaker cabinets before clipping that thing.
 
Last edited:
HAving a 1400 watt bass rig is not about being louder than everyone. it is about making the sound smooth and effortless. Bass can be really peaky, and a smaller amp will be plenty loud enough, but the peaks will bang their heads against the power rails.

It is like towing a travel trailer down the highway. A 400 horsepower truck can do it, and so can a VW Beetle. But the Beetle will be straining for all it is worth, while the truck will hardly notice the load.
 

wg_ski

Member
2007-10-10 5:21 pm
Yes, your idea is fine, no reason it won't work fine.

What "I" would do is use a larger power supply, you'll note that the one you linked to recommend 400W amp as upper limit, and then put an extra fan or two for the whole enclosure you mount them inside.

What will probably happen is the power supply will current limit, turning your 500 watt amp into a 400 watt amp. Depending on speaker impedance you may be limited by voltage anyway - any you may not get full power except at unsafe supply voltages.

If you do use a class D amp as an instrument amp you want one “bigger” than you need anyway. The sound of class D clipping is not good for guitar or bass, so you will want some sort of clipping or limiting ahead of the amp to get whatever sound you want (ie, tube distortion). To do this with a “clean” amp you need headroom so it never actually clips. A larger class D amp does not generate the waste heat of an oversized class AB doing the same thing so it is practical to do.
 
What will probably happen is the power supply will current limit, turning your 500 watt amp into a 400 watt amp. Depending on speaker impedance you may be limited by voltage anyway - any you may not get full power except at unsafe supply voltages.

If you do use a class D amp as an instrument amp you want one “bigger” than you need anyway. The sound of class D clipping is not good for guitar or bass, so you will want some sort of clipping or limiting ahead of the amp to get whatever sound you want (ie, tube distortion). To do this with a “clean” amp you need headroom so it never actually clips. A larger class D amp does not generate the waste heat of an oversized class AB doing the same thing so it is practical to do.

Yes, I figured as much. My issue is that I need a power supply and amp that will work together well, as I'm really only joining the dots here and don't really have the skills to work out what's wrong if it doesn't work. It also needs to be fairly cheap, or once ive put it all in an enclosure with sockets etc etc I could be spending the same as a commercial offering. Sacrificing power wouldn't be so bad. I've used 250w Class D bass heads before, and they are okay for the type of thing I do.
 

Gnobuddy

Member
2016-03-01 4:10 pm
I think it would be wise to set things up so the amp is capable of no more than 400 W RMS maximum output. Even at 90% efficiency, that would require 444 watts from the power supply, and that's starting to get uncomfortably close to its 500 W rating.

Luckily, the power supply you're considering has many different voltage options. Using +/- 55V (rather than +/- 65V) is probably all that's needed.

Do you already have a preamp design you've chosen? If not, these two articles from Rod Elliott's website might be useful:
1) Bass Guitar Amp 1
2) Bass Guitar Amp 2

Full disclosure: I haven't built either of these, nor have I heard them. Elliott appears quite convinced that valves are useless in an instrument amplifier, and I happen to disagree with that opinion.

That having been said, the fact is that there are precious few schematics out there for a DIY bass guitar preamp, so Elliott's designs might at least give you a useful starting point.

If it were me, I would probably cheat and just use one of these as my bass preamp: Access to this page has been denied.

The little ART MP/C includes just about everything you need in a bass guitar preamp, including a very nice (switchable) optical compressor, level metering for the output, level metering for the compressor, a tube stage you can push for just a tiny trace of valvey distortion, and multiple options for input and output connectivity and signal level. All of this at a price and size you almost certainly can't match with a DIY build that includes the same features.

The only thing not included in the MP/C is tone controls. If the ones built into your bass don't provide enough control, you'll have to add something else to the pot. Maybe a bass graphic EQ pedal between MP/C and class D power amp.

I've used the MP/C as a bass guitar preamp and DI box myself, for jams with friends, and on some of my home recordings. But my bass-guitar skills are novice level, and I play through either a 20-watt bass amp (Acoustic B20) or a little 30-watt little P.A., so I doubt my impressions are of much use to anyone used to 500 watt and 900 watt bass rigs. :D


-Gnobuddy