Hi,
I'm trying to build a small practice bass guitar amp. The main goal is to have something easily portable that can be carried around when jamming at someone's house, for example. My idea is to use a basic class D (like the Lepai 2020) for the main amplifier, and build a simple solid-state preamp. House the whole thing in a ported box with a 6-inch woofer.
Is this a reasonable goal?
I'm looking for suggestions for circuits I could use for the preamp stage.
Also, most 6-inch woofers I've seen seem to have a freq response of 50Hz at the low end. Given that a bass can go below that, how does that impact port tuning?
Thanks.
I'm trying to build a small practice bass guitar amp. The main goal is to have something easily portable that can be carried around when jamming at someone's house, for example. My idea is to use a basic class D (like the Lepai 2020) for the main amplifier, and build a simple solid-state preamp. House the whole thing in a ported box with a 6-inch woofer.
Is this a reasonable goal?
I'm looking for suggestions for circuits I could use for the preamp stage.
Also, most 6-inch woofers I've seen seem to have a freq response of 50Hz at the low end. Given that a bass can go below that, how does that impact port tuning?
Thanks.
Yes.
To play alone 6" may do, to play with others try to get at least to 8" and 10" would be even better.
Use this one as a guide, works very well.
Crate B10 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
It's as generic as can be, this basic circuit is used by many.
Just replace the TDA20xx power amp with the Lepai.
I suggest this particular one because it's generic, sounds good, is simple and inexpensive but most important, is single supply so the Lepai supply can feed it.
Others will require +/- 15V , this one will be happy even with +16 to +20 V, whatever the Lepai needs.
It can be simplified somewhat, consider it just a reference.
For example you don't need Gain and Master, gain alone is enough.
Also midrange and bright controls are optional.
And maybe you need a little les gain.
Not even the mighty 8 x 10" SVT speaker reaches 40 Hz 😱
Don't worry about that; reaching , say, 60Hz flat or with a slight bump is eceptional 😱
@JMFahey, thanks a lot, that's exactly the sort of information I needed. Will get started soon 🙂
@Vasquo, because its more fun to DIY!
@Vasquo, because its more fun to DIY!
Don't look for a woofer. It's much more important with good sensitivity for such a small practice amp. If a small speaker goes low, it will also be ineffective and very low SPL with the Lepai. Try go for 100 Hz with a bump. Maybe this visaton (better if someone with real experience can comment on it).
Visaton BG 17 8Ohms - Thomann UK
I have tried 6" fullrange (Visaton for HiFi purpose) with low fs (soft surround low sensitivity), and it was not good. A high fs 10" midrange (Fane Studio 10M) was much better. Note that i build these for guitar, but have also tried bass through these and I still prefer less bass but good nondistorted bass.
Visaton BG 17 8Ohms - Thomann UK
I have tried 6" fullrange (Visaton for HiFi purpose) with low fs (soft surround low sensitivity), and it was not good. A high fs 10" midrange (Fane Studio 10M) was much better. Note that i build these for guitar, but have also tried bass through these and I still prefer less bass but good nondistorted bass.
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Visaton dual cone is cool bandwith wise if ever he slap and will allow to get the good treble balance by simply shutting the excessive trebles using the bass tonality pots, with fingered playing it will give the necessary attack when using non active basses.
If weight is a big factor - think about a Neodymium magnet speaker. They are about half the usual weight - but can be more expensive.
I'm currently working on a simple op-amp based bass preamp with a compressor at the moment, I'll post it onto this thread when I'm done with the circuit.
@Monty78pg, cool, would love to see the design.
Based on all the advice here, I've changed my original plan from 6" to 8", full-range rather than woofer, if possible neodymium. Not sure if neodymium drivers are available locally, but will go out and check this weekend.
Based on all the advice here, I've changed my original plan from 6" to 8", full-range rather than woofer, if possible neodymium. Not sure if neodymium drivers are available locally, but will go out and check this weekend.
OK, I'm not very big and not that young and I find that a single 12" combo bass amp is easy to carry around. I built a bass amp using a SE tube amp that uses a single EL34 to drive a single 12" speaker in a ported cabinet. The cabinet is 18" x 15" X 10" deep. I find it easy to cary around. Weighs around 30 lbs. a 6" speaker is too small. You will be fine playing quietly in a bedroom, but you will not be heard over drums and or a guitar. If you want to make a 30 or so watt transistor amp, weight of the amp would probably drop by 5 lbs. In my experience, I have found that an amp the size of my little practice amp is the minimum for bass. Low frequencies are just not easily produced via small speakers and small cabinets. A bass amp needs to reproduce frequencies from around 40hz to over 5Khz. So you can't have a speaker that is flapping too much at the lower frequencies or you end up with some very sick sounding overtones.
I think I'd go for a very high power 8-10" PA midbass, tiny ported box, and throw a pile of power at it.
Port at 80Hz or so, and get a high-pass filter in below that. Forget reproducing the fundamentals. Small + loud means no real bass. You might be able to get the pretend-bass with some clever software, but I'll leave that as an exercise for you to figure out.
The latest class D power amplifiers are showing up some ridiculous power densities, so I'd start by looking there.
Something like...
Speaker Detail | Eminence Speaker
Plus a high-power amplifier. Say, 500w continuous, minimum. Maybe look at 2nd-hand PA amplifiers, and strip the guts out.
Not the cheapest way of doing it, but you'd be able to play small gigs with no PA with this setup: a 10" going to 80Hz (ported) can be very loud.
Chris
Port at 80Hz or so, and get a high-pass filter in below that. Forget reproducing the fundamentals. Small + loud means no real bass. You might be able to get the pretend-bass with some clever software, but I'll leave that as an exercise for you to figure out.
The latest class D power amplifiers are showing up some ridiculous power densities, so I'd start by looking there.
Something like...
Speaker Detail | Eminence Speaker
Plus a high-power amplifier. Say, 500w continuous, minimum. Maybe look at 2nd-hand PA amplifiers, and strip the guts out.
Not the cheapest way of doing it, but you'd be able to play small gigs with no PA with this setup: a 10" going to 80Hz (ported) can be very loud.
Chris
Buy cheap, buy twice
Buy this, be happy forever:
Speaker Detail | Eminence Speaker
Match it with 500 class-D watts and you'll have a small but perfectly formed rig that you can take anywhere and fear no guitarist.
Buy this, be happy forever:
Speaker Detail | Eminence Speaker
Match it with 500 class-D watts and you'll have a small but perfectly formed rig that you can take anywhere and fear no guitarist.
I built the preamplifier based on the Crate design and it seems to be fine. I later noticed that I had left out part of the circuit (red circle in the attached image). It ties the input of the opamp to a 6v reference voltage through a 220K resistor. There is a similar section on the next stage, only this time with a 47K resistor. What is the significance of these? I could not find such connections in the op-amp datasheet examples.
Attachments
They are the bias resistors for the opamp input stage. If it seems to work without those (and assuming you have C2 in place) then its by pure chance that the opamp input is "floating" in such a way as to acquire some voltage.
They are vital... fit them.
They are vital... fit them.
Thanks, that was a useful piece of information. I found some more background about biasing opamp inputs from this TI document. I'll fit these in right away.
Your welcome 🙂
Its always useful to know the basic opamp theory, then you can tweak and alter things to suit your requirements.
Its always useful to know the basic opamp theory, then you can tweak and alter things to suit your requirements.
The basic preamp section is working well, connected to a TA-2020-based main amplifier. I tried implementing the tone controls section of the Crate circuit, but this does not work at all. The output drops to a whisper, you can barely hear it if you put your ear right up to the speaker. I've checked and rechecked my circuit and it looks identical to the one in the Crate diagram. I've attached the relevant section, does anything stand out that I should be checking? Also, the pot on the top right is not labelled, is that the high eq?
Thanks for your help!
Thanks for your help!
Attachments
Its a passive circuit and so does introduce quite a loss depending on pot settings.
With the left hand volume pot on full and the unmarked pot (yes, you could call that Hi Eq) also up full (wiper to C12) you should at least get plenty of hf audio coming through. Does it ?
In your opamp circuit above I just spotted the input coupling cap at 0.01uf. That's very small and means the response falls away below about 100hz.
With the left hand volume pot on full and the unmarked pot (yes, you could call that Hi Eq) also up full (wiper to C12) you should at least get plenty of hf audio coming through. Does it ?
In your opamp circuit above I just spotted the input coupling cap at 0.01uf. That's very small and means the response falls away below about 100hz.
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