Hi
I am in the process of building a set of portable speakers. I am having great difficulty finding a suitable equalizer. I started building this schematic and board in eagle based on this http://www.circuitstoday.com/3-band-graphic-equalizer-circuit-2 but figured it will only work with a mono signal? If i built 2, i would have 6 knobs, 3 for each channel? Could I hook 1 pot upto both circuits so they would both be set to the same amount of gain for that frequency?
I would prefer to buy a already made (cheap) circuit on ebay. I have found some guitar ones but appear to have the same issue only 1 input.
regards
Fudam
I am in the process of building a set of portable speakers. I am having great difficulty finding a suitable equalizer. I started building this schematic and board in eagle based on this http://www.circuitstoday.com/3-band-graphic-equalizer-circuit-2 but figured it will only work with a mono signal? If i built 2, i would have 6 knobs, 3 for each channel? Could I hook 1 pot upto both circuits so they would both be set to the same amount of gain for that frequency?
I would prefer to buy a already made (cheap) circuit on ebay. I have found some guitar ones but appear to have the same issue only 1 input.
regards
Fudam
Hi Fudam
You are building portable speakers, why does a portable speaker need an equalizer ? Less is actually more in audio if accuracy is needed.
However with our best feet forward if designing op amp circuits on single rail Nat Semi have solved most of the headaches with their LM324 four Opamp package that is designed for single rail. You could gather info to design a stereo equalizer possibly from Nat Semi product data. LM324 - Low Power Quad Operational Amplifier
The schematic you provided a link for is awkward as DC offset issues ( due to the use of single rail ), are sure to arise. You may also want to look at products made by DBX who managed to design half decent audio tonal adjustment products, and some very decent companders, and they come up on eBay quite regularly.
Cheers / Chris
For stereo you need two circuits and 3 dual potentiometers. Remember also... when speaking of a 3-band eq it's not that far removed from the Bass-Midrange-Treble tone controls of a typical audio receiver. Maybe the name isn't quite as hip.
"Why does a portable speaker need an equalizer?" Of course it's personal preference. In my experience with common 2" to 4" drivers in a portable app, they're "peaky" in the midrange so applying a "gullwing" eq can squeeze a little more performance out of them. I wouldn't claim it as being more accurate, though.
"Why does a portable speaker need an equalizer?" Of course it's personal preference. In my experience with common 2" to 4" drivers in a portable app, they're "peaky" in the midrange so applying a "gullwing" eq can squeeze a little more performance out of them. I wouldn't claim it as being more accurate, though.
Who knew it was so easy?🙂
The aim of the equalizer is basically to increase the base.
the base and midrange is coming from 2x 10inch rated 100wrms. P.Audio HP-10W 10 Inch 100 Watt Low Frequency Public Address Systems | Portable PA Systems | DJ Equipment & Lighting
Have tested the setup with audio coming from iphone to a sureelectronics headphone amp as a pre amp then going into a sureelectronics tk2050 2x 100w amp. powered by a 24v lifepo4 battery pack, outputting 26v at the time of testing. It had heaps of volume with the iphone set to max volume and the tk2050 volume control board also maxed out it was loud enough that a mate and I could not hear each other standing infront of 1 speaker box, no audible distortion that I could tell of. The bass seemed to be lacking a bit, it wasnt too bad when it was cranked but at lower volumes was lacking.
I am not sure what you mean by single rail?
Will have a look on ebay to see If i can find any of your suggestions.
the base and midrange is coming from 2x 10inch rated 100wrms. P.Audio HP-10W 10 Inch 100 Watt Low Frequency Public Address Systems | Portable PA Systems | DJ Equipment & Lighting
Have tested the setup with audio coming from iphone to a sureelectronics headphone amp as a pre amp then going into a sureelectronics tk2050 2x 100w amp. powered by a 24v lifepo4 battery pack, outputting 26v at the time of testing. It had heaps of volume with the iphone set to max volume and the tk2050 volume control board also maxed out it was loud enough that a mate and I could not hear each other standing infront of 1 speaker box, no audible distortion that I could tell of. The bass seemed to be lacking a bit, it wasnt too bad when it was cranked but at lower volumes was lacking.
I am not sure what you mean by single rail?
Will have a look on ebay to see If i can find any of your suggestions.
A single rail supply is when you have a tension ( voltage , potential ) between two poles , like a battery . The minus is what you you call 0 V .
In a dual supply , often used in preamplifiers and amplifiers , there are two ( equal ) tensions , both referred to 0 V but one having positive and one negative potential .
This can be done by putting two batteries in series , the joint being 0 V , and plus and minus at the other points .
At home , it's obtained by having two equal transformers with same secondary windings , or a center tapped transformer . After AC rectification , the smoothed voltages are referred to the central tap , which is of course 0V .
For your application , you can find many circuits that suit . Dual supplies are not a problem , and since preamplifiers do not absorb much current , it can be done with two 9 V batteries in series . That is frequently seen also in some portable guitar effects !
In a dual supply , often used in preamplifiers and amplifiers , there are two ( equal ) tensions , both referred to 0 V but one having positive and one negative potential .
This can be done by putting two batteries in series , the joint being 0 V , and plus and minus at the other points .
At home , it's obtained by having two equal transformers with same secondary windings , or a center tapped transformer . After AC rectification , the smoothed voltages are referred to the central tap , which is of course 0V .
For your application , you can find many circuits that suit . Dual supplies are not a problem , and since preamplifiers do not absorb much current , it can be done with two 9 V batteries in series . That is frequently seen also in some portable guitar effects !
Thanks for your replies
That is the trouble I am having finding some circuits to suite.
I don't understand the basics here. Like why is a dual supply needed? Am I able to provide a dual power supply somehow from a single battery?
At the time of testing the speakers I ran the pre amp off a seperate 12v power supply. Is it fine to run it off say a linear 12v regulator that shares the same ground as the amplifier?
If you know of any sites that explain this stuff please post a link.
That is the trouble I am having finding some circuits to suite.
I don't understand the basics here. Like why is a dual supply needed? Am I able to provide a dual power supply somehow from a single battery?
At the time of testing the speakers I ran the pre amp off a seperate 12v power supply. Is it fine to run it off say a linear 12v regulator that shares the same ground as the amplifier?
If you know of any sites that explain this stuff please post a link.
For a portable system where small size is a plus, just get an automotive audio equalizer unit and make a small AC to DC power supply.
I wounder if you could shed some more light on the Duel Rail power supply, for example This Item off ebay shows a AC-0-AC input. Now is it possible to get something like that from a battery. We have a 24v 40ah LiFePo4 batter, which are not cheap, so we are not really up for getting a second one, they also weigh a lot so...
Hi Fudam
The unit on ebay just needs 15v AC ( AC refers to alternating current ) to work. If you look you will see a Dip size bridge rectifier mounted on board that converts AC to DC this is what is called AC rectification that then supplies the components in this case NE5532 op amps with dual rail supply.
If you really need to do this with batteries then 2x 12v batteries will be needed. Batteries also need charging As other members have suggested you would need to connect the batteries in series, like :
+....... - + ....... - The middle being common or ground and each end being the polarity of DC voltage. Much less expensive though with a AC 15v plugpack supply. These can be easily found, 😉 The plugpack models are quite safe, as 15v AC is not a very high voltage and quite safe to work with. With AC there is no polarity either to be concerned with, meaning one wire goes to AC terminal 1 and the other to AC terminal 2 , and I refer to the blue colored terminals shown in the product you have described
The relationship between 15v AC to the DC voltage will be 15/.707 this is really AC/ RMS value which refers to Root Mean Square ( too much detail, but showing you the mechanics of AC to DC conversion ) Working this out you can see 21v DC, composed of approx 10.5 volts positive and 10.5 volts negative is in this first part of the circuit - if 15v AC is supplied. No need to be too fussy anywhere between 15v AC and 18v AC ( if you cannot find a 15v plugpack AC transformer) Now, if 18v AC is used which converts to 12v positive to 12v negative will be fine supplied to this circuit. WHY ?
Straight after rectification and capacitors are two fixed volt regulators, you can almost be certain that they are models 7805, and 7905 meaning that really the op amps are working at 5 volts positive and negative.
So this little circuit you have found might do the job.🙂
Cheers / Chris
So everything is on board
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Thank you Chris.
I don't think 2 12v batteries would be possible in this project, and its main purpose is for camping, so AC is sort of an issue also. I could get something like an inverter, but that seems pointless, going from DC to AC then back to DC again on the board. So I wonder, Using the same eBay chip as a reference, if I could use a Virtual Ground chip and bypass the AC to DC conversion on the eBay chip, would this essentially give me the same result?
More Info:
Virtual Ground Circuits
I don't think 2 12v batteries would be possible in this project, and its main purpose is for camping, so AC is sort of an issue also. I could get something like an inverter, but that seems pointless, going from DC to AC then back to DC again on the board. So I wonder, Using the same eBay chip as a reference, if I could use a Virtual Ground chip and bypass the AC to DC conversion on the eBay chip, would this essentially give me the same result?
More Info:
Virtual Ground Circuits
Sorry for the double post, but it doesn't seem to let me edit posts.
I have also seen this one, I'm not really sure of these, as they are from eBay, but then so are some of the better amps. This particular one accepts DC in directly, But I don't even see an op amp in sight, and I'm not sure of the quality. I am building a portable unit, so I am not looking for studio quality, but I also don't want crackling, or humming that is audible while playing music. I would love it if someone has had some experience with these first hand, but if not, any advise would be nice.
Thank You
I have also seen this one, I'm not really sure of these, as they are from eBay, but then so are some of the better amps. This particular one accepts DC in directly, But I don't even see an op amp in sight, and I'm not sure of the quality. I am building a portable unit, so I am not looking for studio quality, but I also don't want crackling, or humming that is audible while playing music. I would love it if someone has had some experience with these first hand, but if not, any advise would be nice.
Thank You
Hi fudam
If its for camping then Yes it has to be portable. My suggestions are to use a single supply circuit designed around LM386, ( LM386 is a neat little power amp - small in power but pretty good too ). It can be powered with a suitable Yaesu battery thats not too heavy and renew that power with a Solar panel ( a fold up one )
So we need next concentrate on a circuit that will do this tone adjustment. You can get op amps generally to do any audio adjustment. You need though to study any application notes that relate to LM386. I noticed page 5 of the datasheet attached to this link:
LM386 - Low Voltage Audio Power Amplifier
gives a Bass Boost circuit. You would then just match its output to a following amp and speaker.
What fun !
Cheers / Chris
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