What always bothered me about hearing tests was that reaction time of me pushing the button or earlier me telling the doctor that I started hearing the tone and he/she taking a reading and noting that.
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To answer the question of the OP (that's what he is here for I think) is: for a quick, easy, low cost and proven design, look at any of the 'chip amp' designs. You can buy complete kits from places like Neurochrome by Tom Christiansen, a member here.
Fast, quick, proven, low cost, complete. Done.
Jan
Fast, quick, proven, low cost, complete. Done.
Jan
Don't know, it's been a while since I actually looked "harder" at this amp.
I do know it's another 3886 amp, and the output power doesn't suggest bridge mode.
More importantly I know that this is the amp that Arta recommends, where specifically saying NOT to use a bridge amplifier (with a typical virtual ground). It's of course virtual ground that's the problem..
I mentioned this on the 3rd post. 😉
Not a low-cost (in total) result though, and no where near the cost of the "completed" PM40C. 😱
Any ideas for an option closer to the very few watts actually needed for measurements? Would be nice to keep things light and compact. The chip-amps I found asked for quite serious transformers...
Whatever are you looking for? Small, low power, high power but small, battery, precision, price, stereo? Any reasonable amp from the thrift store will be vastly more perfect in FR, distortion, noise, and square waves than the speakers you want to examine.
Frankly speaking from lots of experience, what you want is any amp that has a large click-stop volume control and some paper tape on the faceplate you can mark with a Sharpie pen so you can return to prior settings (or that you can calibrate the VC gain with a voltmeter).
Buy a few non-inductive precision resistors and sweep them on the same chart as the driver impedance to bracket the driver plot. That will benchmark your measurement system.
B.
Frankly speaking from lots of experience, what you want is any amp that has a large click-stop volume control and some paper tape on the faceplate you can mark with a Sharpie pen so you can return to prior settings (or that you can calibrate the VC gain with a voltmeter).
Buy a few non-inductive precision resistors and sweep them on the same chart as the driver impedance to bracket the driver plot. That will benchmark your measurement system.
B.
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As you won't draw a lot of power you don't have to feed it a lot of power, so a small transformer will do. Same with the heatsink.
You can start out with 2 9V batteries.
Don´t overthink it.
You need a Class AB amp, able to feed a few Watts into the speaker, a few Amperes so it can cope with weird - too low - too reactive impedance,and so LM1875 , TDA2030, etc. are perfect.
You do not want wild load sensitive networks, no HF hash, etc so preferrably no Class D amps.
What for?
Who cares about slightly colder or more efficient stage in a "few Watts" amplifier which to boot is used for *measuring*?
You MUST be able to ground one speaker trerminal so no bridging either.
You want the most transparent one and the chipamps mentioned above are more than competent.
Fed from 3 AA batteries? ... is this a joke?
Not even two 9V batteries will do.
You need a Class AB amp, able to feed a few Watts into the speaker, a few Amperes so it can cope with weird - too low - too reactive impedance,and so LM1875 , TDA2030, etc. are perfect.
You do not want wild load sensitive networks, no HF hash, etc so preferrably no Class D amps.
What for?
Who cares about slightly colder or more efficient stage in a "few Watts" amplifier which to boot is used for *measuring*?
You MUST be able to ground one speaker trerminal so no bridging either.
You want the most transparent one and the chipamps mentioned above are more than competent.
Fed from 3 AA batteries? ... is this a joke?
Not even two 9V batteries will do.
Thanks JMFahey. I have decided to build an 11875 with a 25-0-25 transformer with a rectifier circuit. I am thinking that inserting a click potentiometer to be able to keep output volume consistent would be helpful. Does that make sense?
If that's a 25-0-25 VAC transformer, that's too much for the lm1875. A 18-0-18 would be the max I would use.
Will 28 a vct transformer (420 mamp) do? As I understand it, this would be 14 VAC but the current would be out of phase. I am looking at using the following rectifier:
https://www.amazon.com/gp/product/B07BJHNLGF/ref=ox_sc_act_title_1?smid=ATCVC199CHVK0&psc=1
Thanks
https://www.amazon.com/gp/product/B07BJHNLGF/ref=ox_sc_act_title_1?smid=ATCVC199CHVK0&psc=1
Thanks
The rectifier and filter cap board is fine, but use a somewhat larger power transformer, say 12+12VAC (or 24V CT, same thing) 1A (basic) to 1.5A (better).
That will give you 16+16V DC which is fine for this use, LM1875/TDA2030 will be happy and safe; the combination will easily put out 1W RMS into any speaker impedance from 4 to 16 ohm you may want to measure with *ample* headroom so you can forget about amplifier worries and focus on measured speaker instead.
That will give you 16+16V DC which is fine for this use, LM1875/TDA2030 will be happy and safe; the combination will easily put out 1W RMS into any speaker impedance from 4 to 16 ohm you may want to measure with *ample* headroom so you can forget about amplifier worries and focus on measured speaker instead.
Sorry to be so dense but just being careful. Would one of these two transformers work? I am looking at either the 241-6-24 Signal Transformer or the A41-25-24 All-4-One at Mouser. Thanks.
For years, I used a basic $15 TPA3116 Class D amp and high quality HP or Dell 19v laptop power supply. This type of amp has low enough distortion below what most speakers can manage. Plus it can do 4ohm loads or 8ohm loads no problem.
Most drivers can not muster any better than -50dB to -55dB distortion at any harmonic. Some horn loaded speakers with good clean drivers get into the -60dB range but they are far and few in between. Most speakers will be in the -40dB to -25dB distortion range and a basic Class D amp will work just fine.
This would work quite nicely for speaker measurements.
https://rover.ebay.com/rover/0/0/99?loc=https://www.ebay.com/p/562455297
Try it, nothing lost but $9 if you don’t think it’s sufficient.
Here are examples of all the drivers I measured with a TPA3116 amp in the “Subjective Comparison Threads”:
A Subjective Blind Comparison of 3in to 5in Full Range Drivers
A Subjective Blind Comparison of 3in to 5in drivers - Round 2
A Subjective Blind Comparison of 2in to 4in drivers - Round 3
A Subjective Blind Comparison of 2in to 4in drivers - Round 4
A Subjective Blind Comparison of 2in to 3.5in drivers - Round 5
Most drivers can not muster any better than -50dB to -55dB distortion at any harmonic. Some horn loaded speakers with good clean drivers get into the -60dB range but they are far and few in between. Most speakers will be in the -40dB to -25dB distortion range and a basic Class D amp will work just fine.
This would work quite nicely for speaker measurements.
https://rover.ebay.com/rover/0/0/99?loc=https://www.ebay.com/p/562455297
Try it, nothing lost but $9 if you don’t think it’s sufficient.
Here are examples of all the drivers I measured with a TPA3116 amp in the “Subjective Comparison Threads”:
A Subjective Blind Comparison of 3in to 5in Full Range Drivers
A Subjective Blind Comparison of 3in to 5in drivers - Round 2
A Subjective Blind Comparison of 2in to 4in drivers - Round 3
A Subjective Blind Comparison of 2in to 4in drivers - Round 4
A Subjective Blind Comparison of 2in to 3.5in drivers - Round 5
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I agree that most cheap amp boards will do, as long as the "cold" output is at GND. A stepped gain switch for reproducible level settings is useful, and a built-in self-recovering protection for shorts and similar mishaps is nice to have.