I have a 16 ohm speaker I made using:
1. 2 RCA 12" 8 ohm woofers in series.
2. 1 Goodmans Midax.
3. 1 Klipsch KG4 tweeter with series resistor to drop the level and equal 16 ohms.
4. Goodmans 15 ohm 3 way crossover.
I currently use the following 15 watt amp kit to drive the speaker.
https://store.qkits.com/electronic-kits/audio-kits/15-watt-mono-audio-power-amplifier-kit-fk607.html
Noticed at full volume it tended to have issues until I put a 16 ohm resistor in parallel with the speaker input on the crossover, however that's power being wasted.
There any audio transformers with an 8 ohm primary and 16 ohm secondary with a frequency response of 30-20kHz or can I use an audio output transformer that has an 8 and 16 ohm tap?
Also is there a small mono or stereo bridgeable amp that has a 16 ohm output or can I use a small stereo amp that can drive an 8 ohm load with an unbalanced to balanced transformer on the input?
The amp and speaker are used in a screen room at work where I test a unit so the amp cannot be class D due to interference that would cause.
How it's all connected is I have the following Edcor stereo to mono balanced transformer connected to my stereo's tape output which is on my desk about 20' away.
https://edcorusa.com/products/wsm-s...2w-distribution-voltage-matching-transformers
I then have the following Edcor 15k balanced/unbalanced to balanced/unbalanced transformer in a box on the screen room to convert the signal back to unbalanced then it is connected to a feedthrough connection on the screen room which then connects to the amplifier.
https://edcorusa.com/products/wsm-s...-matching-transformers?variant=41117605462203
It isn't possible to feed the balanced signal into the screen room given there are four other feedthrough connectors on the screen room with one in use and the other three not fitting any adapters I have available that could convert to BNC.
1. 2 RCA 12" 8 ohm woofers in series.
2. 1 Goodmans Midax.
3. 1 Klipsch KG4 tweeter with series resistor to drop the level and equal 16 ohms.
4. Goodmans 15 ohm 3 way crossover.
I currently use the following 15 watt amp kit to drive the speaker.
https://store.qkits.com/electronic-kits/audio-kits/15-watt-mono-audio-power-amplifier-kit-fk607.html
Noticed at full volume it tended to have issues until I put a 16 ohm resistor in parallel with the speaker input on the crossover, however that's power being wasted.
There any audio transformers with an 8 ohm primary and 16 ohm secondary with a frequency response of 30-20kHz or can I use an audio output transformer that has an 8 and 16 ohm tap?
Also is there a small mono or stereo bridgeable amp that has a 16 ohm output or can I use a small stereo amp that can drive an 8 ohm load with an unbalanced to balanced transformer on the input?
The amp and speaker are used in a screen room at work where I test a unit so the amp cannot be class D due to interference that would cause.
How it's all connected is I have the following Edcor stereo to mono balanced transformer connected to my stereo's tape output which is on my desk about 20' away.
https://edcorusa.com/products/wsm-s...2w-distribution-voltage-matching-transformers
I then have the following Edcor 15k balanced/unbalanced to balanced/unbalanced transformer in a box on the screen room to convert the signal back to unbalanced then it is connected to a feedthrough connection on the screen room which then connects to the amplifier.
https://edcorusa.com/products/wsm-s...-matching-transformers?variant=41117605462203
It isn't possible to feed the balanced signal into the screen room given there are four other feedthrough connectors on the screen room with one in use and the other three not fitting any adapters I have available that could convert to BNC.
Your 11 dollar IC mono amp board is only rated at 15 W music power into 4 ohms (around 7.5 W continuous or RMS power into 4 ohm).
The amp will likely struggle to push 2 W RMS into your 16 ohm speaker system, even with a suitably beefy power supply.
The most obvious solution to me, as you mentioned, is finding a more appropriate amplifier - one with a high enough RMS power output into 8 ohm that it doesn't run out of steam into 16 ohm.
Something like the following board which is capable of outputting 70 W RMS into 8 ohm:
https://quasarelectronics.co.uk/Item/velleman-k8060-discrete-power-amplifier-200w-kit
Note the requirement for a substantial heatsink and a high power transformer.
Last edited:
P.S. The transistor amplifier above should drive a 16 ohm load without a problem.
The way it goes is like this: If 35 W into 16 ohm is the target, then look for 70 W into 8 ohm, or 140 W into 4 ohm.
The way it goes is like this: If 35 W into 16 ohm is the target, then look for 70 W into 8 ohm, or 140 W into 4 ohm.
If you want something classic, a Peavey M-2600 is about 70 w per channel. I bought mine working on ebay for ~$110. I then put all new e-caps in it and cleaned the heat sink. No fans. I listen to it up to 14 hours/day. Watch the freight price, UPS from the coast is prohibitive for me. <70 lb will go USPS which does not charge for distance. Peavey made a monaural 75 w warehouse amp MMA-875 without fans. I bought one for $35 with freight. Equivalent product crown 160ma. The mma-875 has multiple slots for input, but usually only come with telephone interface cards. There is one direct line level RCA jack input.
There is also the dynaco ST70 or Mark 3 with a 16 ohm tap. However the used ones are rediculously expensive. triodeelectronics.com of Chicagoland has kits to build new ones.
If you want something quick and short lived, parts-express.com has some class AB amps. Look for Pyle.
There is also the dynaco ST70 or Mark 3 with a 16 ohm tap. However the used ones are rediculously expensive. triodeelectronics.com of Chicagoland has kits to build new ones.
If you want something quick and short lived, parts-express.com has some class AB amps. Look for Pyle.
Last edited:
That amp would work, but I'd need a chassis to mount it in.
A bit too large given the space I have.
Here's a kit that looks to be small.
https://store.qkits.com/electronic-kits/audio-kits/25w-mono-amplifer-kit.html
This is a similar kit
https://www.amazon.com/HiLetgo-TDA2050-Amplifier-Digital-5W-120W/dp/B0CDWTL57H
The heat sink on qkits is too small for class AB 25 w. Might work as class D. No sign of a mains capable power supply. boards without grounded metal case tend to pick up AM radio, CB radio, etc etc.
I don't look at amazon, they tend to lock up my operating system requiring a reboot. I'm working up the nerve to buy 8 gb dimm for the PC, which last time came in too short to fit the slot. DIMM were for a laptop, 2 of which were stolen.
I don't look at amazon, they tend to lock up my operating system requiring a reboot. I'm working up the nerve to buy 8 gb dimm for the PC, which last time came in too short to fit the slot. DIMM were for a laptop, 2 of which were stolen.
Last edited:
The heatsink is usually small with those amp kits so I planned on using a larger heatsink anyways.
That said running at 16 ohms there won't be near as much speaker current drawn so the smaller heatsink might be ok. Either way I'll likely use a larger heatsink anyways.
I do have to be concerned whether or not that TDA2050 is an actual chip or a clone and if a clone is it made to spec?
That said at $11 for two if it is a fluke I'm not out much.
I currently have the 15 watt amp in a small metal case which is where the new amp board may go.
Now given there are two amp boards I could use them both in bridged mode only requiring a phase splitter before the amps.
That said I'm kind of wondering if a transformer with a secondary that has an 8 and 16 ohm tap will work feeding the amp to the 8 ohm tap and the speaker to the 16 ohm tap with the common going to the speaker and amp.
Went ahead and ordered the amp off Amazon as if it is not suited for this project or if the transformer works I can always use it for something else.
I do have a Hammond 1620 I could try.
Not sure I understand how the impedance taps work as it doesn't seem right.
That said running at 16 ohms there won't be near as much speaker current drawn so the smaller heatsink might be ok. Either way I'll likely use a larger heatsink anyways.
I do have to be concerned whether or not that TDA2050 is an actual chip or a clone and if a clone is it made to spec?
That said at $11 for two if it is a fluke I'm not out much.
I currently have the 15 watt amp in a small metal case which is where the new amp board may go.
Now given there are two amp boards I could use them both in bridged mode only requiring a phase splitter before the amps.
That said I'm kind of wondering if a transformer with a secondary that has an 8 and 16 ohm tap will work feeding the amp to the 8 ohm tap and the speaker to the 16 ohm tap with the common going to the speaker and amp.
Went ahead and ordered the amp off Amazon as if it is not suited for this project or if the transformer works I can always use it for something else.
I do have a Hammond 1620 I could try.
Not sure I understand how the impedance taps work as it doesn't seem right.
Last edited:
The qkits board is an LM1875 based mono amplifier module.
The Amazon board is a TDA2050 based mono audio amplifier module.
Both could be good for around 10 W RMS into 16 ohm given the use of a power supply with the maximum voltage and current specifications.
P.S. I have to admit to having no practical experience with either of these amp chips.
I did try the transformer and it seems to work ok, however I do not want to tie up a tube output transformer as something that just steps up a speaker level signal.
I bought the Amazon board.
Looks like it might be small enough to fit in the same space as the 15 watt board does.
It's likely they used the datasheet single supply example circuit and just added a volume control.
https://www.st.com/resource/en/datasheet/cd00000131.pdf
I have a 0-40V 3A supply at work that I currently use to power the 15 watt amp so I'll use that for this amp.
Now if I used both amps bridged using a transformer or OP-AMP phase splitter I could likely eliminate the 1,000uF speaker coupling cap on each board depending on if both boards have the same exact DC offset on the speaker output pin.
I bought the Amazon board.
Looks like it might be small enough to fit in the same space as the 15 watt board does.
It's likely they used the datasheet single supply example circuit and just added a volume control.
https://www.st.com/resource/en/datasheet/cd00000131.pdf
I have a 0-40V 3A supply at work that I currently use to power the 15 watt amp so I'll use that for this amp.
Now if I used both amps bridged using a transformer or OP-AMP phase splitter I could likely eliminate the 1,000uF speaker coupling cap on each board depending on if both boards have the same exact DC offset on the speaker output pin.
I hope this board solves your problem.
P.S. I've just seen your edit to post #7. I will simply bow out of those discussions and others as all that is really required is a suitably specified amplifier and power supply.
Plus it will be a few days before the modules arrive.
That said I will not be using the transformer as it is a transformer I could use if I decided to build a tube amp with triode connected 6F6 tubes given the 6.6k impedance is close to the 6k impedance required.
I do have an Edcor WSM 15k-15k balanced/unbalanced to balanced/unbalanced transformer I ca use to split the signal so I might indeed try both amps provided they fit in the case.
I will try just one first though to see if its enough.
The listing says a max of +24V for the amp, however the chip is rated higher provided it's an actual TDA2050 and not some copy.
I do have a 60mm X 10mm fan in the case that pulls air over the heatsink of the current 15 watt amp so I'll leave that in to keep the new amp cool which might negate the need for a better heatsink. Now given I can run the amp on a B+ higher than 16Vdc I'll need to figure the best B+ voltage and increase the series resistor to the fan so that it can run on the higher B+.
One thing nice about the Chinese often following the datasheet example circuit of a chip is it is a manufacturer done circuit and as such should be good.
That said I will not be using the transformer as it is a transformer I could use if I decided to build a tube amp with triode connected 6F6 tubes given the 6.6k impedance is close to the 6k impedance required.
I do have an Edcor WSM 15k-15k balanced/unbalanced to balanced/unbalanced transformer I ca use to split the signal so I might indeed try both amps provided they fit in the case.
I will try just one first though to see if its enough.
The listing says a max of +24V for the amp, however the chip is rated higher provided it's an actual TDA2050 and not some copy.
I do have a 60mm X 10mm fan in the case that pulls air over the heatsink of the current 15 watt amp so I'll leave that in to keep the new amp cool which might negate the need for a better heatsink. Now given I can run the amp on a B+ higher than 16Vdc I'll need to figure the best B+ voltage and increase the series resistor to the fan so that it can run on the higher B+.
One thing nice about the Chinese often following the datasheet example circuit of a chip is it is a manufacturer done circuit and as such should be good.
Last edited:
The current amp used is specified for 4 or 8 ohms.
Running it on 16 ohms if I turned the volume near full I could hear what sounded like the amp starting to go into oscillation.
The new amp I'll try just one and see how well it drives the 16 ohm load.
If need be I can install the second amp run them bridged and use a transformer as a phase splitter.
Running it on 16 ohms if I turned the volume near full I could hear what sounded like the amp starting to go into oscillation.
The new amp I'll try just one and see how well it drives the 16 ohm load.
If need be I can install the second amp run them bridged and use a transformer as a phase splitter.
An amplifier oscillating under those conditions would be considered unusual.
It's also a marginal decision to go bridged if it could reasonably be avoided (IMHO), but don't let me stop you 🙂
It's also a marginal decision to go bridged if it could reasonably be avoided (IMHO), but don't let me stop you 🙂
I suspect the reason for what I think was oscillations is due to the speaker cable which is maybe 20', but I only heard the noise when the amp was turned up near full.
Yes bridged is a last resort for this project.
One concern is the 24 volt B+ maximum the description says. I'm thinking something got lost in translation such as maybe they think it's max 24V on the + power terminal even when the - power terminal is grounded.
The power supply I have can go up to 40V at 3A. So I'll start the voltage at 25V and increase it from there depending on how much output I really need.
Yes bridged is a last resort for this project.
One concern is the 24 volt B+ maximum the description says. I'm thinking something got lost in translation such as maybe they think it's max 24V on the + power terminal even when the - power terminal is grounded.
The power supply I have can go up to 40V at 3A. So I'll start the voltage at 25V and increase it from there depending on how much output I really need.
The amp boards arrived.
They have a 1000uF 35V cap on the input and also a 1,000uF 35V cap to couple the speaker to the amp.
I still wonder if the Chinese read the datasheet wrong and think the chip can only handle 24Vdc or if the chip is a poorly done clone and is only rated at the lower voltage.
I'll know tomorrow when I apply a higher voltage to the board.
They have a 1000uF 35V cap on the input and also a 1,000uF 35V cap to couple the speaker to the amp.
I still wonder if the Chinese read the datasheet wrong and think the chip can only handle 24Vdc or if the chip is a poorly done clone and is only rated at the lower voltage.
I'll know tomorrow when I apply a higher voltage to the board.
So here's the datasheet version of the amp.
Here's calculations of the capacitors.
C1
C4
C7
Here's the actual circuit. Only two resistors were changed in value. Not sure how that will affect the circuit though.
Here's the calculation of the one cap where the resistor changed value.
The plan is to use the amp as is only removing the volume control and using the volume control already mounted to the box the amp will go in.
The speaker itself I know won't play down to 20Hz.
Now If I wanted to reduce the low frequency phase shift I know that I can for sure up the value of C1 with no real adverse effects. 10uF would get the phase shift near 0 degrees at 20Hz.
Not exactly sure what increase of switching on and off means for C4. I'd need a 220uF cap to get the phase shift near 0 at 20Hz. That one I seriously doubt I would want to increase the value that high.
Now increasing the value of C7 will increase the turn on thump which is neither good for the speaker nor the amplifier chip as that means the charge current for C7 has increased.
I'm also concerned about the value chosen for R6.
I figure they either:
1. Had a bunch of 4.7 ohm resistors and used them and found the amp still stable.
2. Found 4.7 ohms improved the sound.
3. Found that 4.7 ohms worked best with the TDA2050 they made.
Also R4 being a little larger in value increases the gain slightly.
Here's calculations of the capacitors.
C1
C4
C7
Here's the actual circuit. Only two resistors were changed in value. Not sure how that will affect the circuit though.
Here's the calculation of the one cap where the resistor changed value.
The plan is to use the amp as is only removing the volume control and using the volume control already mounted to the box the amp will go in.
The speaker itself I know won't play down to 20Hz.
Now If I wanted to reduce the low frequency phase shift I know that I can for sure up the value of C1 with no real adverse effects. 10uF would get the phase shift near 0 degrees at 20Hz.
Not exactly sure what increase of switching on and off means for C4. I'd need a 220uF cap to get the phase shift near 0 at 20Hz. That one I seriously doubt I would want to increase the value that high.
Now increasing the value of C7 will increase the turn on thump which is neither good for the speaker nor the amplifier chip as that means the charge current for C7 has increased.
I'm also concerned about the value chosen for R6.
I figure they either:
1. Had a bunch of 4.7 ohm resistors and used them and found the amp still stable.
2. Found 4.7 ohms improved the sound.
3. Found that 4.7 ohms worked best with the TDA2050 they made.
Also R4 being a little larger in value increases the gain slightly.
Here's some photos of the amp installed.
I added the volume control from the amp board to the rear so that the volume control isn't as sensitive. I also have yet to replace the labels.
The schematic changes to this with the addition of the pots.
The amp sounds a little better than the other amp. Seems like the bass is a little better. Running the amp on 24Vdc the amp is more than capable of driving that speaker very loud.
The only thing I might do at some point is replace the cheap Chinese electrolytic caps with some good quality caps.
I added the volume control from the amp board to the rear so that the volume control isn't as sensitive. I also have yet to replace the labels.
The schematic changes to this with the addition of the pots.
The amp sounds a little better than the other amp. Seems like the bass is a little better. Running the amp on 24Vdc the amp is more than capable of driving that speaker very loud.
The only thing I might do at some point is replace the cheap Chinese electrolytic caps with some good quality caps.
