Hi
I was watching this video.
He is using a 15 watt chip amp and he uses 0.22 Ohms 2 watt resistors
to combine 2 channels into one 30 watt channel .
His speaker is 8 ohms.
I have a similar situation I am repairing a guitar amp but I have
A 4 ohm speaker...
What resistors should I be using?
Thanks
I was watching this video.
to combine 2 channels into one 30 watt channel .
His speaker is 8 ohms.
I have a similar situation I am repairing a guitar amp but I have
A 4 ohm speaker...
What resistors should I be using?
Thanks
Welcome to the forum!
I'm not going to comment on the YouTube video as I have no means to duplicate then assess the effectiveness of the procedure.
What I will say is this:
If the requirement is for guitar and not stereo reproduction, it would be simpler to use just one amplifier channel while leaving the other unconnected at both input and output.
Attempting to double the power output into one speaker as suggested is not really worth the effort as the increase in loudness would hardly be noticeable.
It takes a ten times increase in power in order to double the loudness.
I'm not going to comment on the YouTube video as I have no means to duplicate then assess the effectiveness of the procedure.
What I will say is this:
If the requirement is for guitar and not stereo reproduction, it would be simpler to use just one amplifier channel while leaving the other unconnected at both input and output.
Attempting to double the power output into one speaker as suggested is not really worth the effort as the increase in loudness would hardly be noticeable.
It takes a ten times increase in power in order to double the loudness.
If it is an advisable option, the manufacturer will tell you how to do it in the datasheet.
That is why they publish datasheets.
If not, don't: or do so at your own risk.
That is why they publish datasheets.
If not, don't: or do so at your own risk.
If you have a power supply, or can use the supply from the amp you are repurposing, find a chip amp that suits the available supply voltage (and current) available.
If you are buying or making a power supply then match the supply to the amp board.
If this is a home practice amp then you won't need a lot of power to annoy the neighbours and a laptop brick and suitable board that can operate from 20V single supply should be adequate.
For greater power, LM3886 would seem a better match as mono boards are available.
If you are buying or making a power supply then match the supply to the amp board.
If this is a home practice amp then you won't need a lot of power to annoy the neighbours and a laptop brick and suitable board that can operate from 20V single supply should be adequate.
For greater power, LM3886 would seem a better match as mono boards are available.
The video explains a way to connect in parallel the power amplifers inside a low voltage stereo chip amp. Each of them is usually internally implemented by connecting two amplifiers in bridge mode, this means that the negative speaker terminal is not shared between the two amplifiers: 4 resistors are needed. On this scenario, the resistor value is not related to the speaker impedence, but mostly to requirements of the specific chip amp. I've seen 1 ohm listed on some datasheets. The end result does waste both power and performance, and a wrong resistor value may bring the chip amp into oscillation, eventually damaging both the amplifier and the speaker. Avoid this arrangement if any real power is needed. If the datasheet or the amplifier manufacturer does not describe a way to parallel the outputs, and you only have one speaker, it is best to just use one channel leaving the other one unused.
This appears to be a TDA7297 amp and he is paralleling the two bridged channels with the 0.22 Ohm resistors. This could give you close to 30W, but only into 4 Ohms. There is no advantage if the load is 8 Ohms. So this video is probably a terrible hack that may lead to device failure and offers no actual benefits. Paralleling outputs combines the potential current available to low impedance loads, but it does not increase the maximum voltage. 30W into 8 Ohms requires a ~25Volt+ power supply for a bridged amp. If the amp was not already bridged, bridging doubles the available voltage to the speaker. An unbridged amp would require a ~45VDC supply for 30W into 8 Ohms. There are other issues, so paralleling outputs is not a recommended solution. Unless you completely understand these issues, you should stick to a solution that is designed exactly to your needs.
TERRIBLE advice, terrible video, there are things that are hard to unsee.
My eyes still hurt (I watched it end to end).
1) in general paralleling power amps is a BAD idea. Period.
Very popular among noobs because of its apparent simplicity, in fact hard to accomplish properly because both amps need to have exact same gain, so output voltage is exact same.
This requires 1% or better resistors all over the place, specially on NFB network, and even so ... it´s not achieved so outputs need added (wasteful, damping killer, etc.) sharing resistors where non insignificant power is wasted.
2) here channel owner plain puts both channels in parallel, period, no special consideration given to resistors, so working or not depends only on chance.
3) and he achieves nothing, certainly not 30W (I doubt even 15W are possible) because supply voltage stays te same, speaker impedance too.
4) even less with meager 12V from an alarm type battery; I guess no more than 6W RMS or so into an 8 ohm speaker.
5) typical of these low grade electronics channels, he offers NO measurements at all, and "proof" is based on showing a cheap speaker no cabinet with its cone flapping around in open air.
Gosh!!!!!!
To @eagleeye :forget this misleading crappy video.
And which guitar amp uses a stereo Class D chipamp?
Please tell us brand, model, and if possible a picture or two.
Do what experienced Forum Members suggest above: build a tried and true schematic, following official datasheets, not dubious YT videos which will publish anything just to get a few clicks.
My eyes still hurt (I watched it end to end).
1) in general paralleling power amps is a BAD idea. Period.
Very popular among noobs because of its apparent simplicity, in fact hard to accomplish properly because both amps need to have exact same gain, so output voltage is exact same.
This requires 1% or better resistors all over the place, specially on NFB network, and even so ... it´s not achieved so outputs need added (wasteful, damping killer, etc.) sharing resistors where non insignificant power is wasted.
2) here channel owner plain puts both channels in parallel, period, no special consideration given to resistors, so working or not depends only on chance.
3) and he achieves nothing, certainly not 30W (I doubt even 15W are possible) because supply voltage stays te same, speaker impedance too.
4) even less with meager 12V from an alarm type battery; I guess no more than 6W RMS or so into an 8 ohm speaker.
5) typical of these low grade electronics channels, he offers NO measurements at all, and "proof" is based on showing a cheap speaker no cabinet with its cone flapping around in open air.
Gosh!!!!!!
To @eagleeye :forget this misleading crappy video.
And which guitar amp uses a stereo Class D chipamp?
Please tell us brand, model, and if possible a picture or two.
Do what experienced Forum Members suggest above: build a tried and true schematic, following official datasheets, not dubious YT videos which will publish anything just to get a few clicks.
How much power do you need?
For practice, 10W s enough, plenty of choices, based on supply voltage, which is the second question.
For large places like a hall, buy one in used condition. Suits a limited budget.
The old CD4440 IC is commonly used in bridged (or BTL) circuit here, the populated boards are dirt cheap here in India.
The 1875 / 2050 / car chip amps are also of interest.
I would simply take an old car cassette player, and hack it as an amp.
For a new mono build, use a mono chip amp with a beefy supply.
Class D, no experience, I stick to Class AB.
For practice, 10W s enough, plenty of choices, based on supply voltage, which is the second question.
For large places like a hall, buy one in used condition. Suits a limited budget.
The old CD4440 IC is commonly used in bridged (or BTL) circuit here, the populated boards are dirt cheap here in India.
The 1875 / 2050 / car chip amps are also of interest.
I would simply take an old car cassette player, and hack it as an amp.
For a new mono build, use a mono chip amp with a beefy supply.
Class D, no experience, I stick to Class AB.
Just parallel amps with current share resistors.
.1 to .22 ohms
possible to use 1% low inductance
expect the usual over reacting when you do so.
.1 to .22 ohms
possible to use 1% low inductance
expect the usual over reacting when you do so.
I see another way advertised: invert mono signal to second channel, then simply run the (subwoofer) speaker +/- connected to the amp +/+ terminals only. Is this the correct way? Any caveats?
It is floating output
Or bridged design.
Follow data sheet for circuit.
Drawback with floating load.
Each amplifier sees one half of driver impedance.
So usually advised for 8 ohm load only.
Since apparent load will be 4ohm for each amplifier.
So benefit is close to double the output voltage swing.
Caution is also double the current.
So normal practice. Large heatsink.
And voltage to amplifier is lowered.
So you dont exceed chip thermal ratings
Consider each amplifier running 4 ohm load.
With actual load being 8 ohms.
A 4 ohm load appears to be 2 ohms to each amplifier
so not advised.
This is why big question mark when people get excited over
parallel load. When bridge load uses more current.
Parallel load is gain matched with 1% or .25% E196
resistors and current sharing resistors on outputs
can also be low inductance 1% resistors.
Same thing, just follow manufacture Application Notes
For parallel or bridged load.
Likely already hundreds of available boards pre made
for either topology. Both done many times
since 1990's
Or bridged design.
Follow data sheet for circuit.
Drawback with floating load.
Each amplifier sees one half of driver impedance.
So usually advised for 8 ohm load only.
Since apparent load will be 4ohm for each amplifier.
So benefit is close to double the output voltage swing.
Caution is also double the current.
So normal practice. Large heatsink.
And voltage to amplifier is lowered.
So you dont exceed chip thermal ratings
Consider each amplifier running 4 ohm load.
With actual load being 8 ohms.
A 4 ohm load appears to be 2 ohms to each amplifier
so not advised.
This is why big question mark when people get excited over
parallel load. When bridge load uses more current.
Parallel load is gain matched with 1% or .25% E196
resistors and current sharing resistors on outputs
can also be low inductance 1% resistors.
Same thing, just follow manufacture Application Notes
For parallel or bridged load.
Likely already hundreds of available boards pre made
for either topology. Both done many times
since 1990's
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Depends what chip your using.
Non specified.
Amplifier in video screenshot looks designed
for 12 volts.
Could already be bridge load.
Is why he is using Current share resistors
for positive and negative.
Parallel bridge loads.
Also done many times for low power car stereo amps
ST has many datasheet for Dual or Quad
Bridged amplifiers. for 12 to 18 volts.
Same thing follow datasheet to parallel
People forget these amplifiers have preset gain
and gain matched on the chip.
Again depends what chip being used.
likely why so easy in video.
Likely using ST dual or quad chip amp
Gain preset.
Outputs tied together with current share resistors.
Just like datasheet
Non specified.
Amplifier in video screenshot looks designed
for 12 volts.
Could already be bridge load.
Is why he is using Current share resistors
for positive and negative.
Parallel bridge loads.
Also done many times for low power car stereo amps
ST has many datasheet for Dual or Quad
Bridged amplifiers. for 12 to 18 volts.
Same thing follow datasheet to parallel
People forget these amplifiers have preset gain
and gain matched on the chip.
Again depends what chip being used.
likely why so easy in video.
Likely using ST dual or quad chip amp
Gain preset.
Outputs tied together with current share resistors.
Just like datasheet
1. I have a BUSTED Roland 20Watt Guitar Mono amp. So I am gutting it and re-cycling the casing.
2. So I am using the casing and 4 OHM speaker to re- use the casing.
3. one of my inputs will have a stereo signal so Since I purchased a bluetooth 15 Watt Amp module, that has stereo inputs and outputs. I wanted to just combine the left and right channels .. not looking for perfect sound, just so the Roland Box can be reused.
I just want to mix the left and right channels, I am not looking to increase the power. So I guess a parallel connection should work. just looking for something functional.
There is NO SPEC on the amp chip, so when I receive it I will post later
Original Roland uses a TDA2050 chip.
I am suspecting its probably a "TPA3110 "
https://www.aliexpress.com/item/100....order_list.order_list_main.35.21ef1802abX3X5
2. So I am using the casing and 4 OHM speaker to re- use the casing.
3. one of my inputs will have a stereo signal so Since I purchased a bluetooth 15 Watt Amp module, that has stereo inputs and outputs. I wanted to just combine the left and right channels .. not looking for perfect sound, just so the Roland Box can be reused.
I just want to mix the left and right channels, I am not looking to increase the power. So I guess a parallel connection should work. just looking for something functional.
There is NO SPEC on the amp chip, so when I receive it I will post later
Original Roland uses a TDA2050 chip.
I am suspecting its probably a "TPA3110 "
https://www.aliexpress.com/item/100....order_list.order_list_main.35.21ef1802abX3X5
Last edited:
Makes perfect sense.
Want a mono amplifier.
Order a stereo amplifier.
Then ask if it will work.
Better to combine the stereo inputs into a mono amp.
Want a mono amplifier.
Order a stereo amplifier.
Then ask if it will work.
Better to combine the stereo inputs into a mono amp.
The amplifier module referenced at post #14 is a 2+1 amplifier. The third "30W bass channel" is a mono combination of left and right stereo inputs, so it may already be the desired solution. Sometimes this channel is low-pass filtered, but sometimes is not because it is cheaper to skip the low pass filter. Just connect the speaker to the bass channel output and try. If high frequencies are missing, the solution may be as simple as removing a capacitor from the circuit related to the "bass" potentiometer. By the way, as JMFahey wrote at post #8, class-D stereo chipamps aren't common on guitar amplifers. Clipping on class-D sounds unpleasant, I am not a guitar amp expert but this may be a reason. You have to try and decide. By the way, next time you do a Youtube search and the result is a video from a channel with a huge number of subscribers but the number of views of each video is less than 1% of the subscriber number, it means that something has likely been done to manipulate the search result and the quality of the content may be questionable. That hack may be harmful to your board. If the bass channel trick does not work, just bridge togheter the left and right contacts of the main volume control cable and use either the left or the right channel. You don't even need to buy power resistors.