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# Small amplifier project power requirements

#### Luposian

Feb 9, 2023
6
I'm using a TDA7265 chip amplifier I bought on Amazon, and an ICL7660 charge pump inverter circuit I designed myself (in KiCad, from a schematic someone else made) and had PCB's made for it (thank you OSH Park!), to make one 9V battery power the TDA7265 chip amp, which requires a dual DC supply (+, -, and Ground). It worked perfectly! Er, well... not exactly.

You see, I was noticing some distortion in one of my music files and then, to check to make sure it wasn't my song file, I decided to play "Dolphin Dance" from Tangerine Dream. I consider that my reference test song, because I like it so much. Anyways, about 15-20 seconds into the song, when the "highs" start, the distortion was quite noticeable. I thought maybe it was the 9V battery I was using. So I grabbed a brand new 9V Rayovac. Same thing. To make sure the song (on YouTube) wasn't bad, I plugged my headphones into another amp I've used and listened to the song. No distortion at all. Cranked up the volume. Same diff. No distortion. So I knew it had something to do with the amp I bought from Amazon. But it's not the chip, because it's the same chip as in the other amp I just tested with (which runs off of AC, so power requirement isn't an issue), which means it has something to do with the power.

So, question is... is it the 9V battery, itself, or the single to dual supply module I designed? Is the battery unable to supply enough power (voltage and/or current (mA)) or is the ICL7660 unable to give the amplifier the power it needs, even if the 9V battery can supply it?

I'm only powering a pair of Drop + HiFiMan HE-X4 headphones, not external speakers, so I wouldn't imagine they're demanding that much power from the amp. since they're 25 Ohms.

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#### kellys_eye

Jun 25, 2010
5,486
The amplifier chip is rated at 25+25W and will draw far more current than either your battery (maybe) but certainly what the 7660 can possibly deliver - in other words you are getting distortion due to an inadequate power supply.
I'm only powering a pair of Drop + HiFiMan HE-X4 headphones, not external speakers
In which case why use such a high powered amplifier? Headphones can be driven perfectly well with much less than 1W per channel which also makes using battery power actually feasible.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,073
There are several possible issues all related to the use of the 7660 charge pump controller ic.
1. The 7660 operates at 10 kHz switching frequency which will be superimposed on the DC output and thus have an audible influence on the amplifier's output signal aka distortion.
2. The TDA7265 is a power amplifier creating up to 20 W into a 4 Ω load with a +-25 V supply voltage. With 9 V supply voltage that is still on the order of 4 to 8 W, see the datashete. This in turn requires 400mA (rough estimate).
At your 25 Ω load the current will be more on the order of 120 mA
On the other hand the 7660 is spec'd at 20 mA output current and the datasheet shows an output resistance of typ. 70 Ω. This output resistance will drop the output voltage whenever the amplifier draws notiveably more than 20 mA -> the voltage controller is completely overloaded.
3. By the way: even a 9 V battery will not last long when subjected to such high load currents.
What you can check: Persists he issue when you use 2 × 9 V batteries in series instead of your voltage controller? If so, the issue may be with the amplifier. If not, the issue is clearly with the overloaded charge pump voltage controller.

#### Luposian

Feb 9, 2023
6
I was going with what I knew and liked. I like the sound of the HCT tube amp, but then discovered this amp (that uses the exact same chip) sounded BETTER than it! I think the tubes do something to the sound, that this other chip amp doesn't do. Or something.

So, the amp itself is asking for more power than it's getting... so even if I used a 9V 2A DC wall wart, it still wouldn't be enough? Or would the ICL7660 be the limiting factor in that case? The amp is demanding more power (at ANY volume) than the 7660 can push out, period? Solved the dual supply problem, but... now a lack of power is the problem! Ugh! :-(

#### Luposian

Feb 9, 2023
6
There are several possible issues all related to the use of the 7660 charge pump controller ic.
1. The 7660 operates at 10 kHz switching frequency which will be superimposed on the DC output and thus have an audible influence on the amplifier's output signal aka distortion.
2. The TDA7265 is a power amplifier creating up to 20 W into a 4 Ω load with a +-25 V supply voltage. With 9 V supply voltage that is still on the order of 4 to 8 W, see the datashete. This in turn requires 400mA (rough estimate).
At your 25 Ω load the current will be more on the order of 120 mA
On the other hand the 7660 is spec'd at 20 mA output current and the datasheet shows an output resistance of typ. 70 Ω. This output resistance will drop the output voltage whenever the amplifier draws notiveably more than 20 mA -> the voltae controller is completely overloaded.
3. By the way: even a 9 V battery will not last long when subjected to such high load currents.
What you can check: Persists he issue when you use 2 × 9 V batteries in series instead of your voltage controller? If so, the issue may be with the amplifier. If not, the issue is clearly with the overloaded charge pump voltage controller.
I was using 2 9V batteries in a dual supply configuration (as shown in pic), but does that give you 18V with half the current capacity, or 9V with more current capacity? I thought only running batteries in parallel would multiply the current capacity, but wasn't sure if a dual supply configuration changes the rules in some way? Do I need:

1) More volts AND current?
2) just more current?
3) just more volts?

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#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,073
Two batteries in series will give you +- 9 V with the same current capacity. In any case you will have a lower resistance and will be able to draw more current than with the 7760 converter (no converter can deliver more output power than input power, there will always be losses).
What happens when you use the dual battery configuration? Do the distortions still persist?

#### Luposian

Feb 9, 2023
6
Two batteries in series will give you +- 9 V with the same current capacity. In any case you will have a lower resistance and will be able to draw more current than with the 7760 converter (no converter can deliver more output power than input power, there will always be losses).
What happens when you use the dual battery configuration? Do the distortions still persist?
The sound was definitely clearer and noticeably less distortion, even when maxed out on the volume knob. Cutting back (from max to about 75%) on the sound output from the computer, going into the amp, also helped. So, my single to dual supply circuit was a waste of time and money... :-( Oh, well, as with any experience in life... "You'll never know [what is there], if you don't go [there]". Live and learn, eh? So a dual 9V battery arrangement is almost enough power to produce solid clean sound, even at max volume. So would 1A of available current be enough at 9V?

So, how would I make a dual supply out of a 9V 1A DC wall wart? Or is that even possible?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,073
how would I make a dual supply out of a 9V 1A DC wall wart?
With a module like this one, or throw your won with a chip like this one.

Using a wall wart is imho the better option as a typical 9 V battery has a capacity of around 500 mAh (up to 1.2 Ah if LiIon based). At 120 mA the typical battery will last 4 to 5 hours only.

#### kellys_eye

Jun 25, 2010
5,486
Again (per my reply in #2 above), if you're driving headphones what's the point of such an amplifier? Save energy, expense, trouble etc by building for the actual application.

If your intent is to use speakers regardless then a good (i.e. 'clean' and capable) power supply is often the most overlooked aspect of design.

Feb 19, 2021
333
9V battery capacity :

Regards, Dana.

#### Luposian

Feb 9, 2023
6
Again (per my reply in #2 above), if you're driving headphones what's the point of such an amplifier? Save energy, expense, trouble etc by building for the actual application.

If your intent is to use speakers regardless then a good (i.e. 'clean' and capable) power supply is often the most overlooked aspect of design.

#### Luposian

Feb 9, 2023
6
Question... which design provides better +9V, -9V, and Ground performance (overall power availability)? How and why? Can you use the schematic for a 9V wall wart power supply (say, 9V 2A) or do you need to increase the component values for more amperage availability?

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#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,073
I type a '$' symbol does the program change it to a maths function? That is an issue with he Latex add-on, see this discussion (actually it's embedded within a bunch of different topics). It should have been resolved. Here's a$ without any escape characters.
Try cleaning your browser's cache? Maybe some old script remnants interfere?

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,073
which design provides better +9V, -9V, and Ground performance
None. In terms of ground both are equal.
Can you use the schematic for a 9V wall wart power supply (say, 9V 2A)
You will need 2 supplies, one to replace each battery.
do you need to increase the component values for more amperage availability?
The amperage is given by the power supply's capabilities. With a suitable "good" power supply you will not even need the additional components of your 2nd circuit.

The HCT tube amp uses the TDA7265 chip, so anything that uses that same chip should sound just as good.
Why should that be so? This amp is for delivering power to speakers. Not necessarily good for earphones. You will likely overdrive the earphones and hear a lot of distortion.
Even witholut distortion: why is there a tube in the tube amp (rhetorical question)? To change the sound, make it "warmer" as tube enthusiasts claim. Without the tube, the sound from the amplifier chip alone will be different from what you are used to hear from the tube amp.

I suggest you reconsider @kellys_eye 's suggestions on post #12.

#### crutschow

May 7, 2021
584
why is there a tube in the tube amp (rhetorical question)? To change the sound, make it "warmer" as tube enthusiasts claim.
The "warm" sound is from the tube rolling off the high frequencies, similar to a low-pass filter.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,073
The "warm" sound is from the tube rolling off the high frequencies, similar to a low-pass filter.
plus the distortions differ from the ones transistor amplifiers produce. See e.g. this discussion.

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