SUPPLY CURRENT QUESTION

[Rengpuia]

Hi this is my first post and I'm very new to building circuits. I have built a 3W amplifier(using TDA7267A) from a schematic I saw on this site. I am thinking of powering the amp circuit along with a TS-808 clone that i've built by another diy power adapter. But the only transformer that I managed to find is a 12V 1.6amp output. The voltage rating of the TS-808 is 9V so i put a 15ohm resistor in series with the power supply. Both circuits will consume around 1amp and if i use this transformer will it cause a problem for the IC's and transistors like shortening their lifespan? If the supply current of 1.6 amps is too much can anyone tell me how to limit the current? Thanks. Please excuse my poor grammar.

[mth5044]

Where did you did find that a tubescreamer will draw 1 amp? At most, a tubescreamer will draw 10mA, that's 0.01 amps.

You need to supply enough amps to the circuit, you cannot supply too much. You are worrying about the opposite thing. That transformer is way more than enough for the tubescreamer, which is fine, but you need to make sure it's enough for the TDA7267A. Take at a look at its datasheet and what load you are running it in to and you should find the amount of amps you need.

Power supplies like the 1Spot supply 1.2A of DC to pedals and they are fine running 1 or 10 pedals at a time. circuits will draw as much current as they need, excess is not a problem, too little current is.

The resistor drop might be fine, but you could also go with a 7809 regulator for a clean 9V.

[smallbearelec]

the only transformer that I managed to find is a 12V 1.6amp output

Hi--

Is this a wall transformer that plugs directly into the mains or does it require that you wire it up. If the latter, please do not use it! If it is a "wall-wart", does it put out AC or DC? Give us a little more info, and we'll try to get you SAFELY to a good place.

[Guitar Poppa]

Hello !

Well your questions are beginners questions, but useful and careful ones ! So I'll be glad to help you (I was a beginner too, 50 years before !)

>>>> If your power supply is designed for a 1,6A current, it means it can give at most 1,6A. If the consumption is higher, the tension will sag, and you won't get 12V. The power supply will get hotter and may ultimately be destructed.
If you use one micro-amplifier connected to speaker with 4 or 8 ohm impedance, the maximum current will be about 1A. So your supply should not suffer !
I didn't take in count the TS808 consumption, because it is only a few milliampers. (the led current is higher as the Opamp's one !)

Just verify the polarity when connecting the amp and the stompbox to the supply : they must be all of them negative grounded. If you use common coaxial jack to connect them, the connection must be center negative.

>>>> Using a drop resistor his a careful idea, 220 to 470 ohms should be better if you want to get 9V from 12V (I write from memory, without knowing the exact consumption of your stompbox).

>>>> Many stompboxes should gently resist to 12V, and even be glad and give more dynamics ! The transistors and Opamps are made for higher tensions and will better work. The only problem would concern the electrolytic capacitors : manufacturers are very stingy and may use capacitors made only for 10V. I hope they use 16V or 25V electrolitycs, which are anyway of better quality. Open your pedal and look inside. The electroliyc capacitors are black or blue vertical cylinders, their capacity is indicated in µF, and their tension in V.

>>>> You talk about a 3 W amplifier. As usual, manufacturers tell pretty stories... With 12V and 4 ohm the maximum output power without saturating CAN'T be more than 1,3W. But real RMS Watts ! and it can be loud if you use a high efficiency speaker.

Tell me if you want more precisions...
guitar poppa

PS You can see something by me on that subject on this site :
http://guitarpoppa.com/?p=2202
http://guitarpoppa.com/?p=2801

[anotherjim]

Diodes are a handy way to drop voltage. Much more consistent than resistors as it doesn't vary much with current draw.
Standard 20mA LED's will drop the most volts per instance. 2 Reds in series would supply near enough 9v to the TS. One of the them could be on show and indicate the TS supply is alive.

[Rengpuia]

Where did you did find that a tubescreamer will draw 1 amp? At most, a tubescreamer will draw 10mA, that's 0.01 amps.

You need to supply enough amps to the circuit, you cannot supply too much. You are worrying about the opposite thing. That transformer is way more than enough for the tubescreamer, which is fine, but you need to make sure it's enough for the TDA7267A. Take at a look at its datasheet and what load you are running it in to and you should find the amount of amps you need.

Power supplies like the 1Spot supply 1.2A of DC to pedals and they are fine running 1 or 10 pedals at a time. circuits will draw as much current as they need, excess is not a problem, too little current is.

The resistor drop might be fine, but you could also go with a 7809 regulator for a clean 9V.

According to the TDA7267A circuit schematics, the current consumption will be 500mA max and after searching around for the TS-808 power adapter i found that the adapter supplies 9V 500mA. So i assume that the max current will be around 1amps when connected in parallel. I'll look into the 7809 right away, thank you very much

[Rengpuia]

Hello !

Well your questions are beginners questions, but useful and careful ones ! So I'll be glad to help you (I was a beginner too, 50 years before !)

>>>> If your power supply is designed for a 1,6A current, it means it can give at most 1,6A. If the consumption is higher, the tension will sag, and you won't get 12V. The power supply will get hotter and may ultimately be destructed.
If you use one micro-amplifier connected to speaker with 4 or 8 ohm impedance, the maximum current will be about 1A. So your supply should not suffer !
I didn't take in count the TS808 consumption, because it is only a few milliampers. (the led current is higher as the Opamp's one !)

Just verify the polarity when connecting the amp and the stompbox to the supply : they must be all of them negative grounded. If you use common coaxial jack to connect them, the connection must be center negative.

>>>> Using a drop resistor his a careful idea, 220 to 470 ohms should be better if you want to get 9V from 12V (I write from memory, without knowing the exact consumption of your stompbox).

>>>> Many stompboxes should gently resist to 12V, and even be glad and give more dynamics ! The transistors and Opamps are made for higher tensions and will better work. The only problem would concern the electrolytic capacitors : manufacturers are very stingy and may use capacitors made only for 10V. I hope they use 16V or 25V electrolitycs, which are anyway of better quality. Open your pedal and look inside. The electroliyc capacitors are black or blue vertical cylinders, their capacity is indicated in µF, and their tension in V.

>>>> You talk about a 3 W amplifier. As usual, manufacturers tell pretty stories... With 12V and 4 ohm the maximum output power without saturating CAN'T be more than 1,3W. But real RMS Watts ! and it can be loud if you use a high efficiency speaker.

Tell me if you want more precisions...
guitar poppa

PS You can see something by me on that subject on this site :
http://guitarpoppa.com/?p=2202
http://guitarpoppa.com/?p=2801

Thank you sir.
I have actually read about the safety of the supply current being higher than the rated current in this forum and i'm actually posting this question because I want to make sure that the excess is not too much.

I did a lot of research when i made my first circuit about the voltage ratings of the capacitors to be used. I learned something here and there and all my electrolytic capacitors are rated 50+V so i think we're safe there(whew )

I followed the link that you gave and i find it very informative and useful, and I've bookmarked your site it for future references. Again thank you very much

[Rengpuia]

Gentlemen, I can't stress enough how grateful I am for your replies. I am amazed by the amount of knowledge you provided me on my first post, they are very informative and will be very useful in the future. Thank you guys, you have my respect

[mth5044]

DA will be mad that we forgot, but welcome to the forum!

[Rengpuia]

Hahahaha Thank you

[antonis]

According to the TDA7267A circuit schematics, the current consumption will be 500mA max and after searching around for the TS-808 power adapter i found that the adapter supplies 9V 500mA. So i assume that the max current will be around 1amps when connected in parallel.

I assume that your assumption for TS-808 is quite wrong..

The current capability of TS adapter supply (500mA) is the maximum one for the specific adapter (without "overloading" it) and it doesn't reflect TS-808 current need..

As mth5044 well said, it isn't more over than 10mA so - comparing to TDA's 500mA - it's negligibe...

If you have a power supply capable for your amp you don't have to worry about TS extra supply because it's (should be) included in your power supply margins..

[duck_arse]

DA will be mad that we forgot, but welcome to the forum!

this is correct, but I thought steve covered it with "Hi--".

hello and welcome, Rengpuia. also, you could use a 78L09, which is smaller/lower current/possibly cheaper to replace the 7809.