I just built an electric 12 string guitar and thought of modding a small 10 watt amp to make it run on batteries to bring out to camp fires and such. I have no knowledge of amp circuitry but I have a UK amp that I cut out the transformer and plugged a 9V to the 2 red wires going to the amp board and it plays fine..... for about 30 seconds, after that the sound becomes distorted a bit and if I unplug the battery and plug it back it sounds good again. If anyone can ether explain why I would love to learn on this.
Sorry, first post jitters I guess. The guitar amp is from the UK and I am in the US so I need a converter to play so I took out the power supply. Basically I have a guitar amp board. The 2 red wires the came from the transformer are connected to a 9V battery and when a guitar is plugged in the sound that comes out is perfect for only 30 secs or so and it becomes distorted, if I unplug the battery and replug it the sound is nice again. Just wanted to know why that is.
Thats no problem 
The important info is what the correct AC voltage between the two red wires from the transformer should be. When you connect a 9 volt battery to where the transformer was, you are feeding 9 volts into (probably) a full wave bridge rectifier. If that is so then that actually safegaurds against reverse polarity mistakes with the battery... it will work either way around. If thats how its configured.
Why does it play and then distort... first thought is just that the battery is giving up under load. What type of battery is it ?
What you really need to know is the transformer specification and from that a suitable battery can be found.
The important info is what the correct AC voltage between the two red wires from the transformer should be. When you connect a 9 volt battery to where the transformer was, you are feeding 9 volts into (probably) a full wave bridge rectifier. If that is so then that actually safegaurds against reverse polarity mistakes with the battery... it will work either way around. If thats how its configured.
Why does it play and then distort... first thought is just that the battery is giving up under load. What type of battery is it ?
What you really need to know is the transformer specification and from that a suitable battery can be found.
OK... gotta ask Whats a regular 9 volt battery. The only common one that comes to mind is a PP3,
http://www.amazon.co.uk/s/?ie=UTF8&...=aps&hvadid=3170116476&ref=pd_sl_3ien531qyf_e
If that is what it is then you need much more current ability than that.
Do you have a multimeter ?
Whats a regular 9 volt battery. The only common one that comes to mind is a PP3,http://www.amazon.co.uk/s/?ie=UTF8&...=aps&hvadid=3170116476&ref=pd_sl_3ien531qyf_e
If that is what it is then you need much more current ability than that.
Do you have a multimeter ?
That's never going to work.
OK, your in the US (110 ? volts) and you have UK (230 volts) tranny. As long as its that way around then you can plug the 230 volt tranny into 110 volts. You don't need the red wires connected to the amp. Measure the AC Voltage on the red wires on 110 volts and then do a bit of maths to work out what it would be on 230 volts. Its just in proportion.
When we know the tranny voltage we can work out what DC voltage would work the amp. From what you say so far I suspect a 12volt VRLA (lead acid gell battery) could be ideal but we need to know for sure.
Be careful with any mains wiring and if in any doubt ask.
OK, your in the US (110 ? volts) and you have UK (230 volts) tranny. As long as its that way around then you can plug the 230 volt tranny into 110 volts. You don't need the red wires connected to the amp. Measure the AC Voltage on the red wires on 110 volts and then do a bit of maths to work out what it would be on 230 volts. Its just in proportion.
When we know the tranny voltage we can work out what DC voltage would work the amp. From what you say so far I suspect a 12volt VRLA (lead acid gell battery) could be ideal but we need to know for sure.
Be careful with any mains wiring and if in any doubt ask.
And for information...
when you rectify AC voltage (from the tranny) to DC to power the amp the DC voltage is approximately the AC voltage times 1.4 assuming the amp uses a "full wave" bridge. So 12 volts DC in the amp would be using a 9 volt tranny.
What made you think of trying 9 volts. Is that voltage marked somewhere such as on the tranny ?
when you rectify AC voltage (from the tranny) to DC to power the amp the DC voltage is approximately the AC voltage times 1.4 assuming the amp uses a "full wave" bridge. So 12 volts DC in the amp would be using a 9 volt tranny.
What made you think of trying 9 volts. Is that voltage marked somewhere such as on the tranny ?
A couple of reasons. The battery when first connected will be showing 9 volts. After a few seconds the load of the amp pulls that voltage down because the battery can not supply much current. When you remove the load the terminal voltage of the battery recovers back quickly to 9 volts ready for next time you connect.
I daren't even ask this
Have you tried this battery connected either way round. In other words, how did you determine the polarity and know which way round to connect it.
Thats very scary
What that proves though is that the amp has a full wave bridge rectifier to convert AC to DC. A little known fact is that that also enables an appropriate DC voltage to be applied irrespective of polarity... which is what you are doing.
You need to try and find out the tranny voltage as I mentioned (thats conclusive proof) but I really think 12 volts DC will be suitable for a battery.
These are the kind of batteries, (site picked at random),
Yuasa NP1.2-12 12 Volt 1.2Ah - VRLA, SLA and Gel Batteries - Yuasa/Yucel Batteries
The Ah rating is the capacity and popular sizes are up to 7Ah. That would run your amp for several hours I imagine.
What that proves though is that the amp has a full wave bridge rectifier to convert AC to DC. A little known fact is that that also enables an appropriate DC voltage to be applied irrespective of polarity... which is what you are doing.
You need to try and find out the tranny voltage as I mentioned (thats conclusive proof) but I really think 12 volts DC will be suitable for a battery.
These are the kind of batteries, (site picked at random),
Yuasa NP1.2-12 12 Volt 1.2Ah - VRLA, SLA and Gel Batteries - Yuasa/Yucel Batteries
The Ah rating is the capacity and popular sizes are up to 7Ah. That would run your amp for several hours I imagine.
That puts a different spin on things. Does your diagram show a single winding from the tranny ?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.