Question about Behringer ULTRATONE K450FX 45 Watt 3 Channel PA System / Keyboard Amplifier

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Transformer blown ultra tone k450fx

I have no idea in dc power output of transformer of ultra tone k450fx

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Can't get this Roland adapter model ACH-120.


I see that´s a pretty expensive power supply.

option 1: buy an equivalent power supply and adapt the cord.
IN: AC 120V 60Hz 12W
OUT: DC +10 V 500mA
DC -10 V 150mA

option 2: Build a new power supply by a kit
something like this:
http://electronics-lab.com/projects/power/011/DUAL%20VOLTAGE%20POWER%20SUPPLY.JPG

Change the 7812 and 7912 by 7810 and 7910. you will get the 10V needed.

option 3: you can try to repair the power supply. check if there is no broken wires or a blown thermal fuse in the transformer.

Jan 28, 2015 | Roland Music

1 Answer

Power supply circuit diagram


There is almost certainly a reason the PSU has blown, these are not very reliable units and the amp has probably gone and taken the PSU with it. You are better off taking it to a dealer and getting it fixed. If there is no power on the seecondary and there is no short the transformer must have blown (assuming you're not trying to check with a DC meter)

Jan 19, 2014 | Mackie Srm450v2 Srm450 Srm 450 V2 Active...

1 Answer

Hello friends an fellow countrymen, I have a Presonus ACP88 compressor limiter with noise gates that melted the bridge, and transformer. I am trying to find a replacement transformer. Called Presonus and...


Transformers rarely need replacing unless they plugged into wrong voltage (high) source. Still, a fuse should have opened. Transformers are dipped in varnish and often look damaged when they are fine. I have Presonus mixers but those all use switching power supplies. You can probably assume that the output of the regulators are around +/-15 volts and that the DC to the regulators will need to be about 20 volts for headroom. With a single diode drop assuming FWB with center tap, we need around a 15 volts either side of center transformer... you MIGHT get by with a 27 volt center tapped... probably not a 24 volt one. Recommendation... get an original one... In audio equipment the transformers often are specially designed to run low on the saturation curve or have magnetic shielding to avoid hum. If you call Presonus, DIRECTLY ask for "Parts" or "Repair Parts" else you are likely put on hold for sales or marketing.

Sep 20, 2011 | PreSonus Acp88 8 Channel Compressor...

2 Answers

Hello, amplifier suddenly stops playing.The loudspeaker is very hot. I do not see the fuse.The control light is on, but the amp does not play.Please help me.This is the amp: Fender Frontman 65R. ...


There is something a bit more serious than the fuse. I would start by checking that the speaker itself is the correct type. This should be a 8 ohm speaker. Then I would play it and see if the output transformer is hot. This may be over driving the speaker. I would also look at the main power transformer. You might have one with the export transformer which can work with 110 or 220. I have no idea of your location so no idea which is your local level. Something is either over volt or over amps. Most of this amp runs at 15 volts and digital runs very cold compared to a tube amp.

I looked over the schematic and I just can't see anything else that would do that other than the things I have mentioned. A hot speaker is "very"unusual. If you can check the voltages with a meter this should be easy to point out the cause. It shouldn't take much for a amp tech to sort it out if you have to take it in. I wouldn't run it that much until fixed. When you see abnormal heat then something is being stressed. So you can cause more damage by using it. There may be a problem with the power transformer or votlage regulator stage but since the speaker is heating that could end up needing replacement if run too long.

Without having it in front of me I would sayy you may be looking at a new power transformer.or diodes and possibly caps. Any of those could cause the base issue. This is different enough with the hot speaker than I'm not that sure without seeing it.

Sep 11, 2011 | Fender Frontman 65R 65W 1x12 Guitar Combo...

1 Answer

Transformer appears dead no lights no output


Transformers are VERY reliable. Look for another problem... rectifier, filter caps, fuses, regulators. There is a main fuse and if it is blown, repair the unit before applying full power. To test the unit, put a 40 watt light bulb in series with the hot side of the power cord. The light will act as a resetable fuse and will light when there is a short within the mixer, thus absorbing most of the voltage. Enough current will flow to diagnose the problem.

Jun 16, 2011 | Mackie 1604 VLZ 3 16 channel Analog Mixer

1 Answer

Hi ther the fuse has blown on the speaker out circet on my new amp any ideas why this would happen?


The fuse blew because of excess current. The cause of the excess current is either excess volume, a short in the speaker, OR the amp has failed and is shorted to one of the power rails internally and is driving DC current out.

Replace the fuse and use a meter to check the output voltage with NO speaker connected. It should be under 1/2 volt period. If it is, then check the resistance of the speaker. The DC resistance should be a little less than the rated impedance. Otherwise if the amp is kicking out a higher voltage or blows the fuse again, have the amp repaired.

Mar 28, 2011 | Ashdown Klystron 500w Bass Amp Head

2 Answers

Hello my roland street cube won't power on, either with dc or batteries....adapter working .could a fuse be blown inside circuitboard? thanks


That is the first thing to check. They are most likely inside the circuit board. Remember to replace them with the same voltage and amperage ratings.

Feb 13, 2011 | Roland Cube-st Battery Powered Amp Cube...

1 Answer

In play mode the sr 16 goes beserk. It makes a pulsed buzzing sound and plays back the drums distorted. any ideas?


The SR-16 uses an external transformer as the power supply which provides 9 volts AC. This ac power is converted to DC positive and negative voltages for the digital and analog portions of the circuit. Although the unit has been reliable generally, this symptoms sounds like of of the main filter capacitors in the DC converter circuit(rectifier, filters and voltage regulator) has broken loose or is defective. This will affect both channel equally. If the problem is in one channel, a broken shield on a cable or the output jack ground connection might have broken on that one channel.

Jan 22, 2011 | Alesis Sr 16 Stereo Drum Machine

1 Answer

I have a Roland AC60 amplifier that I brought from Australia to the US. The Australian version of this amp runs on 240 volts not 110. My question is; 1) does anyone know if converting this amp to...


The only simple way that I could think of is for you to purchase a STEP DOWN TRANSFORMER rated at 500 watt, 110 volts, 60cycle. The transformer inside that amplifier have four output 12v and 15v DC.2amps It will be hard to get the transformer for that! Hope that might help you! taah!

Nov 18, 2010 | Roland Ac60 Acoustic Chorus Guitar...

2 Answers

Alesis SR-16 distorted sounds


The distorted and low volume output plus noise is usually caused by using the wrong power supply adapter. The Alesis SR-16 takes a 9V "A/C" supply not "DC". The A/C supply provides a negative voltage swing which wouldn't exist with a DC supply. So check and make sure you have 9V A/C output supply not DC.

Nov 18, 2008 | Alesis Sr 16 Stereo Drum Machine

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