I had to replace the original toroidal transformer as that burned up. I found a 300w with the same output voltage for this amp. I also upgraded the caps to audio caps and replaced sole very old resistors and zener diodes, all following the specs. I also replaced the NE5332 opamp to an OPA compatible version. I have rebias both channels of the amp according to Arcam specs. That's to the extend of the modifications. Did I do something wrong? The amp sounds very very good and very powerful. Playing it at loud volumes seems to be no issues and it can play for months. Problem is only when I turn the amp on.
- It's ok. But you wrote somewere here that power transistor blowed up? So we dont understand situation, when exactly it happens? If it was long time ago than everything is ok.
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As I understand, this new power transformer is more powerful, than old one? It can has smaller primary winding resistance (than less powerful one), and so - causes larger inrush current (when energized). It is one of the reasons why fuse blows more often. Toroidal transformers have the biggest inrush current from other types (with same nominal power), so big toroids "want" current-limitting schemas.
An additional NTC (as we decided earlier) should help.
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Thanks, i've ordered the thermistor and shall install inside the circuit. I assume the thermistor is installed in the primary windings of the transformer.
I can't recall if it is more powerful. But based on the fuse rating of 1.25A @ 240 volts, it should be maxed at 300w, hence that was what I have ordered and replaced. Let me see after installing the time delayed fuse and thermistor once I have installed it. Will advice back.
Hi, I installed the time delay fuse, problem solved. The amp can be switched on and off without issues.
Latest update. The best thermistor which worked was the CL-140 NTC which cna be bought from element14.com.
It has 50 ohm thermistor which has max energy of around 4.02 J and nominal current at 1.1A. I've had it installed into the 240v mains right after the primary 1.25A fuse in the amp. So far, I have tested the amp by turning it on and off (interval of 30 sec between turn ons) and the fuse didnt blow. I tried it also with normal 1.25A fuse, the fuse was also intact. Thermistor wasn't that hot, and you could touch it, hence it could be the optimal one to use.
Of course I used back the slow blow fuse, but kept the thermistor as double protection.
It has 50 ohm thermistor which has max energy of around 4.02 J and nominal current at 1.1A. I've had it installed into the 240v mains right after the primary 1.25A fuse in the amp. So far, I have tested the amp by turning it on and off (interval of 30 sec between turn ons) and the fuse didnt blow. I tried it also with normal 1.25A fuse, the fuse was also intact. Thermistor wasn't that hot, and you could touch it, hence it could be the optimal one to use.
Of course I used back the slow blow fuse, but kept the thermistor as double protection.
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I would beginning measuring Your mains Voltage first.
If there is a voltage increase out of tolerance it could explain many things.
If mains is Ok I then would measure the rail Voltage, and depending on age perhaps changing the bridge and the PSU caps.
By the way ... is there DC on speaker terminals ?
If there is a voltage increase out of tolerance it could explain many things.
If mains is Ok I then would measure the rail Voltage, and depending on age perhaps changing the bridge and the PSU caps.
By the way ... is there DC on speaker terminals ?
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