• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

65 + 65VAC 1kVA Toroidal Transformer

Hi,
I just bought a cheap PA amp (Cmark) that runs +-95Vdc on the rails.
The transformer is 4*64Vac and other low current tappings for low level control etc.
But it is about 1.5kVA or possibly bigger.
Judging by the spec sheet the transformer limits 4ohm power output to 525w + 525w driving both channels together or 350w + 350w into 8ohm together. Yes 4ohm power is 1.2db down from 8ohm and a well specified PSU should only be 0.5db to 1db down at 4ohm.
If you also want to drive a difficult 4ohm speaker you should be looking at 2ohm spec and the ability to push enough current to produce about 1kw + 1kw together (-1.5db)
1kVA should be good for a monoblock at the voltages you seem to be aiming for or 2kVA for a stereo amp.
 
Those are rated for 55-0-55 ar 115vac or 57-0-57 @120vac. I think calling them 62-0-62 is misleading. These will give rails of 81-0-81vdc

The Avels we looked at are 60-0-60 at 115vac and do 62-0-62 at 120v These gives rails of 87-0-87vdc.

I am looking for a 65-0-65 at 115vac that will be 68-0-68 at 120vac and give me rails of 96-0-96vdc.

As you can see +/-96 vdc is far from that guy's +/- 81 or 82vdc.

K-amps.
 
K-amps said:
Those are rated for 55-0-55 ar 115vac or 57-0-57 @120vac. I think calling them 62-0-62 is misleading. These will give rails of 81-0-81vdc

The Avels we looked at are 60-0-60 at 115vac and do 62-0-62 at 120v These gives rails of 87-0-87vdc.

I am looking for a 65-0-65 at 115vac that will be 68-0-68 at 120vac and give me rails of 96-0-96vdc.

As you can see +/-96 vdc is far from that guy's +/- 81 or 82vdc.

K-amps.


I bought one of these back in February and have it hooked up in my Leach Superamp. I read +/- 90VDC after rectification but I have about 122VAC line current at my house.

I'm not saying these will do the job for you, I was just pointing them out in case they would. I paid $69 including shipping for one.


Blessings, Terry
 
C-Mark amplifier Power Toroid

Hi,

the C-Mark amp is probably the same as the Audiohead AH-1000 I have which has 4 x 64V 900VA marked on the transformer. ( and a low-voltage winding which runs the front panel ).

They claim 525 Watts per channel into 4 ohms, but I know it can't do it on both channels at the same time without overheating. 'Music Power' rules...

Mine has one dead channel which keeps frying the replacement transistors I fit despite having tested every component on the board seperately. ( yes, I really have taken them ALL out and checked them ) I think I've got a hairline crack in the board but I can't find it...

My next step will be to try the channel module on a smaller supply - preferably with some current limiting for safety.

Does any one have a schematic?

Source Manufacturing ( in China ) who made these units won't supply one, and so far I have had no luck with any of the companies in Europe who bought them and had their own names put on the front - including C-Mark and Thomann in Germany.

The circuit is so simple - a dual op-amp on the input which floats with the signal and a pair of driver transistors followed by 4 pairs of power devices, but I can't seem to get a handle on the fault.

Any help gratefully appreciated.

Graham
 
Hi Andrew,

Yes, that's the configuration.

I was just trying to point out that the toroid isn't rated for the claimed output power in the first place. If you run it inside that rating you'd be lucky to get 250Watts per channel RMS and you'd probably have to use 16 ohm loads to do it...

I hadn't stopped to work out what the power dissipation iwould be in the output devices - I haven't had it working to worry about it, but I agree that the way the thing is designed there will be a lot of wasted power. The voltage is needed to get the swing into 8 ohm loads, but becomes a nuisance into 4 ohms.

Toshiba's data sheet for the output devices claims 230 Volts and 16 Amps but only 150 Watts each - that's always been the problem with plastic packages.

In theory, it should be OK on both peak current and working voltage, but obviously not at the same time...

I was given the amp with the output stages fried and all the ventilation slots in the front panel were solid with dust, so the protection circuits don't work either...

I've replaced ALL the devices in both channels and now I've one which works and one which doesn't, so I'm not sure where to go next.

All the best, Graham.
 
Toshiba's data sheet for the output devices claims 230 Volts and 16 Amps but only 150 Watts each - that's always been the problem with plastic packages.
Hi,
plastic packages can do much better than Toshiba's 1943/5200.
This particular device claims 230Vce0 but it's higher voltage performance is terrible. The knee in the SOA curve is at 45V and by the time it's asked to work on 92Vdc supply rails the cold (Tc=25degC) current is down to <500mA. That is a derating for operating voltage down to just 45W. Onsemi's MJL4302/4281 can do about 1.25A @ 92Vce (~=115W) in the same To264 package.

To complicate the matter of a failed channel. Consider that it uses components probably sourced in China, those 1943/5200 may well be fakes that have even poorer performance.

Genuine Toshiba 1943/5200 are a bad choice for any high voltage amplifier.

Run them off +-40Vdc to +-55Vdc and they perform very well.
 
Hi again...

Thanks for your comments - my large amlifier experience is all with Hitachi MOSFETs - I don't know much about the bigger bipolar stuff apart from a few Darlingtons.

The replacement devices I've used came from Farnell's and are SEMELAB, not Toshiba. ( That's what the originals were labelled, but as you say they might have been fakes ).

I'm still hoping to locate a schematic for the amp I've got or at the very least, some indication of what the three trimmers on the board are supposed to be set to...

If I can get the beast working it will only be used as a test amp in my workshop as I wouldn't trust it with good speakers knowing its' history.

Graham.