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Which transformers are the best choice for a dual mono amp?

Luca

pfm Member
Hello everybody,
I'm building a power amp with Qudos boards inside and I'm looking for the transformers. I've in my reach a pair of options and, kind experts, I ask you for an advice about which is the best solution for a dual mono power amplifier: two center tapped transformers with secondary 35x0x35 or two transformers with 2x35 secondary?

Thanks in advance for the replies,
Luca
 
IME transformers do sound different to each other. I would go for one large transformer with 2 set of 30-0-30. That will give about 70W into 8R - enough for most applications.

What I would like to know is why some transfomers sound better than others. Can this extra cost be justified?:

http://www.intuneaudio.co.uk/Hi-Fi-...io-Grade/Nuvotem-Audio-Grade-Transformer-Naim
http://www.intuneaudio.co.uk/Hi-Fi-...-Grade/Toroidal-Transformer-Audio-Grade-600VA

3 X the cost for "Super annealed cores"

What does this mean?
 
I'd like to see that tested, or even measured at the rail. Never seen it. But believe it.
 
All that matters about a transformer is the VA rating, output voltage and will it fit in the amp. If for sensitive applications then think about screen and belly band etc.
 
Funnily enough I read those same pages.
However, we don't know what electrical parameters "super annealing" affects and by how much (other than an unquantified reduction in core losses). And then, how does this affect the sound?

Canterbury Windings has a great reputation. Are their cores super-duper annealed??
 
For the purchase I'm looking at some sources. Last monday RS insanely increased (+50%) the prices in the Talema range. Rs is out of my BOM now. I have in poll position Canterbury Windings whom products, seem me, more consistent and better made than many others on the market. Thank you Jez and S-Man for the advices about the voltage. I'll keep them in mind.
 
Last edited:
Hi Luca, having just built a 220 and being very happy with the results, my advice would be to go with the recommendation of the designer of the amplifier. Email Les if you are not sure.
 
...(ie, works, and is silent).

Is that enough though?
I have tried a few different transformers with my Leach amp and my preferred one is a 1KVA toroid with interwinding screen. It's actually an early Michell Alecto prototype, it sounds great but hums like a bag of wasps if the mains is grotty.

I have some really nice EI cores with a belly band that are silent and have no switch-on throb. The sound is good but just a tad behind the Alecto toroid.

On balance, I prefer to use the sometimes noisy toroid rather than the well behaved EIs.
 
Hi Luca, having just built a 220 and being very happy with the results, my advice would be to go with the recommendation of the designer of the amplifier. Email Les if you are not sure.

I already did but Les didn't answer.
 
Terry at Canterbury windings is usually the default recommendation. Using one of his here in my Qudos amp and as far as I can tell it does the job (ie, works, and is silent). Not the cheapest, but v good.

What specifications does your CW transformer have?
 
What specifications does your CW transformer have?
Just had a hunt through my mail archive, this appears to be my last order from him, so I think it's this one

Type no: TM242A
Power rating: 300VA
Primary: 0-240V @ 50Hz
Electrostatic screen
Secondaries: 35-0-35V @ 4.29A rms
GOSS band
Regulation: approx 7.5%
Estimated dimensions: 124mm diameter away from leadouts x 60mm high
Mounting: potted centre with threaded insert
Leadouts: approx 200mm long flexible (stranded)
Audio grade construction

That's being used in a stereo voyager clone (ie shared vbe front end and output stage psus)
 
Just had a hunt through my mail archive, this appears to be my last order from him, so I think it's this one

Type no: TM242A
Power rating: 300VA
Primary: 0-240V @ 50Hz
Electrostatic screen
Secondaries: 35-0-35V @ 4.29A rms
GOSS band
Regulation: approx 7.5%
Estimated dimensions: 124mm diameter away from leadouts x 60mm high
Mounting: potted centre with threaded insert
Leadouts: approx 200mm long flexible (stranded)
Audio grade construction

That's being used in a stereo voyager clone (ie shared vbe front end and output stage psus)

Thank you for the fast answer. Does your transformer have two 150 VA secondaries and are they more than enough? I use efficient loudspeakers (90 db) and don't like to listen to high volume. For instance, a Nap 140 has more than enough power to my need.
 
Single 35-0-35 secondaries - I'm not dual mono in this amp. 86db speakers and only ever low level listening here (small single bedroom home office...)
 
Is that enough though?
I have tried a few different transformers with my Leach amp and my preferred one is a 1KVA toroid with interwinding screen. It's actually an early Michell Alecto prototype, it sounds great but hums like a bag of wasps if the mains is grotty.

I have some really nice EI cores with a belly band that are silent and have no switch-on throb. The sound is good but just a tad behind the Alecto toroid.

On balance, I prefer to use the sometimes noisy toroid rather than the well behaved EIs.

I should have added that the sound quality of my amp improved; to my ears any way.
 


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