Thanks for the suggestions. I know this is a cheek but can anybody recommend a specific transformer to match the Antek AN-2222 or AS-2222 that Tom indicates. I am not expecting you to troll round the suppliers for me, it was more if you have obtained one that actually works well. You can probably tell I'm a novice at this sort of thing. I've built a few turntables and speakers over the years but never really tackled electronics. I retired this year and promised myself I would learn at least one new skill
. I'm hoping I can follow the recipe even if I don't understand all the ingredients!
. I'm hoping I can follow the recipe even if I don't understand all the ingredients!what is the spec required?
Secondary Vac and VA?
Toroid or EI?
Speaker impedance?
I'll guess your normal Mains voltage is in the range 240Vac to 245Vac.
All the new transformers will be built to a nominal 230Vac Mains voltage and so you will get an extra ~5% from whatever you buy.
Secondary Vac and VA?
Toroid or EI?
Speaker impedance?
I'll guess your normal Mains voltage is in the range 240Vac to 245Vac.
All the new transformers will be built to a nominal 230Vac Mains voltage and so you will get an extra ~5% from whatever you buy.
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Standard Range Toroidal Transformers: CM0160222: 160VA 230v to 2x22v
Pay the extra for the electrostatic screen if you can stretch for it.
Pay the extra for the electrostatic screen if you can stretch for it.
Thanks for rapid answers. Spec of Antek is:
200VA, Output Voltage 22V, Current 4.5A
Airlink as recommended by Bill
160VA, Output Voltage 22V, Current 3.64A
I presume these are close enough. Price of Airlink seems very reasonable, about right for a Christmas present from one of my poor children
200VA, Output Voltage 22V, Current 4.5A
Airlink as recommended by Bill
160VA, Output Voltage 22V, Current 3.64A
I presume these are close enough. Price of Airlink seems very reasonable, about right for a Christmas present from one of my poor children
I won't argue, I'll just present the same information as always.
Use a transformer with a VA rating of one to two times the total maximum power of the two amplifiers in the stereo build.
For two 60W amplifiers that would be a range from 120VA to 240VA.
160VA, 200VA and 225VA all fit that range. An even bigger transformer could be selected, the amplifier will still work.
It really is that simple.
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What are your speaker impedances?
The UK tends to use either 8ohms, or 4 to 8ohms.
Hardly anyone makes a 6ohms speaker, even though some manufacturers specify a 4 to 8 ohms as such (they should know better).
This affects the secondary voltage.
22+22Vac is usually specified for a 3886 driving 4ohms speaker.
25+25Vac is more usual for 8ohms speakers.
The UK tends to use either 8ohms, or 4 to 8ohms.
Hardly anyone makes a 6ohms speaker, even though some manufacturers specify a 4 to 8 ohms as such (they should know better).
This affects the secondary voltage.
22+22Vac is usually specified for a 3886 driving 4ohms speaker.
25+25Vac is more usual for 8ohms speakers.
Main speakers alternate between a pair of Frugel Horn XL's with Alpair 10p drivers and a pair of Proac Response 1.5's. The Alpairs have a nominal impedance of 6 ohm, the Proacs I think are 8.
Tom recommends a voltage of between 20V to 28V if both 4 and 8ohm speakers are likely to be used. I will probably want to go nearer 28V as I will be using a passive pre at least to begin with. Does this sound right?
Tom recommends a voltage of between 20V to 28V if both 4 and 8ohm speakers are likely to be used. I will probably want to go nearer 28V as I will be using a passive pre at least to begin with. Does this sound right?
It's incorrect. Use of a passive pre affects gain structure (see the DIY Audio article on such) but is unrelated to the output power required for a given SPL---higher rails don't provide additional voltage gain to compensate for attenuation in the pre.
Perhaps. But usually not. If you're among the 10% of folks using such signal levels it's likely an infrequent---rather than routine---requirement.
I often listen with average levels around the 100mW level into 87dB speakers.
If I turn that up 10dB to around the 1W level, I can hear the sound change a bit.
Another 5dB to become a 3W average level and the sound has become unpleasant.
That is because the 65W amplifier is clipping the peak currents.
Now repeat the exercise with 20% lower supply rails.
If I turn that up 10dB to around the 1W level, I can hear the sound change a bit.
Another 5dB to become a 3W average level and the sound has become unpleasant.
That is because the 65W amplifier is clipping the peak currents.
Now repeat the exercise with 20% lower supply rails.
Thanks for your reply although I don't really understand it. According to Tom, going from 24V to 28V supply raises the output from 28W to 38W. Now I realise that an increase in 10W will not make a huge difference in sound pressure levels but surely it will give a little increase in headroom before clipping takes place.
I believe that that clipping headroom is very important to the sound quality.
I generally aim for average to peak, to help avoid gross clipping, of at least 20dB
I.e. for 65 W of max output then average <0.65W
Of my three examples above, only the 100mW complies. 1W and 3W break that 20dB headroom rule.
I believe the changes in sound that I hear are due to clipping.
I generally aim for average to peak, to help avoid gross clipping, of at least 20dB
I.e. for 65 W of max output then average <0.65W
Of my three examples above, only the 100mW complies. 1W and 3W break that 20dB headroom rule.
I believe the changes in sound that I hear are due to clipping.
It's only simple if you explain the underlying math and assumptions. I explain the math on my Taming the LM3886 website.
For sine wave operation, the required transformer size works out to 121 VA per channel. Assuming a crest factor of 14 dB for music signal, this can be reduced to 51 VA per channel. Both these numbers assume ±28 V rails and 4 Ω load.
As few people listen to sine waves continuously, I recommend a 200 VA transformer for a stereo build of a MOD86. 160 VA would work as well. In my 4xMOD86, I used a 300 VA transformer.
Tom