Transformer advice needed.

[Nigel Goodwin]

The amplifier modules are very expensive for a Chinese copy of a 48 to 50 years old design.
The modules will severely over-heat since they are designed to be mounted on the huge heatsink in the original Quad 405 amplifier.
The design is class-A that makes a lot of heat.

Completely wrong on all counts AG.

The modules are fairly expensive because it's a high quality and very highly regarded design.

Plus it's NOT class A, it doesn't run hot, and it doesn't have particularly massive heatsinks.

There's a link above that goes to a page that has a link to the original article about the current dumping technology (feed forward), and how it uses a low power class A (cool running) amplifier, with the high power added in class B.

 

[Count Yorga]

Okay so what transformer do I need to give me at least 40 volts but no more than 50 after the rectifier?

 

[Visitor]

What nobody has explicitly pointed out that these amp modules require bipolar 30VDC – 50VDC; you need a positive supply AND a negative supply. So you need something like a 30–40 volt centertapped transformer. TWO windings of 30 – 40 volts.

Someone posted a schematic of a bipolar supply earlier.

 

[MaxHeadRoom78]

Okay so what transformer do I need to give me at least 40 volts but no more than 50 after the rectifier?

40vdc is 40 x 0.7 = 28vac
50vdc is 50 x 0.7 = 35vac.
Customize a Toroidal if necessary as posted earlier.

 

[rjenkinsgb]

Okay so what transformer do I need to give me at least 40 volts but no more than 50 after the rectifier?

Something like one of these should be reasonable:

RS PRO 115 V ac, 230 V ac, 2 x 30V ac Toroidal Transformer, 225VA 2 Output | RS

uk.rs-online.com

 

[Count Yorga]

Thanks have looked at one similar to this. 2 x 30v this is where I get confused, the multiple secondary outputs. Connect these together to get 60v x 0.7 which will give me 42 volts AFTER it has passed through the rectifier? I was expecting the voltage to increase not decrease when goes through the rectifier.

Can anyone recommend a respectable publication so I can actually learn this stuff for myself.

 

[Visitor]

The amp modules require a bipolar supply. That means 30 - 50 volts between common and V-positive, and 30 - 50 volts between V-negative and common. The sketch here shows what this would look like with two DC supplies (battery symbol represents the D supply).

Starting with a transformer, you'll need a center-tapped winding of about 80 volts (each winding providing 40 volts). Rjenkins showed how to do this in this post:

Transformer advice needed.

I need some help understanding transformers. I need a transformer for an audio project, preferably a toroidal transformer. I want to out 240v UK mains into it and get 18 volts out if it. All the various ones I see to buy online have multiple secondary outputs. I wish to understand if I can buy a...

www.electro-tech-online.com

 

[Diver300]

Thanks have looked at one similar to this. 2 x 30v this is where I get confused, the multiple secondary outputs. Connect these together to get 60v x 0.7 which will give me 42 volts AFTER it has passed through the rectifier? I was expecting the voltage to increase not decrease when goes through the rectifier.

Can anyone recommend a respectable publication so I can actually learn this stuff for myself.

The amplifier needs ±30 V to ±50 V. That means that it needs a negative supply that is between -30 V and -50V, as well as a positive supply that is between +30V and +50V. The total voltage, measured between the -ve supply and the +ve supply will be 60 to 100 V.

Your 2 x 30 V transformer will give 60 V ac between the ends of the secondary windings if they are in series. 60 V ac will give around 80 V dc when rectified, which is what you want.

Having the windings as 2 x 30 V in series instead of 1 x 60 V makes no difference to the overall voltage. However it does give you a mid-point so that the supply 80 V will be evenly split, with the positive and negative ends about equally far from ground.

 

[Count Yorga]

Aaaaaah that is quite clear. Thank you very much. I've been reading up on this, all more complicated than I thought it would be, but logical. Thank you.

 

[audioguru]

Completely wrong on all counts AG.

The modules are fairly expensive because it's a high quality and very highly regarded design.

Plus it's NOT class A, it doesn't run hot, and it doesn't have particularly massive heatsinks.

There's a link above that goes to a page that has a link to the original article about the current dumping technology (feed forward), and how it uses a low power class A (cool running) amplifier, with the high power added in class B.

I copied a review that talked about Class-A and did not describe "current-dumping". Now I saw the article about current dumping and it is what I used to eliminate crossover distortion in Korean speakerphones.
Sure the Quad 405 amplifier uses little modules that the Chinese copied but the original amplifier mounted their modules on a massive heatsink.

 

[Nigel Goodwin]

I copied a review that talked about Class-A and did not describe "current-dumping". Now I saw the article about current dumping and it is what I used to eliminate crossover distortion in Korean speakerphones.
Sure the Quad 405 amplifier uses little modules that the Chinese copied but the original amplifier mounted their modules on a massive heatsink.

I wouldn't have called that 'massive', and it's as much a cosmetic feature as heat sinking, with only short fins.

The older 33/303 Quad (45W per channel) had more substantial heat sinks, but they were class AB.

 

[MaxHeadRoom78]

This is one supplier I have used in the past, he also has made custom units at one time, maybe still does.

Transformers - Page 1 - AnTek Products Corp

www.antekinc.com