What amp to build ?


I have some 'piece of iron' at home:
basically it is a big transformer 2KVA, in : 220V out: 2 x 60-0-60 V
plus some 6800 micro/120V caps and MKP caps around 10 micro/250V
Since tey are a quite expensive part of amps, I would like to reuse them for a DiY amp.

After having browsed the forum, I am still a bit confused

Knowing how N.P.'s amps sounds (I've listened to Thresholds and Alephs) I am tempted by the SOZ or the Aleph 4, but concerned because my +/- 60 volt seems too high for both of them.
My 'technical' preference goes to the SOZ, whose circuit is very simple and a PC board is not necessary.

I've also cosidered to modify the PS with choke filter (see roddyrama post) in order to have a cleaner current and reduce the volts, but I am not an expert in electronics and I don't know if this makes sense or not.

One more info: my DiY speakers have an impedance curve around 3.5/4 Ohms at low freq, although with favorable phase.

Anyone has some hint?

Thanks in advance
sandro said:
I've also cosidered to modify the PS with choke filter (see roddyrama post) in order to have a cleaner current and reduce the volts, but I am not an expert in electronics and I don't know if this makes sense or not.

Choke input is the way to go if your amp has a constant draw (ie Class A) and other factors are in line. You would end up with raw rails of about 54-0-54.



2001-10-18 12:22 pm
Use asym. supply

you can work with one ac supply of 60v
resulting in ca 82V DC (+ and ground)and use inputcaps for pos and neg input and bias the amp with resistors 200k from gate(of course both sides) to + supply and also 200k to ground. This will bias the amp at ca. supply/2 Volts. You also can try to tweak the values of the resistor. (maybe 180K to + and 140k to ground, just try.)
With your transformer you can paraller both 60-0-60 when you open connection 0(two wires)
then measure the coils and collect both coils
on one side and measure voltage from resting pins
(you have to put ac in!),if 120V then flip one coil at the connection and collect both resting
wires. - so you have one coil only for each channel.
sorry for being complicated.

I have built a SOZ with a 600VA 25-0-25 toroid transformer per channel, with two 150.000uF capacitors per ch. wich brings the tension to 30V.

I have one heatsink per ch (that I will replace soon) that is PR170 from www.alutronic.de with 375 x 200 x 40 mm with 4kg.

Both heatsinks costed +- €100

The temperature that it has after 30 mins of operation is 100ºC, wich is way to much. (it should be +-50ºC for the transistors and a little more for the resistors).

Before you make a SOZ with that kind of power consider very well the amount of heatsink that is required. see SOZ temperature post for further info.



2002-01-07 6:02 pm
Can't help you with which design to build, but if you want to mess around simulating different PSU topologies, there is an excellent FREE simulator available at <a href="http://www.duncanamps.com/psud2/index.html">Duncan Amps</a>

Whoa !!!

60-0-60VAC will end-up unregulated at around 80V for a SOZ.

This will be a gigantic furnace, which you will not be able to lift on your own.

Have a look at the pictures at the bottom of the following page. Note the size and the operating temperature !!!


BTW, I don't think 2kVA will be enough at 80VDC rails for a stereo amp....

And ..... I can't lift this one either :(



2001-10-18 12:22 pm
Schematic for SOZ with asym. supply.

Hallo Sandro,
look at the attachment for better understanding.


  • soz asymsupply.jpg
    soz asymsupply.jpg
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2000-11-24 12:02 am

Are you not afraid, that you will inject a lot of hum 100/120hz and amplify that again?

The SOZ is what I would call a current hog. So even the best, read smoothest DC, you can get from a CLC power supply, you are liable to inject some ripple in the gates.

I build something very similar (sorry, I did not do any simulation then and now), and had this problem.

However, you can think of different solutions for this problem.

Thanks to everybody who replied, definitely I did NOT wanted to build a SoZ feeded at +/- 60V!

Basically my wish is to have some fun in building a good amp, but since I am not an electronic expert I don't want to invest too much money in it, so I would play using stuff already available.
After building some experience (and the usual side-work with my 'other half of the moon' !) I will try a 'no compromise' amp investing all that I reasonably can.

Well, apparently the only way to have a suitable voltage out of this 20kg of wired copper is to serialize the primary and one secondary, obtaining 40+40 on the other secondary.
If this will not work, the only thing to do is to wire all secondaries in series, obtain a 1:1 transf and use it for an AC power filter.

Another question, about mosfets:
the IRF244 are not available anymore here, the suggested replacement is IRF450.

Since the cost is about $ 20 each, and I have 12 x IRFP350 at home, the question is if they could be an acceptable replacement.

The IRFP350 data are N-fet, 400V, 16A 180W while IRF450 are N-Fet, 500V, 13 A , 150W
Also the datasheet available at irf.com does not look awfully different.
So, looking at this data it looks the 350 are suitable, if not for a 'true' Aleph for a similar shaped mosfet A class amp..

In summary, given the available components my ideal is to build a
'Low-Budget-kind-of-Aleph-5' with this specs:

- supply rails 45 V ( 40+20% - 3 volts lost for inductive filter)

- using IRFP350 instead of 244 (450)

Is it doable in your opinion ?

thanks for any feedback, just 'don't shoot the piano player' if I am totally out of aim!