Aleph-X builder's thread

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#765
usually low voltage high VA transformers have to be custom wound.
ie: 18V 500VA or 18V 750VA, etc...

i usually order mine from Victoria Magnetics, just be prepared to
wait a little bit for your order.

There are other transformer companys that will custom wind to,
and i'm sure someone will drop a name 🙂

good luck!



---------------------------------------
thanks for the reply Grey!
 
#767
dggs said:
still4given,

Look for transormers with dual primary windings and use them in series instead of parallel. For example link
will give you 20V+20V instead of 40V+40V.
Click to expand...


If you drop the volts to 20 won't that drop the VA to 250?

Isn't vA = V*A or in this case wouldn't it be 500va/40V = 12.5A
12.5A*20V=250VA?

If I've got this wrong please show me what is the right way to look at this.

Thanks

Moe,

I'll look into Victoria

Thanks, Terry
 
#768
still4given said:



If you drop the volts to 20 won't that drop the VA to 250?

Isn't vA = V*A or in this case wouldn't it be 500va/40V = 12.5A
12.5A*20V=250VA?

If I've got this wrong please show me what is the right way to look at this.

Thanks

Moe,

I'll look into Victoria

Thanks, Terry
Click to expand...

Terry, you think just like me, I started a thread on this exact question a while back when I was looking at xformers for this project. See this link.

FYI, I just went to Victoria, a 700 VA will cost about $90 and take about double the time they tell you.
 
#769
still4given said:

Can you suggest one? I can't seem to find any?
Click to expand...
Since I live in Europe and have the same problem to get a 18-0-18 700/800VA I don't have much to add to the help offered above.
If Victoria or Plitron or whatever good vendor can wind low quantities for you, I would be happy and wait patiently.
Somewhere there was a thread about winding your own. 😉

/Hugo
 
#770
OK next question.

If you start with a 22-0-22 400vA transformer and then you use say a CRCRCRC to drop the volts to say 25 or 26V rails, do the watts for the transformer drop as well? The Excel spread sheet shows watts for the trans not VA. Can someone tell me how to determine the transformer wattage (line 22 in the excel sheet), based on Voltage and VA rating?

Thanks, Terry
 
#771
Let's say you want 320VA, you could get two of 160VA (with each 120V primary& 18-0-18 secondary) and wired the secondary in parallel for each transformer. Check out AVEL part # Y236502 from this link http://avellindberg.com/transformers/y23_range_specs.htm

You'll get your transformer in a week if in stock. Call 860-355-4711. They are very reasonably priced.

If unsure of how to wire up the secondary, they have a technical section on their web site that will show you how.
 
#772
The transformer wattage in the spreadsheet seems to be double the power in the FETs. I'd use the "dissipation for one channel" figure and double that. The power in your CRC etc. comes from the transformer, so it adds to what is in the FETs. The advantage is that resistors can run hotter than FETs so you won't need as much heat sink on them as the FETS. Yes, you'll probably need to heat sink your resistors, if only on the case.

Another transformer possibility is AVEL Y236903 800VA 40V+40V available from parts express (p/n 122-700, $70) or the factory (1KVA also available). I am using one of these in my 4 channel Leach amp, it makes no mechanical noise. It has dual primaries so you can wire it to give you 20VAC, giving you rails before CRC of 27V or so. You should be able to run about 4A bias, giving you about 225W dissipation in the channel.
 
#773
originally posted by Dennis Hui
Congrats on the Aleph-X. How do they compare with your Susy GC?
Click to expand...

That's going to be a tough one to answer. Well, let me start by saying they are more alike than different.

The GC Susy is more forward and incisive, where the Aleph-X has a more relaxed signature. Using the analogy of stage lighting in a jazz club, the GC Susy puts a single bright spotlight on each performer, where the Aleph-X gives less spotlighting to the individual performers but more general illumination to the spacing in between them. I don't think one gives more information than the other, just presents it in a different way.

Further, the GC Susy has a very dynamic presentation. It doesn't sound strained, but it lets you know it's throwing lightning fast punches, and it doesn't let you miss any part of the recording. The Aleph-X is just as fast, but has a sense of ease with the dynamics that even on explosive transients seems like it isn't even trying, and all the subtleties and nuances are there for you to explore. If this makes any sense, the GC Susy is more dynamic, but the Aleph-X has a wider range of dynamics!?!

Lastly, the GC Susy presents itself as having better bass slam, but the Aleph-X clearly goes deeper into the lower frequency extremes.

Keep in mind that in these descriptions I am trying to emphasize differences that are measured in shades of grey. If I had to answer which one I like better, I'd answer both. For watching blockbuster movies, or rocking out, the GC Susy is more fun than a barrel of monkeys. For losing myself immersed in beautiful music the Aleph-X has a naturalness that can't be beat. The only conclusive statements I can make are that considering the difference in cost, the GC Susy sounds way better than it has any right to, and that the Aleph-X sounds so good that you don't care how much it cost.

If you wish to be further confused, I will be to happy to continue to ramble on incoherently on the subject.

Terry
 
#774
Originally posted by Blues
XA60 = +/-34V(?); XA30=+/-25V(?)

&

I'm guessing the upcoming XA60 will have rails of +/-25V and bias of about 2A each balanced side; developing 60W Class A and dissipating about 200W per channel.
Click to expand...

That doesn't quite seem right. Is my understanding correct?

I assume the XA60 is a 60W output into 4 or 8 ohms. I further assume an ~2V loss to the Fet+Source Resistor from the voltage rail.

VxV / 8 ohms = 60 Watts --> V(RMS,Output) = 21.9V

V(max, output) = 21.9V x 1.414 = 31V

Balanced output means each side of the circuit outputs half of the voltage swing, therefore the rail voltage is half the max output voltage plus the Fet+Source resistor loss:

(31/2)+2 = 17.5V

So the power supply needs to have a minimum of +17.5V and -17.5V for the rails.

Next the bias current.

IxI x 4 ohms = 60 Watts --> I(RMS, Output) = 3.87A

I(max, output) = 3.87A x 1.414 = 5.5A

If the Aleph current source is set to 50% current gain, then the minimum bias required for each side of the balanced circuit is:

5.5A / 2 = 2.75A,

and the minimum requiremen for total bias, both sides is then 5.5A.

So the XA60 would run +/- 17.5V rails and a 5.5A bias. Please correct me if I am mistaken.

Terry
 
#776
My way of calulating things is a bit faster than metalman's:
Desired wattage= 60W
Amp Pd= 3*Desired wattage= 3*60W= 180W
Transformer VA= 2* Amp Pd= 2*180W= 360VA
Done.
Okay, it's not accurate to six decimal points. So sue me. You may or may not find a transformer exactly matching that VA rating, either. +- a few VA isn't going to hurt you (or the amp). So look for a 350VA, 375VA, 400VA, or maybe even a 300VA if you ventillate it well.
See? Nearly painless.
Now all you have to do is rob a little old lady of her lunch money in order to afford the transformer. Just don't admit that you did so and we'll all pretend it didn't happen.
But it would be kind to send her a card on her birthday thanking her.
Just don't sign your name.

Grey
 
#777
BobEllis said:
The transformer wattage in the spreadsheet seems to be double the power in the FETs. I'd use the "dissipation for one channel" figure and double that. The power in your CRC etc. comes from the transformer, so it adds to what is in the FETs. The advantage is that resistors can run hotter than FETs so you won't need as much heat sink on them as the FETS. Yes, you'll probably need to heat sink your resistors, if only on the case.

Another transformer possibility is AVEL Y236903 800VA 40V+40V available from parts express (p/n 122-700, $70) or the factory (1KVA also available). I am using one of these in my 4 channel Leach amp, it makes no mechanical noise. It has dual primaries so you can wire it to give you 20VAC, giving you rails before CRC of 27V or so. You should be able to run about 4A bias, giving you about 225W dissipation in the channel.
Click to expand...


Hi Bob,

OK, I'm more confused now. Let me ask some questions in an attempt to get a picture in my head of how the vA of a transformer is come by.

1) Is vA = to the AC volts of the secondary * the amp rating of the secondary? For example the AVEL Y236903 that is rated at 40v + 40V, 800vA. Can I find the amps of the transformer by dividing 800 by 40? 800vA/40v=20A

2) If I wire the same transformer for 20VAC secondaries do I then get 20V*20A+400vA?

3) The 16V + 16V 300vA transformer that I asked about earlier would then be 300vA/16V = 18A Is this correct?

4) The transformer that MikeW suggests would then be 330vA/18v = 18.3A Correct?

5) Is a couple of amps all that big of a deal?

6) In the example of the AVEL Y236903, How do you wire it for 20VAC? Is there an additional center tap? Almost all of my transformers have dual secondaries but how do you split them without the seperated center tap?

Thanks, Terry
 
#778
You are on the right track - except that there are two secondary windings, causing a swing of twice the rated voltage, so your amperage ratings should be cut in half. 40-0-40 is 80V swing, 10A rated.

A transformer with its two 120V primary windings in series will give half the rated voltage. Just follow the directions for 240V input. You cannot significantly increase the current, so it becomes rated for half its original VA rating.
 
#779
metalman said:

...
The only conclusive statements I can make are that considering the difference in cost, the GC Susy sounds way better than it has any right to, and that the Aleph-X sounds so good that you don't care how much it cost.
....
Terry
Click to expand...

Thanks for your comments. It looks like I owe it to myself
to restart my Aleph-X project after the XBOSOZ.

Cheers,
Dennis
 
#780
BobEllis said:
You are on the right track - except that there are two secondary windings, causing a swing of twice the rated voltage, so your amperage ratings should be cut in half. 40-0-40 is 80V swing, 10A rated.

A transformer with its two 120V primary windings in series will give half the rated voltage. Just follow the directions for 240V input. You cannot significantly increase the current, so it becomes rated for half its original VA rating.
Click to expand...


Ok, so with that in mind, there is no advantage to reducing a 40-0-40 800vA to 20VAC over just usings a 20-0-20 400vA. Is this correct?

So these should be correct as well.

22-0-22 400va = 9.1A

18-0-18 330va = 9.16A

16-0-16 300vA = 9.3A

12x4 1.2k = 25A? Not sure about this one.


So now my question is, is there a lot of difference between 9.1A and 10A when it comes to powering a Class A amp?

I hope I'm not being a nuisance. I’m just trying to get the picture in my head.

Thanks, Terry
 
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