Well for some, maximum overkill is the flavor of the month. 
But note that Terry used 30VA for his positive rail and 15VA for the negative which is equivalent to what I am planning. If it worked well for Terry I think its good enough for me.
You can find that here:
http://www.diyaudio.com/forums/showthread.php?postid=763865#post763865
The PS is so well regulated that I seriously doubt (but hey what do I know) a massive trafo would have audible benefits.
Cheers!
Russ
But note that Terry used 30VA for his positive rail and 15VA for the negative which is equivalent to what I am planning. If it worked well for Terry I think its good enough for me. You can find that here:
http://www.diyaudio.com/forums/showthread.php?postid=763865#post763865
The PS is so well regulated that I seriously doubt (but hey what do I know) a massive trafo would have audible benefits.
Cheers!
Russ
I don't profess to know a great deal about the transformer issue but in Hugh Deans artical on power supplies for his ASKA power amps he says and I quote:
The physics of transformer dimensioning in audio is not particularly well understood as it relates to sonics. Suffice to say that the transformer, rectifiers and filter capacitors comprise a system, together with the amplifier, whose primary function is to modulate a current through a low impedance voice coil in exact replica of a tiny alternating voltage applied at the input of the amplifier. We have found that a larger transformer slows the sound, while a smaller transformer lacks bass punch and impact. A middle course is recommended; two 160VA transformers and 4 x 4,700uF for the 55W stereo AKSA, and two 300VA transformers and 8 x 4,700uF for the 100W AKSA. You may use other transformer sizes and capacitor values, but in our experience the sonics will not be optimised.
Surely there must be some middle ground in this case also? Has anyone got some ideas?
Ian
The physics of transformer dimensioning in audio is not particularly well understood as it relates to sonics. Suffice to say that the transformer, rectifiers and filter capacitors comprise a system, together with the amplifier, whose primary function is to modulate a current through a low impedance voice coil in exact replica of a tiny alternating voltage applied at the input of the amplifier. We have found that a larger transformer slows the sound, while a smaller transformer lacks bass punch and impact. A middle course is recommended; two 160VA transformers and 4 x 4,700uF for the 55W stereo AKSA, and two 300VA transformers and 8 x 4,700uF for the 100W AKSA. You may use other transformer sizes and capacitor values, but in our experience the sonics will not be optimised.
Surely there must be some middle ground in this case also? Has anyone got some ideas?
Ian
Power rating of trafo
The circuit will draw 80 ma per side. For stereo this is 320 ma. With a 50 volt output this is 16 watts. With a higher output voltage and some heating loss this should come to around 20 watts VA.
A 30 watt unit should ber great for mono use, a little undersized for a stereo supply. The lower output voltage needed for the negative supply makes this easier.
One small trick for stereo supply using a single stereo. Alternate the polarity of the ac coming into the diode bridge. This should help lower the peak currents and make life a little easier for the transformer.
George
The circuit will draw 80 ma per side. For stereo this is 320 ma. With a 50 volt output this is 16 watts. With a higher output voltage and some heating loss this should come to around 20 watts VA.
A 30 watt unit should ber great for mono use, a little undersized for a stereo supply. The lower output voltage needed for the negative supply makes this easier.
One small trick for stereo supply using a single stereo. Alternate the polarity of the ac coming into the diode bridge. This should help lower the peak currents and make life a little easier for the transformer.
George
Clarification
Here are the specs I presented for the trafo. I was was guessing about 30VA for the trafo, but now that I actually calculate it it looks like this:
dual primaries
56V secondary .5A (28 VA)
22V secondary .5A (11 VA)
So that's 39 VA.
Avel says they will round up a bit so it works out to around 50VA.
One of those should be absolutely bountious current for a stereo pair, but you can always use one per channel and have huge reserves.
Cheers!
Russ
Here are the specs I presented for the trafo. I was was guessing about 30VA for the trafo, but now that I actually calculate it it looks like this:
dual primaries
56V secondary .5A (28 VA)
22V secondary .5A (11 VA)
So that's 39 VA.
Avel says they will round up a bit so it works out to around 50VA.
One of those should be absolutely bountious current for a stereo pair, but you can always use one per channel and have huge reserves.
Cheers!
Russ
Banned
Joined 2002
Banned
Joined 2002
I think that you can COUNT on them being custom... and remember, this is one torroid.
Her's the 300Va version of the Avel at PE.
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=129-095
Probably this is not so suitable for European fokes with 230 V.
I see my house supplier Amplimo of toroids doesnot make small (50VA or so) toroids with 56V secondairies (a special will be more expensive), 22V is not a problem.
However these Talema Nuvotems might be interresting. They have small toroids for 230 V AC with 55V secondaries. Don't know how much they cost though. (a 15V 50VA Talema is about 15 euro)
http://www.talema-nuvotem.com/
http://www.nuvotem.com/en/products/pdf/0050P1_0209.pdf
http://www3.schukat.com/schukat/sch...631AA3DDCE1B756DC1256D7900261D0A?OpenDocument
I see my house supplier Amplimo of toroids doesnot make small (50VA or so) toroids with 56V secondairies (a special will be more expensive), 22V is not a problem.
However these Talema Nuvotems might be interresting. They have small toroids for 230 V AC with 55V secondaries. Don't know how much they cost though. (a 15V 50VA Talema is about 15 euro)
http://www.talema-nuvotem.com/
http://www.nuvotem.com/en/products/pdf/0050P1_0209.pdf
http://www3.schukat.com/schukat/sch...631AA3DDCE1B756DC1256D7900261D0A?OpenDocument
Perhaps some good advice someone can use.
When tapping aluminium, i always use a tap made for stainless steel. ( It's very hard to break the tap if you are careful).
Use it with at battery driven drill maschine with thyristor speed control. (i use a Bosch).
Tap it at low speed and without the torque mechanism OFF.
For aluminium, use ordinary spirits in the hole.
This procedure makes a perfect result everytime for me.
Remember to drill before you tap, muhahahaha
This is the way we do it at my work (Elektromechanic...BIG Elektro motors and stuff).
Just my 50 cents
When tapping aluminium, i always use a tap made for stainless steel. ( It's very hard to break the tap if you are careful).
Use it with at battery driven drill maschine with thyristor speed control. (i use a Bosch).
Tap it at low speed and without the torque mechanism OFF.
For aluminium, use ordinary spirits in the hole.
This procedure makes a perfect result everytime for me.
Remember to drill before you tap, muhahahaha
This is the way we do it at my work (Elektromechanic...BIG Elektro motors and stuff).
Just my 50 cents
Banned
Joined 2002
Yup, they sell Irwin taps. That's what I've been using until now, and likely will continue to use for small jobs.
The Tapmatic replaces the chuck in the drill press. It taps the hole, then automatically backs out at 1.75x the drill speed (internal planetary gearing). Made for high-volume production tapping. They are several hundred dollars new, but you can find them on ebay if anyone is interested.