Here is how you count: you have a 50 VA trafo that divides into two secondarys. That is 25 VA per secondary. You need each secondary to provide power to 0,6 A. Divide 25 VA with voltage 15 and you get the allowed current per rail 1,67A. You seem to be on the safe side if Antek (poor guys, factory just went up in smokes) holds specs, which they usually do.
Thing with audio equipment is that you dont want to max the trafos since that, even if they take the power they start to vibrate and generate physical hum.
I think your good tho.
GL
Staffan
I will for any circumstance update on my own post. If you are designing for class A as this and most preamps are, you dont have to take head up for any temporary current draw. Some class B amps, especially in the buyers segment is designed for class B but cheaps on the tranny and relies on the caps in the PSU rail. Rotel and Denon is good examples as they built good amps in their own concepts. Rotel relied more on big trannys, Denon calculated a lot on good caps. Both succeded but Denon won since it was cheaper.
In class A I wouldnt worry about caps. Keep them as low as possible and as good quality as possible. If your tranny keeps up and ripple is decent, dont go for larger caps.
You will severely overheat your transformer doing as you suggest.
1.) the 1.67Aac is the AC current that is allowed to feed a resistor load.
2.) the power output when fed to a Capacitor input filter becomes Idc * Vac * Sqrt(2) This MUST be less than the VA of the transformer.
3.) all transformer manufacturers de-rate the transformer output to take account of the additional heating effect of the pulsing current when feeding a capacitor input filter. This reduces the available power output to well below that predicted in 2.) The usual de-rating factor is around 0.7
The result of all of these is that Idc ~ = Iac/2 when taking continuous DC current from a capacitor input filter.
For the example you gave the maximum continuous DC current will be ~840mAdc
Drawing 600mAdc from the 50VA 15+15Vac transformer will be using ~70% of maximum continuous capability.
I have posted similar information in many previous posts, but Members like you refuse to read any of my unhelpful posts.
Is this another of those unhelpful posts?
Last edited:
Sorry about that. I forgot about multiplying Sqrt(2) for VDC. I was writing on the phone on the sub and just tried to be helpful. He is still in the spec and it wont blow in his face. It might get lukewarm and give some hum. No need to blow your top Andrew.
Staffan
and worse, you did not mention the manufacturer's Derating for Capacitor Input Filter. Were you even aware that it exists and must be incorporated into any modeling?
When Members post rubbish and the Moderators take no action, then what is one to do?
I have taken a step back for the last few weeks and I am seeing Rubbish and Lies being posted on this Forum and no one seems to take any heed !!!!!
Last edited:
Moderators are here not to scold members and not to vet technically but to keep the quality of discussion up and the noise down besides running janitor's chores. Technical accuracy is to be promoted by members civil exchange of facts. Your inadequate outburst yet again and the characterizations you use earn you the deployment of the recent mods team private warning to you about your long term conduct. I.e. 15 days in the bin and permanent moderation now with option for ban if you keep intimidating members by browbeat and offensive language. No matter who is right in tech nobody is a headmaster here. See rule #1.
Darbost, you'll be fine plugging it in. If you feel uncomfy with eventual heat or hum generated by the transformer at this load, then upgrade to 100 VA.
Staffan
When you get this finished can you post pics and maybe a schematic of your layout? And what kind of volume control/trim scheme will you use for the movie setup? I'm doing something similar (only 6 channels) and I'm very interesed in your project - not so much the balanced aspect but definitely the 8-channel.
Will do. Plan is to use lightspeed *8. A friend had some PCBs but the optos was bad so I guess I have to buy a 100ish and match away. Anyone wanna sell some spare Silonex NSL-32SR2S from old matching?
Staffan
I dont know yet but I just build a plug for matching the SK170 toghether with the 5 glowbugs. If i upload pic here Andrew would shoot me point blank, but I will try to match the cards as decently as I can. Its also for learning. Teabag sent me very nicely matched SK170 for the buffer section, I have run them and they are on spot looking at each card per se but per card they differ between the cards from 0,72 to 0,85 (3 quadrupels is on 0,82 to 0,85 but one is on 0,72). Im to dumb to tell you if that will affect channel balance or not.
And after that its about matching the optos I guess. If you meen the "steering" of the lightspeeds they are, if I remember right, steered by 5 V and a pot so that shouldnt be a problem. I think
best
Staffan
Last edited:
Thanks for the warning from both of you. The little I've heard from lightspeed I liked. Think about the cost of 8 ladders.
Staffan
Actually I'm not talking about compensating for differences in the cards, which are sure to be minimal, but matching front/center/surround/sub channels to compensate for room acoustics and differences in speaker efficiency, amplification, etc. My current setup requires around a 15dB range, and I imagine most setups will require something similar. I actually thought of putting a lightspeed in front of a ladder for this purpose. I like the lightspeed in the right application - in the wrong one it sounds dreadful. Deciding which is a matter of trial and error.