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Old 21st December 2001, 08:06 PM   #11
JoeBob is offline JoeBob  Canada
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I was actually just reading the soft-start circuit, thinking that I should use that. Jamie F, you say you're version is better, but more expensive, you wouldn't have any documentation on your version of the circuit would you, like a web page?

Thanks again...
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Old 22nd December 2001, 12:28 AM   #12
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JoeBob

Rod has used cheap resistors and provided the "heat removal" mechanics himself. Not being a great mechanic, I went for far higher rated resistors (metal cased) that saved me this hassle, but cost more.

I'll put some details together for you, and post tomorrow.

P.S. I don't know if you're following the thread on charging spikes, but this could become relevant to you. I feel am starting to get closer to an answer on this.
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Old 22nd December 2001, 03:00 AM   #13
JoeBob is offline JoeBob  Canada
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Thanks, I'd rather not go the cheap route. I'd greatly apreciate it if you posted it.

As for the route on charging spikes, if I should read it I will...
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Old 22nd December 2001, 05:56 AM   #14
JoeBob is offline JoeBob  Canada
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Well, my friends mothers boyfriend is an electrician so he said he'd explain solid state relays/switches to me, but my questions is as follows. I was reading as ESP about powersuplies, since I know know exactly how the amp modules are going to be (actually started work on them). And for example if I make a powersuply composing of a gloryfied version of ESP's project 04 with the two 750VA toroids that AudioFreak pointed out as well as a soft start circuit (haven't read up on it, was about to after this post, so correct me if there's such a thing in it already), either Robs of Jamie F's (depending on if his post explains enough for me to understand, would I need a solid state switch to turn it on?

Because I looked at the project 04, and it's composed mostly of the transformer, bridge rectifiers and caps, am I missing something (I obviously am)?

Just trying to understand more about the psu, I guess I'll read up on the soft-start circuit now, hopefully it'll reveal some answers to me...
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Old 22nd December 2001, 06:13 AM   #15
JoeBob is offline JoeBob  Canada
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I apologise for my naivety (is that even a word) but realys were just mentioned in the ESP pages on sort-start circuits, I'll read this over before asking anymore stupid questions... Sorry.
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Old 22nd December 2001, 07:18 AM   #16
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Even with the soft start circuit, a solid state relay using a Triac or similar (there is a circuit that runs straight off ac) is still a good idea as your power supply will still draw reasonable current at least some of the time.
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Old 22nd December 2001, 07:50 AM   #17
JoeBob is offline JoeBob  Canada
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Well, I read the esp pages o nthe soft start circuit, and they contain a relay, now I'm not clear on the differences between just relay as in the esp pages, and what you mean by solid state relay, but if I'm better off using both the solid state relay as well as the soft start circuit, I'll look into that, I'll ask my expert to explain it to me, not wanting to ask too many questions here.

As for power point, you mean actuall wall plug, correct? I understand what you mean by neutral to neutral, hot to hot, ground to ground, but something that I've been wondering (and probably need to know) is which one is hot and which is neutral?

Also the ESP pages explaining the soft-start circuit, and I was thinking I'd be best off with the first circuit encorperating the small transformer, but using an EI one here would be fine, no need for an expensive toroidal, right?

Another quick question to slip in, are chock input filters worth it? I know they're alot more expensive, but is worth the extra cash/effort, or is that same cash/effort better spent elsewhere (as I gather, considering I haven't heard much about them)?
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Old 22nd December 2001, 08:05 AM   #18
JoeBob is offline JoeBob  Canada
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Ah, I understand the wall socket part now. I guess having the extra head room would be a good thing, considering it's completely free...
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Old 22nd December 2001, 11:41 AM   #19
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Project 4 describes a linear power supply (switches, fuses, transformer, bridge rectifiers, smoothing caps). This takes mains and makes it into two DC rails of the right value for your amps. It allows you to manually switch on and off. It will work without anything else.

However, there are two improvements you can make, which are in addition to the above:

1) Management of in-rush current on power-up to avoid lights dimming, etc and enhancing the life of your power supply. Rod's circuit does this, a triac will as well. Only needed because of the size of the power supply and use of toroids - only large commercial amps use these techniques.

2) Relay switching of power to the amp. Allows you to remote the amp power on. My very minor adaption of Rod's circuit does this, and has the side benefit of making Rod's circuit a bit safer.

As far as triacs are concerned, Rod provides the pro's and con's in his soft start documentation. AudioFreak is right to say that a triac will provide protection after power-up. The soft-start is a better way of protecting the amp every time you switch it on (often), the triac route comes into its own when things go horribly wrong or you overcook it (hopefully not often). My healthy respect for mains AC means that Rod's warnings are enough to put me off triacs, and the noise issues concern me.

If you want to do the soft start circuit, your decision is how to power the relay control circuit. Rod provides two options, but strongly recommends the former (separate transformer). You definitely shouldn't try the latter.

Having dismissed deriving the power from your main supply rails, you need to think where your 12Vdc is going to come from. One option is everything to the right of R3 (2k2) in Rod's Figure 2 circuit.

I have 12V easily available in my pre-amp, so I omit the components mentioned above. If you have an easy source of 12V, you don't need this either. The pre-amp is a good place to control the power-up of your power-amp, because it means you only have to turn everything on in one place, and the pre-amp output settles before the power amp comes on avoiding nasty pops. If your pre-amp is a commercial unit, you won't want to do this.

If you don't, an EI transformer will do the job, but I wouldn't put this in the same box as your amp modules, as they have strong stray fields which can lead to pickup. You could always just use a 12Vdc wall block (my circuit draws about 120mA) - very easy.

Because my adaptation of Rod's circuit was very basic, I didn't bother drawing it. However, I'll do this today with some block diagrams to make this easier for you to follow. I will also provide a parts list.

Let me stress the safety aspect again - if you haven't done much of this stuff before, heed all of Rod's warnings, and get your electrician friend to check particularly the mains wiring before you switch on. Always unplug before doing any work on this stuff.
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Old 22nd December 2001, 02:38 PM   #20
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Jamie F,

Rod's points regarding Triac's are valid.........

but.......

It should be no surprise that a triac adds some noise to the supply line..... all diodes add some noise and a triac is effectively 2 diodes connected in parallel with their terminals reversed relative to each other and controlled by a small current ... to this end a Triac will also cause a small drop in the supply voltage of 0.5% or less but when driven properly neither are of great concern.

The noise from the triac is the harmonics of the 50Hz or 60Hz mains supply so most of the noise will be at 100Hz and 150Hz for a 50Hz mains or 120Hz and 180Hz for a 60Hz mains....

The fundamental frequency of the noise from the bridge rectifier is twice that of the frequency of the mains supply so for 50Hz most of the noise will be @ 100Hz, 200Hz and 300Hz ..... for 60Hz mains the noise will mostly be @ 120Hz, 240Hz and 360Hz...

As one can see some of the noise is shared by both the Triac and the rectifier so will require more attenuation at these frequencies... but all said and done if the power supply is designed well then the little noise that does get thru will be taken care of by the PSRR of the amp circuit .... of course if you are building a Zen or SoZ amp which dont have great PSRR then more care must be taken in the power supply. In this case the PSRR of the amp is quite good so none of this is really of any concern and as far as the other issues go ...

1. The control circuit runs @ ac mains voltage.... well this is the whole point of it

2. There is a risk of insulation breakdown ... use a good quality insulation and a non metallic screw to attach it to the heatsink and it is highly unlikely that there will ever be a problem.
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