Good point, Alex. I'm actually getting hold of PGA2311 and LDR based volume controls to avoid this problem. I haven't been too worried about it so far since most of the music I listen to requires the volume up at 70% or so with my speakers, but it'll be nice to have a better volume control, especially when I get more sensitive speakers. (I listened to some Pluto clones yesterday, which I thought were absolutely marvellous, so I plan to build some of my own some time. 🙂 )
Micky: my local store has 2 left. I'll pick them up for you today. Please email me your address details and I'll let you know how much it all costs. Email is "jeremy[AT]howard[DOT]name"
Case layout
I bought a case today. I had planned to build mono-blocks, but I'm not sure that fits my lounge room, so I got a single 2U case. It seems to fit:
(Click to view larger.) Does that layout look OK (I haven't stuck anything together yet - just laid it out on the floor to see what might work)? I'm thinking I'll cut a hole out of the side panel (shown lying on the right) and stick the heatsink through that. I'll try again to do a tap in the heatsink, so I can screw it directly onto the case.
It seems only the transformers create noise, so I've tried to keep them away from everything else. I'll stick a bit of aluminium between them and the rest of the case too.
For star earth, does that simply mean attaching to the chassis? :
I bought a case today. I had planned to build mono-blocks, but I'm not sure that fits my lounge room, so I got a single 2U case. It seems to fit:
(Click to view larger.) Does that layout look OK (I haven't stuck anything together yet - just laid it out on the floor to see what might work)? I'm thinking I'll cut a hole out of the side panel (shown lying on the right) and stick the heatsink through that. I'll try again to do a tap in the heatsink, so I can screw it directly onto the case.
It seems only the transformers create noise, so I've tried to keep them away from everything else. I'll stick a bit of aluminium between them and the rest of the case too.
For star earth, does that simply mean attaching to the chassis? :
- Earth from IEC socket
- 0V from each transformer output
- Each RCA sleeve
- Speaker ground
- Each heatsink
Diode switching noise
On my headphone amp, Alex suggested that I pop a little capacitor across the +/- outputs of the transformer, in order to reduce diode switching noise.
Would that be a good idea for this amp too? If so, what type/spec cap would be appropriate?
On my headphone amp, Alex suggested that I pop a little capacitor across the +/- outputs of the transformer, in order to reduce diode switching noise.
Would that be a good idea for this amp too? If so, what type/spec cap would be appropriate?
Jeremy,
I would use insulated RCA type sockets and utiise the input earthing provided on the amplifier PCB for correct earthing of the input, just my preference.
As an aside just would to confirm you received the LM4562HA's ?
Robert
I would use insulated RCA type sockets and utiise the input earthing provided on the amplifier PCB for correct earthing of the input, just my preference.
As an aside just would to confirm you received the LM4562HA's ?
Robert
Re: Case layout
Make your "chassis" safe by connecting the IEC earth direct to chassis with a permanent mechanical fixing.
Make your Main Audio Ground by connecting all the audio return leads to a common, but floating, point best located between all the audio components using this reference.
Finally make the Audio side safe by connecting from chassis to audio ground. This can simply be done with a wire capable of carrying fault current or, more complicated, by using a disconnecting network that must also be capable of carrying fault current.
BTW, fault current can approach, or exceed, kA until the main's fuse ruptures.
treat the Safety Earth as a completely separate issue from the star ground (main Audio Ground).jp_howard said:
Make your "chassis" safe by connecting the IEC earth direct to chassis with a permanent mechanical fixing.
Make your Main Audio Ground by connecting all the audio return leads to a common, but floating, point best located between all the audio components using this reference.
Finally make the Audio side safe by connecting from chassis to audio ground. This can simply be done with a wire capable of carrying fault current or, more complicated, by using a disconnecting network that must also be capable of carrying fault current.
BTW, fault current can approach, or exceed, kA until the main's fuse ruptures.
Well - it all fits!
That took a bloody long time to get everything placed and screwed in! But it looks like I've achieved my goal to have no protruding screws on the outside of the case. 🙂 I had to grind a couple of slots in the bottom of each heatsink to allow room for the case's mounting bars, which was a bit scary to do (since I know nothing about metal work). I think I looked a bit odd standing on our balcony to do it, wearing my motorbike gloves and jacket to get a bit of protection!...
I've put the heatsinks inside the case - would you guys expect I'll need to cut a lot of vents (or even remove the case sides) to handle their heat? Or should I be able to just let the inside get warm and use the chassis itself (which has a few little vents already) to disperse the heat? Or would you expect I might need a little fan?
Next step is to wire everything up and test it still works, then look after earthing, and do the panel. I think my wife will be most pleased to see all this crap off our lounge room floor, when it's done! 🙂
That took a bloody long time to get everything placed and screwed in! But it looks like I've achieved my goal to have no protruding screws on the outside of the case. 🙂 I had to grind a couple of slots in the bottom of each heatsink to allow room for the case's mounting bars, which was a bit scary to do (since I know nothing about metal work). I think I looked a bit odd standing on our balcony to do it, wearing my motorbike gloves and jacket to get a bit of protection!...
I've put the heatsinks inside the case - would you guys expect I'll need to cut a lot of vents (or even remove the case sides) to handle their heat? Or should I be able to just let the inside get warm and use the chassis itself (which has a few little vents already) to disperse the heat? Or would you expect I might need a little fan?
Next step is to wire everything up and test it still works, then look after earthing, and do the panel. I think my wife will be most pleased to see all this crap off our lounge room floor, when it's done! 🙂
SC 200W LD
Jeremy
Nice work !
Provided that your top cover is also ventilated , you shouldn't have any problems, unless you take up residence near that chimp !
Just keep an eye on the temp for a while,and if O.K. , recheck when things start to warm up again in spring.
Alex
Jeremy
Nice work !
Provided that your top cover is also ventilated , you shouldn't have any problems, unless you take up residence near that chimp !
Just keep an eye on the temp for a while,and if O.K. , recheck when things start to warm up again in spring.
Alex
Re: Diode switching noise
Sorry to bump my own post, but I'm still curious about this. Can anyone advise about adding such a diode?jp_howard said:
200m watt LD amplifier
Jeremy
This capacitor was across the outer sides of the transformer secondary winding. The values used were approximately those recommended in a chart posted some months back in DIYAudio.
Alex
Jeremy
This capacitor was across the outer sides of the transformer secondary winding. The values used were approximately those recommended in a chart posted some months back in DIYAudio.
Alex
No luck searching the forum for that chart - but from the various posts I did find, it looks like a 5-10nF 2kV ceramic should do the trick. Would I be right to assume that most off-the-shelf bridge rectifiers wouldn't already have something like this built in?
Sharing an IEC socket
Is there any reason I can't share a single IEC socket (with switch) for my two amps (which I've combined into a single case)? Obviously I'd need to make sure the fuse was big enough for the combined load. Anything else I'd need to be aware of?
Is there any reason I can't share a single IEC socket (with switch) for my two amps (which I've combined into a single case)? Obviously I'd need to make sure the fuse was big enough for the combined load. Anything else I'd need to be aware of?
"it looks like a 5-10nF 2kV ceramic should do the trick. Would I be right to assume that most off-the-shelf bridge rectifiers wouldn't already have something like this built in?"
Jeremy
Bridge rectifiers don't have anything like that built in.
In the SC HA amplifiers which use (usually) a 30VA transformer, something in the vicinity of 470pF sounds about right.
I will forward a copy of the chart by email. It is unlikely to be clearly legible if posted.
Alex
Jeremy
Bridge rectifiers don't have anything like that built in.
In the SC HA amplifiers which use (usually) a 30VA transformer, something in the vicinity of 470pF sounds about right.
I will forward a copy of the chart by email. It is unlikely to be clearly legible if posted.
Alex
Re: Sharing an IEC socket
I suggest that each mains load gets it's own dedicated and correctly rated mains fuse.
yes, share one mains input to the various mains loads inside the case.jp_howard said:
I suggest that each mains load gets it's own dedicated and correctly rated mains fuse.
Diode switching noise cap calculation
SandyK was kind enough to email me the chart. I'm sure the proper formula for calculating the caps is around somewhere, but I couldn't find it, so I did a quick regression. For those interested, you can get a very close approximation of the cap required for a center tapped transformer by using the following formula:
SandyK was kind enough to email me the chart. I'm sure the proper formula for calculating the caps is around somewhere, but I couldn't find it, so I did a quick regression. For those interested, you can get a very close approximation of the cap required for a center tapped transformer by using the following formula:
F is cap required, in pF, VA is VA of the transformer, and V is VAC of one side of the transformer. So for instance, in my case, I have 50V+50V 300VA transformer: -5.02*300 + 8.22*50 + 1.91*50*300 = 27555pF = 27.5nF .
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