The PCB looks very good Suzy!
I only have a few small comments that you may like to consider.
The copper pours around the mounting holes and some of the tracks may a bit too close to the screw heads unless you are planning on using insulating washers under them.
You may wish to change the 10R resistor for a lower value or make it a higher power type. I have seen these self destruct due to ground currents.
It is a good idea to have a marking on your overlay that shows electrolytic polarity outside the component so that you can inspect the board after assembly.
It can also be a good idea to have a link to the power stage power rails that you can isolate them for fault finding.
A test point where you can ground a CRO probe is wise investment.
The holes for what I'm guessing are spade connectors for the power entrymay be a bit small.
The PCB makers prefer a board outline on Mech 1, either a very
small trace of 1mil or the width of the router bit.
All really minor stuff.
I look forward to seeing the stuffed PCB's.
Cheers,
Ralph.
I only have a few small comments that you may like to consider.
The copper pours around the mounting holes and some of the tracks may a bit too close to the screw heads unless you are planning on using insulating washers under them.
You may wish to change the 10R resistor for a lower value or make it a higher power type. I have seen these self destruct due to ground currents.
It is a good idea to have a marking on your overlay that shows electrolytic polarity outside the component so that you can inspect the board after assembly.
It can also be a good idea to have a link to the power stage power rails that you can isolate them for fault finding.
A test point where you can ground a CRO probe is wise investment.
The holes for what I'm guessing are spade connectors for the power entrymay be a bit small.
The PCB makers prefer a board outline on Mech 1, either a very
small trace of 1mil or the width of the router bit.
All really minor stuff.
I look forward to seeing the stuffed PCB's.
Cheers,
Ralph.
Hiya Ralph,
Nice to see someone with an interest 🙂
Good idea regarding isolating the power rails - I was vaguely thinking it would be nice to have a couple of links so that everything but the output transformers could be run off a separate (lower power) supply. That way, one could drive the gates of the power FETs beyond their drains. Is that ever done? It works nicely in simulation, and would allow the use of a lower voltage power transformer, for the same sort of distortion/power. Though one imagines that the onset of clipping would be rather harder.
In any case, a couple of links on the supply rails are a good thought.
As for sizing of terminal holes etc, I simply went by the standard hole sizes that we use at work - out 1/4" terminals have a pair of 1.2mm tabs, that fit nicely in a 0.05" hole.
I've also bunged a couple more designs up, if you're interested.
A preamp board:
PDF file
GIF file
SCH file
PCB file
and a power supply board:
PDF file
GIF file
SCH file
PCB file
There's aso a Q&D autocad drawing of the whole box:
http://www.atnf.csiro.au/people/sjackson/Amplifier.dwg
I'll bung the control board and the video switch board up tomorrow (assuming I remember to put them on my USB key).
Everything's pretty rough at the moment. I generally use keep-outs to define the edge of boards while I'm drawing them, then draw in the mech1 stuff just before I send out the panel. I've still got some work to do cleaning up silkscreens etc as well.
Cheers,
Suzy
Nice to see someone with an interest 🙂
Good idea regarding isolating the power rails - I was vaguely thinking it would be nice to have a couple of links so that everything but the output transformers could be run off a separate (lower power) supply. That way, one could drive the gates of the power FETs beyond their drains. Is that ever done? It works nicely in simulation, and would allow the use of a lower voltage power transformer, for the same sort of distortion/power. Though one imagines that the onset of clipping would be rather harder.
In any case, a couple of links on the supply rails are a good thought.
As for sizing of terminal holes etc, I simply went by the standard hole sizes that we use at work - out 1/4" terminals have a pair of 1.2mm tabs, that fit nicely in a 0.05" hole.
I've also bunged a couple more designs up, if you're interested.
A preamp board:
PDF file
GIF file
SCH file
PCB file
and a power supply board:
PDF file
GIF file
SCH file
PCB file
There's aso a Q&D autocad drawing of the whole box:
http://www.atnf.csiro.au/people/sjackson/Amplifier.dwg
I'll bung the control board and the video switch board up tomorrow (assuming I remember to put them on my USB key).
Everything's pretty rough at the moment. I generally use keep-outs to define the edge of boards while I'm drawing them, then draw in the mech1 stuff just before I send out the panel. I've still got some work to do cleaning up silkscreens etc as well.
Cheers,
Suzy
Hi Suzy,
I know there are some pro power amps that use multiple rails, so I'm guessing they are probably doing just what you suggest. It's certainly a good idea where you need the efficiency.
I've had a look at your power supply. I like it a lot! The soft-start circuit is a nice touch. Very clever the way you have used the split rails on the '358 to power the relays.
Circuits that rely on short term overload capability always worry me however. Maybe a PTC would be a better choice instead of the 20W resistor?
I'd like to see a larger spacing between the mains terminals and the mounting screws. Maybe you're planning on using plastic hardware, but I'm sure a lot of people will want to build your design, and you can't always assume they're gonna build it the same way.
Lastly, don't forget to terminate the unused inputs on the '00.
Cheers,
Ralph.
I know there are some pro power amps that use multiple rails, so I'm guessing they are probably doing just what you suggest. It's certainly a good idea where you need the efficiency.
I've had a look at your power supply. I like it a lot! The soft-start circuit is a nice touch. Very clever the way you have used the split rails on the '358 to power the relays.
Circuits that rely on short term overload capability always worry me however. Maybe a PTC would be a better choice instead of the 20W resistor?
I'd like to see a larger spacing between the mains terminals and the mounting screws. Maybe you're planning on using plastic hardware, but I'm sure a lot of people will want to build your design, and you can't always assume they're gonna build it the same way.
Lastly, don't forget to terminate the unused inputs on the '00.
Cheers,
Ralph.
Here's a turn-up for the books.
I was just chatting with my supervisor (who recently generously gave me a gorgeous pair of Infinity RS-5b speakers), and it turns out the first amplifier that drove my Infinity speakers, back in the mid-80's, was... wait for it... an ETI5000!
My supervisor built a pair when he was at Sydney Uni. Apparently in order to get really good distortion levels took quite a bit of trial and error, mainly in optimising the power wiring (and grounding). He spent quite a bit of time with an old HP audio spec-an, fiddling with power rail connections and such-forth.
So now I know I'm on the right track 🙂
Cheers,
Suzy
I was just chatting with my supervisor (who recently generously gave me a gorgeous pair of Infinity RS-5b speakers), and it turns out the first amplifier that drove my Infinity speakers, back in the mid-80's, was... wait for it... an ETI5000!
My supervisor built a pair when he was at Sydney Uni. Apparently in order to get really good distortion levels took quite a bit of trial and error, mainly in optimising the power wiring (and grounding). He spent quite a bit of time with an old HP audio spec-an, fiddling with power rail connections and such-forth.
So now I know I'm on the right track 🙂
Cheers,
Suzy
An update
Hi guys,
I've (finally) got my boards back, and am part way through populating them. While I wait for my capacitors to wing their way from Digikey, I thought I'd post a couple of pics:
Cheers,
Suzy
Hi guys,
I've (finally) got my boards back, and am part way through populating them. While I wait for my capacitors to wing their way from Digikey, I thought I'd post a couple of pics:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Cheers,
Suzy
Populated monoblocks
Hi guys,
Here's a couple of photos of a populated monoblock, mounted to its heatsink. They have a nice weight to them. I'm now building the rest of the amplifier, complete with a pair of thumping great toroidal transformers.
It's taken a while, as I don't have terribly much spare time to devote to the project these days, but it's plenty rewarding.
More details of the design are on a webpage I put together, at http://www.littlefishbicycles.com/poweramp/index.html
Cheers,
Suzy
Hi guys,
Here's a couple of photos of a populated monoblock, mounted to its heatsink. They have a nice weight to them. I'm now building the rest of the amplifier, complete with a pair of thumping great toroidal transformers.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
It's taken a while, as I don't have terribly much spare time to devote to the project these days, but it's plenty rewarding.
More details of the design are on a webpage I put together, at http://www.littlefishbicycles.com/poweramp/index.html
Cheers,
Suzy
Wish we had parts of that quality here!
So how does the final product sound??? I'm sure you've run it with your preamp, even if not at great power levels...
Cheers
So how does the final product sound??? I'm sure you've run it with your preamp, even if not at great power levels...
Cheers
I must confess that I haven't yet powered it up. I figured I'd do all the power supply wiring properly first.
I'm actually a little leery of just applying power to it - I imagine there could be terrible consequences if something isn't right. What's the usual procedure for smoke testing large amps? I imagine a few ohms in series with the transformer would probably prevent most fires...
Cheers,
Suzy
I'm actually a little leery of just applying power to it - I imagine there could be terrible consequences if something isn't right. What's the usual procedure for smoke testing large amps? I imagine a few ohms in series with the transformer would probably prevent most fires...
Cheers,
Suzy
Hi Suzy,
My usual suggestion is to put series incandescent lamps on both rails. If anything 'funny' happens, the lamps light up, and you know that you've saved some $$$... lamps tend to have a longer life than series resistors when used this way.... 🙂
Start with zero-biased outputs, do a quick 'scope test to verify its actually working, then bias it. The rest of the testing, including resistive and resistive-capacitive loads can be used to verify that your amp isn't going to misbehave and kill your loudspeaker's HF units...
Cheers!
My usual suggestion is to put series incandescent lamps on both rails. If anything 'funny' happens, the lamps light up, and you know that you've saved some $$$... lamps tend to have a longer life than series resistors when used this way.... 🙂
Start with zero-biased outputs, do a quick 'scope test to verify its actually working, then bias it. The rest of the testing, including resistive and resistive-capacitive loads can be used to verify that your amp isn't going to misbehave and kill your loudspeaker's HF units...
Cheers!
suzyj said:
My normal method is some 10R 1/2W resistors which are cheaper than a fuse if there is something amiss. A quick read across the resistor allows you to check current.
If you can, go for potted TXs (RS Components has the Talema range) to avoid any chance of buzz - they also look much nicer than the unpotted ones (audio jewellery again).
Your PCBs look great. Who did you get to fabricate them? I am trying to get some low volume fabs done at the moment. How was the soldering experience with 4oz Cu?
Nigel
nigeljking said:
I bought a pair of cheapy Jaycar 300VA 40-0-40 Toroids. They looked to be reasonably well made. I'll give them a go for starters, but may end up getting something better down the track.
I had BEC in Queensland do the PCBs. They do a 16.6" x 10.6" panel for ~$400-500, and duplicates for ~$80-100. I put two power amps, a 50W (2 FET) version of the power amp, and a couple of different power supply boards on the panel, and asked for a pair of panels. They're pretty good for hobby stuff (ie cheap) but we've drifted away from them at work because we've had a couple of quality issues.
Soldering was a doddle. I have a really gorgeous Metcal soldering iron in my lab at work, which is good for 80W or so. With the appropriate tip, it can solder anything from 0402 chip parts right up to 1/4" terminals. Best iron I've ever used.
Cheers,
Suzy
Hi suzy
i just want to say congratulations on the professional
job you have done, us diyers dont always do this good
quality of work, you are truly amazing
john
i just want to say congratulations on the professional
job you have done, us diyers dont always do this good
quality of work, you are truly amazing
john
suzyj said:
Thanks for the info. It seems difficult to find PCB fabs in Aus that handle low volumes for a reasonable price.
Being realistic, unless they buzz they should be fine. In an existing setup I have 4 300VA ILP Txs, that have a very small amount of buzz on initial startup until the back EMF kicks in (no soft start, so the lights always dim a little). Now if you were talking about the quality of the caps from Jaycar that could be a different matter.
Iron wise I use a combination of Weller TCP and a MiniScope. For years I just used the Scope - I always liked the instant heat.
If you continue with the hifi bug you must investigate active crossovers. They make a huge difference. I am part way through a new pair of amps each with 4 amp modules in them. And if you are really enthused you might like to consider building an active dipole designed by Siegfreid Linkwitz which has some very enthusiastic owners. See linkwitzlabs.com.
Nigel
Oops one more question - how do you panelise your boards? I am just using FreePCB to create my layouts and gerbers.
thanks
Nigel
thanks
Nigel
nigeljking said:
I've got a Weller TCP iron at home. They're pretty-much ubiquitous. Once you've been spoilt by a really good iron it's hard to go back.
At some point (probably after I've finished writing my thesis) I was thinking of building some speakers. Lynn Olson's Ariels look to be a fairly nice design. Certainly the woodwork involved got the juices flowing.
nigeljking said:
I'm using Protel. I just cut and paste (using paste special, to allow duplicate designators).
The situation with PCBs in Aust has improved markedly since the Internet came along. It wasn't that long ag when board houses would sneer at you if you wanted less than fifty boards. I think it's much more competitive these days.
Cheers,
Suzy
Very nice work Suzy!
It looks like everything fitted together perfectly!
Maybe you can post a picture of the underside?
Congratulations,
Ralph
PS. I've also had a few issues with BEC recently. I think they had some staff leave, and for a while the quality wasn't too good. Which was a pity, because before that the quality was excellent. But they may be back on track now.
It looks like everything fitted together perfectly!
Maybe you can post a picture of the underside?
Congratulations,
Ralph
PS. I've also had a few issues with BEC recently. I think they had some staff leave, and for a while the quality wasn't too good. Which was a pity, because before that the quality was excellent. But they may be back on track now.
ralphs99 said:
Thanks.
Here's what it looks like from the bottom:
An externally hosted image should be here but it was not working when we last tested it.
Boring, huh!
BEC can be really, really good when they're on their game. I've had them do boards with 7 thou tracks and spaces (horrid great things with 240 pin chips). It's just occasionally things pass through the cracks. That's fine when it's hobby stuff (as long as you spot the problems before you solder hundreds of dollars of parts to the boards) but for work stuff, it's unacceptable.
Cheers,
Suzy
Hi Suzy,
Boring? Not at all! The under side pictures show the same attention to detail as those of the top side. I was interested in the way you heatsink the drivers.
I've just had a look at your write-up. Truely excellent! I especially appreciated your discussion about the stability of the amplifier. A topic that too often gets very little attention. Thankyou!
I hope you get to do some performance measurements to see how the simulations compare.
I'm also looking forward to reading about your listening tests!
Cheers, Ralph
Boring? Not at all! The under side pictures show the same attention to detail as those of the top side. I was interested in the way you heatsink the drivers.
I've just had a look at your write-up. Truely excellent! I especially appreciated your discussion about the stability of the amplifier. A topic that too often gets very little attention. Thankyou!
I hope you get to do some performance measurements to see how the simulations compare.
I'm also looking forward to reading about your listening tests!
Cheers, Ralph
ralphs99 said:
Thankyou for the compliments. A bunch of 50W 1Ohm power resistors just turned up on my desk from Farnell. I'll pick up another couple of Conloy heatsinks on the weekend and knock together a huge dummy load so that I can test them.
I've noticed a lot of hatred of lateral MOSFETs on DiyAudio, and can't help but think most of the bad experiences that people have with them appear to be attributable to oscillation. Hence I thought it would be useful to run through the compensation aspects of the amplifier fairly thoroughly.
Of course all the simulations in the world are useless if the layout introduces too many parasitics, so I've really strived to do a good, clean layout.
Speaking of such things, I noticed on another couple of threads some talk about redesigning the AEM6000 for flatpack transistors. I guess that means that there are a few people who might be interested in boards. Doing the math, if there's interest in more than a dozen or so boards, then the costs come down to around $AU50-60 per board.
Would there be any interest? Is this even the right place to post such a thing?
Anyway, I'm getting ahead of myself - I should get them up and running and properly sorted first.
Cheers,
Suzy
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