Progress on the 6 channel amp.
I have removed the old amps (I'll reuse them somewhere) and installed the new ones. New holes for screws, as the old ones didn't line up exactly with the new ones. Speaking of screws, I use ordinary sheet metal screws, you know, with the course thread. I just drill the appropriate size hole and drive them in. I've read about others tapping holes, and breaking taps, when there really isn't any need. Through many different amp builds, I've never had a problem.
I have made up a soft start for the power supply and it is very simple. It uses a 10 amp thermistor that is bypassed with a pair of relays (in parallel). The design is adapted from a National Semi power supply ap note and uses the power supply voltage to close the relays.
The 10 resistors and zener cut the rail voltage to 12VDC. It has no delay, but relies on the fact that the power supply needs to be up before the relays close. I can add a delay if I find this is not working as expected.
I have removed the old amps (I'll reuse them somewhere) and installed the new ones. New holes for screws, as the old ones didn't line up exactly with the new ones. Speaking of screws, I use ordinary sheet metal screws, you know, with the course thread. I just drill the appropriate size hole and drive them in. I've read about others tapping holes, and breaking taps, when there really isn't any need. Through many different amp builds, I've never had a problem.
I have made up a soft start for the power supply and it is very simple. It uses a 10 amp thermistor that is bypassed with a pair of relays (in parallel). The design is adapted from a National Semi power supply ap note and uses the power supply voltage to close the relays.
The 10 resistors and zener cut the rail voltage to 12VDC. It has no delay, but relies on the fact that the power supply needs to be up before the relays close. I can add a delay if I find this is not working as expected.
My original idea for a power switch for this amp didn't pan out (capacitive touch switch) so I've added a rocker switch to the back panel. This beats turning the thing off by unplugging it and since this amp will remain on for most of the time, this is as convenient as I need.
I vacuumed out all of the metal cuttings from the drilling and I'm ready to put the power supply boards back in. I managed to drop it when I took it out and though I didn't damage it, I broke 1 fuse and lost another. I was running on empty when I finished this before and I don't have any replacements. Not a big deal - I have plenty to do before I use this amp again. I want to completely finish it this time.
I've tried something different for thermal compound. When I built the heatsink, I used a stick lubricant that has paraffin and silicone. This has proven to be a very effective thermally conductive compound and I have used it exclusively for this amp. All of the drivers, outputs and Vbe multipliers have this.
It occurred to me when I spent time looking at Digikey for some new thermal grease (mine is old and has taken on a "cottage cheese" consistency). I found this stuff on the web site that looks similar to the stick lub I have, but it is a thermal compound:
It's not cheap - $30 Canadian. I believe my substitute is just as good at a lot lower price ($5). Time will tell.
I vacuumed out all of the metal cuttings from the drilling and I'm ready to put the power supply boards back in. I managed to drop it when I took it out and though I didn't damage it, I broke 1 fuse and lost another. I was running on empty when I finished this before and I don't have any replacements. Not a big deal - I have plenty to do before I use this amp again. I want to completely finish it this time.
I've tried something different for thermal compound. When I built the heatsink, I used a stick lubricant that has paraffin and silicone. This has proven to be a very effective thermally conductive compound and I have used it exclusively for this amp. All of the drivers, outputs and Vbe multipliers have this.
It occurred to me when I spent time looking at Digikey for some new thermal grease (mine is old and has taken on a "cottage cheese" consistency). I found this stuff on the web site that looks similar to the stick lub I have, but it is a thermal compound:
It's not cheap - $30 Canadian. I believe my substitute is just as good at a lot lower price ($5). Time will tell.
Thank you spind. 🙂
It was turning into a blog there...not unusual, I guess. No abstract design points to debate, just building. Boring for many.
I have the power supply boards back in - took a break to burn some leaves, twigs and dead grass, old speakers, bodies...oops! in my backyard (beautiful day here).
I am trying to route the wires neatly and I think I'll need to drill some more holes in the bottom, for tie downs. More metal cuttings to vacuum out.
It was turning into a blog there...not unusual, I guess. No abstract design points to debate, just building. Boring for many.
I have the power supply boards back in - took a break to burn some leaves, twigs and dead grass, old speakers, bodies...oops! in my backyard (beautiful day here).
I am trying to route the wires neatly and I think I'll need to drill some more holes in the bottom, for tie downs. More metal cuttings to vacuum out.
It's the little things that add up and make a big difference. To be able to secure the leads that run from the power supply boards back to the transformer may seen insignificant, but that's not the case. These are high power AC lines and keeping them in place and away from other wires (in this case the output leads that run along the bottom of the case) is bound to pay off.
A single tie wrap on each side holds it.
I put the transformer in and took care of the ground scheme. Here it can be seen that the chassis ground is connected directly to the IEC, but is isolated from the main star ground by the 10 watt resistor bypassed with opposing diodes. I have set up the star ground here, with returns from the speaker binding posts, the power supply boards and the transformer centre tap.
I've found that this is the best way to set up the ground and I haven't had any problems with hum or ground loops.
With the transformer and ground scheme taken care of, all I have left to finish for the power supply is to install the new soft start board.
I added a pair of aluminum angles to the side shield to mount the board. I hooked it up and turned it on (I put a 5 amp fuse in the SS board) and it worked, but I haven't connected the relay circuit yet, so I can't say if it will be effective. The fuse didn't blow, so the thermistor is cutting the inrush current. A test of the soft start will be if it the 5 amp fuse blows when the relays kick in.
I have the power leads to each amp module to run and the input leads, plus a few odds and ends before I can turn my attention to the outside of the case. I have the front panel finished (seen earlier in this thread) but I'm not quite sure how I will close the top.
A single tie wrap on each side holds it.
I put the transformer in and took care of the ground scheme. Here it can be seen that the chassis ground is connected directly to the IEC, but is isolated from the main star ground by the 10 watt resistor bypassed with opposing diodes. I have set up the star ground here, with returns from the speaker binding posts, the power supply boards and the transformer centre tap.
I've found that this is the best way to set up the ground and I haven't had any problems with hum or ground loops.
With the transformer and ground scheme taken care of, all I have left to finish for the power supply is to install the new soft start board.
I added a pair of aluminum angles to the side shield to mount the board. I hooked it up and turned it on (I put a 5 amp fuse in the SS board) and it worked, but I haven't connected the relay circuit yet, so I can't say if it will be effective. The fuse didn't blow, so the thermistor is cutting the inrush current. A test of the soft start will be if it the 5 amp fuse blows when the relays kick in.
I have the power leads to each amp module to run and the input leads, plus a few odds and ends before I can turn my attention to the outside of the case. I have the front panel finished (seen earlier in this thread) but I'm not quite sure how I will close the top.
Nice work John. You don't mess around!
Say, who makes those white terminal blocks shown near the IEC connector?
Say, who makes those white terminal blocks shown near the IEC connector?
andy_c said:
Thanks Andy,
I only mess around here...🙂
Those terminals are from The Source By Circuit City (yes, a mouthful - it used to be Radio Shack). They were on sale for $1 or something and I grabbed a handful. They are actually longer, the ones in the pic were cut.
john:
very nice work!!!
but be careful - someone may want to debate your choice of wire colors
😀
mlloyd1
very nice work!!!
but be careful - someone may want to debate your choice of wire colors
😀
mlloyd1
Thanks for that info John. I'll have to see if I can find something like that at Mouser. Nice and safe for high voltages.
mlloyd1 said:
Thanks,
I'm surprised it hasn't been the topic of huge thread or two - "wire insulation colour: I don't believe it make a difference, any input?" 😀
My toroid for this project has funny lead colours - the primary's fine, black, but the secondary is white and red, with the red as the centre tap. Shocking!
andy_c said:
Yes, these are great. All of the conductive parts are "out of reach".
I've epoxied in the aluminum wire race for the input leads that I removed (with extreme difficulty) earlier. Another tactic to keep everything neat and in place. Worth the extra effort, IMO.
Done for now, I need to let the epoxy cure and I'm back to work tomorrow.
I'm still thinking about the top...I have some 1/2" aluminum tubes that are long enough to go front to back, if I used these spaced about a 1/4" apart. Maybe good, maybe not. I'll mock it up to see.
MJL21193 said:
You are only surprised because you haven't been "enlightened" by the self-appointed experts in this area. 😀
Those terminals are "european barrier strips", they come
in any size from 3mm to 10mm (holes) real handy for
star grounds/rails .. you can cut them (they come in groups
of 8-12)..
OS
Mouser has them, a direct search of "european" won't get
anything. But "terminal blocks" 8mm ,10mm , 12mm gets it.
Datasheet calls them "eurostyle" ,molex makes them..
http://www.molex.com/molex/products/datasheet.jsp?part=active/0391001210_TERMINAL_BLOCKS.xml&channel=Products&Lang=en-US
OS
anything. But "terminal blocks" 8mm ,10mm , 12mm gets it.
Datasheet calls them "eurostyle" ,molex makes them..
http://www.molex.com/molex/products/datasheet.jsp?part=active/0391001210_TERMINAL_BLOCKS.xml&channel=Products&Lang=en-US
OS
These terminal blocks caused me to loose 15% on my total number of points when I presented my "end work" at school. (50 Watt guitar amp)
It was 1970 then and these terminal blocks seemed to be "Do not use!!!" in electronic equipment. True as far as the jury members were right?
They are used on a regular basis then and today and why not?
Nice amp I must say, really nice.
Tarzan
It was 1970 then and these terminal blocks seemed to be "Do not use!!!" in electronic equipment. True as far as the jury members were right?
They are used on a regular basis then and today and why not?
Nice amp I must say, really nice.
Tarzan
andy_c said:
Ah, I should have know better. This now has me second guessing my choices...perhaps a different shade of green will sound fresher, less moody...or, instead of the cold black I go with a warm and smoky charcoal gray...
🙂
Tarzan said:
Hi Tarzan, how's Jane? 😀
I hope you found some non-violent way to make that instructor suffer for the wrong he commited...
I think these are mains rated - seem heavy enough, I'm not going to worry. But the colour...yes, the colour may be to stark, to sterile and this will undoubtedly have an effect on the sound.
🙂
Thanks, BTW.
454Casull said:
I'm not sure. I didn't buy it. It is not very good, so Jobmate would fit. I had 3 or 4 of them (given to me) and all but one is broken - the plastic breaks when you tighten it. Don't know my own strength when I squeeze the grip, I guess.
MJL21193 said:
I just did some searching at Mouser. The easiest way to find them seems to be to search on "39100" (without quotes), then select Molex as the vendor, then "terminal blocks" as the category. They have voltage ratings of 300V and 600V, with current ratings from 20A to 65A. That should cover it I think 🙂.
Well I'm gobsmacked.
We can find terminal blocks in any old hardware or DIY shop here. Are they truly difficult to find?
Brian.
We can find terminal blocks in any old hardware or DIY shop here. Are they truly difficult to find?
Brian.
andy_c said:
I just looked at the package. Rating is 35A, 600V.
Pingrs said:
It used to be easier to find these things here too, but more and more the small stores are getting swallowed up by big ones and the ones that are left need to trim the inventory to compete.
The best bet here for most of this stuff is to find it and buy it on the internet.
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