Thanks jaycee, but I've already submitted the boards for processing; im going to do the drilling myself, got a nice craft drill that works really nicely for that kind of thing.
I ordered my components today, should have a quoted price by tomorrow, but its pretty cheap; R180 ($30) per channel, for amp and PS. If I get the parts by the weekend, I'll get building soon.
2 Final Questions; the transformer again: I've yet to buy one, the PS schematic for the DX on Greg Erskines website shows the Amp running off two 200VA transformers, single-tapped.. Is this better than a 225VA central tapped transformer, and will the circuit even work with a single tapped? I say this, because I set up a spice simulation of the PS, wouldnt work properly with a center tapped, but fine with two single taps. And is 225VA going to be enough to run this amp? Also, I'm bolting the transformer to my case; with enough ventilation, that should be sufficient cooling?
My other question; this is a three stage amp, as Nordic said above, so I'm checking one final time, I don't need to plan a preamp, at least not yet, can always throw one in later?
So yeah.. got some nice heatsinks, threw up a picture of them, they look pretty at high quality, had to scale them down so the jpgs were small enough :/ Still, should be enough for 50W per channel im sure. Just gotta grab a nice enclosure now; trying to find a suitable base.
I ordered my components today, should have a quoted price by tomorrow, but its pretty cheap; R180 ($30) per channel, for amp and PS. If I get the parts by the weekend, I'll get building soon.
2 Final Questions; the transformer again: I've yet to buy one, the PS schematic for the DX on Greg Erskines website shows the Amp running off two 200VA transformers, single-tapped.. Is this better than a 225VA central tapped transformer, and will the circuit even work with a single tapped? I say this, because I set up a spice simulation of the PS, wouldnt work properly with a center tapped, but fine with two single taps. And is 225VA going to be enough to run this amp? Also, I'm bolting the transformer to my case; with enough ventilation, that should be sufficient cooling?
My other question; this is a three stage amp, as Nordic said above, so I'm checking one final time, I don't need to plan a preamp, at least not yet, can always throw one in later?
So yeah.. got some nice heatsinks, threw up a picture of them, they look pretty at high quality, had to scale them down so the jpgs were small enough :/ Still, should be enough for 50W per channel im sure. Just gotta grab a nice enclosure now; trying to find a suitable base.
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Yep, no preamp needed, at worst you can increase gain for weak sources by adjusting a resitor or two...
There is no reason a centre tapped transformer should not work... (50 to 55V centre tapped), as only one bridge rectifier is needed. and even a dual secondary transformer will get two of its taps connected for this goal anyway in the basic configuration.
Just a reminder to check your yellow pages for a source of transformers rather than the traditional outlets... we have many small industries, and their machines are reliant on haveing a source of transformers and repairs to keep going... at much lower rates than you'd expect... I can on average have two 300VA EI's made for the price of one toroidal from RS... The company is called AC DC, and they may have an outlet in your neck of the woods, I know of branches down here in CT and JHB, so I can;t see why thry would skip durbs.
Where did you get that sink...? its lovely
I would seriously push for more than 200VA, I am running on 300VA per channel, and those babies get quite hot after a night of playing.
There is no reason a centre tapped transformer should not work... (50 to 55V centre tapped), as only one bridge rectifier is needed. and even a dual secondary transformer will get two of its taps connected for this goal anyway in the basic configuration.
Just a reminder to check your yellow pages for a source of transformers rather than the traditional outlets... we have many small industries, and their machines are reliant on haveing a source of transformers and repairs to keep going... at much lower rates than you'd expect... I can on average have two 300VA EI's made for the price of one toroidal from RS... The company is called AC DC, and they may have an outlet in your neck of the woods, I know of branches down here in CT and JHB, so I can;t see why thry would skip durbs.
Where did you get that sink...? its lovely
I would seriously push for more than 200VA, I am running on 300VA per channel, and those babies get quite hot after a night of playing.
They are pretty sinks! I got them off one off the senior technician at uni, traded him an old text book for them and the printing of my 4 PCBs; his son has just started the same degree as me. He was really supportive of me anyway, gave me some great guidance on building the amp. So, a pretty sweet deal! I think they were supposed to be used for motor drive transistors, but the company went under, had to dump most of their stuff, my senior technician got donated a whole lot of them, and now two of them are all mine. They were custom made by a company here in Durban i think, rather tasty looking.Yeah, I took your much earlier advice, phoned the smaller places and found cheaper transformers; think a 400va, center tapped was about R450.. I'll check again before I go off to buy one. I've checked for AC DC in my phone book, the only possible match is AC-DC Dynamics; I'll give them a phone call tomorrow, see if they produce transformers. In the end, I think I'll try and play safe; probably grab 2 0-25, Single tapped 350VA transformers; as long as they're not too much more expensive.
As for the power transistors, I decided to avoid Mantech because you warned me about those fakes. So I got a referral by Ron Tomlin Electronics in Durban to go to a place called Protec; they have a huge stock in shop, and focus mainly on audio; the shop is adorned with speakers, custom amps and DJ stuff. They stocked both those transistors, at R15 each, hoping they're the real deal.
Oh, and one other thing. I got standard mica, thermal conductive insulators for the transistor; will that and a relatively thin layer of thermal paste do the trick for attaching the transistors to the heatsink, I've only done smaller heatsinks for some regulators on power supplies, never anything quite so daunting?
I'll get my PCBs tomorrow or friday, throw some photos up when i start building. I think Im pretty confident from here on out, at least as far as construction is concerned, but I will need some of you wizened amp-builders' help afterwards; on how best to set up that bias.
Again, thanks a lot
I think Carlos even build some with 3055/2095 jsut to check... so try your transistors...
Yep, AC DC Dynamics is the co I use...
If you use them, they can custom wind the transformers.... so ask for a 26V, loaded with the amp it will give you the 35VDC, although anything up to about 38V is good.
Can you get me a phone number for the transistor shop... would like to get a reliable SA source.. found one, but need to buy in 100's...
The paste is just to fill microscopic air spaces, to avoid a thermal flask effect caused by traped air... so it makes the thermal interface more efficient... you get thermal PASTE which is literaly glue, but I don't think that is what you are thinking about...
Buy a 2.5mm drill bit, drill the holes (prefferably with a drill press for straightness) and tap an M3 thread in for M3 screws...
I'll take some measurements of my last DX classic for bias setting. (are you building the original or HRII - sorry no shortterm memory)
Yep, AC DC Dynamics is the co I use...
If you use them, they can custom wind the transformers.... so ask for a 26V, loaded with the amp it will give you the 35VDC, although anything up to about 38V is good.
Can you get me a phone number for the transistor shop... would like to get a reliable SA source.. found one, but need to buy in 100's...
The paste is just to fill microscopic air spaces, to avoid a thermal flask effect caused by traped air... so it makes the thermal interface more efficient... you get thermal PASTE which is literaly glue, but I don't think that is what you are thinking about...
Buy a 2.5mm drill bit, drill the holes (prefferably with a drill press for straightness) and tap an M3 thread in for M3 screws...
I'll take some measurements of my last DX classic for bias setting. (are you building the original or HRII - sorry no shortterm memory)
The original DX, im playing it cool for now. I read Greg Erskine's instructions on biasing; they're pretty straight forward... But its seldom life goes smoothly, so any help would be grand
I'll get in touch with AC DC tomorrow, see what they can offer me.
I was speaking of thermal paste for CPU heatsinks, etc... The white stuff, for enhancing thermal conductivity. It is a little sticky.. wouldnt call it glue. Anyway, I've got tubes of the stuff around, from working with PCs, was just checking if it was even necessary, from my experience with heatsinks in computers it is, and this old sony has a smear under each of its transistors.. Just checking.
That company is called Protech or PQ Sound, seems like a merged company, based off Umgeni Road in Durban central. Their number is 031 313 4700; probably best if you see if my transistors are worthwhile first, before making any arrangements.
As for drills, I have a drill press, but that technician recommended a hand-held drill; I have a craft drill, about the size of an electric tooth brush, was going to use that... I'll decide whats best when I get drilling.
I'll get in touch with AC DC tomorrow, see what they can offer me.
I was speaking of thermal paste for CPU heatsinks, etc... The white stuff, for enhancing thermal conductivity. It is a little sticky.. wouldnt call it glue. Anyway, I've got tubes of the stuff around, from working with PCs, was just checking if it was even necessary, from my experience with heatsinks in computers it is, and this old sony has a smear under each of its transistors.. Just checking.
That company is called Protech or PQ Sound, seems like a merged company, based off Umgeni Road in Durban central. Their number is 031 313 4700; probably best if you see if my transistors are worthwhile first, before making any arrangements.
As for drills, I have a drill press, but that technician recommended a hand-held drill; I have a craft drill, about the size of an electric tooth brush, was going to use that... I'll decide whats best when I get drilling.
I would still go for the drill press, God knows, I have a number of diffirent drills, but would never concider handdrilling for that job again... it is humanly imposible to drill down in a straight line.... I tired many times...
I still tap by hand though, except straight through holes in thinnish plates... I stick the tap in my small battery powered drill and set the torque so that the tap won't snap if it gets stuck...
Also use some lubricant, if nothing else available try some WD40...
I still tap by hand though, except straight through holes in thinnish plates... I stick the tap in my small battery powered drill and set the torque so that the tap won't snap if it gets stuck...
Also use some lubricant, if nothing else available try some WD40...
vegetable oil is a reasonable alternative lubricant. Some lub must be used in tapping aluminium.Nordic said:
The inertia of the chuck and clutch mechanism is sufficient to break a small tap even when slowly machine driven. You need the compliance of a sensitive hand to absorb the shock of a sudden stop. Malleable materials require a chip breaker, This is usually done by technique rather than buying the special taps for each material. Two half turns forward and one half turn backward, then take up the slack and repeat.
Absolutely, which is why I do not use the tap in my drillpress...
This is only for small things like heatspreaders etc...
for normal tapping (deeper holes) I tap by hand... and depending on the tap you use, 2 turns forward my be too much, as the material is not brittle like other metals, which form small enough chunks to get in the "cleaning grooves" of the tap.
This is only for small things like heatspreaders etc...
for normal tapping (deeper holes) I tap by hand... and depending on the tap you use, 2 turns forward my be too much, as the material is not brittle like other metals, which form small enough chunks to get in the "cleaning grooves" of the tap.
A lot to consider there, but I've got some unexpected help.
My girlfriend and her father, are both silver/gold smiths; jewelers; so she is quite proficient with the drill press when working on some of her pieces, and has all the delicate hands required; working with jewelery makes electronics look easy. Anyway, I showed her the PCBs, explained what I had to do; she thinks it'll be pretty simple, and she offered to help me drill them. We'll get kicking tomorrow, I'll keep in mind your tips on tapping, she mentioned hand-tapping somewhere, i think.. So we'll probably do that... Let you know how it went.
On another topic and mainly aimed at Nordic as he knows the local market; transformers. I got in touch with AC DC, they were helpful enough, but steeper than other branches; a 300VA was around R550, while another company, VA, offered me R530 for a 400VA, R470 for a 300VA, or R410 for a 250VA, any voltage rating I wanted, custom wound, custom tapped. So I was going to go with them.. But! I checked bidorbuy.co.za (SA's Ebay), and I saw some 0-29V, 250VA trans for R200, which sound pretty neat. In addition, others can be requested, so I requested a 300VA or 400VA.
One more question, for 35-36Vdc, and a centre tapped transformer, what Vrms should one be getting at my transformer outputs? Ie: 25-0-25, 55-0-55, etc. I ask this, cos I was sure it was 25-0-25, but I've been building a somewhat similar power supply in multisim/SPICE, for a uni design project, putting out 40-0-40Vdc. My calculations said I needed +-29-0-29Vrms transformer for correct rating, but my SPICE simulation didn't give me the right Voltage with that transformer, and needed a considerably bigger transformer to give me the 40-0-40. So yes, for a center tapped transformer, requiring 35-36Vdc, what Vrms should I be looking at?
Got my SC5200 and SA1943 today, picking up the rest tomo, I'll put some pre-build photos up soon.
My girlfriend and her father, are both silver/gold smiths; jewelers; so she is quite proficient with the drill press when working on some of her pieces, and has all the delicate hands required; working with jewelery makes electronics look easy. Anyway, I showed her the PCBs, explained what I had to do; she thinks it'll be pretty simple, and she offered to help me drill them. We'll get kicking tomorrow, I'll keep in mind your tips on tapping, she mentioned hand-tapping somewhere, i think.. So we'll probably do that... Let you know how it went.
On another topic and mainly aimed at Nordic as he knows the local market; transformers. I got in touch with AC DC, they were helpful enough, but steeper than other branches; a 300VA was around R550, while another company, VA, offered me R530 for a 400VA, R470 for a 300VA, or R410 for a 250VA, any voltage rating I wanted, custom wound, custom tapped. So I was going to go with them.. But! I checked bidorbuy.co.za (SA's Ebay), and I saw some 0-29V, 250VA trans for R200, which sound pretty neat. In addition, others can be requested, so I requested a 300VA or 400VA.
One more question, for 35-36Vdc, and a centre tapped transformer, what Vrms should one be getting at my transformer outputs? Ie: 25-0-25, 55-0-55, etc. I ask this, cos I was sure it was 25-0-25, but I've been building a somewhat similar power supply in multisim/SPICE, for a uni design project, putting out 40-0-40Vdc. My calculations said I needed +-29-0-29Vrms transformer for correct rating, but my SPICE simulation didn't give me the right Voltage with that transformer, and needed a considerably bigger transformer to give me the 40-0-40. So yes, for a center tapped transformer, requiring 35-36Vdc, what Vrms should I be looking at?
Got my SC5200 and SA1943 today, picking up the rest tomo, I'll put some pre-build photos up soon.
Wow AC DC prices went up then as my last two 300VAs were R800 and something together....
The bridge rectifier will drop some voltage, and it is not a steady amount, it will increase with current drawn... but in practical terms I get a bit under 36V unloaded and 35.5V loaded from a 2x26VAC transformer...
The bridge rectifier will drop some voltage, and it is not a steady amount, it will increase with current drawn... but in practical terms I get a bit under 36V unloaded and 35.5V loaded from a 2x26VAC transformer...
Yep, thats what I thought, I learnt a long time ago not to trust SPICE... just wanted to make sure, I'm gonna order a 350VA/400VA center tapped 26-0-26 on monday. Anyway, I've got all my components at the mo, just need to get to the drill press, have to pick up some drill bits first, a couple in each size hopefully, as those carbide bits have a bad habit of breaking. I was thinking steel, but they blunt so easily on the board... I suppose for 4 boards they'd be fine, but still.
I know .8mm is probably optimal for most holes, but those are just too fragile... I leave holes that small for the factory to deal with...
Personaly I find a 1mm bit is small enough if you use a press, with the hand it wobbles more and makes a bigger hole...
For the medium transistors a 1.2mm bit is good (don't want too small holes as it makes it hard to remove blown parts), and for output pair 1.5 to 2mm is fine...
I buy those cheap bits, R4.50 they do go blunt after some time but at that cost, I don't worry, buy a few at a time... leave minimal bit of drill sticking out from chuck or pinvice..., the trick with those cheap bits is to hold them up to the light to make sure they have a sharp point... many of them are blunt straight from the shop....
P.S. remember some small heatsinks for the driver pair, I don;t remember those being marked in the schematic.
Personaly I find a 1mm bit is small enough if you use a press, with the hand it wobbles more and makes a bigger hole...
For the medium transistors a 1.2mm bit is good (don't want too small holes as it makes it hard to remove blown parts), and for output pair 1.5 to 2mm is fine...
I buy those cheap bits, R4.50 they do go blunt after some time but at that cost, I don't worry, buy a few at a time... leave minimal bit of drill sticking out from chuck or pinvice..., the trick with those cheap bits is to hold them up to the light to make sure they have a sharp point... many of them are blunt straight from the shop....
P.S. remember some small heatsinks for the driver pair, I don;t remember those being marked in the schematic.
Already got the little heatsinks, im sorted! One of my current problems is those inductance coils on the power supply; never made an induction coil, always get them premade, so a tip or two would be nice?
Thanks for the tips on drills; I was going to buy 0.8mm, I'll step that up to 1mm, and I'll check their quality first.
Also, that bias circuit. What's best to build it on? Was going to use vero board, or one of those punched plastic boards with no conduction stuff; advice?
Thanks for the tips on drills; I was going to buy 0.8mm, I'll step that up to 1mm, and I'll check their quality first.
Also, that bias circuit. What's best to build it on? Was going to use vero board, or one of those punched plastic boards with no conduction stuff; advice?
Veroboard is an easy build
The bias servo's are used to set the biasing level as well as keep the amplifier stable through thermal tracking, the transistors should be mounted on the heatsink, between the output pair, and should be isolated.. It is a simple piece of hardware consisting of 3 components.
There are also some drawings on Greg's site... For the Basic DX.
P.S. Some people preffer mounting it through the same screw on top of one of the output transistors to track temperature directly.
Inductance coils do not need to be thick, from what I am seeing in Carlos's builds, I used some damn thick stuff 1.2mm, and it was a pain to wind... 2 layers of 20 turns around the resistors, with thin enameled wire, it is childsplay though.
The bias servo's are used to set the biasing level as well as keep the amplifier stable through thermal tracking, the transistors should be mounted on the heatsink, between the output pair, and should be isolated.. It is a simple piece of hardware consisting of 3 components.
An externally hosted image should be here but it was not working when we last tested it.
There are also some drawings on Greg's site... For the Basic DX.
P.S. Some people preffer mounting it through the same screw on top of one of the output transistors to track temperature directly.
Inductance coils do not need to be thick, from what I am seeing in Carlos's builds, I used some damn thick stuff 1.2mm, and it was a pain to wind... 2 layers of 20 turns around the resistors, with thin enameled wire, it is childsplay though.
Thanks, just never actually wound my own inductor before, didn't know if there was something special I should be doing. Yeah, I know what the bias does, studied it a bit further; just wasn't sure what the best means of putting it together was; I'll get some veroboard.
Ok, things will probably go quiet on my front for a couple days; won't have access to a drill until later in the week now; got a couple design prjects I've been neglecting that are due early this week, and checking and double checking these components has got a little old I'll keep you posted on construction, and if I think of anything before then, I'll shout. Again, thanks for the help guys, especially Nordic and Jaycee, you two really made things easy for me, your advice is most appreciated.
Until later, keep well!
Ok, things will probably go quiet on my front for a couple days; won't have access to a drill until later in the week now; got a couple design prjects I've been neglecting that are due early this week, and checking and double checking these components has got a little old
I'll keep you posted on construction, and if I think of anything before then, I'll shout. Again, thanks for the help guys, especially Nordic and Jaycee, you two really made things easy for me, your advice is most appreciated.Until later, keep well!
A long day... I drilled all my boards, cut them (a mission, as I had to make use of hacksaws, knifes, grenades, small children and other unsuitable hardware). Nevertheless; Its all done! Well.. not quite, I have to mount the PCBs onto my heat sinks, so a couple more holes to drill before I get building. Put up a preeeety pre-build picture, about to pack all that stuff up into a more organized fashion so I can build efficiently.
A couple questions before I call it a night; the schematic and board have terminals ELink + and Elink -... I had been presuming up until now that those are just earth terminals, that I should earth to my chassis.. Just wanting to make sure? And on the chassis base; any recommendations on what metal i should be looking at?
A couple questions before I call it a night; the schematic and board have terminals ELink + and Elink -... I had been presuming up until now that those are just earth terminals, that I should earth to my chassis.. Just wanting to make sure? And on the chassis base; any recommendations on what metal i should be looking at?
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Alright, quick question; I've built one channel, PS, bias and amp, heatsinked and everything. Can I test that off my transformer; i'm picking up a 26-0-26 350VA tomorrow, but I don't have the parts or the time for the second channel just yet. Will running off that transformer blow only one channel, or should it be fine?
Do you want to test both channels off the one 350VA transformer?
The transformer does not push curent... it gets drawn to sustain x voltage over x resistance.. (ohms law) so it will not "blow" your channel....
It should work, just keep an eye (thumb) on the transformer when driving it hard...
Adjust the bias trimpot until you get about 2.84K between the two points where it connects to the board, this should put you in a safe ballpark.
Please go buy two 10R 10 to 17W resistors.. these go in the + ad _ rail between the amp and the psu... attach multimeter around it on DC mode...
If on power-on DC is much higher than 3V, power off, and adjust the bias trimpot a little, check again, to see if you are turning screw in right direction.... You want to have about 550mV over the resistor in the + rail....
By quickly powering off the amp and giving it a few seconds to cool down offended parts, you can get the amp tuned in without blowing any transistors...
The transformer does not push curent... it gets drawn to sustain x voltage over x resistance.. (ohms law) so it will not "blow" your channel....
It should work, just keep an eye (thumb) on the transformer when driving it hard...
Adjust the bias trimpot until you get about 2.84K between the two points where it connects to the board, this should put you in a safe ballpark.
Please go buy two 10R 10 to 17W resistors.. these go in the + ad _ rail between the amp and the psu... attach multimeter around it on DC mode...
If on power-on DC is much higher than 3V, power off, and adjust the bias trimpot a little, check again, to see if you are turning screw in right direction.... You want to have about 550mV over the resistor in the + rail....
By quickly powering off the amp and giving it a few seconds to cool down offended parts, you can get the amp tuned in without blowing any transistors...
I'm just testing one channel off the 350VA.. but eventually will run both off it, that be ok?
I've got those high power rated resistors, they were recommended on Greg Erskines, so i shall do that. So transformer rating is its tolerance level... should have known that...
Anyway, I'll put a pic of the first amp up once I've hooked it up, just before I blow it thanks Nordic, I'll keep you posted
I've got those high power rated resistors, they were recommended on Greg Erskines, so i shall do that. So transformer rating is its tolerance level... should have known that...
Anyway, I'll put a pic of the first amp up once I've hooked it up, just before I blow it
thanks Nordic, I'll keep you posted- Status
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