Awesome!
Impressive, looks like perfection on that O'scope
So it looks like your amp has no trouble delivering high power now, but because of the lower supply rails, it looks like you need less than 2 ohms to get 1000W.
I'm pretty sure your amp could drive over 1000W into 1 ohm. A 4 ohm sub then for you should be a nice, easy load on that amp!
IMO an amp that can drive a much lower impedance than the speaker you are using, always sounds better, with more powerful and cleaner sounding bass.
BTW, if your load resistors are smoking, than that's a good sign you built one he11 of an amplifer!!! 
Impressive, looks like perfection on that O'scope
So it looks like your amp has no trouble delivering high power now, but because of the lower supply rails, it looks like you need less than 2 ohms to get 1000W.
I'm pretty sure your amp could drive over 1000W into 1 ohm. A 4 ohm sub then for you should be a nice, easy load on that amp!
IMO an amp that can drive a much lower impedance than the speaker you are using, always sounds better, with more powerful and cleaner sounding bass.
BTW, if your load resistors are smoking, than that's a good sign you built one he11 of an amplifer!!!
Re: Awesome!
Thanks again EW,
The insulation on the lead outs is sizzling, the wire gets that hot. The water itself is getting noticeably warmer, with bubbles forming around the resistors.
The fact that it can easily drive such a low impedance is good news, I won't have any concerns at 4 ohms.
I still need to get the LT working and check it's performance. It is a complete duplicate of the one in the original amp, so it should be fine, barring any of my usual missteps.
Here's the winning schematic. The only extra compensation component is the 100pF cap on U4. Without this, there was some nonsense in the lower wave during clipping. None of the extra base stoppers were needed.
I increased the bootstrap R's to 4K, as I felt that ~10mA was too hot for the VAS I am using. No ill effects.
Also, I need to move U3 out to the centre of the heatsink, to get better thermal tracking.
EWorkshop1708 said:Impressive, looks like perfection on that O'scope
BTW, if your load resistors are smoking, than that's a good sign you built one he11 of an amplifer!!!
Thanks again EW,
The insulation on the lead outs is sizzling, the wire gets that hot. The water itself is getting noticeably warmer, with bubbles forming around the resistors.
The fact that it can easily drive such a low impedance is good news, I won't have any concerns at 4 ohms.
I still need to get the LT working and check it's performance. It is a complete duplicate of the one in the original amp, so it should be fine, barring any of my usual missteps.
Here's the winning schematic. The only extra compensation component is the 100pF cap on U4. Without this, there was some nonsense in the lower wave during clipping. None of the extra base stoppers were needed.
I increased the bootstrap R's to 4K, as I felt that ~10mA was too hot for the VAS I am using. No ill effects.
Also, I need to move U3 out to the centre of the heatsink, to get better thermal tracking.
Attachments
Re: Re: Awesome!
well done mate !!!
-dan
MJL21193 said:
Thanks again EW,
The insulation on the lead outs is sizzling, the wire gets that hot. The water itself is getting noticeably warmer, with bubbles forming around the resistors.
The fact that it can easily drive such a low impedance is good news, I won't have any concerns at 4 ohms.
I still need to get the LT working and check it's performance. It is a complete duplicate of the one in the original amp, so it should be fine, barring any of my usual missteps.
Here's the winning schematic. The only extra compensation component is the 100pF cap on U4. Without this, there was some nonsense in the lower wave during clipping. None of the extra base stoppers were needed.
I increased the bootstrap R's to 4K, as I felt that ~10mA was too hot for the VAS I am using. No ill effects.
Also, I need to move U3 out to the centre of the heatsink, to get better thermal tracking.
well done mate !!!
-dan
The higher emitter resistors are good to have at higher rail voltages to help balance the current. The current hogging effect gets worse the higher the rail voltage is and the higher thermal resistance to heatsink is.
If the combination of resistors, rail voltage and thermal resistances are wrong then one transistor will take all the current regardless of how well the matching of Vbe:s and thermal resistances were done.
Have a look at the attached LTSpice simulation, try playing with the values of thermal resistances and changing Gm to reflect different emitter resistor values and see when it runs away
If you multiply effective Gm * Rail voltage * Vbe tempco * thermal resistance you get a number indicating the amplification of mismatch. Vbe tempco = 0.0022V/deg C. When it is 1 there is so much positive feedback that mismatches will get infinite amplification. For 0.5 there will be a gain of 2 for mismatches. This works out to below 0.2 for this amp as the transistors should have very good thermal resistance when mounted directly to the heatsinks.
It might be possible to reduce the resistors a bit, but there isn't really any need I think as there are effectively 16 in parallell driving the loudspeaker. I would worry a bit about the cooling evenness if reducing them though, when using a tunnel like this the transistors furthest from the fan will draw more current.
If the combination of resistors, rail voltage and thermal resistances are wrong then one transistor will take all the current regardless of how well the matching of Vbe:s and thermal resistances were done.
Have a look at the attached LTSpice simulation, try playing with the values of thermal resistances and changing Gm to reflect different emitter resistor values and see when it runs away
If you multiply effective Gm * Rail voltage * Vbe tempco * thermal resistance you get a number indicating the amplification of mismatch. Vbe tempco = 0.0022V/deg C. When it is 1 there is so much positive feedback that mismatches will get infinite amplification. For 0.5 there will be a gain of 2 for mismatches. This works out to below 0.2 for this amp as the transistors should have very good thermal resistance when mounted directly to the heatsinks.
It might be possible to reduce the resistors a bit, but there isn't really any need I think as there are effectively 16 in parallell driving the loudspeaker. I would worry a bit about the cooling evenness if reducing them though, when using a tunnel like this the transistors furthest from the fan will draw more current.
Re: Re: Re: Awesome!
Thanks Luka,
PM me your email and I'll send the file. Simulated performance is very good, with THD at 0.08 % at full output.
Thanks Dan,
With a little perseverance on my part, I could be doing a test run on the subwoofer by tomorrow. I haven't connected it to a speaker yet, so I don't know how it sounds.
Buttoning up a few loose ends like the terminals for speaker connection and the permanent Thiele and Zobel in place. Every step requires a test to see if I have cocked something up, so it's slow going.
I need to figure a way to mount the heatsink to the chassis. One that doesn't conduct electricity or will break if the amp is roughly handled. Maybe some pieces of plexiglass, bent with heat to the right shape.
Squarewave @500Hz. A little blurry again.
luka said:
Thanks Luka,
PM me your email and I'll send the file. Simulated performance is very good, with THD at 0.08 % at full output.
danieljw said:
Thanks Dan,
With a little perseverance on my part, I could be doing a test run on the subwoofer by tomorrow. I haven't connected it to a speaker yet, so I don't know how it sounds.
Buttoning up a few loose ends like the terminals for speaker connection and the permanent Thiele and Zobel in place. Every step requires a test to see if I have cocked something up, so it's slow going.
I need to figure a way to mount the heatsink to the chassis. One that doesn't conduct electricity or will break if the amp is roughly handled. Maybe some pieces of plexiglass, bent with heat to the right shape.
Squarewave @500Hz. A little blurry again.
Attachments
One problem with the LT - decoupling cap on the negative rail was backwards. Nothing happening for a few seconds then poof, up in smoke! Just that cap though. I replaced it and the LT works fine now.
Examined the output just from the LT on the scope. Output goes from 1Vrms at 120Hz to 4.25Vrms at 20Hz, so gain is pretty much on the money.
Connected to the amp with no load the input of 300mVrms at 20Hz will drive the output to maximum voltage (~49Vrms).
I'm getting closer.
Here's how it looks now. Addition of the small board on the end of the heatsink that holds the output terminal block and the Zobel components. As seen in the pic, I have the supply hardwired to the end of the heatsink.
Examined the output just from the LT on the scope. Output goes from 1Vrms at 120Hz to 4.25Vrms at 20Hz, so gain is pretty much on the money.
Connected to the amp with no load the input of 300mVrms at 20Hz will drive the output to maximum voltage (~49Vrms).
I'm getting closer.
Here's how it looks now. Addition of the small board on the end of the heatsink that holds the output terminal block and the Zobel components. As seen in the pic, I have the supply hardwired to the end of the heatsink.
Attachments
Dr.EM said:
Thanks Doc,
Tight! That's how it all fit's.
When we consider that the top half of this large enclosure is taken up with the chimney tubes, I'm not left with much room. Bad enough for space constraints, but running all of the wires back and forth is a bit of a nightmare.
I may have been hasty in thinking I could have a listen tomorrow - there's just too much to do.
One thing I did manage to finish is the mounting for the heatsink. Many trips to Goodwill and other thrift shops has left me with a wide assortment of junk. One of these is a Sharp record player with a cool smoked plexiglas lid. It has some nice 90* corners, so I just cut it into 4 brackets. Screwed these to the aluminum shroud that covers the PS and then to the heatsink. The heatsink shouldn't get hot enough to affect this plastic
Here's it partially assembled. Clearly seen are my brackets, already screwed to the shroud but not to the heatsink yet.
Attachments
danieljw said:i love the amsplab style hard wired layout !!!
i have built a few myself (the actualy ampslab kit also in the signature line and on the avatar pic
from experience this hard wired layout style is very strong in to low impedance loads (2 Ohm 1kW sine sort of thing)
-Dan
Hi Dan,
For kicks, and because I got a bit sick of working on the actual amp, I did a full PC board layout for the entire amp circuit, minus the LT. Now that I have it down to a stable design, I thought it might be a worthwhile exercise.
I was able to make it fairly compact too - 255mm x 70mm (10.25 x 2.75 inches).
If I (when I
) build another one, this is how I'd do it. To wire every thing up like I did, is very tedious.Attachments
More progress. The truly tedious stuff is now done. I have all of the auxiliary boards mounted and wired.
Hopefully everything is correct.
Although I did spend a fairly long time planning this, and even went to the lengths of drawing it out in sketch-up, it's hard to account for everything. Really, as large as the case is, it would be better if it was a bit bigger. Putting different functions on different boards helped with the efficient use of space at the expense of complexity, with wires connecting these boards.
If I had it to do again, I'd do a few things different. As they say: "hindsight is 20/20"
Here's how it looks. Quite tightly packed, but everything fit, so that's all that matters.
I may work up the nerve to give is a try later.
Hopefully everything is correct.
Although I did spend a fairly long time planning this, and even went to the lengths of drawing it out in sketch-up, it's hard to account for everything. Really, as large as the case is, it would be better if it was a bit bigger. Putting different functions on different boards helped with the efficient use of space at the expense of complexity, with wires connecting these boards.
If I had it to do again, I'd do a few things different. As they say: "hindsight is 20/20"
Here's how it looks. Quite tightly packed, but everything fit, so that's all that matters.
I may work up the nerve to give is a try later.
Attachments
MJL21193 said:
Hi Dan,
For kicks, and because I got a bit sick of working on the actual amp, I did a full PC board layout for the entire amp circuit, minus the LT. Now that I have it down to a stable design, I thought it might be a worthwhile exercise.
I was able to make it fairly compact too - 255mm x 70mm (10.25 x 2.75 inches).
If I (when I
The most recent high(ish) power amp i have made was the infamous Quasi's ACTRK600 with 94Vdc rails and 110Vdc driver rail, the layout you just posted is not unlike the layout for this amp and it seems to work very well, i think keeping the output stage grouped together is good from a resistive loss and thermal tracking standpoint on the pcb as long as your heatsink is substantial.
to be completely honest the ACTRK600 layout and your layout which you just posted are much easier to work with and practically i have not found any problems.
what program are you using is it protel ?
-Dan
MJL21193 said:
Here's how it looks. Quite tightly packed, but everything fit, so that's all that matters.
I may work up the nerve to give is a try later.
Nice power supply module! Looks like a single powersupply unit!
It's kinda like a computer in a way, you have a tower case, and a separate power supply that wires into the *main board (your amplifier)
Keep us posted, this keeps getting more interesting.
danieljw said:
Hi Dan,
This is one of the things that I will do differently the next time. When nothing about the design is in question, it only makes sense to use a PCB for the whole thing. Especially if it can be kept fairly compact.
I'll be building another one of these within the next year, so I get to try it then.
EWorkshop1708 said:
Nice power supply module! Looks like a single powersupply unit!
It's kinda like a computer in a way, you have a tower case, and a separate power supply that wires into the *main board (your amplifier)
Keep us posted, this keeps getting more interesting.
Hi EW,
I have a bit of a problem. There seems to be a problem with the +/-15V supply. It uses the same transformer as the relays, and I think I may have fooled something up. Long and short of it is that the supply is way to ratty now, with the relays operating.
I think I only have 2 options:
Another separate +/-15V supply, isolated from the soft start and relays or drop the main amp supply with resistors and zeners. There is only one place left in the amp for another transformer - the back panel. It's doable and probably the best bet.
Besides, I already have the supply board, just need to reconfigure the relay supply, maybe change the transformer to a smaller unit.
Lots of fun and games, it's never easy, is it? Speed up the process if I knew what I'm doing.
I'll second this. Easy way to get the voltage you need from the toroid.
About the secondary power................
Now I used the Radioshack 2A 12.6V-0-12.6V myself for my amp project, and used it both for the relays and preamp, and it was ok. My difference was a lower regulated +/-12V instead with 2200uf per rail for the preamp, and for the relays, I use resistors in series with the relay coils to drop some voltage to run them cooler. I ran the relays just from the unregulated +12V (17VDC) rail only. The whole amp + logic circuits all share common ground. Now this transformer also runs 6 fans as well, but the fans run at regulated 6VDC taken from unregulated 12V from a seperate bridge rectifier just for the fans only.
Are you getting pops and clicks when using the relays? Try using them on their own regulated rail, or use unregulated, so that your regulated rails only run the preamp.. If you still have problems, you can give the relays and preamp its own bridge rectifier and caps.
Those RadioShack transformers are good ones, and you can load them quite a bit, however, if you still have problems, then use the main power toroid as another transformer and wrap another winding around it for +/-15V.
About the secondary power................
Now I used the Radioshack 2A 12.6V-0-12.6V myself for my amp project, and used it both for the relays and preamp, and it was ok. My difference was a lower regulated +/-12V instead with 2200uf per rail for the preamp, and for the relays, I use resistors in series with the relay coils to drop some voltage to run them cooler. I ran the relays just from the unregulated +12V (17VDC) rail only. The whole amp + logic circuits all share common ground. Now this transformer also runs 6 fans as well, but the fans run at regulated 6VDC taken from unregulated 12V from a seperate bridge rectifier just for the fans only.
Are you getting pops and clicks when using the relays? Try using them on their own regulated rail, or use unregulated, so that your regulated rails only run the preamp.. If you still have problems, you can give the relays and preamp its own bridge rectifier and caps.
Those RadioShack transformers are good ones, and you can load them quite a bit, however, if you still have problems, then use the main power toroid as another transformer and wrap another winding around it for +/-15V.
TheMG said:
Actually a good idea to do from the start, but I missed the boat on that one too. With the big toroid wired up and bracketed in place, it's none to appealing. Next time though.
Digging around in my transformer stash (I have tons of different ones, salvaged from thrift shop $5.00-$10.00 receivers and radios), I have found a dual secondary, with 20-0-20 and 16-0-16. I will use this in place of the 12.6-0-12.6 I'm now using. This will fix my problem and not take up any more space.
I'll use half of the 40V secondary for my relay supply.
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