I'm worried now...
The schematic in this post is the one I used, the dots where the wires join are very vague, so a mistake could have been made.
(any designers out there care to redraw the dots...pretty please)
It sounds great at medium vol, no distortion on the scope.
Where oh where do I start to sort this out, I'm not a beginner, but don't have ton's of experience either....
The schematic in this post is the one I used, the dots where the wires join are very vague, so a mistake could have been made.
(any designers out there care to redraw the dots...pretty please)
It sounds great at medium vol, no distortion on the scope.
Where oh where do I start to sort this out, I'm not a beginner, but don't have ton's of experience either....
Yes, those I have connected as shown.
I will try heat TR10 totally on it's own, or because it's mostly for a sub, just convert it to pure class B, but I feel that would be a waste
I was not sure about between TR13 and TR14, are they only connected together with the 180 Ohm resistor, and to the base of the output transistors?
That part of the circuit looked odd to me
I will try heat TR10 totally on it's own, or because it's mostly for a sub, just convert it to pure class B, but I feel that would be a waste
I was not sure about between TR13 and TR14, are they only connected together with the 180 Ohm resistor, and to the base of the output transistors?
That part of the circuit looked odd to me
13 and 15 sorry
Thanks for all the advice Perry
I am going to double check the circuit and values step by step, move TR10 on it's own, and get some heavier heatsink.
I would love to get this sorted as it needs to sound as good as it looks.
If I can get it all working, will post all the PCB's as it's a nice project for a sub amp.
Thanks for all the advice Perry
I am going to double check the circuit and values step by step, move TR10 on it's own, and get some heavier heatsink.
I would love to get this sorted as it needs to sound as good as it looks.
If I can get it all working, will post all the PCB's as it's a nice project for a sub amp.
Hi!
At bottom of the schematic is some note present: TR10 HARUS DIPASANG BERSAMA PENDINGIN POWER TRANSISTOR... I am not able to translate this, but I think it is saying, that at least TR10 should be on the heatsink with the power transistors together
Diodes alone are not enough, though...
Regards
At bottom of the schematic is some note present: TR10 HARUS DIPASANG BERSAMA PENDINGIN POWER TRANSISTOR... I am not able to translate this, but I think it is saying, that at least TR10 should be on the heatsink with the power transistors together
Diodes alone are not enough, though... Regards
I build mostly big PA amps. Because I build exclusively from stuff obtainable on the surplus market, there isn't always the luxury of one big perfectly sized and machined heat sink for everything to mount to. MOst of the time, power transistor banks get split up and the NPN and PNP banks may see slightly different thermal environment. It looks like this could happen here as well. I've battled thermal runaway that sometimes takes DAYS of idling to set in and it's due to these slight temperature variations that are responsible.
To minimize the possibility here, mount D1 as close as possible to TR13, mount D2 next to the hottest of TR16-19, Mount D3 next to the hottest of TR20-23, and mount TR10 next to TR15. The closer the better. AS for D1-D3, do not use diodes. Use diode-connected transistors (B shorted to C) in fully-insulated TO-126 cases. You can put them anywhere that way, and not worry about thermal contact or getting cases or leads shorted to heatsink.
To minimize the possibility here, mount D1 as close as possible to TR13, mount D2 next to the hottest of TR16-19, Mount D3 next to the hottest of TR20-23, and mount TR10 next to TR15. The closer the better. AS for D1-D3, do not use diodes. Use diode-connected transistors (B shorted to C) in fully-insulated TO-126 cases. You can put them anywhere that way, and not worry about thermal contact or getting cases or leads shorted to heatsink.
ricsmuts said:WOW, you don't go easy on the heatsinks! I don't think you will have any heating problems there
If you ever consider posting that thermal track design, look me up please....
It's still in the works, but when it's finished, I'll be glad to post the design.
I'm still working out all the resistance values and the final design of the schematics and also components layout.IMO There's nothing better than really large heatsinks to ensure reliable temps and avoid runaway. Even if you have little or no thermal compensation, a big sink will stabilize temp after a while, and usually will not thermally runaway.
*I recommend for a good heatsink, is a really thick mounting base, so you don't get hotspots, and the sink warms as a whole.
*Also, I recommend large and dense fins to carry the heat away faster, and allow use of a fan if needed. If you can't get one with nice big fins, or any fins at all, substitute for that by having a much larger mounting base instead.
Attachments
Big heatsinks are always a good idea, but Its more important that the circuitry is first stable enough for even a small heatsink.
This is particularly important to me as this is a car amp that will be pushed extremely hard under less than the best conditions.
I am facinated by those Thermaltraks and am keen to see how they perform in a good design.
This is particularly important to me as this is a car amp that will be pushed extremely hard under less than the best conditions.
I am facinated by those Thermaltraks and am keen to see how they perform in a good design.
WG_SKI
Your fix worked like a charm, thanks.
Amp is stable and I can turn up the Bias now.
If I switch on the amp cold and immediately run a 100Hz sine wave at high volume, the current draw peaks for about half a second , but recovers without damage. Thermal lag in the heatsinks I guess.
(need to get the componets real close together as I dont want to stress the output transistors)
As it's a car subwoofer amp, I'm trying to simulate all the things people do to their amps.
Your fix worked like a charm, thanks.
Amp is stable and I can turn up the Bias now.
If I switch on the amp cold and immediately run a 100Hz sine wave at high volume, the current draw peaks for about half a second , but recovers without damage. Thermal lag in the heatsinks I guess.
(need to get the componets real close together as I dont want to stress the output transistors)
As it's a car subwoofer amp, I'm trying to simulate all the things people do to their amps.
ricsmuts said:
Experiment with R20 and R25. I haven't done a full analysis of the quiescent currents in this exact circuit, but I have plenty of experience with ones just like it. I usually bias TR9 and TR11 between 8 and 12mA and if you do that the triple darlington will drive a welding rod with enough outputs in parallel. They will need heat sinking. The jury is still out on whether R21 and R24 are necessary. Leach used to include them, but recent incarnations of the circuit have done away with them. Increasing those or eliminating them gives more available drive, but they are useful in tailoring the open-loop gain for stability.
The minimum value I'd use for Re is at least 10 times the intrinsic emitter resistance (26/Ie in mA). For 8mA, it's about a 30 ohm minimum. But how much current is actually there with any given resistor is dependent on what's on the base side. Just reduce Re until you get between 8 and 12mA - more current isn't needed. Measure the drop and calculate what you need to change it to - if you need to at all. If your rails are only at +/-40V, they'll only get a little warm, but heat sinking will let them settle on final bias faster. At my typical +/-100 volt or higher rails they get toasty. They're supposed to run class A and run the same temp idling or at full blast.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.