Hi,
A while ago, I started my first audio DIY-project, to build a Death of Zen power amp. I completed the power supply, boards and attached some heatsinks, so I was ready to put it in an enclosure.
After asking at a number of local hifi-shops, I got an old Kenwood KA-601 amp that didn't work anymore, to use as an enclosure. A pic of the amp can be found at http://aa-audio.dk/224.jpg.
For heatsinks, I bought four Fischer SK34's (specs can be found here). They're rated at 0.75 K/W. Since I use two of them per channel, I figured I'd get 0,375 K/W per channel. Since Rode says anything under 0.5 K/W per channel should do, I thought this would provide more than enough cooling capacity. In addition, I use four output transistors per channel instead of two, in order to reduce the thermal resistance (from junction to sink) even further.
The problem is that, during tests, the quiescent current doesn't seem to stabilize. I placed all heatsinks on pieces of wood, in such a way that one side of the sinks rests on the wood. Nevertheless, the quiescent current rises continuously, although very slowly. I think this is because the sinks don't provide enough cooling (temperature increases => resistance decreases =>current increases => temperature increases)
I was planning to mount the heatsinks to both sides of the enclosure, so that the fins are vertical. That way, the enclosure (which is made out of iron) will provide some additional cooling (since the sinks will be able to pass some of the heat to the case). The question is, will it be enough? I was already quite surprised to see that, in my test setup, the sinks didn't seem to provide enough cooling to the amp. So I'm very hesitant to mount them this way. I could also mount them horizontally, and place a fan on each side of the amp, in between the sinks. This would probably take care of the cooling problem, but I don't like the idea of hearing the noise of two fans while I'm listening to music.
Any thoughts?
A while ago, I started my first audio DIY-project, to build a Death of Zen power amp. I completed the power supply, boards and attached some heatsinks, so I was ready to put it in an enclosure.
After asking at a number of local hifi-shops, I got an old Kenwood KA-601 amp that didn't work anymore, to use as an enclosure. A pic of the amp can be found at http://aa-audio.dk/224.jpg.
For heatsinks, I bought four Fischer SK34's (specs can be found here). They're rated at 0.75 K/W. Since I use two of them per channel, I figured I'd get 0,375 K/W per channel. Since Rode says anything under 0.5 K/W per channel should do, I thought this would provide more than enough cooling capacity. In addition, I use four output transistors per channel instead of two, in order to reduce the thermal resistance (from junction to sink) even further.
The problem is that, during tests, the quiescent current doesn't seem to stabilize. I placed all heatsinks on pieces of wood, in such a way that one side of the sinks rests on the wood. Nevertheless, the quiescent current rises continuously, although very slowly. I think this is because the sinks don't provide enough cooling (temperature increases => resistance decreases =>current increases => temperature increases)
I was planning to mount the heatsinks to both sides of the enclosure, so that the fins are vertical. That way, the enclosure (which is made out of iron) will provide some additional cooling (since the sinks will be able to pass some of the heat to the case). The question is, will it be enough? I was already quite surprised to see that, in my test setup, the sinks didn't seem to provide enough cooling to the amp. So I'm very hesitant to mount them this way. I could also mount them horizontally, and place a fan on each side of the amp, in between the sinks. This would probably take care of the cooling problem, but I don't like the idea of hearing the noise of two fans while I'm listening to music.
Any thoughts?
I have some Doz boards that I will use someday...
Are you sure you have good thermal conduction between the transistors and the heat sinks? That's the problem I had when Istarted playing with the boards; one transistor was getting much hotter than the others. Check if there is a significant temperature difference between the transistor case and the heatsink.
Are you sure you have good thermal conduction between the transistors and the heat sinks? That's the problem I had when Istarted playing with the boards; one transistor was getting much hotter than the others. Check if there is a significant temperature difference between the transistor case and the heatsink.
When the case is hot... inside can be worst!
Put fans on it, inside, under, over...the way you can.... reduce the voltage to reduce speed and noise.
I like this amplifier very much, it is one of the best i have heard, but you can cook some egg or prepare a good coffee with it too.... i do not like this hot...mine works warm....have four fans in a wind tunnel construction.
This way i already post in forum....
"Gonne with the wind...the heat!"
regards,
Carlos
Put fans on it, inside, under, over...the way you can.... reduce the voltage to reduce speed and noise.
I like this amplifier very much, it is one of the best i have heard, but you can cook some egg or prepare a good coffee with it too.... i do not like this hot...mine works warm....have four fans in a wind tunnel construction.
This way i already post in forum....
"Gonne with the wind...the heat!"
regards,
Carlos
Well, maybe you do need a fan or just reduce the quiescent current. Are you using the zener-stabilized option for the DoZ?
I think with a Class-A design you're faced with either modifying the heatsink / enclosure arrangement for a given voltage / current, or using a given enclosure arrangement and modifying the current so it doesn't heat up too much.
Let us know how it all turns out...
By the way, what are you using for output transistors?
I think with a Class-A design you're faced with either modifying the heatsink / enclosure arrangement for a given voltage / current, or using a given enclosure arrangement and modifying the current so it doesn't heat up too much.
Let us know how it all turns out...
By the way, what are you using for output transistors?
Re: When the case is hot... inside can be worst!
What fans do you use? I have a Spire 8cm fan (intended to cool computers), but it's ball-bearing so it isn't very quiet (although, at lower speeds, it's a lot better).
Not yet, but I'm going to add this (needed to build the amp and check the voltage first).
2N3055. After I bought them, I read that MJ15003s sound a lot better with this amp... so I intend to replace them (after I get the amp stable).
destroyer X said:
What fans do you use? I have a Spire 8cm fan (intended to cool computers), but it's ball-bearing so it isn't very quiet (although, at lower speeds, it's a lot better).
paulb said:
Not yet, but I'm going to add this (needed to build the amp and check the voltage first).
2N3055. After I bought them, I read that MJ15003s sound a lot better with this amp... so I intend to replace them (after I get the amp stable).
hey starbase218
im also about to build the DoZ at the moment, everything is in parts and drilled, just have to get onto the next stage!
i was going to use 0.78C/W heatsinks per channel, but now im worried
few questions:
did you use rods boards?
are you using metal package 2N3055s? TO-3s? rod says plastic ones will not keep under that amount of heat generated!
have you added the zenner diodes to stabilise shifts in quiescent current? these are ESSENTIAL!
ta
Paul
im also about to build the DoZ at the moment, everything is in parts and drilled, just have to get onto the next stage!
i was going to use 0.78C/W heatsinks per channel, but now im worried
few questions:
did you use rods boards?
are you using metal package 2N3055s? TO-3s? rod says plastic ones will not keep under that amount of heat generated!
have you added the zenner diodes to stabilise shifts in quiescent current? these are ESSENTIAL!
ta
Paul
phs said:
No, I use universal (epoxy) grid boards. Perhaps not the best solution wrt sound quality, but the amp requires very few components and the boards allow me to modify the circuits very easily. Besides, I made sure the signal paths are very short.
I use all-metal TO-3s
.No (see my previous reply). But if it makes that much of a difference, I will measure the temp and current again after I applied the zener(s).
Btw, I found that the Kenwood amp has a big transformer with two seperated secondary windings. So I salvaged that one. Power usage of the Kenwood is rated at 550 watt, so I think it might be possible to use that transformer for the DoZ. Still have to measure secondary voltages, though.
The link to the scematic (if that is what the link is) doesn't work. However, one point that hasn't been discussed here is temperature coefficient. Does this circuit have a bias servo transistor? If so it should be mounted with outputs. BJT's require less Vbe bias to turn on as it is heated. It sounds like this circuit lacks thermal compensation, or its just misconstruction. Then it could be design but I doubt it. I am not familiar with other peoples ideas...only my own.
I am using old computer CPU fan
I can buy them here, 6 for a dollar, and someone in very good condition....have to put the hand inside the basket and have the ones the luck gave to you... sometimes one or two burned...the rule is not to test, this way so cheap...because some of them do not work anymore.
But spending 5 dollares, you can have a good stock after junk the burned ones.
I use two, one each side...and some cover, wooden cover as a tunnel, the exaust one is outside the case..... or facing the case, to exaust to outside environmnet, despite not making too much noise, i do not like things completely cold.... i reduce voltage to feel some warm on the sinks, they are sandwiched with wooden insulators... also i evaluate power feeling the AC voltage with my fingers..... fingermeter..hehe.
regards,
Carlos
I can buy them here, 6 for a dollar, and someone in very good condition....have to put the hand inside the basket and have the ones the luck gave to you... sometimes one or two burned...the rule is not to test, this way so cheap...because some of them do not work anymore.
But spending 5 dollares, you can have a good stock after junk the burned ones.
I use two, one each side...and some cover, wooden cover as a tunnel, the exaust one is outside the case..... or facing the case, to exaust to outside environmnet, despite not making too much noise, i do not like things completely cold.... i reduce voltage to feel some warm on the sinks, they are sandwiched with wooden insulators... also i evaluate power feeling the AC voltage with my fingers..... fingermeter..hehe.
regards,
Carlos
Banned
Joined 2002
I just ordered some 27 volt zeners (along with some other components) for stabilizing the quiescent current, and I will post my findings here once I have them. Unfortunately, I can't use the old Kenwood transformer because the secondary voltage is too high. It could come in handy for a future project though .
I was also wondering if anyone knows the input impedance of the DoZ. It doesn't say on Rod's site, and I can't find it here either. But if it's not too low, I plan to build a passive preamp.
.I was also wondering if anyone knows the input impedance of the DoZ. It doesn't say on Rod's site, and I can't find it here either. But if it's not too low, I plan to build a passive preamp.
Well, I soldered the two zeners AND replaced the 2N3055s with MJ15003. I also replaced some of the internal wiring with tinnid wire (to prevent corrosion). The amp now apparantly stabilizes out at about 1.45 Amps quiescent current and just under 44C (heatsink temp). But it's very difficult to be sure, because my computer is in the same room, providing airflow, the door is sometimes open, etc.
I also wonder what would happen if the ambient temperature was higher (like in the summer). The heatsinks would be warmer as well, so the current would also rise.
All in all, I think I will add a couple of fans, just to be safe. But they must be temperature-controlled so they only work if it's absolutely neccesary.
O, the sound is IMO amazing. This amp is definately going to replace my Marantz SR1100. Only one thing to do: putting it in an enclosure.
I also wonder what would happen if the ambient temperature was higher (like in the summer). The heatsinks would be warmer as well, so the current would also rise.
All in all, I think I will add a couple of fans, just to be safe. But they must be temperature-controlled so they only work if it's absolutely neccesary.
O, the sound is IMO amazing
. This amp is definately going to replace my Marantz SR1100. Only one thing to do: putting it in an enclosure.
Swedish Chef said:
I use two transistors for each half of the push-pull stage, instead of one. I have connected two 0.1 ohm resistors to the collector of each transistor, and the emitters are connected to each other, followed by a single 0.22 ohm resistor (http://sound.westhost.com/heatsinks.htm#11.2).
It's been a while, but I've finally completed most of the amp. I've resoldered the power supply PCB, added a passive preamp and put the amp in a 19" enclosure (wish I had a digital camera ). Still sounding great.
As for cooling, the heatsinks are on both sides of the amp, not yet mounted. Now that the amp is between two shelves, the temperature is higher again. So I'll buy a few fans. Probably Papst, as they have a reputation for being very silent.
One question though - not about cooling: I feel the amp lacks some deep bass. Apart from the MJ15003's, I've only used parts listed on Rod's site (BC559, BD139, etc). The input cap is an Audyn-Cap, but all the other components are pretty standard (resistors are carbon).
Would it help to replace the parts with better ones? If so, what transistors or resistors would I need? And would replacing the output cap help?
). Still sounding great.As for cooling, the heatsinks are on both sides of the amp, not yet mounted. Now that the amp is between two shelves, the temperature is higher again. So I'll buy a few fans. Probably Papst, as they have a reputation for being very silent.
One question though - not about cooling: I feel the amp lacks some deep bass. Apart from the MJ15003's, I've only used parts listed on Rod's site (BC559, BD139, etc). The input cap is an Audyn-Cap, but all the other components are pretty standard (resistors are carbon).
Would it help to replace the parts with better ones? If so, what transistors or resistors would I need? And would replacing the output cap help?
I also just got a DoZ up and running. In addition to cooling issues, I have a problem with EMI. I'm getting a couple of 80mm Vantec Stealth fans for cooling. The Pabst fans are excellent, but pretty expensive (about $15+ each) around here, but are probably quieter than the Vantec's.
The single most important factor in bass response on this amp is the output cap. I happen to have found a good quality computer-grade 4700µf 50V cap for output, and I hear nothing wrong with the bass at all. For the input cap, I happened to have a few 1.2µf metal polypropylene caps instead of the 1µf called for in the design, but I doubt that it makes a difference here unless your input transistor is really low gain (I used a Zetex ZTX795A).
If you suspect bass loss, hook it up to a scope and signal generator and see where the -3db point is...
The single most important factor in bass response on this amp is the output cap. I happen to have found a good quality computer-grade 4700µf 50V cap for output, and I hear nothing wrong with the bass at all. For the input cap, I happened to have a few 1.2µf metal polypropylene caps instead of the 1µf called for in the design, but I doubt that it makes a difference here unless your input transistor is really low gain (I used a Zetex ZTX795A).
If you suspect bass loss, hook it up to a scope and signal generator and see where the -3db point is...
Tnx for the advice. I don't have a scope and signal generator, but tnx anyway.
There's another problem with my DoZ. In the last couple of days, I noticed some small plops or ticks in the left speaker. As that speaker is fairly close to a halogen lamp (with a transformer), I thought that might be the cause. But even after unplugging it, the plopping continued.
This morning, while playing music, the same speaker began emitting a roaring noise. Not very loud, but noticeable. I immediately pulled the power plug. When I put it back in and wanted to turn the amp on, I discovered the fuse had been blown.
Looking inside the amp, I can't see anything wrong. The only thing that might explain what happened, is that some of the screws by which the wires from the left-channel MJ15003's are connected to the PCB, were not tightened very well. So maybe one of the MJ's was disconnected, forcing the other one to do all the work, increasing its temperature, thereby increasing the quiscent current? It's the only thing I can think of right now.
Anyone knows what else might be causing this?
There's another problem with my DoZ. In the last couple of days, I noticed some small plops or ticks in the left speaker. As that speaker is fairly close to a halogen lamp (with a transformer), I thought that might be the cause. But even after unplugging it, the plopping continued.
This morning, while playing music, the same speaker began emitting a roaring noise. Not very loud, but noticeable. I immediately pulled the power plug. When I put it back in and wanted to turn the amp on, I discovered the fuse had been blown.
Looking inside the amp, I can't see anything wrong. The only thing that might explain what happened, is that some of the screws by which the wires from the left-channel MJ15003's are connected to the PCB, were not tightened very well. So maybe one of the MJ's was disconnected, forcing the other one to do all the work, increasing its temperature, thereby increasing the quiscent current? It's the only thing I can think of right now.
Anyone knows what else might be causing this?
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