Hi All,
A friend just donated a partly broken Sony reciever. It is rated at 5x110w RMS into 8ohms and uses +/- 50v rails. I've fixed this thing once, one channel had dead output transistors, plus minor damage to ancillary resistors etc. It is now clear that it's a little too fragile for my tastes, so I'm thinking of replacing the 5 amplifiers with GC's...
So, do any of the current crop of chipamps work well from 50v rails...I checked the NatSemi site and their product seems limited to high 30's and low 40's. I'd like to be able to safely use 4ohm speakers, so using any of the 3886 based amps seems out of the question with rails this high...
The next critical quality is size, the heatsink has enough room and is drilled for 5 pairs of T0247 transistors (mounting surface is ~10" x ~2"), so size is an issue, a major plus for a chipamp based solution...a PCB can extend about 2" in front of the heatsink, along it's entire length...or 5 2"x2" pcbs could stand in front of the thing...
At a lower priority, the amp modules should allow muting, and of course since I ultimately need 5 of them, they need to be reasonable in price...
I know you guys will have ideas...
Stuart
A friend just donated a partly broken Sony reciever. It is rated at 5x110w RMS into 8ohms and uses +/- 50v rails. I've fixed this thing once, one channel had dead output transistors, plus minor damage to ancillary resistors etc. It is now clear that it's a little too fragile for my tastes, so I'm thinking of replacing the 5 amplifiers with GC's...
So, do any of the current crop of chipamps work well from 50v rails...I checked the NatSemi site and their product seems limited to high 30's and low 40's. I'd like to be able to safely use 4ohm speakers, so using any of the 3886 based amps seems out of the question with rails this high...
The next critical quality is size, the heatsink has enough room and is drilled for 5 pairs of T0247 transistors (mounting surface is ~10" x ~2"), so size is an issue, a major plus for a chipamp based solution...a PCB can extend about 2" in front of the heatsink, along it's entire length...or 5 2"x2" pcbs could stand in front of the thing...
At a lower priority, the amp modules should allow muting, and of course since I ultimately need 5 of them, they need to be reasonable in price...
I know you guys will have ideas...
Stuart
excellent ideas...
I thought of regulating and since I'm still 'thinking' it may end up being part of the answer, just wanted to hear from the community here to make sure I was considering all the options...
The UCD modules would be great if they were cheaper, the 180 module might fit with no problem, need to take some accurate measurements ...no worries from heat and more efficiency, probably represent a quality and quantity upgrade for this receiver...However, the cost of ~300euro for 5 channels is, IIRC, more than the unit cost new...
WRT the GB150, IIRC the price was approx $40. I'm pretty sure I'll have all the parts so the real question is does he sell pcb's? Not sure why, but Gregs website seems to be down, so unless someone else can chime in with sizes & prices, not sure whether this is a solution or not...
Thanks
Stuart
I thought of regulating and since I'm still 'thinking' it may end up being part of the answer, just wanted to hear from the community here to make sure I was considering all the options...
The UCD modules would be great if they were cheaper, the 180 module might fit with no problem, need to take some accurate measurements ...no worries from heat and more efficiency, probably represent a quality and quantity upgrade for this receiver...However, the cost of ~300euro for 5 channels is, IIRC, more than the unit cost new...
WRT the GB150, IIRC the price was approx $40. I'm pretty sure I'll have all the parts so the real question is does he sell pcb's? Not sure why, but Gregs website seems to be down, so unless someone else can chime in with sizes & prices, not sure whether this is a solution or not...
Thanks
Stuart
...tda7294...
After a little more searching the TDA7294 comes to light... Has anyone used it? Searching shows a number of people were thinking of using it, but not much seems to have happened since...
It is spec'ed to survive at +/-50v as long as it is only operated at +/- 40v...not sure if I can guarantee that part yet, I need to measure the power supply and see how fast it's voltage drops as the current draw is increased...couple of resistors might be all this needs to work...
Kits are available from a number of places that seem to be in the $20-$30 / channel range, so it might be a real contender...
Wondering at this point if it has any serious drawbacks not obvious from the specs...
Stuart
After a little more searching the TDA7294 comes to light... Has anyone used it? Searching shows a number of people were thinking of using it, but not much seems to have happened since...
It is spec'ed to survive at +/-50v as long as it is only operated at +/- 40v...not sure if I can guarantee that part yet, I need to measure the power supply and see how fast it's voltage drops as the current draw is increased...couple of resistors might be all this needs to work...
Kits are available from a number of places that seem to be in the $20-$30 / channel range, so it might be a real contender...
Wondering at this point if it has any serious drawbacks not obvious from the specs...
Stuart
Hi Stuart
The TDAs are just about the only chips I haven't used, simply 'cos I couldn't get hold of any. I suspect that is the only one that will go that high, the National ones go to about 42 V and TI's usually around 30V, and the OPA541 only gets to 40V.
Have you looked at the Class D kits from 41Hz? I keep looking at their site and thinking I really must give them a go one day.
The TDAs are just about the only chips I haven't used, simply 'cos I couldn't get hold of any. I suspect that is the only one that will go that high, the National ones go to about 42 V and TI's usually around 30V, and the OPA541 only gets to 40V.
Have you looked at the Class D kits from 41Hz? I keep looking at their site and thinking I really must give them a go one day.
Check the TDA7293, the older sibling of the 7294. It's datasheet states it can work from +-50V (+-60V no signal).
I'm just about finnish instaling two of these in an older broken amp but I'm only running them on +-35V. Bought 10 of them fairly cheap of ebay about a year ago. Can't find them there now but there was a guy there selling them for a long time.
At +-50V into 4 ohm you probably should put 3 in parallell. (These chips are very easily parallelled.)
space
I'm just about finnish instaling two of these in an older broken amp but I'm only running them on +-35V. Bought 10 of them fairly cheap of ebay about a year ago. Can't find them there now but there was a guy there selling them for a long time.
At +-50V into 4 ohm you probably should put 3 in parallell. (These chips are very easily parallelled.)
space
good info...
I'll check out the older version...safe operation at 50v sounds will remove one worry. Did you hard wire the ICs or make the reference PCB? Much as I'd like to try hardwiring it doesn't make for a quick and easy fix, more like a work of art.
I think it very unlikely the power supply in the sony will maintain 50v even with just one of the amps driving into 4 ohms, so assuming the TDA family thermal and current protection works as advertised I think/hope it will be safe...
The receiver was spec'ed as ~110w into 8ohms, all channels driven. This would imply at full power the supply droops into the low 40's. The transformer doesn't look anywhere near big enough for 550va, perhaps it is a very short term specification.
If the board fits I'd love to use the gb150d, heard nothing but great things about it, just need to talk to Greg and see what's what.
I checked out the 41hz site and nothing 'sane' fits, price or sizewise, the kits seem to fall into 2 distinct power bands, too small and too big...
I considered the STK parts, I've used them successfully before, but they seem hard to get now, the obsolete comment may be spot on, either that or you just have to buy a bunch...lastly they are physically quite large, not sure I could fit five of the higher powered, single channel critters on the heatsink.
Keep 'em coming
Stuart
I'll check out the older version...safe operation at 50v sounds will remove one worry. Did you hard wire the ICs or make the reference PCB? Much as I'd like to try hardwiring it doesn't make for a quick and easy fix, more like a work of art.
I think it very unlikely the power supply in the sony will maintain 50v even with just one of the amps driving into 4 ohms, so assuming the TDA family thermal and current protection works as advertised I think/hope it will be safe...
The receiver was spec'ed as ~110w into 8ohms, all channels driven. This would imply at full power the supply droops into the low 40's. The transformer doesn't look anywhere near big enough for 550va, perhaps it is a very short term specification.
If the board fits I'd love to use the gb150d, heard nothing but great things about it, just need to talk to Greg and see what's what.
I checked out the 41hz site and nothing 'sane' fits, price or sizewise, the kits seem to fall into 2 distinct power bands, too small and too big...
I considered the STK parts, I've used them successfully before, but they seem hard to get now, the obsolete comment may be spot on, either that or you just have to buy a bunch...lastly they are physically quite large, not sure I could fit five of the higher powered, single channel critters on the heatsink.
Keep 'em coming
Stuart
jacco is quite right...
...this thing has the mn.... and mp.... sanken darlingtons, which are apparently overdriven by the NEC driver chip, the resistor in series with the base keeps getting fried. Not sure if the resistor is a culprit or a victim, or perhaps it's the NEC part thats at fault. In any case if I were to use darlingtons in the output again I'd assemble them myself from mpsa42/92 and mj4302/3201s, since I have a bunch of each...
The 4702 is definitely an option, I just hadn't seen a nice small PCB to make my life easy...
Stuart
...this thing has the mn.... and mp.... sanken darlingtons, which are apparently overdriven by the NEC driver chip, the resistor in series with the base keeps getting fried. Not sure if the resistor is a culprit or a victim, or perhaps it's the NEC part thats at fault. In any case if I were to use darlingtons in the output again I'd assemble them myself from mpsa42/92 and mj4302/3201s, since I have a bunch of each...
The 4702 is definitely an option, I just hadn't seen a nice small PCB to make my life easy...
Stuart
Stuart Easson said:
Figures.
Problem with the GB150 is that you'll need enough room for 4 output devices, if the rail voltage really drops that much a single pair could do.
Second item is that the GBs need a decent PS, 5 of them certainly will.
Other than that i'll take a GB over a GC any day, smart cookie amp and very small.
You could give Russ a buzz, Stuart.
=> www.diyaudio.com/forums/showthread.php?postid=951392#post951392
tda7293 looks like a winner...
the price is right at <$7 each, footprint is small, verging on tiny if I use point to point wiring...
It seems Gregs website has moved to be a part of the diyhifi.org site, once I figured that out I could take a closer look...unfortunately even with a single output pair the board is 4"x2"...I don't think 5 of these can be crammed onto the heatsink...I need to dismantle the receiver to actually measure the sink, going from memory is likely to screw me up...
I think a switched mode regulator would be cool but probably overkill on this project. A linear regulator seems more my speed, but perhaps at this point more trouble than it's worth, assuming the tda7293 is 'real' that is...
Stuart
the price is right at <$7 each, footprint is small, verging on tiny if I use point to point wiring...
It seems Gregs website has moved to be a part of the diyhifi.org site, once I figured that out I could take a closer look...unfortunately even with a single output pair the board is 4"x2"...I don't think 5 of these can be crammed onto the heatsink...I need to dismantle the receiver to actually measure the sink, going from memory is likely to screw me up...
I think a switched mode regulator would be cool but probably overkill on this project. A linear regulator seems more my speed, but perhaps at this point more trouble than it's worth, assuming the tda7293 is 'real' that is...
Stuart
Re: tda7293 looks like a winner...
The LM3886 has a much lower distortion than pretty much all of the TDAxxx line - I'd reccomend it.
At large voltage drops (for example, +/- 50v to +/- 30v) linear regulators are very inefficient, and the NatSemi regulators are really simple - I looked into using one for a class-D amplifier's power supply, and they only require a few parts.
Stuart Easson said:
The LM3886 has a much lower distortion than pretty much all of the TDAxxx line - I'd reccomend it.
At large voltage drops (for example, +/- 50v to +/- 30v) linear regulators are very inefficient, and the NatSemi regulators are really simple - I looked into using one for a class-D amplifier's power supply, and they only require a few parts.
the 'power' design tools Net Semi have
for the switch mode regulators are pretty cool...
I'll play some more, but presently it looks like there isn't a single part solution to generating a 38v rail at 5A from the baseline of 44-50v...
They can generate the BOM for a vast range of simple designs and from what I can see order the entire set of parts for you if you want...
Makes the concept of 'design' a little redundant, just put the numbers in and out pops the result read to go...
Stuart
for the switch mode regulators are pretty cool...
I'll play some more, but presently it looks like there isn't a single part solution to generating a 38v rail at 5A from the baseline of 44-50v...
They can generate the BOM for a vast range of simple designs and from what I can see order the entire set of parts for you if you want...
Makes the concept of 'design' a little redundant, just put the numbers in and out pops the result read to go...
Stuart
About the TDA7293. Yes I did wire them P2P and it wasn't the bigges job I ever did.
Space considerations. Mine are measuring about 2 cm x 4 cm x 2 cm + the (near chip) ~1000uf supply caps (about the same size), so fitting 2 (minimum for +-50V into 4ohm even if the supply sags to 40V at full load) should not be to hard to make room for.
space
Space considerations. Mine are measuring about 2 cm x 4 cm x 2 cm + the (near chip) ~1000uf supply caps (about the same size), so fitting 2 (minimum for +-50V into 4ohm even if the supply sags to 40V at full load) should not be to hard to make room for.
space
This is a ( hotly debated ) grey area. Better measurement figures does not necessarily mean better sound .
I haven't yet seen a listening comparison done with the two chips with fairly identical supplies.
I will know when I complete my TDA7293 board .
Caution: Do remember to search the forum about the TDA chip. It has some supply requirement between pins . The input stage and output stage supply have separate pin outs . If the voltage between them is not maintained ( as specified ) your chip is fried .
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