I've just inherited an amplifier, which was in a bunch of projects my late father didn't have the chance to get round to. Not sure of it's history, but I assume he was going to use it as a base for a new build.
One of the Amplifier PCBs was missing and had been removed at some point. The other I have just removed - I can't find any details of it anywhere. There are 4 x IRFP240 on the board.
Not sure of the quality of the internal components - however, the transformer is rated at 500VA and I've tested both regulated supplies, which are putting out +/-55v.
I'd love some recommendations on which amp boards I could put in there as replacements. There isn't much room for a PCB larger than the one I removed.
One of the Amplifier PCBs was missing and had been removed at some point. The other I have just removed - I can't find any details of it anywhere. There are 4 x IRFP240 on the board.
Not sure of the quality of the internal components - however, the transformer is rated at 500VA and I've tested both regulated supplies, which are putting out +/-55v.
I'd love some recommendations on which amp boards I could put in there as replacements. There isn't much room for a PCB larger than the one I removed.
Okay - after some further investigation, I've identified it as a GB150D - a Greg Ball design from some time back. I think the amplifier PCBs are originals, purchased as a kit. The other parts are 'off the shelf' type items. Not sure if these were offered as an all in one kit at some time?
Looks like it will not be possible to get hold of a replacement PCB, so may have to change both - which is a shame.
Looks like it will not be possible to get hold of a replacement PCB, so may have to change both - which is a shame.
That is really tiny for taking such powerful rail voltage & current.
You'd have a real hard time finding something equivalent. I built an AX6 on a 3.5"x5" board because the stock layout is 4" x 4" and my case is not that tall. But it won't take that high rail voltage.
Standard diyaudio.com answer, the honey badger, is about 4.5" x 10". Which is why I will never buy one.
I sense some overkill on the cap board. 6 capacitors for a 2 output pair amp? One 4700 uf plus and minus would be overkill IMHO. The PV-4c uses 3300 @ 80. That leaves a lot more room for drivers & output transistors.
Whatever you do I suggest you invest in a couple of speaker protection boards to put after the output transistors. Split supply amps can tear a suspension or melt a voice coil if one of the output transistors shorts the rail cap to it. This board does not look totally bank vault reliable.
You'd have a real hard time finding something equivalent. I built an AX6 on a 3.5"x5" board because the stock layout is 4" x 4" and my case is not that tall. But it won't take that high rail voltage.
Standard diyaudio.com answer, the honey badger, is about 4.5" x 10". Which is why I will never buy one.
I sense some overkill on the cap board. 6 capacitors for a 2 output pair amp? One 4700 uf plus and minus would be overkill IMHO. The PV-4c uses 3300 @ 80. That leaves a lot more room for drivers & output transistors.
Whatever you do I suggest you invest in a couple of speaker protection boards to put after the output transistors. Split supply amps can tear a suspension or melt a voice coil if one of the output transistors shorts the rail cap to it. This board does not look totally bank vault reliable.
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Greg has closed his GB150 forum and ended support for the amplifier and various developments from it but we have already covered the amplifier, PCB and parts issues in an earlier thread. Take a look here: SKA AMPS GB150 kits/complete build
Thank you. I'd like to get up and running with something simple to install in the existing case.
Some interesting reading to be done here - I like the look of the TGM7 thread, so will take some time to read that tonight.
I realise that the PSU might be overkill, but I guess it won't hurt to leave it as it is?
I will take note of the speaker protection though - is this something you need active circuits/relays for - or can a quick blow fuse work in the same circumstance?
Some interesting reading to be done here - I like the look of the TGM7 thread, so will take some time to read that tonight.
I realise that the PSU might be overkill, but I guess it won't hurt to leave it as it is?
I will take note of the speaker protection though - is this something you need active circuits/relays for - or can a quick blow fuse work in the same circumstance?
No, quick blow fuse is not fast enough. They were tried in the early days on reviled amps like the SWTC tigersaurus.
Diyaudio store up top has a speaker protector kit.
There are lots of them on ebay, but the relay is usually something small enough that the contacts are likely to weld shut under the 3000 amps a 10000 uf rail cap can put out.
Best is the Michael Bean back to back nfets protector, driven by a photovoltaic fet driver to make the gate voltage higher than the rail voltage. I use a Panasonic APV1122 as driver. I put the driver input in series with a green LED that displays the amp is okay (and resistor to limit the current). I use a flip flop to remember there is a problem, a 74AHC74 driving a npn transistor. DC on speaker detector is a 47000 resistor driving a 2.2 uf ceramic cap series a 8 v bipolar diac powertec bsd08. Equivalent to the diac are two back to back 7.5 v zener diodes. The nFets are between the output transistors and the speaker jack. The sensor stack is parallel that to speaker return.
Diyaudio store up top has a speaker protector kit.
There are lots of them on ebay, but the relay is usually something small enough that the contacts are likely to weld shut under the 3000 amps a 10000 uf rail cap can put out.
Best is the Michael Bean back to back nfets protector, driven by a photovoltaic fet driver to make the gate voltage higher than the rail voltage. I use a Panasonic APV1122 as driver. I put the driver input in series with a green LED that displays the amp is okay (and resistor to limit the current). I use a flip flop to remember there is a problem, a 74AHC74 driving a npn transistor. DC on speaker detector is a 47000 resistor driving a 2.2 uf ceramic cap series a 8 v bipolar diac powertec bsd08. Equivalent to the diac are two back to back 7.5 v zener diodes. The nFets are between the output transistors and the speaker jack. The sensor stack is parallel that to speaker return.
The michael bean schematic is on here already but bing can't find it.
The DC detection circuit that triggers the flip-flop is part of most Peavey amps, for example the output board of the PV-1.3k schematic on eserviceinfo.com
The 47k series 2.2 uf series the sbs (diac) that triggers the triac on the output.
inverting that signal and triggering a flip flop is up to you.
Another schematic of the same thing is the bonsai solid state relay protection thread. His circuit is surface mount, which is for people with a $20000 wave solder machine after they have made a circuit board. The APV1122 is through hole and can fit on a dip project board from newark.
The DC detection circuit that triggers the flip-flop is part of most Peavey amps, for example the output board of the PV-1.3k schematic on eserviceinfo.com
The 47k series 2.2 uf series the sbs (diac) that triggers the triac on the output.
inverting that signal and triggering a flip flop is up to you.
Another schematic of the same thing is the bonsai solid state relay protection thread. His circuit is surface mount, which is for people with a $20000 wave solder machine after they have made a circuit board. The APV1122 is through hole and can fit on a dip project board from newark.
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Probably would be helpful if you provide some insight as to the dimensions of those heat sinks. There are web calculators that will allow you to assess the thermal resistance to ambient of such heatsinks, if you enter their dimensions.
Based on the K/Watt parameter, you would have a better feel as to what kind of power can be wasted in the form of heat on those heatsinks, so as not to fry the transistors.
Or more generally speaking, what kind of Watts of Music are you looking at, in terms of the thermally possible.
Based on the K/Watt parameter, you would have a better feel as to what kind of power can be wasted in the form of heat on those heatsinks, so as not to fry the transistors.
Or more generally speaking, what kind of Watts of Music are you looking at, in terms of the thermally possible.
Yeah this board looks like it is attempting the impossible. 150 w/ch with TO92 drivers? The board I'm using is 50 w/ch nominal, 70 by test, on +-35v rails, has TO220 drivers with heatsinks on them, also the VAS has a heat sink. As did the ST120 amp boards I replaced. You need more room to screw the drivers to the main heatsink as many boards do, or install a fan to cool individual heat sinks on the transistors out in space. Hence I suggest tightening up the rail capacitor board, which does not need all that heat sink it is using up. If those capacitors add up to more than 3300 uf, I'd delete some on the end and cut the end of the cap board off. If they do, one modern 3300 uf capacitor will do, delete the other 2 and cut the end of the cap board off. If generous, use 4700 uf cap, but Peavey got away with 3300 uf on the 250 W/ch (4 ohm) 130 w/ch (8ohm) PV-4c. The heatsinks down the side of the case are generous, but the only transistors using them are the outputs. That is sleazy. The PV-4c has a fan for all it's internal driver heatsinks.
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Reorganizing the "geography" of the internals of the chassis would help gain access to the full potential of the heat sinks. I would try to arrange the capacitor banks in the front central part of the chassis, so as to get the side lines free, allowing for some copper thermal spreader along the full width of the heat sinks that are available.
Possibly, this could imply a different make of the capacitor board.
Frankly speaking, the amplifier boards, without a detailed schematic, are somewhat ambigous / unknown. Consider populating the heat sinks with a wholly new solution. A "different amplifier", two boards, stereo, using the same power supply, toroidal, caps, and chassis, .... but a totally different amplifier. Something well documented and tested.
Possibly, this could imply a different make of the capacitor board.
Frankly speaking, the amplifier boards, without a detailed schematic, are somewhat ambigous / unknown. Consider populating the heat sinks with a wholly new solution. A "different amplifier", two boards, stereo, using the same power supply, toroidal, caps, and chassis, .... but a totally different amplifier. Something well documented and tested.
As it turns out, I think that the amplifier boards were relatively well know (back in their day) as the 'Greg Ball' design GB150D - also known on here as SKA. The information from the designer/manufacturer has since disappeared from the internet, but some is available at:
SKA sponsored Audio Forum - Products
I agree with your thoughts on reorganizing the chassis to better spread the heat from any future solid state devices.
As indianajo has suggested, I would also like to make some room for speaker protection, so it will be better to look into the power supply required to make some more space.
indianajo - thank you for the further information on the protection circuit. I had a look at the schematic suggested for the PV-1.3k and now understand. I'm assuming that once the 74AHC74 driving the NPN transistor has flipped (or flopped), a power off/on is necessary to 'reset' the circuit? After investigating the issue obviously.
SKA sponsored Audio Forum - Products
I agree with your thoughts on reorganizing the chassis to better spread the heat from any future solid state devices.
As indianajo has suggested, I would also like to make some room for speaker protection, so it will be better to look into the power supply required to make some more space.
indianajo - thank you for the further information on the protection circuit. I had a look at the schematic suggested for the PV-1.3k and now understand. I'm assuming that once the 74AHC74 driving the NPN transistor has flipped (or flopped), a power off/on is necessary to 'reset' the circuit? After investigating the issue obviously.
Yes that is how is reset the 74HC74. I have a resistor capacitor as a timer connected to the reset of the flip flop. A further wrinkle is a diode to power supply cap to discharge the timing capacitor once the amp is turned off.
The trouble with the triac connected to the speaker that peavey uses is that when it shorts the speaker to speaker negative, all the energy in the rail caps goes through the overheated output transistors until the mains circuit breaker blows. This can blow more output transistors than the first one, and they are $5 apiece. Michael Bean nfet circuit disconnects the speaker once a fault occurs.
I didn't print my whole schematic because PV-1.3k has "flying speaker ground" which means the two channel speaker grounds can be at different voltages. So I used a lot of optoisolators to communicate the fault to the 74AHC74 on it's own power supply. Took a separate wall transformer 5 v in the dirty AC corner of the box.
There are threads on here about what kind of boards available from e-bay or alibaba to copy famous amps. There are threads about that on here. A couple of respected ones I remember are "naim" and "parasound". Or westhost in Australia sells boards I believe. Try find one where the drivers (smaller transistors) use the heat sink on the flat plane, also.
I build speaker capacitor amps that don't need a protection board like the AX6, TGM8, TGM1i, Ron Ellis basic 50. But they don't go up to 150 watts, my AX6 does 70 W on single 70 v rail. Your +-65 v transformer necessitates a 2 output transistor pair per channel amp I believe. For those I buy junk Peavey or Crown PA amps and rebuild them.
The trouble with the triac connected to the speaker that peavey uses is that when it shorts the speaker to speaker negative, all the energy in the rail caps goes through the overheated output transistors until the mains circuit breaker blows. This can blow more output transistors than the first one, and they are $5 apiece. Michael Bean nfet circuit disconnects the speaker once a fault occurs.
I didn't print my whole schematic because PV-1.3k has "flying speaker ground" which means the two channel speaker grounds can be at different voltages. So I used a lot of optoisolators to communicate the fault to the 74AHC74 on it's own power supply. Took a separate wall transformer 5 v in the dirty AC corner of the box.
There are threads on here about what kind of boards available from e-bay or alibaba to copy famous amps. There are threads about that on here. A couple of respected ones I remember are "naim" and "parasound". Or westhost in Australia sells boards I believe. Try find one where the drivers (smaller transistors) use the heat sink on the flat plane, also.
I build speaker capacitor amps that don't need a protection board like the AX6, TGM8, TGM1i, Ron Ellis basic 50. But they don't go up to 150 watts, my AX6 does 70 W on single 70 v rail. Your +-65 v transformer necessitates a 2 output transistor pair per channel amp I believe. For those I buy junk Peavey or Crown PA amps and rebuild them.
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Just a recommendation...
Check out shaan's PeeCeeBee amp V4H PeeCeeBee V4H GB - diyAudio. It would be a good match for your voltage. I have the single output transistor version (v4) and the sound quality is excellent. You can get the Exicon lateral MOSFET outputs from ProfusionPLC in UK.
He also had PSU boards with protection circuitry; PeeCeeBee PSU GB - diyAudio. The last group buys have passed but he may still have boards available. You could ask if you're interested.
There are many other great amp designs here, too many to list. It looks like you have a good setup to build on and should end up with a very nice completed amp.
Check out shaan's PeeCeeBee amp V4H PeeCeeBee V4H GB - diyAudio. It would be a good match for your voltage. I have the single output transistor version (v4) and the sound quality is excellent. You can get the Exicon lateral MOSFET outputs from ProfusionPLC in UK.
He also had PSU boards with protection circuitry; PeeCeeBee PSU GB - diyAudio. The last group buys have passed but he may still have boards available. You could ask if you're interested.
There are many other great amp designs here, too many to list. It looks like you have a good setup to build on and should end up with a very nice completed amp.
Ray - thank you - more reading!! 
Still a little undecided, but I have purchased some protection boards from another guy on the forum. For the time being I am going to try out the TGM7 amps (by 'Bigun'). I've just ordered some PCBs, which will be on the slow boat from China - so hopefully start to build in 2-3 weeks time. These should come in around £60 the pair built. I like the idea that I can try these, then opt for something a bit different in the future - and the PeeCeeBee V4H GB is a great suggestion.
Still a little undecided, but I have purchased some protection boards from another guy on the forum. For the time being I am going to try out the TGM7 amps (by 'Bigun'). I've just ordered some PCBs, which will be on the slow boat from China - so hopefully start to build in 2-3 weeks time. These should come in around £60 the pair built. I like the idea that I can try these, then opt for something a bit different in the future - and the PeeCeeBee V4H GB is a great suggestion.