Hey guys.
I have the chassis of an old Alesis poweramp, which I would like to turn into a relatively low power (20-40 watts I guess) stereo speaker amp for my living room TV.
I'd like to use the chassis as-is, and each channel has space for 7 transistors on its heat-sink. Is there any class AB design that you guys could recommend? I'm willing to design my own boards if needed, no need for a complete DIY kit.
Thanks 🙂
I have the chassis of an old Alesis poweramp, which I would like to turn into a relatively low power (20-40 watts I guess) stereo speaker amp for my living room TV.
I'd like to use the chassis as-is, and each channel has space for 7 transistors on its heat-sink. Is there any class AB design that you guys could recommend? I'm willing to design my own boards if needed, no need for a complete DIY kit.
Thanks 🙂
If your speakers are 8 ohms, you need one pair output transistors on the heatsink, and perhaps a temperature sense transistor.
If your speakers are 4 ohms, you need 2 pairs output transistor per channel.
40 watts is dead easy, my Apex AX6 does 75 with one pair: for 5 seconds only. 72 v single P.S. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html diyaudio/ax6
You don't have to put the output transistor on the driver board as on the artwork. I did not.
What is the rectified voltage on the mains capacitors no load? Does transformer have a center tap? Does transformer have a separate winding for +- 15 volt for op amps?
If +-42 and op amp voltages, the Peavey M-2600 could be copied. TL072 input op amp, 2 transistor VAS, 2 drivers 4 output transistors. I like the drivers to have small separate heat sinks but you could put them on the main heat sink. 70 w/ch. Search for the schematic. I would leave out the protection transistors, VI limiter is not much protection.
Elvee Archosaurus has a heat sensing transistor instead of 2 diodes like the M-2600. Schematic on this forum. Single 60 v power supply.
Elvee oldfashionedmax has single 50 v power supply. Has heat sensing diodes.
Bigun TGM7 Rev 9 has one pair nfet output transistors but he has a layout.
If your speakers are 4 ohms, you need 2 pairs output transistor per channel.
40 watts is dead easy, my Apex AX6 does 75 with one pair: for 5 seconds only. 72 v single P.S. https://www.diyaudio.com/forums/solid-state/236256-retro-amp-50w-single-supply-42.html diyaudio/ax6
You don't have to put the output transistor on the driver board as on the artwork. I did not.
What is the rectified voltage on the mains capacitors no load? Does transformer have a center tap? Does transformer have a separate winding for +- 15 volt for op amps?
If +-42 and op amp voltages, the Peavey M-2600 could be copied. TL072 input op amp, 2 transistor VAS, 2 drivers 4 output transistors. I like the drivers to have small separate heat sinks but you could put them on the main heat sink. 70 w/ch. Search for the schematic. I would leave out the protection transistors, VI limiter is not much protection.
Elvee Archosaurus has a heat sensing transistor instead of 2 diodes like the M-2600. Schematic on this forum. Single 60 v power supply.
Elvee oldfashionedmax has single 50 v power supply. Has heat sensing diodes.
Bigun TGM7 Rev 9 has one pair nfet output transistors but he has a layout.
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Not all of the transistors need to go on the heat sink. At 20-40 watts per channel, only the 2 outputs and vbe multiplier per channel need to go on the main heat sink. Drivers can benefit from a small heat sink on each, or they could go on the main heat sink. If good sustained beta outputs are used, the drivers don’t even necessarily need heat sinking. The rest of them wont need heat sinking.
I'm building from the ground up. I'm using the transformer that came with it on another project. I'll be powering it from an off the shelf smps, so I can create pretty much any voltage I want/need.
And yeah I should have specified I don't NEED all 7 transistors occupied on the heat sink. Less will obviously do (especially considering this was built as a 75 watt per channel PA amp.)
Just kinda looking for directions as I've only ever repaired (and blown up) amps up until this stage.
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What about the TGM8? Or does that dissipate too much heat.
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So what supply voltage were you planning to run off of, and what kind of transistors fit the heat sink? If I were to venture a guess I’d assume it takes TO-3P’s, which are easy to work with, easy to get, and easily up to the task.
20 wpc requires +/-21.5V (43V single supply) at full load. 40 watts requires +/-30V (60V) at full load.
Most of the shelf SMPSs are regulated, which helps. The only caveat is they need to supply about 3X the maximum average current demand just to reproduce full output voltage without limiting. Some can, some can’t. You can always oversize by a factor of 3 and never have a problem, but that could blow the budget. The other issue is that you usually need two if you are doing a split supply DC coupled amplifier. But output capacitors aren’t that much of a hardship at these power levels and with speakers that can’t respond to 20 Hz anyway - then a single voltage works just fine.
20 wpc requires +/-21.5V (43V single supply) at full load. 40 watts requires +/-30V (60V) at full load.
Most of the shelf SMPSs are regulated, which helps. The only caveat is they need to supply about 3X the maximum average current demand just to reproduce full output voltage without limiting. Some can, some can’t. You can always oversize by a factor of 3 and never have a problem, but that could blow the budget. The other issue is that you usually need two if you are doing a split supply DC coupled amplifier. But output capacitors aren’t that much of a hardship at these power levels and with speakers that can’t respond to 20 Hz anyway - then a single voltage works just fine.
I was looking for TGM8 but could not find it quickly. I think that had artwork too.
Don't sweat the output transistors. One has DH45 one has 2n3055 I used MJ15003 clones (NTE181) in TO3 on Apex AX6 and they worked fine. Do not buy fast output transistors like NJW1302/4502, dodgy layout can make them oscillate. If you need plastic cases to save $5 a transistor, NJW21193/21194 are 4 mhz Ft, much safer than 1302/4502. The njw#### in To3-p have exposed metal corners that can be sawed off if you don't want real TO3 packages at $11 each. I did that once. 30 MH ft drivers like MJ15028/29 sound better than 6 mhz TIP31c/32c, by direct experiment. My first AX6 with TIP31/32c had bad highs compared to a Dyna board with 20 mhz 2n5320/22. Don't buy transistors from ebay amazon or alibaba, counterfeits are everwhere. If you listed your continent I'd mentions reliable sources. In US I use newark, digikey, mouser, aliiedelec. Lots of 100 resistors are cheaper at newark. Especially if you buy 1%ers a little off the standard EIA values. All distritbutors all hate 2 of this and 3 of that, may hit you with a handling charge if the order is not $50 or over.
Note the sales voltage of power transformers produces 1.4*nominal -1.4 v actual rectified voltage. Surplus single winding transformers are cheaper online than center tap versions. SMPS, the nominal voltage is what comes out. To keep RF howls out of the linear parts, Peavey puts SMPS in a separate grounded steel enclosure with RF fiters on all inputs and outputs, see CS800s. A steel divider installed in your salvage chassis may help, but you'll need a RF filtering IEC input to the switcher supply, and some ferrite beads on the DC wires running over to the linear side, at least.
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Build the honeybadger amp in this forum
Your heat sinks are likely 1 temp sense beta multiplier and 3 outputs per rail , so up to 200w per channel. Sizing the transformer determines your wattage output.
Your heat sinks are likely 1 temp sense beta multiplier and 3 outputs per rail , so up to 200w per channel. Sizing the transformer determines your wattage output.
A really nice board from diystore, but enormous PCB and output transistor positions might not fit your heatsink. Probably won't IMHO. Did not fit my salvage chassis. Split supply too, which may require buying a 2nd SMPS. Output cap boards are single supply.
I have output transistors and heat sense (diode stack or transistor vbe) remote from my AX6 driver boards, I run the driver wires and the temp feedback wires 2" away from each other, and put a 6 turn coil on the temp sense input to the driver transistors (on the driver PCB) to prevent any oscillation from buiding up. All modern product has the output transistors located right on the driver board.
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Buy ready plate amps as per transformer volts, plenty of choices are available, some with heat sink.
LM 1875, and 1943/5200 plate amps are very common here, a step up are 'mosfet' plate amps.
Not worth the hassle of sourcing PCB and parts, and building, in my opinion.
But then I boug lots in the flea market for absurd prices, and most turned out working...
LM 1875, and 1943/5200 plate amps are very common here, a step up are 'mosfet' plate amps.
Not worth the hassle of sourcing PCB and parts, and building, in my opinion.
But then I boug lots in the flea market for absurd prices, and most turned out working...
Ye
I think I'll have a look at a 40wpch TGM8. I'll ask around on that forum thready if anything comes up. Thanks 👍
Nothing I had in mind. I'm gonna go with two 36V SMPS that can do ~52 watts each and use a regulator (plus the adjustment on the power supply) to bring it to the +/-30 that you suggested for 40W.
Yep, should have pointed that out. I type faster than I think hahaha.
Already have that somewhat planned out 🙂
I think I'll have a look at a 40wpch TGM8. I'll ask around on that forum thready if anything comes up. Thanks 👍