So tell me what I'm missing. I'm completely new to diy electronics, but I wanted to give it a run and my 1150D went so I thought I'd build an amplifier. Box is still in the making but the amp is currently as basic as you can get. I have a transformer with a simple thermistor for inrush limiting and two bridge rectifiers with a small cap bank. 3A fuse and a power button connects the TF and I have two L12-2 amps for stereo music. Plan on using it with my Kirishima horns.
Should I add speaker protection and a soft start? If so whats my best bet for a kit or pre-designed circuit? I lack the know how to do a custom fit. The box pictures will be uploaded after I make it, plan on an aluminum enclosure 13"×10"×3" with netic s3-6 steel to shield the ps section. Not sure i need the shielding but we had extra material at work.
Should I add speaker protection and a soft start? If so whats my best bet for a kit or pre-designed circuit? I lack the know how to do a custom fit. The box pictures will be uploaded after I make it, plan on an aluminum enclosure 13"×10"×3" with netic s3-6 steel to shield the ps section. Not sure i need the shielding but we had extra material at work.
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You are lacking the heat sinks on the output transistors. The layout of these stupid boards means you need four heatsinks instead of two. Heatsinks are usually more expensive than the import boards, unless you can salvage them. The ones in discarded flat screen TV's would be useful, about 4 cm x 10 cm x 2.5 cm. But you can't buy discarded flat screen TV's, you have to pick one up on garbage day. You can pay about $20 apiece for new heat sinks from a distributor. Don't forget the silicon rubber thermal pads between output transistors & heat sink. Make sure mount screw doesn't touch the OT metal flange.
Then the heat has to get out of the amp somehow. Either vents in the metal case top and bottom, and tall feet to allow flow from the bottom. Or a fan blowing in one side and a grill to keep out the mice on the other side. I'm not sure a soft start is necessary but a speaker protection board is if your speakers cost more than the $30 these boards probably cost. My speakers were $300 each used, and since they were stolen & used ones are 1000 miles away, replacements will cost $600 apiece. I use as a result transformer coupled amps (MMA-875T), or speaker capacitor single supply amps like the AX6 or TGM8. Or a blown amp with competent speaker protection as the low wattage cs800s I bought for $200 and put $40 of parts in. That project also solved the case, heat sink, fan, speaker connector, input connector & circuit breaker problem, in one ebay box.
Then the heat has to get out of the amp somehow. Either vents in the metal case top and bottom, and tall feet to allow flow from the bottom. Or a fan blowing in one side and a grill to keep out the mice on the other side. I'm not sure a soft start is necessary but a speaker protection board is if your speakers cost more than the $30 these boards probably cost. My speakers were $300 each used, and since they were stolen & used ones are 1000 miles away, replacements will cost $600 apiece. I use as a result transformer coupled amps (MMA-875T), or speaker capacitor single supply amps like the AX6 or TGM8. Or a blown amp with competent speaker protection as the low wattage cs800s I bought for $200 and put $40 of parts in. That project also solved the case, heat sink, fan, speaker connector, input connector & circuit breaker problem, in one ebay box.
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I was under the impression that these amps don't get terribly warm unless pushed and I will likely not drive them too hard. So I was planning on using the box itself as a heat sink with an extra 1/8th inch thick piece of aluminum backing the transistors. I don't have the pads but I've got a few extra tubes of thermal paste I'd planned on using. My design for the box has bottom vents along the edges and the top will have my name in script cut out spanning the majority of the surface.
Is there a good speaker protection circuit kit? I don't understand them too much and it seems everyone has their tweaks that "need" to be made to each kit so I'm kinda lost.
Is there a good speaker protection circuit kit? I don't understand them too much and it seems everyone has their tweaks that "need" to be made to each kit so I'm kinda lost.
That is a huge bank of capacitors and a big transformer. When an OT shorts it could possibly supply 1000 A. Most of those $5 speaker protection kits have tiny relays that would weld together under that much DC current. There is one board that the guys here respect, but I didn't save the thread #. One reason I bought a aged cs800s, it has two competent protection relays that would cost $80 if you bought them from Peavey. Enzo the repair shop owner said to trust it on my speakers.
If you have heat sink compound, you can use mica washers instead of silicon rubber. Cheaper, not as good as rubber, more available at newark.
30 w (15 wpch) NAD amps used the case as the heatsink. Don't go above that. Spreader bars delay the meltdown for the hour duration of a FTC watts rating test, but don't actually transfer the heat to the air. If you are going to run your amp for more than an hour, you need fins or fans. I run my amps 14 hours some days with the FM tuner on.
If you have heat sink compound, you can use mica washers instead of silicon rubber. Cheaper, not as good as rubber, more available at newark.
30 w (15 wpch) NAD amps used the case as the heatsink. Don't go above that. Spreader bars delay the meltdown for the hour duration of a FTC watts rating test, but don't actually transfer the heat to the air. If you are going to run your amp for more than an hour, you need fins or fans. I run my amps 14 hours some days with the FM tuner on.
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Yeah the TF is 330VA, and thats 10 4700uF caps, plenty to do some damage. Would an FF rated fuse at ~3A do enough or should I get a full protection board made up? I've been reading through Rod Elliot's stuff and was thinking about trying to build his project 33 and 198. Trouble there is I'm not sure i can test it all as I don't have a means to feed it. I can get my hands on a scope but I don't have a bench power supply, dummy load, or function generator. I could buy it all, but I'd go broke with the treats I'd have to get for the wife so she didn't get mad.
Good to know on the heatsinks, just in case the volume gets turned up I will look around for a block that'll work with them, I do have several smaller heatsinks sitting around that were intended for or removed from computer motherboards. If any are from newer gaming boards they'll fit the bill nicely.
Good to know on the heatsinks, just in case the volume gets turned up I will look around for a block that'll work with them, I do have several smaller heatsinks sitting around that were intended for or removed from computer motherboards. If any are from newer gaming boards they'll fit the bill nicely.
Yes, the Pentium II heatsink I salvaged was very useful. About 4" x 3" x 1" lots of fins. I have 5 TIP147 on it as a regulator.
I don't have a bench power supply, or function generator. I use a battery radio I fished out of the trash & put a new volume pot in. I buy transformers at charity resale shop or ebay, bridge rectifier from salvage PCAT supply or newark. Used filter caps are not reliable for a 2000 hr a year amp, but are okay for test gear power supply.
If you see a flat screen TV on the curb, you can get rid of the screen by folding it up and put in construction grade garbage bag. Wear gloves & safety glasses. Use plywood as a hinge. Plastic case you break up. AC surge filter board next to IEC socket useful for preventing damage to amp internals. Filter caps are trash, heat sinks +++good, silicon pads galore for TO-247. The TO-247 nfet transistors are usually good, but are vfets, not laterals.
Diyaudio store sells a protection board. I suppose their protection relay is competent. Look at various protection threads on this board.
The Michael Bean Nfet back to back series the speaker is competent, the salvage nfets from flat TV would be perfect. You need a DC detect circuit (speaker out to 7.5 v zener line to line, series 47k, series 2.2 uf film cap. Junction 47k & 2.2 cap is a positive DC detect signal. I use a 74AHC74 IC as a fault latch, to remember there was a fault, with a Power up reset on the reset input. (5 v supply to 1 meg series 1 uf ceramic cap, junction is reset signal). 74AHC74 Q drives red led & fet driver (panasonic apv1122) Qbar drives green LED. Needs a 5 v supply.
BTW the signal from the dc detect is bipolar, I use a bipolar input opto isolator to normalize it to +3 v or 0 signal.
I don't have a bench power supply, or function generator. I use a battery radio I fished out of the trash & put a new volume pot in. I buy transformers at charity resale shop or ebay, bridge rectifier from salvage PCAT supply or newark. Used filter caps are not reliable for a 2000 hr a year amp, but are okay for test gear power supply.
If you see a flat screen TV on the curb, you can get rid of the screen by folding it up and put in construction grade garbage bag. Wear gloves & safety glasses. Use plywood as a hinge. Plastic case you break up. AC surge filter board next to IEC socket useful for preventing damage to amp internals. Filter caps are trash, heat sinks +++good, silicon pads galore for TO-247. The TO-247 nfet transistors are usually good, but are vfets, not laterals.
Diyaudio store sells a protection board. I suppose their protection relay is competent. Look at various protection threads on this board.
The Michael Bean Nfet back to back series the speaker is competent, the salvage nfets from flat TV would be perfect. You need a DC detect circuit (speaker out to 7.5 v zener line to line, series 47k, series 2.2 uf film cap. Junction 47k & 2.2 cap is a positive DC detect signal. I use a 74AHC74 IC as a fault latch, to remember there was a fault, with a Power up reset on the reset input. (5 v supply to 1 meg series 1 uf ceramic cap, junction is reset signal). 74AHC74 Q drives red led & fet driver (panasonic apv1122) Qbar drives green LED. Needs a 5 v supply.
BTW the signal from the dc detect is bipolar, I use a bipolar input opto isolator to normalize it to +3 v or 0 signal.
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I have built the L12 boards and am more than satisfied. They dont run very hot, but i wouldnt recommend running them without a heatsink.
There are many power supply boards available with built in speaker protection. I also highly recommend fuses on both boards, both on the + and - supplies.
I purchased a Bryston clone ps board from Electronic-mall on ebay. It features dual mono, soft start, and speaker protect all on one pcb. This solves the issues of wiring 3 different pcbs. Mike Beeny on youtube does this build. Very informative.
There are many power supply boards available with built in speaker protection. I also highly recommend fuses on both boards, both on the + and - supplies.
I purchased a Bryston clone ps board from Electronic-mall on ebay. It features dual mono, soft start, and speaker protect all on one pcb. This solves the issues of wiring 3 different pcbs. Mike Beeny on youtube does this build. Very informative.
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