So I've been playing keyboard in a band for the past year and have never actually had an keyboard amp to rehearse with. After looking at the prices for amps like the Roland KC series, I've been looking at cheaper diy options.
I've looked at some schematics for amplifiers based around the 2N3055 transistor and they seemed pretty comprehensible, and not that hard to build. Has anyone taken a project of this kind? Is there something I should be aware of before I take this on? Any circuits I should look into?
I've looked at some schematics for amplifiers based around the 2N3055 transistor and they seemed pretty comprehensible, and not that hard to build. Has anyone taken a project of this kind? Is there something I should be aware of before I take this on? Any circuits I should look into?
There shouldn't be anything really special about the Roland amps, other than perhaps a more sensitive input stage.
Do you have a stereo at home? If you do try plugging the keyboard into it. If it works and gives you adequate volume then you've on easy street because you can buy any number of pre-assembled DIY boards and simply hook up with a speaker... the work would be in packaging it like a musician's amp with a decent speaker(s) in the cabinet...
One example to look at ... Yeeco Digital Amplifier Board Mono ... but a little searching will find dozens more.
If you want to build from a bag of parts, I would suggest you peruse schematics and find one you're comfortable with. Kits make it easier if you can find one.
2n3055 is a historic part much counterfeited these days. I you want something cheap & real get MJ15015 from ON semi, or 2SC5200 from ST or ON. Buy from an authorized distributor like farnell, digikey, RS, german names I don't know.
The hard parts to get are transformer heat sinks & enclosure. Cheapest way I've found for full frequency amps is a PA amp for parts or repair on ebay. Gumtree is in UK, craigslist is worldwide but not popular outside the US. I've repaired Peavey PV-4c, ($20) Peavey PV-1.3k ($51.75) CS800s (part of $1000 band closeout, probably $200, sort of worked). Peavey schematics are easy to come by. Other respected brands of PA amp are Crown & QSC. You need 200-300 watts for PA amp for a 50 person audience. Especially piano sounds require high peak wattage at the hammer strike, but not much sustained wattage. 100 is fine for guitar or voice.
Scratch building, the hard part is finding the transformer. Ones without the center tap are easier to find on ebay. You want 36-50 v rated one for a 4 ohm speaker, can go as high as 65 v on a 8 ohm 300 w speaker. The rail voltage will be 1.4 * the label voltage on the transformer. Junk amps usually come with good transformers.
With no center tap, single supply amps with a speaker cap are required. Newbies should also use a speaker cap, cheap protection for your $150 300 W speaker. I've built an AX6 point to point see this thread Retro Amp 50W Single Supply - Page 22 - diyAudio
With MJE15028-29 drivers & heat sinks on them & the VAS, you can parallel two output transistors top & bottom for a 100W/ch or maybe more amp.
Another simple one is TGM8.
I installed mine in a ST120 chassis that originally had 40406 which were specially selected 2n3055. Chassis had a habit of blowing output transistors. MJ15003 or MJ15025 or MJL21194 are tougher, more soa. Don't forget a big heat sink, and on mine I used a fan. Other things you can get from a junk PA amp. Also enclosure to keep the RF interferance out, circuit breakers, power switch, IEC socket, binder terminals for speaker, bla bla.
New transformers are toroids, with 2 windings that you stack up by connecting top to bottom to make a double quoted voltage CT transformer. This make a split supply amp with NPN & PNP output transistors. As 2n3055 MJ2955 or MJ15015 MJ15016 or MJL21194 MJL21195. Those amps require speaker protector boards after the output to avoid destroying your speaker with DC voltage if something goes wrong.
Happy shopping & building.
The hard parts to get are transformer heat sinks & enclosure. Cheapest way I've found for full frequency amps is a PA amp for parts or repair on ebay. Gumtree is in UK, craigslist is worldwide but not popular outside the US. I've repaired Peavey PV-4c, ($20) Peavey PV-1.3k ($51.75) CS800s (part of $1000 band closeout, probably $200, sort of worked). Peavey schematics are easy to come by. Other respected brands of PA amp are Crown & QSC. You need 200-300 watts for PA amp for a 50 person audience. Especially piano sounds require high peak wattage at the hammer strike, but not much sustained wattage. 100 is fine for guitar or voice.
Scratch building, the hard part is finding the transformer. Ones without the center tap are easier to find on ebay. You want 36-50 v rated one for a 4 ohm speaker, can go as high as 65 v on a 8 ohm 300 w speaker. The rail voltage will be 1.4 * the label voltage on the transformer. Junk amps usually come with good transformers.
With no center tap, single supply amps with a speaker cap are required. Newbies should also use a speaker cap, cheap protection for your $150 300 W speaker. I've built an AX6 point to point see this thread Retro Amp 50W Single Supply - Page 22 - diyAudio
With MJE15028-29 drivers & heat sinks on them & the VAS, you can parallel two output transistors top & bottom for a 100W/ch or maybe more amp.
Another simple one is TGM8.
I installed mine in a ST120 chassis that originally had 40406 which were specially selected 2n3055. Chassis had a habit of blowing output transistors. MJ15003 or MJ15025 or MJL21194 are tougher, more soa. Don't forget a big heat sink, and on mine I used a fan. Other things you can get from a junk PA amp. Also enclosure to keep the RF interferance out, circuit breakers, power switch, IEC socket, binder terminals for speaker, bla bla.
New transformers are toroids, with 2 windings that you stack up by connecting top to bottom to make a double quoted voltage CT transformer. This make a split supply amp with NPN & PNP output transistors. As 2n3055 MJ2955 or MJ15015 MJ15016 or MJL21194 MJL21195. Those amps require speaker protector boards after the output to avoid destroying your speaker with DC voltage if something goes wrong.
Happy shopping & building.
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If economics is your problem then DIY is probably not the best solution. Unless you have years of experience you will spend more on failed builds. I suggest you look at cheaper brands, including Chinese brands like Pyle. It can be cheaper to rebuild such a product if it fails you than start from scratch.
You'll need a decent DVM about E20, I suggest a farnell house brand. You'll need decent soldering iron, I bought a variable temp one recently for $55. If you run into trouble you might need an analog VOM to trace signals, about $25 from ebay etc.
I did first SS project, ST120, poorly before internet with no schematic, for $50 junk amp and $60 in parts. It did work at 10 w/ch. Having a schematic and builder's manual really helped the 2nd effort, getting to 60 w/ch.
The PV-4c was $20 purchase, $26 in e-caps, $20 in transistors, $4 in auxillary heat sinks (had new transistors 4 times before).
The CS800s was $1 in resistors (toasted by a 75 W guitar amp I imagine), $5 in Power Supply parts, (fuse,cap) still needs $40 in new long life electrolytic caps to balance volumes and make reliable. People on ebay do really hate Peaveys, and the 90's built ones do have a few bad solder joints it takes patience to find. Look good, stop passing music when you're not probing it.
I don't have a scope & don't need one. If there is oscillation I can find it with the analog VOM and various blocking caps.
Switcher power supplies can be dangerous, DON'T repair one. Transformer rectifier supplies ended about 2005, so buy gear that old. You also want junk with leaded components, so stop about 2000.
You may need extra gain than a power amp has with a keyboard signal which can be too soft. The PV-4c or AX6 or TGM8 you can parallel one feedback resistor to make it smaller and increase the gain.
Junk amps can be dogs. The PV-1.3k needed $50 in transistors, $40 in rail caps, and 112 other cheap parts. Had a bad solder joint that 3-4 techs previously hadn't found since 1993 when it was built. Took me 2 years to fix off & on, but I learned a lot. Plus it is a 1300 W amp if I ever have an audience of 600 in a parking lot (not likely).
There are real bargains in monaural amps & mixer amps for part or repair on ebay. Musicians don't need stereo unless doing a leslie speaker sim. BTW mixer amps have more gain than a regular amp, for a soft keyboard signal. Also rudimentary tone controlls and usually a volume meter or led display stack. Often mixer amps have phantom power to XLR connectors so you can use a close to head condensor mike and sing over the keyboard, too.
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Bunch of top-flight advice, there indianajo! Many fine successes, too.
I don't know how you get by without a 'scope, though -- most of my troubleshooting was on the back of an old 10 MHz B&K. There was a spell when the company-provided DMM was having emotional problems. Soon I discovered there were all kinds of extra clues jumping out at me, just for poking around with a 'scope instead of the DMM.
Great recommending for our friend in Portugal. Should have him on a good path.
Regards
I don't know how you get by without a 'scope, though -- most of my troubleshooting was on the back of an old 10 MHz B&K. There was a spell when the company-provided DMM was having emotional problems. Soon I discovered there were all kinds of extra clues jumping out at me, just for poking around with a 'scope instead of the DMM.
Great recommending for our friend in Portugal. Should have him on a good path.
Regards
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I got a tiny 25w orange bass combo with a blown speaker that I think I could salvage a transformer from, would that be appropriate from a use case like mine?
It is a start. 25 W of cheap music is better than none.
You'll want a replacement driver. I've salvaged some good full frequency 6" 8 ohm ones from projection TV's sitting on the curb for garbage truck. Pop the bottom cover off with a flat blade screwdriver in the crack, then take the drivers out with phillips or 1/4" hex driver. Pull out & cut wire with diagonal cutters or toenail clipper. I was classy & put the grill back on. Salvaged power cord, too.
The toshiba drivers had a whizzer cone which improves high freq response. I'm using those in 12" long cardboard boxes (farnell) with a 15 mm square hole poked in the back to improve bass response. Those are in the TV room on the PV-4c. Until I work up the nerve to take the grill off the T-300 hi-freq projectors and replace the insta-short 1/4 phone jacks on the back. Grill is glued in and pretty fabric work replacing torn grill is not in my skill set.
You can buy a driver but don't buy one for a bass guitar. Keyboards have high frequencies, too.
Something that small you could use a 25-50 W class D amp board, about $30 from parts-express.com . Dayton Audio KAB-60M 1x60W Class D Audio Amplifier Board with Bluetooth 4.0 . I don't know who your european supplier of cheap TI class D boards is. The amp board I bought took a 19 v power supply usually sold for Dell laptop computers, about $20 in the parts-express catalog. An additional 5.5-2.1 mm barrel jack is required to get the power into the box. Those 3 parts would come in a parts-express $6.99 box, whereas If I bought the 3 parts individually on ebay there would be 3 freight bills. Look at the download on any amp board you buy to see what power supply it needs. There are $40 stereo ones amp boards have a built in power supply from AC, but buy a European one, our AC mains supply is different than yours. Then you need an approriate size fuse for the holder your Orange amp has. Make sure any bluetooth amp you buy also has a line level (1.6 to 2 vac) input. The world is going smart phone crazy; my $60 flip one doesn't produce bluetooth. Nor do smart phones have a 61 key input function.
You'll need a drill motor to mount the barrel jack. Also a drill of appropriate size.
Happy building.
You'll want a replacement driver. I've salvaged some good full frequency 6" 8 ohm ones from projection TV's sitting on the curb for garbage truck. Pop the bottom cover off with a flat blade screwdriver in the crack, then take the drivers out with phillips or 1/4" hex driver. Pull out & cut wire with diagonal cutters or toenail clipper. I was classy & put the grill back on. Salvaged power cord, too.
The toshiba drivers had a whizzer cone which improves high freq response. I'm using those in 12" long cardboard boxes (farnell) with a 15 mm square hole poked in the back to improve bass response. Those are in the TV room on the PV-4c. Until I work up the nerve to take the grill off the T-300 hi-freq projectors and replace the insta-short 1/4 phone jacks on the back. Grill is glued in and pretty fabric work replacing torn grill is not in my skill set.
You can buy a driver but don't buy one for a bass guitar. Keyboards have high frequencies, too.
Something that small you could use a 25-50 W class D amp board, about $30 from parts-express.com . Dayton Audio KAB-60M 1x60W Class D Audio Amplifier Board with Bluetooth 4.0 . I don't know who your european supplier of cheap TI class D boards is. The amp board I bought took a 19 v power supply usually sold for Dell laptop computers, about $20 in the parts-express catalog. An additional 5.5-2.1 mm barrel jack is required to get the power into the box. Those 3 parts would come in a parts-express $6.99 box, whereas If I bought the 3 parts individually on ebay there would be 3 freight bills. Look at the download on any amp board you buy to see what power supply it needs. There are $40 stereo ones amp boards have a built in power supply from AC, but buy a European one, our AC mains supply is different than yours. Then you need an approriate size fuse for the holder your Orange amp has. Make sure any bluetooth amp you buy also has a line level (1.6 to 2 vac) input. The world is going smart phone crazy; my $60 flip one doesn't produce bluetooth. Nor do smart phones have a 61 key input function.
You'll need a drill motor to mount the barrel jack. Also a drill of appropriate size.
Happy building.
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