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Single BJT Amp Design
Single BJT Amp Design
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Old 21st January 2019, 09:06 AM   #11
dwaniks is offline dwaniks
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Thanks for the Suggestions guys,
Being a beginner I think I should start with JLH69 design. I feel it is simple and easy to do. My ultimate aim is to enjoy the essence of amp building . If JLH69 is success I will move to higher desings,,, So I would like to know whether I can use following power transistors "2SC5200 / MJ21193" as they are much regarded in web forums and reviews. Should I do any modifications in the original circuit if I introduce them ?.
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Old 21st January 2019, 09:34 AM   #12
kokoriantz is offline kokoriantz  Lebanon
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See also sublimed JLH1969
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Old 21st January 2019, 09:55 AM   #13
feedForward is offline feedForward  United States
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I think these may interest you:
MCA son of ZCA
Another variation to the MCA amplifier
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Old 21st January 2019, 01:57 PM   #14
indianajo is offline indianajo  United States
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QUOTE So I would like to know whether I can use following power transistors "2SC5200 / MJ21193" as they are much regarded in web forums and reviews. Should I do any modifications in the original circuit if I introduce them ?. END QUOTE
MJ21193 is a TO-3 transistor, and the drilling of four holes for that in the heat sink has to be very accurate. MJL21193 is the single hole version of that. 2SC5200 requires a single hole so the location is not so difficult to maintain. I find small drills tend to wander off to the side from the location I started from.
These are both rather powerful transistors and the gate capacitance may be too high for some sources to drive. No schematic for JLH69 was linked to so I don't know what it uses to drive the output transistor. If the base driver source is the earphone jack of a radio or CD player, then probably there is enough drive current.
Frankly, if you can't buy a circuit board the lowest wire count is a LM1875 IC amp, the schematic is on the datasheet which you can download from electronic vendors newark, digikey, mouser. You can run an LM1875 to about 15 watts off a 24v doorbell transformer from the home store. Plus a rectifier bridge, capacitor,, input jack, speaker jack, fuse & switch, heat sink, fan, bare project board, wire. If you want to get experienced at the machining part without the circuit building part, one of the class D amp boards from parts-express.com will run off a 19 v computer power supply from the same place. Buy the 2.5 mm power receptacle on the same order, they are hard to find otherwise. P-E also has dual banana binder post speaker jacks, rca jacks and dual audio volume pots for the input. I use metal recipe boxes for this sort of thing. Wear safety glasses when drilling.
If you don't like the idea of building boxes before learning circuits, buy a blown up amp on e-bay and repair it. I like the Peavey PV-4c, very cheap, schematic and transistor crossover are available online. CS800 is dirt cheap, revisions c and later actually sound good. The later ones like X & S have a grill in the front, although S has a switcher supply which is dangerous to work on. Crown amps are also respected although some schematics you might have to pay for.
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Last edited by indianajo; 21st January 2019 at 02:26 PM.
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Old 21st January 2019, 06:11 PM   #15
kstagger is offline kstagger  United States
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I vote for the 25WPC Nelson Pass Aleph J - easy to build, most of the parts can be bought in the DIY Audio store, but the 2SJ74s, however, can be difficult to source and/or are relatively pricey.
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Old 21st January 2019, 08:30 PM   #16
xrk971 is offline xrk971  United States
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Single BJT Amp Design
The Alpha 20 uses the same Aleph CCS as the Aleph J and uses easy to find BJTs on the front end vs $55/pair matched J74’s needed for the Aleph J (that’s what I ended up spending from DIYA store).
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Old 21st January 2019, 11:03 PM   #17
Bigun is offline Bigun  Canada
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Single BJT Amp Design
Quote:
Originally Posted by dwaniks View Post
Thanks for the Suggestions guys,
Being a beginner I think I should start with JLH69 design. I feel it is simple and easy to do. My ultimate aim is to enjoy the essence of amp building . If JLH69 is success I will move to higher desings,,, So I would like to know whether I can use following power transistors "2SC5200 / MJ21193" as they are much regarded in web forums and reviews. Should I do any modifications in the original circuit if I introduce them ?.
The JLH is a great place to start, wish Id suggested it !

You can get kits on eBay, no shame starting there. People have used the more modern power devices in that circuit but I think youd be better to start with something slower. Theres a lot of good advice on the net and this forum about the JLH.
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Old 21st January 2019, 11:50 PM   #18
steveu is offline steveu  United States
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Quote:
Originally Posted by Bigun View Post
If you want to get into building a discrete amplifier and learn about the basic workings then I would suggest 3 options:

a) simple usually means Class A, for that, best to go to the Nelson Pass forum where there are many proven designs and lots of people to help and in many cases you can buy a PCB to use. Such amps are simple in concept but need bulky power supplies and heatsinks.

b) Class AB - consider a chip amp, many people have been impressed with this approach

c) Discrete - the real DIY approach perhaps - something along the lines of a traditional 3 stage design: DX Blame MkIII - 2013 builders thread.

There are so many amp kits on eBay these days that for first time - unless you have a big parts bin already - it's just easier to buy on-line.

Go on eBay and search for 'LM3886 chip amp kit'
and search for 'power amplifier 2SC5200/A1943 class AB kit'

edit: also what Mooly said (posts crossed)
Excellent summary.
Unfortunately the "simple" class-A circuits are real dogs. For example the MOSFET amplifier above is biased at half the supply voltage, which is a huge mistake because the 15 Ohm pull-up will produce a positive swing of about 4 volts into 8 Ohms (12V*8/(8+15)), while the MOSFET will give you about -12 volts negative swing. Better to set the bias about 8 Volts for symmetrical clipping. At best this circuit produces about 5 Watts of audio and 25 Watts of heat, per channel.
I recommend buying a kit of some sort, which you can expect to destroy. If you persist and fix it a few times you will eventually learn enough to make an amp that lasts and provides a satisfying sound.
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Old 22nd January 2019, 01:56 AM   #19
feedForward is offline feedForward  United States
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I second the LM1875 suggestion by indianajo. Some claim the LM1875 sounds better than the LM3886. You can buy a complete mono LM1875 amp kit on eBay for around $2. The LM1875 device is most likely a clone of the original so I would just buy real Texas Instuments devices elsewhere. I bought two LM1875 kits from eBay and replaced the input cap with a known good poly one and it didn't sound bad. Used some old 19.5V laptop power supplies. It bugs me I likely have fake ICs so will replace with authentic ones soon.
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