After the issues with my LM3886 (solved in the meantime) I started thinking about a small discrete power amp that is suitable for active speakers. I made the list of what I'd like:
- all discrete, no IC's
- about 10-20W in 8 Ohm, should be plenty for active speakers in a living room
- "good enough", let's say 0.05% distortion or so over power and bandwidth
- stable with enough margin to make it foolproof
- easy to find current components. No matched pairs, ring-emitters, IGBT's or exotic values for resistors or capacitors. Somehow I prefer BJT over FET.
- working from a dual voltage supply
- cheap enough to be an alternative for a chip amp. I will probably be more expensive but it shouldn't be 10x more expensive.
So not the ultimate amp in terms of performance. Does not need to have the least components but let's say the minimum for good function.
The closest I could find is the JLH. The class A working makes it a bit problematic for active speakers. But maybe there is something more recent in class AB around. I have been out of it so long that I probably missed a lot.
- all discrete, no IC's
- about 10-20W in 8 Ohm, should be plenty for active speakers in a living room
- "good enough", let's say 0.05% distortion or so over power and bandwidth
- stable with enough margin to make it foolproof
- easy to find current components. No matched pairs, ring-emitters, IGBT's or exotic values for resistors or capacitors. Somehow I prefer BJT over FET.
- working from a dual voltage supply
- cheap enough to be an alternative for a chip amp. I will probably be more expensive but it shouldn't be 10x more expensive.
So not the ultimate amp in terms of performance. Does not need to have the least components but let's say the minimum for good function.
The closest I could find is the JLH. The class A working makes it a bit problematic for active speakers. But maybe there is something more recent in class AB around. I have been out of it so long that I probably missed a lot.
You could have a look at all the simpler class-AB amps out there with like 3 stages or so.
Digi-125 is as simple as it gets, or Baby Aksa, Rod Elliots P3 etcpp.
All of these can be downscaled via smaller rail voltages with minor adjustments.
Then again, you maybe would like some more power for the woofer and use the same PSU for all amps (bass,mid, tweeter).
I´m using LM3886 for my active setup and am quite happy with them but will try a Baby Aksa soon for which I have done a layout.
If it works I could even part with some PCBs if you´re interested.
That said, I would argue that there is no completely discrete amplifier that is 100% foolproof.
Maybe some single-ended class-a design with an output capacitor would come close but that isn´t very practical.
If foolproof is your priority I´d stick with the LM3886 and use a proven PCB-design/-kit.
Digi-125 is as simple as it gets, or Baby Aksa, Rod Elliots P3 etcpp.
All of these can be downscaled via smaller rail voltages with minor adjustments.
Then again, you maybe would like some more power for the woofer and use the same PSU for all amps (bass,mid, tweeter).
I´m using LM3886 for my active setup and am quite happy with them but will try a Baby Aksa soon for which I have done a layout.
If it works I could even part with some PCBs if you´re interested.
That said, I would argue that there is no completely discrete amplifier that is 100% foolproof.
Maybe some single-ended class-a design with an output capacitor would come close but that isn´t very practical.
If foolproof is your priority I´d stick with the LM3886 and use a proven PCB-design/-kit.
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25 W Apex AX6. Most of this thread is about 50 W AX6, but there is one schematic with the voltages & resistors modified for 25 W version.
Retro Amp 50W Single Supply - Page 22 - diyAudio
6 transistors, 70 wires. I built mine point to point & it didn't oscillate. Which the LM1875 did, both channels, irredemeably w/o a ****ese speaker burner (split supply) PCB.
HD in the sub .1% area. Speaker capacitor to prevent DC damage if a solder joint pops loose, as happens in home build devices.
the 25 W version is after the page I linked you to. I listen at 1/4 W average, but my amp has ability to put out 70 W during the cannon shot in 1812 Overture. Not enough output pairs (1) to put that out continuously.
Current stable of transistors, I'd use MJ15003 or MJ15015 outputs, MJE15028/29 drivers & VAS, MPSA06 or 2n5550 2n5551 input transistor. I heat sinked everything but the input transistor. Watch the drivers & VAS, 3 mhz TIP31c/32c really limited the high frequency accuracy. Men deaf above 7000 hz won't notice the inaccuracy. Original 200 khz 40111 or homotaxial 2n3055 output transistors limited the high frequencies too, but the problem goes away with modern >2mhz Ft epitaxial outputs.
Big advantage, you can use single supply transformers like 44 v for 70 w, 24 v for 25 w, which are much cheaper than 2 winding modern parts. I found a 44 v @ 7 A Vermont transformer for $60 ebay. I found 95 vct @ 2 A transformers from Mojave for $12, of which I only use one half of.
Don't understand the "active speaker" purpose. Active speakers have their own internal amp, designed to burn out in 6 to 10 years. Passive speakers have no amp, require a diy amp or some commercial substitute. The cheapest thing is to repair old Peavey PA amps, I've found. Case, fans, heatsinks, connectors, pots, IEC, all for $40-100. The last one I bought for $105, came operational! has a dirty volume pot.
Retro Amp 50W Single Supply - Page 22 - diyAudio
6 transistors, 70 wires. I built mine point to point & it didn't oscillate. Which the LM1875 did, both channels, irredemeably w/o a ****ese speaker burner (split supply) PCB.
HD in the sub .1% area. Speaker capacitor to prevent DC damage if a solder joint pops loose, as happens in home build devices.
the 25 W version is after the page I linked you to. I listen at 1/4 W average, but my amp has ability to put out 70 W during the cannon shot in 1812 Overture. Not enough output pairs (1) to put that out continuously.
Current stable of transistors, I'd use MJ15003 or MJ15015 outputs, MJE15028/29 drivers & VAS, MPSA06 or 2n5550 2n5551 input transistor. I heat sinked everything but the input transistor. Watch the drivers & VAS, 3 mhz TIP31c/32c really limited the high frequency accuracy. Men deaf above 7000 hz won't notice the inaccuracy. Original 200 khz 40111 or homotaxial 2n3055 output transistors limited the high frequencies too, but the problem goes away with modern >2mhz Ft epitaxial outputs.
Big advantage, you can use single supply transformers like 44 v for 70 w, 24 v for 25 w, which are much cheaper than 2 winding modern parts. I found a 44 v @ 7 A Vermont transformer for $60 ebay. I found 95 vct @ 2 A transformers from Mojave for $12, of which I only use one half of.
Don't understand the "active speaker" purpose. Active speakers have their own internal amp, designed to burn out in 6 to 10 years. Passive speakers have no amp, require a diy amp or some commercial substitute. The cheapest thing is to repair old Peavey PA amps, I've found. Case, fans, heatsinks, connectors, pots, IEC, all for $40-100. The last one I bought for $105, came operational! has a dirty volume pot.
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Apex designs are great for discrete low count. Check out the directory and keep going until you hit the max number of actives you can handle. My experience with the Apex FH9 *hexfet variant of FX8* is that it is super sounding, easy to build, low cost, and can be assembled in an hour with $7 in parts if you cheap it out with no-name Chinese parts and $23 with name brand parts from Mouser.
A Directory of Apex Audio Amplifiers
There is also the DX amp by Carlos:
Destroyer x Amplifier...Dx amp...my amplifier
I have built it and it sounds really nice too.
A Directory of Apex Audio Amplifiers
There is also the DX amp by Carlos:
Destroyer x Amplifier...Dx amp...my amplifier
I have built it and it sounds really nice too.
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kolibri amp from bimo's blog
Kolibri Amplifier – Anistardi's Blog
16watt 8ohm. tested, clean stable and very cheap
Kolibri Amplifier – Anistardi's Blog
16watt 8ohm. tested, clean stable and very cheap
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Doesn't quite meet spec but an elegant simple design
Personally, I like Lazy Cat's VSSA. 6 devices, efficiently used. The only issue is that it uses lateral MOSFETs for the output transistors.
VSSA Lateral MosFet Amplifier
Paul
Personally, I like Lazy Cat's VSSA. 6 devices, efficiently used. The only issue is that it uses lateral MOSFETs for the output transistors.
VSSA Lateral MosFet Amplifier
Paul
Something from our local audioforum..
danwatt-lka-sch — ImgBB
Measured performance
Danwatt-LKA-50-V-steps-1and25-W-4-R — ImgBB
danwatt-lka-sch — ImgBB
Measured performance
Danwatt-LKA-50-V-steps-1and25-W-4-R — ImgBB
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As this seems to be become a nice collection of simple amps,
here´s one on my list from lineup:
Class A, 4 Watt, No Feedback, Simple Circuit, Great Sound
here´s one on my list from lineup:
Class A, 4 Watt, No Feedback, Simple Circuit, Great Sound
Quite a lot of ideas. Funny how you can trace back a lot of these designs to the JLH. (and probably earlier) Just some reactions to things mentioned/asked:
- I'm building the active speakers myself, so I need the amplifiers. Most important reason is to be able to use digital filters.
- there are 2 Visaton W250S bass speakers. It is a kind of scaled down "Monitor 890", the mid and tweeter are already a long time on the shelf. The living room isn't large, about 70m³. I'm not playing music at high levels either. So 20W for each woofer seems more than enough.
- I looked at the Self Blameless (got the book). But this isn't "simple". Could be a long term project to replace the LM3886 that I'll use for starters with these ones.
Thanks for all the ideas so far.
- I'm building the active speakers myself, so I need the amplifiers. Most important reason is to be able to use digital filters.
- there are 2 Visaton W250S bass speakers. It is a kind of scaled down "Monitor 890", the mid and tweeter are already a long time on the shelf. The living room isn't large, about 70m³. I'm not playing music at high levels either. So 20W for each woofer seems more than enough.
- I looked at the Self Blameless (got the book). But this isn't "simple". Could be a long term project to replace the LM3886 that I'll use for starters with these ones.
Thanks for all the ideas so far.
Going with LM3886 and then replacing them at will sounds like a good plan.
Did the same with relatively cheap class-d amps (Aiyima A04) that is still used for the woofers.
Now replacing with LM3886 and Baksa in future and possibly others for comparison fun etc.
This one is also tempting.
It´s small, it´s a diamond, available parts and some iterations even get by without a heatsink. And SuzyJ is really making some beautiful layouts. What´s not to like?:
Cascading diamond buffers - a cheap low THD 10W amp with TIP41C
Did the same with relatively cheap class-d amps (Aiyima A04) that is still used for the woofers.
Now replacing with LM3886 and Baksa in future and possibly others for comparison fun etc.
This one is also tempting.
It´s small, it´s a diamond, available parts and some iterations even get by without a heatsink. And SuzyJ is really making some beautiful layouts. What´s not to like?:
Cascading diamond buffers - a cheap low THD 10W amp with TIP41C
vsqc mosfet amp
Havoc,
this one could also be interesting.
Very simple quasi complimentary MOSFET amplifier
Read a bit up right there, if you like.
Dacz has done a compact layout too.
Mine first build was with prasi rev4.3 board and tested with 35VDC.
Not needed much heat think.
Havoc,
this one could also be interesting.
Very simple quasi complimentary MOSFET amplifier
Read a bit up right there, if you like.
Dacz has done a compact layout too.
Mine first build was with prasi rev4.3 board and tested with 35VDC.
Not needed much heat think.
Attachments
How about one of Elvee's amplifiers?
Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners
Old-fashioned amplifiers with a new twist (1)
Should meet the brief pretty well.
Easy-MOS is a simplistic, efficient and evolutive all-MOS amplifier for beginners
Old-fashioned amplifiers with a new twist (1)
Should meet the brief pretty well.
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