Hi mark...nice you drop by...yes i like the sound of this mini amp so i was tweaking to get the most power that it can deliver at 24v rail into 8 ohms. I had used vfet's from SMPS for testing..is there a great effect if i will use this Vfet instead of the orig LatFET in your ZCA?
BTW, I am using SmPS 24.5v 10A to power up this amp with add'll 20.000uf cap,will this need choke?
If you do not get whistling from the SMPS you can use it. It should have no hum so choke reuired. I wouldn't use a SMPS. Go for a linear traditional PS.
You can try a number of FETs. I use the ones I did because they are rated as audio FETs and local electronics stores sells them.
yes,and I tried several Power Mosfet From Fuji Electricand hitachi that also suited for amplifiers even those with 4v gate drive Mosfets and they worked good. i just wonder if they can hold the 8 ohms load since some are rated at 125 to 250w.
I heard no hum from SMPS but a little hiss like sound is heard at full volume.
I heard no hum from SMPS but a little hiss like sound is heard at full volume.
If the FET are more powerfull they may work with a lower load. But just bias them up slowly.
Hi, well I have now had the opportunity to knock up this circuit.24V supply, 15R drain load, 8R resistor output load.The Fet is IRFPC50.Feeding in a 400Hz sine wave, and adjusting the bias pot I settled on 9.3V as being the optimum 'mid point' drain volts. This was not so much about getting equal clipping but minimal overall distortion.The distortion was quite high as the waveform could be seen to contain a fair degree of second harmonic.At this point the max votage swing was 8.8V peak to peak (and I was being generous)This is 4.4V peak which is 2.4W peak, 1.2W rms.The amp was consuming almost exactly 1 A, so total power consumtion 24Watts. Overall efficiency, 5%, not great.The distortion level was, as stated, quite high, being clearly visible on the 'scope.When tried with a 'real' 8 Ohm speaker load the output dropped further, but there was a reasonably audible sound being produced and adequate for normal listening levels.This would probably improve given the right choice of speaker, something like a 15R Lowther probably being most suitable.It has to be said that the output is very load dependant so will sound very different on different speakers depending on their impedance characteristic.To conclude this is a very simple amp to build and eminently suitable for complete beginners who will get fair results for thier efforts, and enjoy listening to music in the half Watt levels.Just make sure your power supply is clean, two car batteries is the simplest source.RegardsHenry
for those who do not believe in Global Negative Feedback correction.
One builder tried car batteries but the sound lacked dynamics compared with a good clean PS. Not what I would have thought but he did try it several times just to make sure. But also different FET to yours.
I tried diffrerent FETs. They didn't work very well that is why I stayed with the 2SK1058. Not sure if you will get the same results as me if you swap the FET out but it maybe worth a try. Do it in stereo and have a listen. Also different input and output caps will have an effect.
It took about three months of constant trial and error before I came up with the final cct. and combination of parts. So try some experimenting.
I tried diffrerent FETs. They didn't work very well that is why I stayed with the 2SK1058. Not sure if you will get the same results as me if you swap the FET out but it maybe worth a try. Do it in stereo and have a listen. Also different input and output caps will have an effect.
It took about three months of constant trial and error before I came up with the final cct. and combination of parts. So try some experimenting.
Generally earthing will let you down here. Go for star earth and make sure all connections are good. Use wire to join your earths and not just an earthed chassis. The other thing which may cause hum is proximity. Try to keep AC things away from DC things. If your choke and power tranni are near each other turn the choke 45 degrees to the power tranni.
Got a pic of the choke? It may be saturating. I used a Mundorf 10mH ferrite core audio grade choke and it worked fine.
Hi,
just got ready with a ZCA. I use 30000 µF per channel and 2 tiny chokes, too tiny.... I had to use a capacitance multiplier (one per channel) to reduce the hum to zero. Now running with ~ 19.5 Volts. I use 12 V 20 watts halogen bulbs instead of the resistors. So far nice warm sound, I like it.
Another user wrote, the ZCA is the most sensitive amp in matter of the input cap. I started with older russion paper in oil condensators resulting in nice natural mids but little dull highs. An Audyn A4 MKP cap was very transparent, but also with a little bit to offensive highs. I just ordered some russian teflons now....
The point is, I found some interesting facts about coupling caps and their behavier. It seems, the higher the output impedance the cap sees, the more the DF and DA of the cap is doing audible distortion and colouration.
Walter G. Jung wrote:
In the ZCA, I guess the input cap works into a pretty high impedance of ~ 1 Mega Ohm, resulting in the need for a VERY good audiophil cap. So it could be a good idea to reduce the impedance down to at least 50-100k or even better to ~ 20k or so, to reduce the effects described by Walter Jung. This would result in a larger input cap, but every good MKP should do the job now with ease.
Could be done by changing the trimmer and gateresistor to lower numbers.
Michael
just got ready with a ZCA. I use 30000 µF per channel and 2 tiny chokes, too tiny.... I had to use a capacitance multiplier (one per channel) to reduce the hum to zero. Now running with ~ 19.5 Volts. I use 12 V 20 watts halogen bulbs instead of the resistors. So far nice warm sound, I like it.
Another user wrote, the ZCA is the most sensitive amp in matter of the input cap. I started with older russion paper in oil condensators resulting in nice natural mids but little dull highs. An Audyn A4 MKP cap was very transparent, but also with a little bit to offensive highs. I just ordered some russian teflons now....
The point is, I found some interesting facts about coupling caps and their behavier. It seems, the higher the output impedance the cap sees, the more the DF and DA of the cap is doing audible distortion and colouration.
Walter G. Jung wrote:
"In a single blind listening test using such various capacitor dielectric types as mica, polyester, tantalum, and polypropylene, it was found that a simple coupling capacitor can degrade sound quality quite strongly if the load impedance is high." ...." The other dielectrics mentioned followed similar patterns: Poor performance into the higher impedance, improvement in clarity with the lower impedance. However, even the best dielectric on hand in a usable size sounded much better into a lower impedance load."
"This factor can very logically explain points of disagreement on whether or not capacitors really do sound bad, as it tends to say they sound bad (within a given dielectric type) to the degree that the DA is allowed to manifest itself. Minimizing load resistance tends to optimize the circuit in terms of suppressing the DA."
http://classic-web.archive.org/web/...om/picking_capacitors/pickcap.htm#performanceIn the ZCA, I guess the input cap works into a pretty high impedance of ~ 1 Mega Ohm, resulting in the need for a VERY good audiophil cap. So it could be a good idea to reduce the impedance down to at least 50-100k or even better to ~ 20k or so, to reduce the effects described by Walter Jung. This would result in a larger input cap, but every good MKP should do the job now with ease.
Could be done by changing the trimmer and gateresistor to lower numbers.
Michael
I just soldered a 150k over the 1M Resistor..., I´m really not shure but may be there`s more transparancy and less annoying highs with the Audyn caps. If I`m not wrong, it should no prob to reduce the 1M down to ~ 68k without any changes, the resulting highpass should be still under 20Hz. This would reduce the impedance at 1/15. Could be a good idea either to parallel the 33µ Cap with a Foil, cause I guess it`s more visible at a ground now. Maybe someone else likes to test if there is an improvement in sound and/or a less strong dependence in choosing caps. For the output cap I now ordered ELNA silmic II electros, should be the best choice (and cheaper...) next to BLACK GATES.
My ZCA, chaos again..., improvised red Audyn caps, the long silver ones are russian PIO, the darlingtons for the gyrator are on the main coolers. Getting tighter inside as I thought...
My ZCA, chaos again..., improvised red Audyn caps, the long silver ones are russian PIO, the darlingtons for the gyrator are on the main coolers. Getting tighter inside as I thought...
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An externally hosted image should be here but it was not working when we last tested it.
What was starting as a toy (and it really looks like that at first….) and cause I wanted just to look into the singleended stuff/sound after some reading, is becoming more and more a serious highend thing for me….
It plays the most musical and transparent, compared to any amp I own, and to others at friends I know, in already a little pricey region. Some weeks in the “tweaking” phase every visitor had to listen to the new amp and I had often fun quickly change to a yamaha a380, a consumerprice amp, “natural sound stereo amplifier” written on it`s front, with “cd direct” switch for “best” cd sound…..
The difference is very clear, the non technical/hifi visitors all stated the yamaha is not sounding nice, but very flat and grey in comparison to the zca. I take the yamaha as example how a consumerpriced push/pull GNF amp sounds in general….
The decision about the input cap
was unexpected difficult and took 3 weeks of intense changing/hearing.
I had different mkp`s, tinnfoil, russian teflon, glimmer, styrene…but not very high priced v-caps or mundorf gold/silver etc.
The favourit, a audyn reference cap did not win, the winner was 6 paralled 47nF styrene 630V caps. I found every other cap was colouring the sound, every mkp even the “reference” did something in the treble region, making some hard “plastic” sound, tried also bypassing with 1837/1832 10nF, didn`t like it, better treble, but not homogen. The russian t3 teflon sounds very spacious, transparent at first, but had some “whiteness”, a kind of texture in the treble either.
With the styrene(s) I can not recognise any colouring, sounds very natural and transparent.
To the use of lamps (what I did)
instead of resistors….I have no glue what nonlinearity it adds. I would imagine some kind of very soft compression effect with a medium to slow time constant. On the other hand you will not find any uncompressed music at all…..Even the cleanest acustical recording is running in a compressor/loudnessmaximizer/brickwall-limiter in the upper 3 dB`s. We have a loudness war getting worser every year. I guess it was metallica rewarding something like the “siver citrus” for the most compressed and most unhearable cd of the year (~ 2004).
I did a lot of homerecording myself and worked with compressors, I did need them and I hate them. I´m pretty allergic against any audible compression artefacts, and I can not hear anything in a zca with 12v lamps.
The output cap:
I ordered Elna silmic II, cause should be good audio elkos….mysteriously they sound ugly, very veil sound, every transparency gone…built back to the cheap sanhwa(?) standarts, excellent! I have no glue why…….
Speakercable:
Years ago I bought any xx….streamline 5 something cable, pretty thick ~ 6mm/2 or so, to unhandy for tweaking around, so I bought the cheapest 2.5 mm/2 to play, nice so far…after finishing my testing I get back to my “good” cable and it sounded nasty….flat, grey treble, bad space. I was pretty surprised, I never took this cable thing serious (voodoo). After again some extended googling I ordered some coaxial speakercable, a very fair priced one, and I find it perfect now. May be I will try a twisted solid core thing with teflonisolation in the future.
May be a non NFB amp is more sensitiv to speakercables?
Will take some distortion measures with ARTA soon, just for my technical interest.
Michael
It plays the most musical and transparent, compared to any amp I own, and to others at friends I know, in already a little pricey region. Some weeks in the “tweaking” phase every visitor had to listen to the new amp and I had often fun quickly change to a yamaha a380, a consumerprice amp, “natural sound stereo amplifier” written on it`s front, with “cd direct” switch for “best” cd sound…..
The difference is very clear, the non technical/hifi visitors all stated the yamaha is not sounding nice, but very flat and grey in comparison to the zca. I take the yamaha as example how a consumerpriced push/pull GNF amp sounds in general….
The decision about the input cap
was unexpected difficult and took 3 weeks of intense changing/hearing.
I had different mkp`s, tinnfoil, russian teflon, glimmer, styrene…but not very high priced v-caps or mundorf gold/silver etc.
The favourit, a audyn reference cap did not win, the winner was 6 paralled 47nF styrene 630V caps. I found every other cap was colouring the sound, every mkp even the “reference” did something in the treble region, making some hard “plastic” sound, tried also bypassing with 1837/1832 10nF, didn`t like it, better treble, but not homogen. The russian t3 teflon sounds very spacious, transparent at first, but had some “whiteness”, a kind of texture in the treble either.
With the styrene(s) I can not recognise any colouring, sounds very natural and transparent.
To the use of lamps (what I did)
instead of resistors….I have no glue what nonlinearity it adds. I would imagine some kind of very soft compression effect with a medium to slow time constant. On the other hand you will not find any uncompressed music at all…..Even the cleanest acustical recording is running in a compressor/loudnessmaximizer/brickwall-limiter in the upper 3 dB`s. We have a loudness war getting worser every year. I guess it was metallica rewarding something like the “siver citrus” for the most compressed and most unhearable cd of the year (~ 2004).
I did a lot of homerecording myself and worked with compressors, I did need them and I hate them. I´m pretty allergic against any audible compression artefacts, and I can not hear anything in a zca with 12v lamps.
The output cap:
I ordered Elna silmic II, cause should be good audio elkos….mysteriously they sound ugly, very veil sound, every transparency gone…built back to the cheap sanhwa(?) standarts, excellent! I have no glue why…….
Speakercable:
Years ago I bought any xx….streamline 5 something cable, pretty thick ~ 6mm/2 or so, to unhandy for tweaking around, so I bought the cheapest 2.5 mm/2 to play, nice so far…after finishing my testing I get back to my “good” cable and it sounded nasty….flat, grey treble, bad space. I was pretty surprised, I never took this cable thing serious (voodoo). After again some extended googling I ordered some coaxial speakercable, a very fair priced one, and I find it perfect now. May be I will try a twisted solid core thing with teflonisolation in the future.
May be a non NFB amp is more sensitiv to speakercables?
Will take some distortion measures with ARTA soon, just for my technical interest.
Michael
@digits
you mean the Elna`s ? The difference was so hefty, I did not even thought about any burnin. On the other hand the standard cap worked fine from the first minute. Regarding the russian teflons I had in mind that teflon`s need 400h to burnin (so said for V-caps...), I waver between voodoo and can be...some guys burn in caps with 100 -200 Volts for 36 hours. The styrene caps did sound fine from the first minute, could not find any burnin effect. I tend to the opinion that if there is any burnin effect, it is pretty subtle. If there is a real flaw the first half hour it will not change in a relevant way over time.
Michael
you mean the Elna`s ? The difference was so hefty, I did not even thought about any burnin. On the other hand the standard cap worked fine from the first minute. Regarding the russian teflons I had in mind that teflon`s need 400h to burnin (so said for V-caps...), I waver between voodoo and can be...some guys burn in caps with 100 -200 Volts for 36 hours. The styrene caps did sound fine from the first minute, could not find any burnin effect. I tend to the opinion that if there is any burnin effect, it is pretty subtle. If there is a real flaw the first half hour it will not change in a relevant way over time.
Michael
I note the comments describing this design as "pure Class A".
The amplifier output stage is half resistive load, using a constant current source is just as pure and using an active other half, ie. push pull is also just as pure.
There are several comments which quite rightly identify the quiescent disspation ( about 20 watts per channel) and the limited power output ( a watt or 2 ). BUT more importantly they identify the need for a very chunky power supply. Big transformer and very big electrolytic smoothing to reduce the inevitable supply hum in the output.
The initial post was looking for a mirror image cicruit to use the spare complementary devices he had purchased, and in the process was likely to incur a vastly greater cost in power supply circuitry and heatsinks to build another example.
Dare I suggest that the effective use of the complementaries would be to build a more efficient push pull class A circuit at lower dissipation, and then buy two more pairs of similar transistors and build the two more amps the gentleman requires.
The overall cost will be less! The existing supply will suffice, the existing heatsinks will still do the job because the dissipation will be very much reduced from each of the four amplifiers. All four channels will probably fit into the same casework. No high power resistors needed and since the amplifier is single supply the only other significant cost will be another two output caps of 4700uF.
Personally I have always been a big fan of negative feedback, for at least 40 years, and I know some people are not keen but I would look out a slightly more elaborate circuit with better performance. An input level shifting transistor stage, a voltage amplifier stage and buffer to the output transistors. One would ideally like a higher supply voltage ( more than 24V. ) to the driver stage to obtain a good output swing from the very modest main supply voltage. One neat alternative way to do this might be to bootstrap the driver stage with capacitors from the output. This is an ancient technique often used in days of yore with bjt's but especially useful also with FET circuits that operate with quite a large different gate to source voltage. This would further improve efficiency.
The amplifier output stage is half resistive load, using a constant current source is just as pure and using an active other half, ie. push pull is also just as pure.
There are several comments which quite rightly identify the quiescent disspation ( about 20 watts per channel) and the limited power output ( a watt or 2 ). BUT more importantly they identify the need for a very chunky power supply. Big transformer and very big electrolytic smoothing to reduce the inevitable supply hum in the output.
The initial post was looking for a mirror image cicruit to use the spare complementary devices he had purchased, and in the process was likely to incur a vastly greater cost in power supply circuitry and heatsinks to build another example.
Dare I suggest that the effective use of the complementaries would be to build a more efficient push pull class A circuit at lower dissipation, and then buy two more pairs of similar transistors and build the two more amps the gentleman requires.
The overall cost will be less! The existing supply will suffice, the existing heatsinks will still do the job because the dissipation will be very much reduced from each of the four amplifiers. All four channels will probably fit into the same casework. No high power resistors needed and since the amplifier is single supply the only other significant cost will be another two output caps of 4700uF.
Personally I have always been a big fan of negative feedback, for at least 40 years, and I know some people are not keen but I would look out a slightly more elaborate circuit with better performance. An input level shifting transistor stage, a voltage amplifier stage and buffer to the output transistors. One would ideally like a higher supply voltage ( more than 24V. ) to the driver stage to obtain a good output swing from the very modest main supply voltage. One neat alternative way to do this might be to bootstrap the driver stage with capacitors from the output. This is an ancient technique often used in days of yore with bjt's but especially useful also with FET circuits that operate with quite a large different gate to source voltage. This would further improve efficiency.
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