Thanks, Hugh - yes, the testing I did for clipping showed that, lower than 4 ohms, the bottom half of the sine wave was the side which clipped first.
Which raises an interesting point - well to me, anyway ... should we in fact build ANs with an asymmetric DC rail supply - say:
* 27v for +DC & 30v for -DC for the AN 8R and
* 22v for +DC & 24v for -DC ... for the AN 4R?
Andy
No dice because you need two different secondary windings; one with 20Vac and another with 22 or 23vac. You can get them, but expensive.
The issue would require careful design and maybe a lossy regulator on only the positive rail. It might be best to relocate the clip led to the lower pmos to better suit the saturation event at the correct half cycle.
A new design project however....
HD
The issue would require careful design and maybe a lossy regulator on only the positive rail. It might be best to relocate the clip led to the lower pmos to better suit the saturation event at the correct half cycle.
A new design project however....
HD
I've upped the ante with my build. Paralleled a 1r over the 0r22 to yield the 0r18 advised by HD for the extra current. Not sure if I'm measuring right but the voltage over the parallel pair seems to have dropped a bit so I don't get the forecast 2.2A. I'm now at about 0.35/0.36V giving 2A.
Thinking on whilst writing this and just been to measure the rails. They are now 27v so have sagged a little more. Maybe this is the reason.
Anyway....playing music nicely again and shall listen. Heat is still very manageable. I added a bypass cap over the input 10uf whilst I had it in bits!.
Thinking on whilst writing this and just been to measure the rails. They are now 27v so have sagged a little more. Maybe this is the reason.
Anyway....playing music nicely again and shall listen. Heat is still very manageable. I added a bypass cap over the input 10uf whilst I had it in bits!.
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Hello guys,
First, I want to wish a Merry Christmas to everybody on this excellent forum. Health and prosperity to all of you from sunny Greece.
Yesterday afternoon, while I was preparing my workbench for stuffing my 2 AN pcbs, I discovered that I didn't order a C111 ( 47uF/35VDC ) capacitor from Andy's 4R BOM. May I use another cap with a different value, let's say 100uF or 33uF I have in my benchstock??
Another critical question is the transformer choice. As I always build in dual mono configuration, I will use 2 transformers with 2 secondaries each. So, two 24V/6A per winding transformers will be OK for my 4R build ( I don't use SLB - I use my own adjustable PS with MJH6284 and MJH6287 for each channel, plus four +-+- CRC boards of diyaudio/firstwatt.
Best regards
Spiros
First, I want to wish a Merry Christmas to everybody on this excellent forum. Health and prosperity to all of you from sunny Greece.
Yesterday afternoon, while I was preparing my workbench for stuffing my 2 AN pcbs, I discovered that I didn't order a C111 ( 47uF/35VDC ) capacitor from Andy's 4R BOM. May I use another cap with a different value, let's say 100uF or 33uF I have in my benchstock??
Another critical question is the transformer choice. As I always build in dual mono configuration, I will use 2 transformers with 2 secondaries each. So, two 24V/6A per winding transformers will be OK for my 4R build ( I don't use SLB - I use my own adjustable PS with MJH6284 and MJH6287 for each channel, plus four +-+- CRC boards of diyaudio/firstwatt.
Best regards
Spiros
C111 is not critical. It’s just to smooth the voltage above the input stage LTP current source. 33uF to 100uF both work. Just make sure it is rated to at least rail voltage.
Regarding trafos, calculate the quiescent current and power requirement in VA. I like to size my trafos at least 2x to 3x that VA rating so that it operates without getting too hot and voltage does not sag too much.
Usually, under Class A load the nominal no load voltage that is on the rated spec will drop a few volts.
So consider the drop through the CRC supply. Usually a few volts. So I would spec my trafo no load voltage to be the amp rail operating voltage (desired) plus 3-4v.
For example, supposing you want 27vdc at say 3.5A. Thats 95W or 95VA. I would choose a 300VA trafo. Since you need 27vdc at the rail, add 2v sag from Class A operation, add 2v drop through CRC PSU. Thats 27v + 4v = 31v. Divide by 1.4 to get 22vac secondaries under no load.
Or 300VA 22vac trafo (two secondaries). This is per channel monoblock.
If getting a single quad secondary trafo it needs to be 600VA.
Regarding trafos, calculate the quiescent current and power requirement in VA. I like to size my trafos at least 2x to 3x that VA rating so that it operates without getting too hot and voltage does not sag too much.
Usually, under Class A load the nominal no load voltage that is on the rated spec will drop a few volts.
So consider the drop through the CRC supply. Usually a few volts. So I would spec my trafo no load voltage to be the amp rail operating voltage (desired) plus 3-4v.
For example, supposing you want 27vdc at say 3.5A. Thats 95W or 95VA. I would choose a 300VA trafo. Since you need 27vdc at the rail, add 2v sag from Class A operation, add 2v drop through CRC PSU. Thats 27v + 4v = 31v. Divide by 1.4 to get 22vac secondaries under no load.
Or 300VA 22vac trafo (two secondaries). This is per channel monoblock.
If getting a single quad secondary trafo it needs to be 600VA.
Thanks a lot, XRK for the analysis.
That is what I thought but I had to ask to be sure.
AN 4R edition must operate with +-20VDC/3A QC. So my Darlington PS will drop 3V plus CRC another 2V...........20V+3V+2V=25V / 1.4=17,8V let's say 18. I will order a 24V/8A per winding because I can adjust it to the proper value with the trimpot.
In my previous construction of Lang class A 20W amplifier ( QC=2A), I ordered 2 X 20V/6A trafos and the maximum I could get with my CRC + PS configuration was just 18V with a load. So I had to order new trafos 2 X 25V/6A for an extra 150 euros. AN will be driven by the famous Marantz 7E MkII tube preamplifier. My CRC caps are rated at 10000uF X 4 / 35VDC.
Do you think that 2 X 24V/8A would be OK for AN 4R configuration?
Thanks again.
@jimk04
I might be wrong but I don’t believe the gain would be any different. Gain for this amplifier is set by two resistors, R126 and R124. Overall gain in the standard setting where R126 is 22k ohms and R124 is 820 ohms is about 28dB. That would be a bad choice for a preamp in modern systems in my opinion. I changed the overall gain of my AN build to about 20dB by changing R124 to 2.2k ohms.
If you change these resistors dramatically (in order to lower the gain further) it can affect stability and the compensation caps may need to be changed.
Best,
Anand.
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Jim,
Anand is 110% correct - you can down scale the output stage to give much less drive for a preamp, but in truth you can run the AN front and second stages as a preamp anyway - see the Melbourne Yarra preamp XRK has championed in the past.
The other issue is that when you change the gain of a power amplifier you need to re-address the compensation issue which is pivotal with audio amplifiers. Compensation confers stability, which a major issue with global feedback amplifiers and MUST be done very carefully to maximise sound quality.
I wish you and your family Merry Xmas, and HNY, and in fact, to all forum members!
We are first up the rank for Santa in Oz, it's only 3 hours until 25th December!
HD
Anand is 110% correct - you can down scale the output stage to give much less drive for a preamp, but in truth you can run the AN front and second stages as a preamp anyway - see the Melbourne Yarra preamp XRK has championed in the past.
The other issue is that when you change the gain of a power amplifier you need to re-address the compensation issue which is pivotal with audio amplifiers. Compensation confers stability, which a major issue with global feedback amplifiers and MUST be done very carefully to maximise sound quality.
I wish you and your family Merry Xmas, and HNY, and in fact, to all forum members!
We are first up the rank for Santa in Oz, it's only 3 hours until 25th December!
HD
As I started stuffing my AN 4R pcbs yesterday, I tried to match the KSA992FTA transistors with my DMM. That wasn't possible. KSA992FTA HFe can't be measured. Is there any specific procedure for matching those transistors?? I tested my DMM and can measure the HFe of other BJT transistors. Any suggestions?
Thanks a lot.
Thanks a lot.
I use a Peak Atlas DCA75; this can measure various things, including:
* whether a semiconductor (diode, transistor, jfet, fet LED) is working or dud.
* Hfe for transistors
* Idss for jfets
* voltage drop for diodes.
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No need for a "Null reply". Highlight the language you want to quote from the previous post. A "quote bubbler" should appear.
Then, you can do this...