Here is a next logical step for the 50W amp. This is what PH104 (Phil) is building at the moment. I think he changed some resistor values in a couple of places. He can inform us what those changes were. No, I do not have a problem with his doing that. He knows what he is doing, and is welcome to make the changes.
As I said, this is a 50W at 8 Ohm amp. With adequate heat sinking and a large enough transformer, this amp will deliver 100W at 4 ohms and 200W at two. Adding two more pair of output transistors will allow 400W into one ohm.
The original 50 and 100W amps are documented on my web site, thanks to Rob_S, PH104 and c2cthomas. I would like to concentrate now on units that drive more difficult loads and/or put out more power into those loads. Of course, if someone decides to build anything I have posted so far, I will be glad to assist in any way I can.
As I said, this is a 50W at 8 Ohm amp. With adequate heat sinking and a large enough transformer, this amp will deliver 100W at 4 ohms and 200W at two. Adding two more pair of output transistors will allow 400W into one ohm.
The original 50 and 100W amps are documented on my web site, thanks to Rob_S, PH104 and c2cthomas. I would like to concentrate now on units that drive more difficult loads and/or put out more power into those loads. Of course, if someone decides to build anything I have posted so far, I will be glad to assist in any way I can.
Nice piece of circuitry! But I can´t see why you would want the input lowpass filter really, allt it does is ruin the slewrate.
A question, are there any special reason to use such heavy transistors for Q13 and Q15? I bet there are smaller and faster ones...
I disagree about the slew rate. The low pass is there to help keep HF noise out of the circuit. As for my choice of transistors for the drivers, if more outputs are added for difficult loads, as I mentioned, the current demands on the drivers can be fairly high with reactive loads. These transistors are fast enough for audio, and using the same transistors for drivers and outputs avoids having to source two more part numbers in order to save perhaps $1 per channel.
if the source , let say a preamp has a caps at his output,
the input differential will see unbalanced bias resistors....
since the output stage is not included in the feedback loop,
there will be some distorsions...
equally, it is assumed that the front end is stable without
added compensations....
can you please shed some light(s) about these matters?
the input differential will see unbalanced bias resistors....
since the output stage is not included in the feedback loop,
there will be some distorsions...
equally, it is assumed that the front end is stable without
added compensations....
can you please shed some light(s) about these matters?
Well, you are correct about the HF noise, but isn´t the circuit quiet enough without the filter? If not, I would try to make it quiet. Slowing down the slewrate isn´t going to help with performance, especially if it turns out to be unnecessary.
Rikard, the input filter stops HF coming in from outside. That has really nothing to do with slew rate or the noise of the circuit. Feel free to leave it out, but be aware that your amp could theoretically suddenly play radio with the bipolars demodulating incoming RF.
Also using faster drivers will not give you a faster amp. Speed is usually dictated by the VAS-transistors, or more correctly by their Cob times gain (=CMiller).
Have fun, Hannes
Yes, I understand the radio problem, but at the same time I think this would only happen if you have really poor cables and ground loops or similar. The input cap can surely short such interference, and also some of the internal noise, but it will still ruin the slewrate. There is no chance you could ever obtain the best slewrate with a cap across the input.
And I wouldn´t quite agree about the drivers either, slow drivers = slow amp just as any other transistor in the signal path will affect speed.
And I wouldn´t quite agree about the drivers either, slow drivers = slow amp just as any other transistor in the signal path will affect speed.
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Rikard, RF does not need cables, or is your portable radio wired?
Standard RCA plugs are not RF-proof, neither are openings in your case.
You make me curious, who or what makes you believe a cap on the input affects the slew rate of an amp? It solely affects how fast an input signal slews, but has nothing to do with the amp itself.
Have fun, Hannes
PS:
Well, if the voltage gain stage is 10 times slower than the drivers, are drivers with half the speed really a big deal?
Standard RCA plugs are not RF-proof, neither are openings in your case.
You make me curious, who or what makes you believe a cap on the input affects the slew rate of an amp? It solely affects how fast an input signal slews, but has nothing to do with the amp itself.
Have fun, Hannes
PS:
Well, if the voltage gain stage is 10 times slower than the drivers, are drivers with half the speed really a big deal?
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Hi Steve!
Good that Krill is back
Dear Guys,
please read previous threads and posts about Krill
and then send yours.
The project is fully debugged and is working!
High frequency limitations of the transistors for this amp are not important, it works without GNFB!
cheers!
That is true. That also applies to differing output impedances for a DC coupled source. That is the reason for R26 and the instructions to set the offset for the VGS to zero with the source you will be using connected to the amp. Anyone building any of my designs is welcome to add capacitor coupling.
Yes. Even with the output stage included in the feedback loop, there will be some distortions.
That has been discussed before also. Added compensation is usually not needed because Q4 capacitance is high enough to take care of that. There is a provision for that cap on the boards I had made, so it is easy to add if needed.
Also, it might ruin the slew rate.
Here are some details on the Krill 50 I am building. It's a little different than what Steve posted, mostly in semiconductor selection.
D17-D20 are UF4007
D13 - D16 are Fairchild FFH30S60S
Q1/Q2 have been replaced by one 2SC3381 monolithic dual NPN at 4 mA
Q3 and Q5 are 2SC3200 and 2SA1268, respectively
Q4 and Q6 are 2SA1360 and 2SC3423, respectively, at 20 mA
I was going to use a dual jfet at the input but decided on the 2SC3381 as that part can also be used for the higher-power versions.
I have only tested the front-end at this point. Offset can be trimmed to about 1 mV. The 100 kHz square wave is very pretty (I'll post 'scope shots later) and clipping is symmetric. So far, no external Miller compensation capacitor is required for stability.
The TO-220 transistors in the output stage will be replaced with the 2SA1360/2SC3423. The 2SA1943/2SC5200 will be used for the drivers and outputs. Q7, Q8, Q10 and Q11 will be mounted on the main heat sink as lgreen showed in his thread:
http://www.diyaudio.com/forums/solid-state/159954-krill-complete.html
Steve's original schematic and parts list showed a simple amplifier that could be built with inexpensive and readily available parts from Mouser. I wanted to stay away from any surgery on Steve's circuit boards and so this version will remain faithful to his original topology.
I also have a stand-alone output stage which uses 4 pairs of outputs for a 150 - 200W amp (8 ohms). It seems to work fine, I just want to test it more before posting details.
D17-D20 are UF4007
D13 - D16 are Fairchild FFH30S60S
Q1/Q2 have been replaced by one 2SC3381 monolithic dual NPN at 4 mA
Q3 and Q5 are 2SC3200 and 2SA1268, respectively
Q4 and Q6 are 2SA1360 and 2SC3423, respectively, at 20 mA
I was going to use a dual jfet at the input but decided on the 2SC3381 as that part can also be used for the higher-power versions.
I have only tested the front-end at this point. Offset can be trimmed to about 1 mV. The 100 kHz square wave is very pretty (I'll post 'scope shots later) and clipping is symmetric. So far, no external Miller compensation capacitor is required for stability.
The TO-220 transistors in the output stage will be replaced with the 2SA1360/2SC3423. The 2SA1943/2SC5200 will be used for the drivers and outputs. Q7, Q8, Q10 and Q11 will be mounted on the main heat sink as lgreen showed in his thread:
http://www.diyaudio.com/forums/solid-state/159954-krill-complete.html
Steve's original schematic and parts list showed a simple amplifier that could be built with inexpensive and readily available parts from Mouser. I wanted to stay away from any surgery on Steve's circuit boards and so this version will remain faithful to his original topology.
I also have a stand-alone output stage which uses 4 pairs of outputs for a 150 - 200W amp (8 ohms). It seems to work fine, I just want to test it more before posting details.
Hi Steve!
Good that Krill is back
Dear Guys,
please read previous threads and posts about Krill
and then send yours.
The project is fully debugged and is working!
High frequency limitations of the transistors for this amp are not important, it works without GNFB!
cheers!
Thanks. I am hoping that this time we can concentrate, at least a little, on the sound. As you pointed out, the design is fully debugged and working. I was attempting to get good sound, and that is the reasons for many of the "odd" things I did here.
Hi Steve, I know you looked at the Fairchild parts, as they have a good range and do the 2SC1845/2SA992 (as KSC/KSA devices)... I was wondering if you had looked at their KSC2690/KSA1220 for the current sources, and perhaps KSC3503/KSA1381 (which are 2SC3503/2SA1381 copies) for the VAS stages.
My Hero .........................Finally amplifiers for real sound and loads Steve ,
your schematics call for 6 outputs , are you suggesting 10 -12 for low imp ?
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I hadn't looked at those parts. They could be used, but would require heat sinking for use in any of the amps I have posted so far. They would also require the addition of the compensation capacitor. This circuit works well with an assortment of different transistors, so there is no reason not to try something you like or have on hand already. The real thing to watch out for is that the ratings are sufficient for the application. I have attempted to show parts that are widely available while using the minimum of different part numbers. These are suggestions, not rules.
Steve ,
your schematics call for 6 outputs , are you suggesting 10 -12 for low imp ?
The schematic I posted in post #1 only has 4 outputs, that is, 2 pair. This should be good down to 2 ohms. For 1 ohm, or reactive low impedance loads, I would add two more pair (4 transistors) of output to insure the amp has no problems even if driven hard. This will, of course, require some serious heat sinks.
OK,
2 pr for 200 watts @ 2 ohm , correct ? 4 Prs for 400 @ 1 ohm ?
Yes i will have generous heatsinks + fans .
The schematic you posted has a VGA output of 42 V , won't this produce 120 @ 8 ?
regards,
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