Hi Anand,
I remember your name......!!
There are two resistors only to change for slightly less current.
The CURRENT SENSE is R131, presently on this schem at 0.27 which gives 2.4A which relates to a Vbe voltage at V121 of 648mV.
If you increase R131 to 0.33R, you will see a quiescent of 1.96A, which is close to what you want. If you want 2A, you'd need 0.324R, but this is NOT a preferred resistor value.
The second resistor to change, perhaps, is R128, on this schem at 865R. If R132 is left unchanged at 0R12, it will change considerably to 680R, or even 700R if you can find this precise value. This resistor sets the dynamic range of the two output devices; that is, we choose a value which ensures both devices see the identical current range, low to high, to maximise the efficiency of the amplifier, that is, maximum clip.
I did the LTSpice again to be sure about this......
Thank you for building the ALPHA! The more the merrier, X and I would LOVE lots of people to build it. It's a corker.....
Hugh
I remember your name......!!
There are two resistors only to change for slightly less current.
The CURRENT SENSE is R131, presently on this schem at 0.27 which gives 2.4A which relates to a Vbe voltage at V121 of 648mV.
If you increase R131 to 0.33R, you will see a quiescent of 1.96A, which is close to what you want. If you want 2A, you'd need 0.324R, but this is NOT a preferred resistor value.
The second resistor to change, perhaps, is R128, on this schem at 865R. If R132 is left unchanged at 0R12, it will change considerably to 680R, or even 700R if you can find this precise value. This resistor sets the dynamic range of the two output devices; that is, we choose a value which ensures both devices see the identical current range, low to high, to maximise the efficiency of the amplifier, that is, maximum clip.
I did the LTSpice again to be sure about this......
Thank you for building the ALPHA! The more the merrier, X and I would LOVE lots of people to build it. It's a corker.....
Hugh
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Thanks for confirming the resistor values, Hugh.
Anand, your PCBs just went out today, so you should have them soon. I threw in 4 unmatched (but consecutive on ammo reel) KSA992's and a set of KSC1845's for you just in case you are stuck and want to get going. Happy building, the more the merrier as Hugh says!
Anand, your PCBs just went out today, so you should have them soon. I threw in 4 unmatched (but consecutive on ammo reel) KSA992's and a set of KSC1845's for you just in case you are stuck and want to get going. Happy building, the more the merrier as Hugh says!
Hugh!
Great that you remember my name. Are you going to Burning Amp, it's a long trek for you though!?
In any case, to summarize...to set the current to 1.96A, then:
1. Change R131 to 0.33 ohms
2. Change R128 to 680 to 700 ohms (closer to 700 preferred)
3. Keep R132 at 0.12 ohms
Is that right?
Thanks!
Anand.
Great that you remember my name. Are you going to Burning Amp, it's a long trek for you though!?
In any case, to summarize...to set the current to 1.96A, then:
1. Change R131 to 0.33 ohms
2. Change R128 to 680 to 700 ohms (closer to 700 preferred)
3. Keep R132 at 0.12 ohms
Is that right?
Thanks!
Anand.
Yes X, I was also looking for a less hot version of the Alpha 4R.
At 1.9A and 4R, distortion starts rising at 26vpp instead of 30vpp for 2.4A and 4R (both with 2.5k as shunt feedback resistor).
That won't be a problem unless your speakers are very inefficient or you like it extremely loud and the neighbors too
At 1.9A and 4R, distortion starts rising at 26vpp instead of 30vpp for 2.4A and 4R (both with 2.5k as shunt feedback resistor).
That won't be a problem unless your speakers are very inefficient or you like it extremely loud and the neighbors too
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Yes, Anand, your figures are correct......
Thank you Danny, the shunt resistor R6 at 2.5k will reduce the gain to (22+2.5)/2.5=9.8, around 19.8dB. This is consistent just as you say with a 4R load since lower impedance speakers should theoretically require less voltage to handle twice the power.... good thinking.
HD
Thank you Danny, the shunt resistor R6 at 2.5k will reduce the gain to (22+2.5)/2.5=9.8, around 19.8dB. This is consistent just as you say with a 4R load since lower impedance speakers should theoretically require less voltage to handle twice the power.... good thinking.
HD
Alpha 20 with 1.96A bias and +/- 24V rails
Danny, Hugh, XRK:
Thank you all!
So in summary for 1.96A bias and overall 20dB gain:
1. Use the schematic in post 2781
2. Change R131 to 0.33 ohms
3. Change R128 to 680 to 700 ohms (closer to 700 preferred)
4. Keep R132 at 0.12 ohms
5. Change R111 to 2.5K or 2.7K ohms.
This should work nicely with my 96 dB efficient speakers that have an impedance nadir of 4.8-4.9 ohms.
Best,
Anand.
Danny, Hugh, XRK:
Thank you all!
So in summary for 1.96A bias and overall 20dB gain:
1. Use the schematic in post 2781
2. Change R131 to 0.33 ohms
3. Change R128 to 680 to 700 ohms (closer to 700 preferred)
4. Keep R132 at 0.12 ohms
5. Change R111 to 2.5K or 2.7K ohms.
This should work nicely with my 96 dB efficient speakers that have an impedance nadir of 4.8-4.9 ohms.
Best,
Anand.
Anand,
You asked if I'm attending Burning Amp.....
I'd love to.
However, your country now has enacted laws preventing foreign visitors without travel health insurance entering the country.
I cannot get health insurance because of my AAA in 2012. I'm a bit of a risk and no company will insure me. Ergo, I cannot travel to USA, and this is not just a bitter pill for me as I love the States but my daughter, Alessandra, lives in NYC, my favourite city.
Such is life, however. I'm vertical, my brain still works, and my Doc tells me if I take my pills, lose weight and do more exercise, I could live to 80. I'm happy about that, but a little bitter I can't travel to the US, particularly as I have more money to travel now that I'm a little older!
Ah, ain't life great? To slightly change quote from Groucho, 'I'd never join any club that would have me as a dementer'
Hugh
You asked if I'm attending Burning Amp.....
I'd love to.
However, your country now has enacted laws preventing foreign visitors without travel health insurance entering the country.
I cannot get health insurance because of my AAA in 2012. I'm a bit of a risk and no company will insure me. Ergo, I cannot travel to USA, and this is not just a bitter pill for me as I love the States but my daughter, Alessandra, lives in NYC, my favourite city.
Such is life, however. I'm vertical, my brain still works, and my Doc tells me if I take my pills, lose weight and do more exercise, I could live to 80. I'm happy about that, but a little bitter I can't travel to the US, particularly as I have more money to travel now that I'm a little older!
Ah, ain't life great? To slightly change quote from Groucho, 'I'd never join any club that would have me as a dementer'
Hugh
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Hugh, so sorry to hear you have AAA. Not being able to travel to see your daughter must be devastating for you, I know it would be for me. I hope she is able to-travel to Australia to see you . ( I hope my comments are not too personal,forgive me if they are )
Since returning from the USA in May I have been diagnosed with coronary stenosis, resulting in life style changes,so my travel options in the future may be limited.
Old age is a bummer, but I'm real glad to have reached it. So many aren't as fortunate.
Best Regards
Alan.
.
Since returning from the USA in May I have been diagnosed with coronary stenosis, resulting in life style changes,so my travel options in the future may be limited.
Old age is a bummer, but I'm real glad to have reached it. So many aren't as fortunate.
Best Regards
Alan.
.
Ah, yes, Alan, when the young ones (!) regard us as fossils I quietly remind them that if they are very, very lucky, and restrain themselves just a little during their youth, they just might get old like me! They smile about that (if they are smart) and then I tell them that the alternatives are unthinkable, and that I have no intention of dying pretty.....
Coronary stenosis is not a death sentence, as you realise. Take your pills, particularly the statins, exercise daily, and you'd be fine if you avoid smokes and booze......
You like motorcycles, huh? I still ride my ZRX1200 at least every couple of weeks. And since my illness I am overcome with a sense of gratitude and wonder almost every day. It makes being alive very enjoyable!
Thank you muchly for your post, we should get back to the normal program now!
Hugh
Coronary stenosis is not a death sentence, as you realise. Take your pills, particularly the statins, exercise daily, and you'd be fine if you avoid smokes and booze......
You like motorcycles, huh? I still ride my ZRX1200 at least every couple of weeks. And since my illness I am overcome with a sense of gratitude and wonder almost every day. It makes being alive very enjoyable!
Thank you muchly for your post, we should get back to the normal program now!
Hugh
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Hugh,
Knowing what I know about AAA’s, I’m so thankful you were diagnosed in time and obviously repaired!
Keep your chin up buddy, time will pass and fingers crossed, elections do occur every 4 years here in the USA. Change will happen and hopefully lessons learned.
Back to building amps
Best,
Anand.
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Anand,
I'm going to surprise you. I'm in the 10% who survived. I appeared at ER with a ruptured AAA, unconscious, with no BP and no pulse. 6 litres of transfused blood and I had a weak pulse again. I had just 30s to depart the mortal coil. There was 27 hours of surgery, and 29 days in an induced coma in ICU. Every single complication happened including pneumonia, stroke and renal failure. I'm kinda proud about getting through that, actually; I'd never realised I was such a tough hombre.
I'm pretty happy now, I can tell you...... but I do not believe that for economic/marketplace reasons the US law about foreign visitors without travel insurance will change, however. The US remains, and will remain, the most expensive country on the planet for health care, and Australia is following along inexorably.
I'm working on my Omega Class A and I need a SOT23 double zener, VERY hard to find in Oz. Damn.......!!
Hugh
I'm going to surprise you. I'm in the 10% who survived. I appeared at ER with a ruptured AAA, unconscious, with no BP and no pulse. 6 litres of transfused blood and I had a weak pulse again. I had just 30s to depart the mortal coil. There was 27 hours of surgery, and 29 days in an induced coma in ICU. Every single complication happened including pneumonia, stroke and renal failure. I'm kinda proud about getting through that, actually; I'd never realised I was such a tough hombre.
I'm pretty happy now, I can tell you...... but I do not believe that for economic/marketplace reasons the US law about foreign visitors without travel insurance will change, however. The US remains, and will remain, the most expensive country on the planet for health care, and Australia is following along inexorably.
I'm working on my Omega Class A and I need a SOT23 double zener, VERY hard to find in Oz. Damn.......!!
Hugh
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Stents can be a good option depending on where it is. In July had 2 installed in RCA and in 2007 had 1 installed in LAD. That stent is still open after 10 years.
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Thank you Hugh. I'm not so excited about looks right now, going to think some modifications on outside.
Soundwise I'll come back later, these have played only my speakers lower end, but seems to be quite powerful. Hopefully this week we'll try these with bigger JBL monitors, playing full range.
Soundwise I'll come back later, these have played only my speakers lower end, but seems to be quite powerful. Hopefully this week we'll try these with bigger JBL monitors, playing full range.