Hello Berlusconi.
You mentioned once that you tried different transistors in the output stage. I also began to experiment (an extra assembled amplifier board and transformer) with MJL4281/4302 transistors and noticed that the radiator began to heat up more with them. Is it necessary to change the values of some resistors when changing transistors? And another question. Is it possible to reduce the number of output transistors, and for example use instead of 8 in the arm of each voltage, let's say only 4? By reducing the number of transistors, I want to achieve a decrease in the temperature of the radiator and the ability to better select pairs of transistors.
You mentioned once that you tried different transistors in the output stage. I also began to experiment (an extra assembled amplifier board and transformer) with MJL4281/4302 transistors and noticed that the radiator began to heat up more with them. Is it necessary to change the values of some resistors when changing transistors? And another question. Is it possible to reduce the number of output transistors, and for example use instead of 8 in the arm of each voltage, let's say only 4? By reducing the number of transistors, I want to achieve a decrease in the temperature of the radiator and the ability to better select pairs of transistors.
@vmk2002
Hello my dear friend,
I have tried MJL, NJW and 5300/1943 pairs. Frankly, I don't know which sound better and I haven't even tried to compare them because the sound was fine with all of them.
When changing transistors you must re-adjust the bias settings, both regarding current and temperatures, carefully.
Please note that A60 and A60+ are almost identical, the main difference is the number of output transistor pairs. So, yes you can operate A60+ with the reduced number of output pairs. However, before removing the output transistors first reduce the bias to the minimum and then re-adjust bias after the startup. However, there is no advantage of reducing the number of the output pairs. Leave them there in case you need more power (for example: when you have a garden party - spring is coming) or if you buy lower impedance speakers.
Have a pleasant day
Hello my dear friend,
I have tried MJL, NJW and 5300/1943 pairs. Frankly, I don't know which sound better and I haven't even tried to compare them because the sound was fine with all of them.
When changing transistors you must re-adjust the bias settings, both regarding current and temperatures, carefully.
Please note that A60 and A60+ are almost identical, the main difference is the number of output transistor pairs. So, yes you can operate A60+ with the reduced number of output pairs. However, before removing the output transistors first reduce the bias to the minimum and then re-adjust bias after the startup. However, there is no advantage of reducing the number of the output pairs. Leave them there in case you need more power (for example: when you have a garden party - spring is coming) or if you buy lower impedance speakers.
Have a pleasant day
That's right. Bring the trimming resistors to the minimum position, turn on the amplifier and gradually adjust both channels with a warm-up of 5 minutes, each turn little by little up to 20mV. Then warm up for 20 minutes and measure, then slowly bring it up to 20-25mV again. Turn off the amplifier to cool down and turn it on again and measure it, after 15 minutes the current will be stable and the temperature will be normal, not more than 50 degrees. I had one channel heated up much more than the first, although the setting was 25mV both. After repeated uniform adjustment, as I wrote 47 degrees, both channels at 25mV. No need to hurry, setting the quiescent current does not like haste.😉
Let me reveal my secret project:
Class A High Power Stereo Dual Channel HiFi Audio Amplifier Board Power Tube AMP Upgrade Accuphase E405/550/KSA50
Ihitially I was considering E550 but my gut feeling told me that this amp takes the cake. I observe serious improvement of Chinese products and I trust when they claim that this amplifier surpasses Krell and Accuphase E550 in class A category. I wonder and I will try.
But when I consider rock solid performance of A60, I doubt anything can beat it.
I expect arrival of the boards in three weeks. Let's see.... and hear.
I also plan to build Alpha Nirvana and Wolverine, but later - during summer.
Something tells me if there will be an improvement, but not by much. You need to switch from Accuphace to something new.
Hi,
I’m modding a tube pre amp for using with A60+. In order to choose the best output capacitors of the pre amp, I need to know the input impedance of this amp. Does anyone know it? I suspect it’s 10k but not sure.
Also does this amp have input capacitor? If yes I think I’ll omit the preamp’s.
Thanks and looking forward to your info
I’m modding a tube pre amp for using with A60+. In order to choose the best output capacitors of the pre amp, I need to know the input impedance of this amp. Does anyone know it? I suspect it’s 10k but not sure.
Also does this amp have input capacitor? If yes I think I’ll omit the preamp’s.
Thanks and looking forward to your info
No, it doesn't have input capacitor. Perhaps that's, among other factors, the secret of good sound.
I am aware that the absence of the input capacitor increases the risk of extreme DC current values at the output, but two design features prevent that: (1) servo and (2) built in 1237 based speaker protection. I've tested this "dooms-day scenario" which might burn the speakers but the response of the amplifier is preventing that: simply: either servo blocks low DC signal shift and in extreme case, when servo fails to compensate quickly, DC step signal at the output disconnects the speakers. You should test this on your amplifier connected to dummy load to verify it it works for you.
It would be pity to use tube preamplifier with this amplifier, completely counter-productive. It is against any design goals of this amplifier: low distortion with just right amount of the 2nd harmonic flavor.
Input impedance A60 47 com. If he needs a pre-amplifier, then only a discrete one. But he plays great without it. Already checked several times. I have an A60 with a relay volume control, I can give a signal with a DAC without problems. 😉
Thanks Berlusconi.
I’ve seen the speaker protection features that you described in action when I stupidly turn on the amp first then pre amp so there’s DC getting through before capacitors are charged. There was a big thumping and the speaker protection circuit tripped. That’s nice to have.
I know it’s not the best idea to use this amp with a tube preamp. But since there are some very cheap Chinese tube preamp that I can mod, i’m tinkering for fun. 🙂
Now Since this amp does not have input capacitor, I can not run my preamp without ones. Given low input impedance of solid state amp, it’ll require huge coupling cap at output of preamp to avoid bass roll off. Another reason to abandon the tube pre amp then 🥲
I’ve seen the speaker protection features that you described in action when I stupidly turn on the amp first then pre amp so there’s DC getting through before capacitors are charged. There was a big thumping and the speaker protection circuit tripped. That’s nice to have.
I know it’s not the best idea to use this amp with a tube preamp. But since there are some very cheap Chinese tube preamp that I can mod, i’m tinkering for fun. 🙂
Now Since this amp does not have input capacitor, I can not run my preamp without ones. Given low input impedance of solid state amp, it’ll require huge coupling cap at output of preamp to avoid bass roll off. Another reason to abandon the tube pre amp then 🥲
Thats exactly what makes fun, otherwise I would have purchased a hefty shiny commercial amplifier. In fact I have one, but I don't use it.
This is also how I use my A60. Passive volume control between amp and DAC. Works great.
