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Hi, I want to ask you for these resistors 0.47 ohm / 5W and bad daping factor. Can I reduce them to 0,2 or 0,1 oma/5W oma/5W? What happens with the scheme? Will work well?
I amnot sure that the resistors will cause a poor damping factor.
I think it is more complicated than that.
Also Sonically and this is just an opinion - large damping factoris not necessarily a good thing. Often it indicates excessive use of feedback to stabilise a poor design - or improve specifications.
However why not try both options the resistors are quite inexpensive.
-Dan
I think it is more complicated than that.
Also Sonically and this is just an opinion - large damping factoris not necessarily a good thing. Often it indicates excessive use of feedback to stabilise a poor design - or improve specifications.
However why not try both options the resistors are quite inexpensive.
-Dan
I measured the output impedance of my 20W - around 1 ohm. That's a damping factor of 8 for a 8 ohm load.
Lowering the value of the 0.47 ohm resistors will only increase the idle current. Not a good idea if you want to avoid burnt output transistors. That being said, 0.33 ohm is a safe value.
Lowering the value of the 0.47 ohm resistors will only increase the idle current. Not a good idea if you want to avoid burnt output transistors. That being said, 0.33 ohm is a safe value.
Hi everyone, I'm from Italy and I'm trying to built a monoblock version of this amplifier. Power supplies are +-34V without any load, with a huge capacitance multipler, I've found original and matched low signal transistors, 2sc5200/2sa1943 output devices (don't know if they are genuine or counterfeit) but never found the driver stage pair, so I've built everything on a "self made protoboard" with a lot of trimmer and replaced 2sc1096-2sa634 with poor bd139-140 just for trying, I've read on this thread that mje15030-40 are way better.
By the way the only channel I've made is not working good: can't eliminate some DC on the output and, worst of all, there is a lot of noise coming out with the sound: If the input signal is low, i've nothing in the output, if I pump up the volume, sound comes out just like there were some bad soldering on the path! seems like the amp works only over a certain level..
Have you got any suggestion?
Bias current are very high, something like 2.1A, zener diodes are 22V, and in this moment i don't have an oscilloscope at home..
Thank you very much!
By the way the only channel I've made is not working good: can't eliminate some DC on the output and, worst of all, there is a lot of noise coming out with the sound: If the input signal is low, i've nothing in the output, if I pump up the volume, sound comes out just like there were some bad soldering on the path! seems like the amp works only over a certain level..
Have you got any suggestion?
Bias current are very high, something like 2.1A, zener diodes are 22V, and in this moment i don't have an oscilloscope at home..
Thank you very much!
Hi Geoff, I saw nobody answered you.
The resistors first of all are needed because the current and Vb in the first stage is lower than in the second, so we need a tiny bit of extra DC (I guestimate 40-50 mV). The resistors are different because the currentamplification in the two halves just are a little bit different.
Hiraga wrote that "this balances the impedance of the two halves". This way you can set the DC more accurate.
The first version used 200 and 300 ohms with 2SC1775 and 2SA872 respectively. When I built one with European transistors I used a potmeter on a breadboard to set the equilibrium of DC, and this sets the initial DC.
Hope this helps
alberti
I have to check for the Altec 416Z (16 Ohms). I am looking for a good amp in the bass for bi amplification and the Hiraga 20 W should be OK.
For information, I found a place in USA where they have all the original Xtors except 2SA 872A, replaced with 2SA970 and the 2SA627 replaced with 2SB 539.
Hiraga 20W & 30 W - Last official technical informations published in l'Audiophile in 1985. Unfortunately in French but fortunately not a problem for me.
On en parle n°34 : modifs ampli Hiraga 20W, tweeter technics 5HH10 ...
On en parle n°34 : modifs ampli Hiraga 20W, tweeter technics 5HH10 ...
This is true, but depends on the output transistors used. I guess that you are using some of the biggest ones from on semi, which have the sweet spot around 1.1A, but also like more VOLTAGE (unless you cascode them).
I didnt check the datasheets, but I'm pretty sure that the original ones chosen by Hiraga were doing their best at 20W output power, or he would just have proposed a 30W amp
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