I have just completed a pair of these Hiraga amplifiers and was amazed with the sound. Was never an advocate of class A but after completing a regulated power supply and using transistors that i had available i can confirm that this simple amp,designed some 30 years ago, is one of the very best as far as sound quality is concerned .For those who want to give it a try and cannot get the specified original transistors here is what i used and its working fine with no problem in setting the bias current and the DC offset. I do not want to get into a debate about the characteristics of the transistors i used. I can only say that they complement the circuit and they do the job. Just bear in mind that you might have to adjust the 47 k bias resistor to give around 380 mv measured across the 0.33 R resistors at 30 v. I got it right at around 34.3 k.
The use of a regulated power supply is highly recommended as with it,the amp is extremely quiet,no hum etc.
Transistors used for the output is the 2SA 1942 and 2SC5200
Drivers BD237 and BD238
Inputs BC 258 and BC630. (TYPING ERROR CORRECTED SHOULD BE BC 639)
The use of a regulated power supply is highly recommended as with it,the amp is extremely quiet,no hum etc.
Transistors used for the output is the 2SA 1942 and 2SC5200
Drivers BD237 and BD238
Inputs BC 258 and BC630. (TYPING ERROR CORRECTED SHOULD BE BC 639)
Last edited:
Bonjour Jacques, i used the 30 w version as per the one in the link below.
Jean Hiraga's Super Class-A Amplifier
Jean Hiraga's Super Class-A Amplifier
By comparing Hiraga's original schematics to the updated one, I noticed that the bottom zener in oriented differently. Which is the correct orientation?
Link to schematics
Jacques
Link to schematics
Jacques
As mentioned in my earlier post, the transistors used were available from my spares because the specified originals were just impossible to get. Bear in mind the replacment transistors are not "direct equivalent" to the originals. I did try a few other transistors, but the one listed below allowed me to set both the bias current and the DC offset very easily. I cannot argue that the original specified transistors will sound better but the ones listed below, do the job very well and the result is a real wonderful sound with clear mids and highs and a surprisingly powerful bass.
The list 2SA872 used BC258B
2CS 1775A used BC 639
2SA634 used BD237
2SC1096 used BD238
Outputs used 2SC 5200 and 2SA1943
The list 2SA872 used BC258B
2CS 1775A used BC 639
2SA634 used BD237
2SC1096 used BD238
Outputs used 2SC 5200 and 2SA1943
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.