What do you thinks about this shematic?

[Pigy]

I know that this shematics is very old,but is is very simple to build.
I have AD161/162 and 2N3055,but tell me for better sound ,which is replacement for 2N3055 transistorsto get more beautiful sound, whether to go with the SA and SC transistors?

[googlyone]

If you have the devices, then just build the amp and enjoy it.

My opinion is that changing the devices will not affect the sound of this amplifier - it really "is what it is". In fact, if I built it I would likely stick to older devices as you have on the schematic - as that is in line with the vintage of this amplifier architecture.

The beauty of this type of amplifier is that whilst it is amazingly low tech, and not even remotely hifi by todays standards, it is:
- Super simple
- Very forgiving to implementation
- The type of thing that you can muck about with

I built something similar to this as a kid, and annoyed the hell out of my family with the noise it made. Was fun. That said, this amplifier belongs in a low cost / low tech application, and would never be found in my stereo setup.

Now for something more of an answer to your question:
The AD161 / 162 devices need:
- Voltage rating of >50volts (would prefer to see more to provide safety margin on the supply rails)
- Current rating of few hundred mA - have not done the sums, but the output drivers will not be that stressed. The AD161 on the input again is being used as a signal transistor - though I note the bias current will cause some dissipation.

Easily available options for these include:
- BD139 / 140
- MJE340 / 350
- MJL15030/31 (more for the output drivers)

For the input device (which is also the Vas) a device with a good gain and bandwidth might be attractive. Look for a Vas device which can dissipate a couple of watts (as this biasing requires here).
- Any of the above would work, but might not be optimal.
- Good Vas transistors include 2sc2682, 2sc3423 - there are quite a few

Which would be preferable? To me, any. If I were sticking part numbers on a schematic, I would likely look to the 15030/31 for the output drivers, and look for something with a bit more bandwidth and gain for the input device - as this is also the Vas. I have used the 2sc2682 successfully.

The output devices?
- I reckon you would have a hard time beating MJL21193/4 or MJL4302 / 4281.

The MJL21193/4 are complete overkill, but are cheap, available, very fine devices and almost bullet proof.

just to reiterate though - I would stick to the cheap parts, as that is more reflective of what the amplifier is.

Oh - and that output capacitor. You are going to get a really solid thump at turn on. Watch the speaker either has protection (god forbid investing in that for this amplifier!) or is able to cope with the thump.


Have fun!

[VladimirK]

As I remember, in the year 1978 this schematics seemed to be sounding very decent. It's stages have enough driving capacity, in distinction to the Post #1 schematics.

[padamiecki]

[QUOTE=Pigy;2543549]...QUOTE]

Hi
use many low impedance ccapacitors in parallel as 5000u output cap like Vladimir did: Modified Follower-99 With HF Transistors

[kzeprf22]

If I am not mistaken this is a Non global feedback topology (the first schematic). I think further investigation is needed!

[lineup]

I have setup in SPICE.
Using BD139/140 for the AD161/162.
And 2N3055A for output.

The circuit has enormous voltage gain.
Because of the 50uF cap across the input transistors emitter resistor.
So, the potentiometer on the input is certainly needed.

Yes, there is no global feedback.
In my circuit I get THD 2.085% at 1 Watt 8 Ohm
And increasing THD with more output power.

[kzeprf22]

Originally Posted by lineup

I have setup in SPICE.
Using BD139/140 for the AD161/162.
And 2N3055A for output.

The circuit has enormous voltage gain.
Because of the 50uF cap across the input transistors emitter resistor.
So, the potentiometer on the input is certainly needed.

Yes, there is no global feedback.
In my circuit I get THD 2.085% at 1 Watt 8 Ohm
And increasing THD with more output power.

I think the prblem with all solid state amp when you remove the FEEDBACK is the big gain of yhe input transistor (output goes to rail) I thought this amp is Ok but as checked this is the case with this amp also. So no use to me

[VladimirK]

Originally Posted by kzeprf22

I think the prblem with all solid state amp when you remove the FEEDBACK is the big gain of yhe input transistor (output goes to rail) I thought this amp is Ok but as checked this is the case with this amp also. So no use to me

I think the main problem here is in interstage interaction. This style minimalistic gesign can not be implemented with bjt transistors. In this case, one needs very low Ciss j-FETs and MOSFETs. Gain can be adjusted be proper choosing of operating point.

[googlyone]

I think this is missing feedback frommthe output to the base of the input transistor.

[Pigy]

I think they avoid global feedback, to get a higher voltage gain, because AD transistors, or even Germanium transistors have poor voltage amplification.
I've heard from some people that sound with 2N3055 desperate, and it is much better if you put MJ3055, and of course SC 3281.
I would keep a driver transistor AD 161/162 and the output would put MJ3055 or MJ802.IN entry would put or BC550 or AC 187 or AC153.What you think?