Hi!
I have a former college that has revived an old amplifier design he thoughts out may, many years ago. The design is highly unusual, where the output stage is "driving the power rails". In the pictures I've posted of this design he is using two 9V batteries as the power source. However, his old design used a +-50 or 60V power supply, and had loads of power. It sounds really good and has very little distortion. I think he's about to make a youtube video about it (the last design he uploaded created some discussion on this forum), so I'll post the video here when it's ready.
I happen to have an old Altec Lansing 9444B power amplifier (manual and schematics here), and I believe this is design around the same principle. It is a two channel amplifier, but it has two secondary transformer windings, two bridge rectifiers and dedicated smoothing capacitors for each amplifier channel. The neat this with this amplifier is that the all the output transistors, both NPN and PNP are connected to the same heatsink without any insulators, and the heatsink is grounded. Apart from this, I don't know why this design is preferred over the more usual ones.
So here are the questions:
I have a former college that has revived an old amplifier design he thoughts out may, many years ago. The design is highly unusual, where the output stage is "driving the power rails". In the pictures I've posted of this design he is using two 9V batteries as the power source. However, his old design used a +-50 or 60V power supply, and had loads of power. It sounds really good and has very little distortion. I think he's about to make a youtube video about it (the last design he uploaded created some discussion on this forum), so I'll post the video here when it's ready.
I happen to have an old Altec Lansing 9444B power amplifier (manual and schematics here), and I believe this is design around the same principle. It is a two channel amplifier, but it has two secondary transformer windings, two bridge rectifiers and dedicated smoothing capacitors for each amplifier channel. The neat this with this amplifier is that the all the output transistors, both NPN and PNP are connected to the same heatsink without any insulators, and the heatsink is grounded. Apart from this, I don't know why this design is preferred over the more usual ones.
So here are the questions:
- What is the benefits of a design like this, compared to the more traditional push-pull designs?
- Have something like this been done by someone else, other than Altec Lansing in the early 90s?
- Does this design or arrangement have a name?
It's a Class AB and I've come across it before. It's really just a matter of moving the reference voltage to a different part of the circuit. Instead of the output swinging in relation to the supply, the supply is swinging in relation to the output. If I remember correctly the advantage is that you can run the rails at a higher voltage than the max voltage the opamp can handle.
It’s called a transnova. It makes a low component count, fairly fault tolerant amplifier. With the only real weakness being the requirement of each channel requiring it’s own power supply, since it floats.
You can also mount the output devices direct to the heat sink without insulators in some cases I have a Chinese clone that does this with about 400 watts a channel I did not know re the transnova title but that makes sense
Trev
Trev
Transnova! That's the name. Thanks!
So are there any famous brands/amplifier models that uses a Transnova design, other than the Altec Lansing 9444B? Having all the output transistors mounted to a grounded heatsink without any insulators is definitly an advantage
So are there any famous brands/amplifier models that uses a Transnova design, other than the Altec Lansing 9444B? Having all the output transistors mounted to a grounded heatsink without any insulators is definitly an advantage
I came about a QSC PA amp from the QSC USA-series 370, 850, 1300.
It had such a the strange topology. Worked for many years. The T03 MJE150xx transistors are directly on the heat sink, no isolation pad. The trimming procedure is quite complicated, it has to be adjusted under full load.
The "Onsemi" replacement transistors had values so different compared to the Motorola originals, I didn't try a repair.
It had such a the strange topology. Worked for many years. The T03 MJE150xx transistors are directly on the heat sink, no isolation pad. The trimming procedure is quite complicated, it has to be adjusted under full load.
The "Onsemi" replacement transistors had values so different compared to the Motorola originals, I didn't try a repair.
Interesting! And I'm able to find schematics as well! I thought the Altec Lansing was the only one, but it's great to see that other manufacturers also have done it. It's the design is quite different, and it took me a while to fully understand how something like this would even work.
The Altec Lansing 9444B I own was a dumpster find. It did work when I found it, but it had a screaming fan that ran at all times. I use it as a subwoofer amplifier in my living room. I replaced the fan, but it has since broken several times. I've replaced a few output transistors that for some reason shorted out and blew the mains fuse. And another time the output of the NE5532 opamp that drives everything started to "jump around", causing crackling noises. But I've never had any issues with the ON semi replacement output transistors for it (TO-3 MJE15024/MJE15025). And I've tested it under full load to make sure it doesn't thermally "run away".
Is there a good reason why output transistors fails short like this? In my case, the amplifier was just powered, with no input signal.
Most Transnova amplifiers I've now seen uses output BJT transistors, while the design I showed in the first post uses mosfets. Is there a good reason why BJTs would preferred in a transnova design?
Common source/emitter and has voltage gain, but it biases like an emitter follower or CFP output stage. It just drives the ground node instead, and takes the speaker out from what is normally supposed to be “ground”.
The 1300/1310 came with MJ15022/3, but require PREMIUM drivers such as 2SA968/C2398. There was a fullpack equivalent that’s also NLA, so the only viable type is MJE15032/3 now. The smaller ones tried to get away with MJ15015/6, and all manner of drivers, with varying degrees of success. They had better luck using 2SD424/B554. Gain is just too damn low on 15015/6.
The 1300/1310 came with MJ15022/3, but require PREMIUM drivers such as 2SA968/C2398. There was a fullpack equivalent that’s also NLA, so the only viable type is MJE15032/3 now. The smaller ones tried to get away with MJ15015/6, and all manner of drivers, with varying degrees of success. They had better luck using 2SD424/B554. Gain is just too damn low on 15015/6.
The first amps I saw that used this topology were QSC about ~1980. Two main advantages are:
1. The limited op-amp voltage range is plenty to drive the common emitter outputs, which handle the high voltage supply. This is probably the best op-amp IPS design because you don't have a lot of extra stuff to adapt the op-amp limitations to serious power amp voltages.
2. The power supply has no DC center tap, only two series capacitors which provides DC failure protection with no startup and down DC thumps.
1. The limited op-amp voltage range is plenty to drive the common emitter outputs, which handle the high voltage supply. This is probably the best op-amp IPS design because you don't have a lot of extra stuff to adapt the op-amp limitations to serious power amp voltages.
2. The power supply has no DC center tap, only two series capacitors which provides DC failure protection with no startup and down DC thumps.