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Question about BJTs

Naja

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At one point a friend of mine bought a very old amplifier from the 1960s and invited me over to try it out. Before listening we opened it up and saw it was running on BJTs, standard for the time period.

So, we hooked it up to a pair of KEF R3s and started blasting after which a very strange but pleasing audio phenomenon happened. It was especially apparent on voices, a kind of echoing decay, it gave the sound a sense of spatiality and layering that is hard to describe, also made it much more interesting to listen to than his modern class AB amp. Although compared to the modern amp the sound was lacking in clarity and speed amongst other things.

I'm wondering what exactly in the amp circuit or the BJTs created this effect?
 

waynel

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At one point a friend of mine bought a very old amplifier from the 1960s and invited me over to try it out. Before listening we opened it up and saw it was running on BJTs, standard for the time period.

So, we hooked it up to a pair of KEF R3s and started blasting after which a very strange but pleasing audio phenomenon happened. It was especially apparent on voices, a kind of echoing decay, it gave the sound a sense of spatiality and layering that is hard to describe, also made it much more interesting to listen to than his modern class AB amp. Although compared to the modern amp the sound was lacking in clarity and speed amongst other things.

I'm wondering what exactly in the amp circuit or the BJTs created this effect?
BJTs have nothing to do with the sound. Just a different kind of transistor.
 

sergeauckland

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BJT as in Bipolar Junction Transistors are pretty much what's used everywhere today in any Class A or AB amplifier. Some use MOSFETs - Metal Oxide Silicon Field Effect Transistor, which work on a different principle, but the results are the same.

Early Solid State amplifiers from the 1960s used Germanium BJTs, which were replaced in the mid 1960s by Silicon BJTs, which are still used today.
Germanium BJTs have much lower bandwidths than silicon, and also suffer from thermal problems, and those early amplifiers consequently often had crossover distortion and poor high frequency distortion. It wasn't hard for an amplifier to have 0.1% distortion at 1kHz and at full power, but at lower powers, distortion often rose, as it did at higher frequencies. Thermal problems, resulting in amplifier destruction also limited usage to 8 ohms and above, 4 ohm loads, or loudspeakers with a severe impedance characteristic would cause thermal runaway, and destruction. Amplifiers like the Leak Stereo 30 were pretty poor in comparison with their valve predecessors, and the Stereo 30 was quickly replaced by the all-silicon Stereo 30+. Quad continued with their KT66 output Quad II until the mid 1960s when the Quad 303 finally replaced it.

There was nothing good about Germanium SS amps, many manufacturers continued with valves until silicon devices (the famous 2N3055 for one) became available and affordable.

S.
 

raindance

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Basically you are saying it was a transistor amplifier that used transistors. Nothing magical about that ;).

BJT = bog standard transistor
FET - field effect transistor
 
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Naja

Naja

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BJT as in Bipolar Junction Transistors are pretty much what's used everywhere today in any Class A or AB amplifier. Some use MOSFETs - Metal Oxide Silicon Field Effect Transistor, which work on a different principle, but the results are the same.

Early Solid State amplifiers from the 1960s used Germanium BJTs, which were replaced in the mid 1960s by Silicon BJTs, which are still used today.
Germanium BJTs have much lower bandwidths than silicon, and also suffer from thermal problems, and those early amplifiers consequently often had crossover distortion and poor high frequency distortion. It wasn't hard for an amplifier to have 0.1% distortion at 1kHz and at full power, but at lower powers, distortion often rose, as it did at higher frequencies. Thermal problems, resulting in amplifier destruction also limited usage to 8 ohms and above, 4 ohm loads, or loudspeakers with a severe impedance characteristic would cause thermal runaway, and destruction. Amplifiers like the Leak Stereo 30 were pretty poor in comparison with their valve predecessors, and the Stereo 30 was quickly replaced by the all-silicon Stereo 30+. Quad continued with their KT66 output Quad II until the mid 1960s when the Quad 303 finally replaced it.

There was nothing good about Germanium SS amps, many manufacturers continued with valves until silicon devices (the famous 2N3055 for one) became available and affordable.

S.

Thanks for the elaborate answer, this also explains why the amp didn't last long until it fried
 

DVDdoug

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It was especially apparent on voices, a kind of echoing decay, it gave the sound a sense of spatiality and layering that is hard to describe
Try reversing the + & - connections to ONE speaker. If the speakers are out-of-phase you'll get a "spacey" sound caused by wave cancelation (especially as you move around a bit) and the bass will be almost completely canceled.

A certain kind of ground failure can cause a similar subtraction/cancelation. That can completely kill "centered" vocals and bass, and anything else in that's identical and in-phase in both channels. A mono file (both sides identical) file will cancel to silence. (That's how a classic vocal remover works.)

If it's not a reversed speaker and if you're connected to a computer with a 3.5mm-to-RCA adapter cable, that cable likely has a broken ground.
 
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Naja

Naja

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Try reversing the + & - connections to ONE speaker. If the speakers are out-of-phase you'll get a "spacey" sound caused by wave cancelation (especially as you move around a bit) and the bass will be almost completely canceled.

A certain kind of ground failure can cause a similar subtraction/cancelation. That can completely kill "centered" vocals and bass, and anything else in that's identical and in-phase in both channels. A mono file (both sides identical) file will cancel to silence. (That's how a classic vocal remover works.)

If it's not a reversed speaker and if you're connected to a computer with a 3.5mm-to-RCA adapter cable, that cable likely has a broken ground.

The speakers weren't out of phase I know how that sounds like.
It might have been a ground issue but I can't check that now since the amp is dead, although the bass sounded fine.
 

MakeMineVinyl

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At one point a friend of mine bought a very old amplifier from the 1960s and invited me over to try it out. Before listening we opened it up and saw it was running on BJTs, standard for the time period.

So, we hooked it up to a pair of KEF R3s and started blasting after which a very strange but pleasing audio phenomenon happened. It was especially apparent on voices, a kind of echoing decay, it gave the sound a sense of spatiality and layering that is hard to describe, also made it much more interesting to listen to than his modern class AB amp. Although compared to the modern amp the sound was lacking in clarity and speed amongst other things.

I'm wondering what exactly in the amp circuit or the BJTs created this effect?
You could be hearing higher distortion from the older amplifier, but this would probably be due either to the circuit design used or the components aging over time which might be causing more distortion than when the amp was new. BJTs would not really enter into the picture. There were some old transistor amplifiers which used quasi-complementary output stages and that could be a source of distortion.
 
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