Unusual amp from 1987

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#42
osscar said:
I remember I built this in the early 90's ... I was a student and I didn't have money - so it was never finished (no enclosure etc) , but it sounded good, as far as I remember😀
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https://www.diyaudio.com/forums/att...3d1594929669-unusual-amp-1987-a-captureap-jpg
861233d1594929669-unusual-amp-1987-a-captureap-jpg

This amp uses Single Floating Supply, a decade before Onkyo, three decades before my presumed invention. The input error stage VT1,VT2, can be replaced by Rush cascode advantageously. It uses current bias, but what controls the crossover? I will simulate to find out. It might be possible to make it non-switching.
 
#45
kokoriantz said:
https://www.diyaudio.com/forums/att...3d1594929669-unusual-amp-1987-a-captureap-jpg

This amp uses Single Floating Supply, a decade before Onkyo, three decades before my presumed invention. The input error stage VT1,VT2, can be replaced by Rush cascode advantageously. It uses current bias, but what controls the crossover? I will simulate to find out. It might be possible to make it non-switching.
Click to expand...

The crossover is controlled by a deep GNFB. Partially VT7, VT8 - voltage controlled current shunt.
Original article
Стр. 57 журнала <<Радио>> № 10 за 1989 год
 
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#46
kokoriantz said:
https://www.diyaudio.com/forums/att...3d1594929669-unusual-amp-1987-a-captureap-jpg

This amp uses Single Floating Supply, a decade before Onkyo, three decades before my presumed invention. The input error stage VT1,VT2, can be replaced by Rush cascode advantageously. It uses current bias, but what controls the crossover? I will simulate to find out. It might be possible to make it non-switching.
Click to expand...

I'm assuming it would work equally well with traditional rails, right?
I guess there must be a reason no one uses floating rails in current designs..
 
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#49
minek123 said:
Does anyone have problems with replying to posts and quoting them?
For most posts, if I hit "REPLY" button, the body of the message is blank.
Only in 1 in 10 cases, the previous post would be quoted in the web form.
It's been like for a week or two...
Click to expand...

:cop:

We changed it deliberately to try and stop the constant posting of the post immediately above.

Multi-Quote This Message Button

🙂
 
#50
kokoriantz said:
This amp uses Single Floating Supply, a decade before Onkyo, three decades before my presumed invention.
Click to expand...
Single supply has been used before, by Quad most notably, and IIRC in RCA application sheets amongst others.
Since the only advantage is the absence of a CT on the transformer, it is now disregarded (Quad used a low-power supply balancer to keep a control on the synthetic ground, which added some components to the BOM).
It is possible to use the amplifier itself as a supply splitter/balancer, but there is no need to resort to such acrobatics when a CT is almost free

OldDIY said:
The crossover is controlled by a deep GNFB. Partially VT7, VT8 - voltage controlled current shunt.
Click to expand...
It is probably possible to operate the circuit in a non-switching mode: I have used a similar topology to that end.
 
#51
minek123 said:
I'm assuming it would work equally well with traditional rails, right?
I guess there must be a reason no one uses floating rails in current designs..
Click to expand...
The Single Floating Supply is not a usual single supply described by Elvee, It is used in most prestigious models of Onken. This type of floating supply enters in the feedback loop of the amplifier which decreases dramatically the impedance of the power supply, producing much more powerful bass compared to split type, and without armada of reservoir capacitors . The dark side, it requires individual isolated one for each channel. On the other hand it doesn't need speaker protection.
I am analyzing only the output stage. It is indeed a current biased. If I ground the output, the current has very low distortion with push pull input current. The problem I am looking for, what making it distorted when I let the output voltage swing. The Early is not the main cause.
The spice model I found for GT308b has Vbe threshold of 0.8v instead of 0.2v, so I am using the AC128.
Hayk
 
#54
attachment.php

This topology is highly promising, R8 is a valuable component to adjust the damping factor of the transfer function. If someone can suggest Russian complimentary pair instead of AC127/128, I try.
 

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#60
Corvette 100UM-048S was produced in three modifications of amplifiers. The diagrams show that the power transformers and output stages are different. Corvette 100UM-048S also class AB. Corvette 068 class G. For the first time, a LAN-class power amplifier with two-level power supply was used here, which made it possible to improve the thermal regime of the amplifier.

Korvet 100U-068S - Russian vintage electronics I also had it, it sounded much worse.
 
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