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Old 5th April 2008, 10:37 AM   #1
sajti is offline sajti  Hungary
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Default One more hybrid idea

Hi,

this schematic is unity gain buffer. I wan to use two of them, bridged, to get 200-220W/8ohms. The input stage will be tube LTP.

Sajti
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Old 5th April 2008, 11:01 AM   #2
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With this much complexity and so many semiconductor junctions in the signal path - why bother with the extra complexity of a differential tube front end?

Just make it all SS - I rather doubt if you'd notice the difference.

Regards, Allen
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Old 5th April 2008, 11:06 AM   #3
sajti is offline sajti  Hungary
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The output is simple 4 stage darlington. If 60W/8ohm is enough, there can be only 3 stage darlington, and SE tube input stage.

Sajti
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Old 6th April 2008, 07:46 AM   #4
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Quote:
With this much complexity and so many semiconductor junctions in the signal path - why bother with the extra complexity of a differential tube front end?
Do not worry the solid state beast!

I recently moved over from a darlington to a triple darlington output stage and sonically it was a big advantage. With the much increased current gain the (tube) VAS is freed from output loading effects. For my amplifier I have measured the current gain: 6.4M. So 1 uA base current in the pre-driver is enough to source 6.4A to the load.

Peter
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Old 6th April 2008, 08:19 PM   #5
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Default Regarding Hybrids

The most important places to have tubes are where an amp
must interface with signal peaks or load reactances beyond
the control of the amp's internal design. The input and output.

The inner stages of an amp deal with signals of known limits
and are unlikely to misbehave. Sand (done right) if fine here.

I wound not classify a tube pre-amp with clearly separate
sold-state final a "Hybrid". I see no inseparable synergy of
Tube and Solid here that makes this a Hybrid.

Let us remember that valves usually react to plate voltage
as well as grid (and screen), and interact with the load in
complex and pleasing ways. It is an equation with at least
2 variables of voltage input for one current output.

Most solid state dumbs this down to a single current or
voltage input (and junction temperature) for one current
out. The only interaction with the load is ugly clipping.
And if feedback is abused, poor recovery.

I see no tube (or tubelike behavior) in this output that
takes over before anything nasty can happen. Unless
you are assured of a purely resistive load, I don't think
you can garauntee this amp will behave as well as a
tube or true Hybrid.

Putting a tube in the front end is only half the battle.

----------------------------------------------------------------------

What is the purpose of C3 & C6 1000uF?
Are you bootstrapping here to widen the effective rail?

Beware of amplifiers driving capacitive loads....
As I see no global feedback loop, it might be alright.

Depending how you were planning to servo out
the bridge, that capacitance might yet become a
feedback loop problem...
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Old 6th April 2008, 10:29 PM   #6
sajti is offline sajti  Hungary
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Default Re: Regarding Hybrids

Quote:
Originally posted by kenpeter

What is the purpose of C3 & C6 1000uF?
Are you bootstrapping here to widen the effective rail?

Beware of amplifiers driving capacitive loads....
As I see no global feedback loop, it might be alright.

Depending how you were planning to servo out
the bridge, that capacitance might yet become a
feedback loop problem...
[/B]
Yes C3 and C6 do boostrapping. But I think that the are not pure cpacitive loads. The load is the two resistor (R2&R3) they coupled to the output of the amplifier.
I attached the tube input schematic.

Sajti
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Old 26th January 2009, 12:58 PM   #7
sajti is offline sajti  Hungary
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I made another simple version. Run with high bias (600mA for each ouput devices), and there is no any complicated ss circuit.

Click the image to open in full size.

Sajti
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