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Improved SPEC 2 Idle Current Stabilization STV-3H STV-4H

P

Petrus

New Member
Dear AK Members
We have worked out an alternative solution to better stabilize the Pioneer SPEC 2 Idle Current.

An alternative solution was required because I did not have enough STV-3H and STV-4H reference diodes and I could not find them anymore.

With the the proven alternative solution it is possible to keep a constant Idle Current for all different Audio Power Levels (e.g. from 0 up to 250 Watt). The theory and the practical implementation aspect will be published in the near future on AK.

I will therefore also soon be in a position to sell my remaining STV-3H and STV-4H reference diodes.

The last question to be answered is what is the most optimal Idle Current Setting for a configuration with only one Amp Running in normal operations (0 to 250 Watt) and additionally for a configurations of two amplifiers running in a bi-amping?

There are many articles on the Internet and some of them contradict each other or are incomplete (Class A, Class AB). The Idle Current should be large enough to avoid cross-over distortion (see literature on Class AB push-pull) and small enough not to overheat the amplifier.

Additionally other non-linearities can be introduced in the region where the loudspeaker current crosses the 2xIdle Current boundary. This is the region where either the lower half Q2/Q4/Q6 or the upper half Q1/Q3/Q5 of the Class AB Push Pull Amplifier closes. Other non-linearities may be introduced when either Q13 or Q12 closes. I have calculated the corresponding Audio Power Levels for both situations. A good setting for small Audio signals (pseudo Class A) may not automatically be optimal for larger signals above or in the 2xIdle Current Region. Also the negative feedback lucilly reduces the distortion by approximately 1/(1+AB) with B= ~ R10/(R10+R18).

My questions is whether anybody has done any further theoretical calculations or practical measurements on what the best possible Idle Current setting is for the SPEC 2 Amplifier?

Petrus
 
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Petrus said:
Dear AK Members
We have worked out an alternative solution to better stabilize the Pioneer SPEC 2 Idle Current.

An alternative solution was required because I did not have enough STV-3H and STV-4H reference diodes and I could not find them anymore.

With the the proven alternative solution it is possible to keep a constant Idle Current for all different Audio Power Levels (e.g. from 0 up to 250 Watt). The theory and the practical implementation aspect will be published in the near future on AK.

I will therefore also soon be in a position to sell my remaining STV-3H and STV-4H reference diodes.

The last question to be answered is what is the most optimal Idle Current Setting for a configuration with only one Amp Running in normal operations (0 to 250 Watt) and additionally for a configurations of two amplifiers running in a bi-amping?

There are many articles on the Internet and some of them contradict each other or are incomplete (Class A, Class AB). The Idle Current should be large enough to avoid cross-over distortion (see literature on Class AB push-pull) and small enough not to overheat the amplifier.

Additionally other non-linearities can be introduced in the region where the loudspeaker current crosses the 2xIdle Current boundary. This is the region where either the lower half Q2/Q4/Q6 or the upper half Q1/Q3/Q5 of the Class AB Push Pull Amplifier closes. Other non-linearities may be introduced when either Q13 or Q12 closes. I have calculated the corresponding Audio Power Levels for both situations. A good setting for small Audio signals (pseudo Class A) may not automatically be optimal for larger signals above or in the 2xIdle Current Region. Also the negative feedback lucilly reduces the distortion by approximately 1/(1+AB) with B= ~ R10/(R10+R18).

My questions is whether anybody has done any further theoretical calculations or practical measurements on what the best possible Idle Current setting is for the SPEC 2 Amplifier?

Petrus
Click to expand...

With regards to the stv-3 and stv-4h situation, were they missing, electronically dead (shorted or open?) or just had broken off wires? Broken off wires I FIX. Just 4 diodes? and the stv-4 is more of a safety feature to keep from destroying the outputs if the connections to the stv-3h break, or the idle current pot becomes defective.
edit: I forgot to say that a string of conventional switching diodes with about the same voltage drop would substitute well.

As for the circuitry, a Vbe multiplier circuit IS a viable alternative.

As for the idle current level, use the factory setting... They weren't just pulled out of a hat, they have to be the result of a long process we can only guess at.

I am also curious as to who "we" are...
 
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They were missing for some boards that I bought. I have already a perfectly-working solution keeping the Idle Current much more stable than the one with the diodes. I hope that somebody really did the calculations or the measurements. My gut feeling, after having looked to about 50 articles, also goes to a lower Idle Current (unless you use it for only the higher frequencies in a bi-amping configurations.
 
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In the mean time i have developed most of the calculations and I will put them on the web in a few days from now.

Petrus
 
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