ericj
Headphoneus Supremus
- Joined
- Aug 2, 2005
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Been collecting. Figured i should put them all in one place.
This is an SRD-5, but my SRD-5 doesn't have the voltage switch, and uses the same kind of bidirectional zener as the other schematics. 5M ballast, 1M reference, and 5k output resistors.
SRD-6 - note that both the ballast resistor and the voltage reference resistor are 3.3M
SRD-7 Pro. 2.2M ballast, 910k reference.
SRD-7 MkII - 2.2M ballast, 910k reference.
And the SRD-7SBMk2. This is the only self-bias official schematic i have seen. The SBMK2 has a third transformer just to feed the bias supply off of the right channel audio.
This differs from the mk1 7/SB and 6/SB which just connects one of the red leads from the output to a unidirectional zener rather than the bidirectional zeners on most units. The SB energizers use the same zener voltage but have an additional multiplying stage.
One thing that's interesting to me is that all of these except for the Pro and Mk2 use a Z1082 bidirectional zener. These *may have been made by Semitec and it appears that they are marked with their working voltage rather than their zener voltage.
Nobody makes a part with that number today, Semitec did until 2005.
If the Z1100 on the Pro and Mk2 schematics is from the same series, it has a working voltage of 100v.
At any rate, my SRD-5, 5, and 7 have the Z1082. That plus a voltage doubler gives you 164v of the 200v bias that the SR-3 it came with would have been rated for.
So are they assuming that the 164v is RMS and 200v is peak?
Doesn't make much sense to me.
I need to get a high impedance probe to see for sure, I guess.
The P6KE100 i started my project with is designated by its zener voltage - the working voltage is closer to 86v. So i switched to the P6KE110 which has a working voltage in the high 90s.
Edit:
I did get a high impedance probe and have switched back to the P6KE100 because the 110 was producing well over 600v on the pro bias output. I was surprised to see how much the 9.1MΩ impedance of my DMM was loading down the voltage multiplier.
The ZL1082 in several of these schematics is roughly equivalent to a P6KE82 and produces a normal bias of about 170v and a 'pro' bias of about 490v so both of them are a bit shy of the ideal in the old designs, compared to what kind of bias voltage you get from direct-drive amps since the mid eighties.
With the P6KE100, the "Normal" bias is about 220v which is surely completely fine given the 230v specs for most NB earspeakers, and the Pro bias is a little bit over 580v, which is probably fine because bias voltage definitions have never been strict. Even so, I think i am going to recommend a 10MΩ ballast resistor when using the P6KE100 and a 6-stage voltage multiplier. I've ordered some P6KE75 and will experiment with an 8-stage voltage multiplier.
My SRD-4SBPro experiment with a 110v unidirectional zener only produces 500v. I've ordered some 120v zeners to see if i can get closer to 580.
This is an SRD-5, but my SRD-5 doesn't have the voltage switch, and uses the same kind of bidirectional zener as the other schematics. 5M ballast, 1M reference, and 5k output resistors.
SRD-6 - note that both the ballast resistor and the voltage reference resistor are 3.3M
SRD-7 Pro. 2.2M ballast, 910k reference.
SRD-7 MkII - 2.2M ballast, 910k reference.
And the SRD-7SBMk2. This is the only self-bias official schematic i have seen. The SBMK2 has a third transformer just to feed the bias supply off of the right channel audio.
This differs from the mk1 7/SB and 6/SB which just connects one of the red leads from the output to a unidirectional zener rather than the bidirectional zeners on most units. The SB energizers use the same zener voltage but have an additional multiplying stage.
One thing that's interesting to me is that all of these except for the Pro and Mk2 use a Z1082 bidirectional zener. These *may have been made by Semitec and it appears that they are marked with their working voltage rather than their zener voltage.
Nobody makes a part with that number today, Semitec did until 2005.
At any rate, my SRD-5, 5, and 7 have the Z1082. That plus a voltage doubler gives you 164v of the 200v bias that the SR-3 it came with would have been rated for.
So are they assuming that the 164v is RMS and 200v is peak?
Doesn't make much sense to me.
I need to get a high impedance probe to see for sure, I guess.
Edit:
I did get a high impedance probe and have switched back to the P6KE100 because the 110 was producing well over 600v on the pro bias output. I was surprised to see how much the 9.1MΩ impedance of my DMM was loading down the voltage multiplier.
The ZL1082 in several of these schematics is roughly equivalent to a P6KE82 and produces a normal bias of about 170v and a 'pro' bias of about 490v so both of them are a bit shy of the ideal in the old designs, compared to what kind of bias voltage you get from direct-drive amps since the mid eighties.
With the P6KE100, the "Normal" bias is about 220v which is surely completely fine given the 230v specs for most NB earspeakers, and the Pro bias is a little bit over 580v, which is probably fine because bias voltage definitions have never been strict. Even so, I think i am going to recommend a 10MΩ ballast resistor when using the P6KE100 and a 6-stage voltage multiplier. I've ordered some P6KE75 and will experiment with an 8-stage voltage multiplier.
My SRD-4SBPro experiment with a 110v unidirectional zener only produces 500v. I've ordered some 120v zeners to see if i can get closer to 580.
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