[DIY Stax self bias conversion?]

Definitely affects volume gain and sub - bass. I've rebuilt a few old SRA-10/12 and 3S amps back to the 230v NB specification and it makes a difference.

Do you happen to have a schematic for a proper 230v bias supply? Every time I track down a thread that looks like it might have a better bias supply design, the image links are dead.

[DIY Stax self bias conversion?]

It's strange that every bias supply schematic I've been able to find is set up that way for normal bias. How important is that extra 30V? I've been told that the koss esp-950 sounds better at 620V bias vs 600V, and that is a smaller relative jump in voltage than 200V to 230V. 

[DIY Stax self bias conversion?]

Ok so I have another question, and this one has been bothering me for a while. How do any of the Stax bias circuits produce 230V bias if they are zener limited to 100V on the input side. Shouldn't normal bias circuits produce a 200V bias, and shouldn't pro bias circuits produce a 600V bias? What am I missing?

[DIY Stax self bias conversion?]

The way it works is that the same transformer that steps up the voltage to drive the headphones also provides high voltage to the bias circuit.  The bias circuit drains off a little bit of current from the signal voltage to fill up the bias capacitors.  Think of the diodes as being one-way doors for the electrons.  Every time the music voltage peaks higher than the voltage that is already on the bias capacitors, some current flows into those capacitors, gradually topping them up.  The reason this works is that the bias requires voltage but almost no current, except when you first start up, so draining a bit off the music signal will do the trick.  If you were to bias the headphones and then disconnect them, they will hold the bias for a significant length of time.  Usually the first couple diodes are zeners to regulate the voltage in the bias circuit to make sure it doesn't go too high.

 

In my powered Stax converters, which run off 117V, the power cord actually goes directly to the bias circuit with only a 0.3 amp fuse as protection, but using an additional transformer as spritzer suggests is much safer.

 

 

I understand how voltage multipliers work, that's not the issue. What I don't understand, and would really like to, is how the SRD-6/SB bias circuit regulates it's voltage to 230V. There don't appear to be any zener diodes in that circuit to limit the voltage before multiplication, so what in that circuit stops it from generating > 230V bias voltages at high input volume? 

[DIY Stax self bias conversion?]

Same as all other voltage multipliers.  Extra parts to keep the circuit in inline but I'd prefer to have the extra transformer.  Makes things a lot easier. 

Please forgive my ignorance, I only have a loose understanding of these concepts, but how exactly does the above circuit maintain a consistent 230v bias voltage when the input voltage from the step up transformer varies so much with the volume of the music being played. As I understood it the purpose of the extra transformer that is absent in this circuit was to ensure that the voltage would generally be well in excess of what the multiplier needs to make the 230v bias, and that excess input voltage was limited by zener diodes. 

The above circuit doesn't appear to have zeners so how does stay consistent? Or am I reading the schematic wrong?

[DIY Stax self bias conversion?]

On 10/12/2015 at 4:33 PM, nopants said:

lower voltage requirement on the secondary

 

So it maintains stable bias at lower output volumes I assume. 

Also I just found this schematic for the SRD-6/SB.

EDIT: DO NOT BUILD THIS CIRCUIT. Look at my post at the bottom of this page for a corrected version of this schematic. This version has no zener diode to limit the input voltage and if built as is will create a very different bias voltage than expected. Basically, depending on the input volume of the audio signal, this one can generate bias voltages well in excess of 230V and will damage normal bias headphones.

There's no transformer in this self bias circuit. It looks like the signal is tapped from the output transformer and sent straight to the voltage doubler. How does this approach work?

[DIY Stax self bias conversion?]

Thanks for the info. Any particular advantage to using the voltage doubler?

[DIY Stax self bias conversion?]

Hello all, I'm working on a little project with my old SRD-6 energizer and a cheapo TA2020 amp. I'm trying to put together a compact transportable setup for my SR-5s. I have done a few modifications to this box already, such as wiring the transformers directly to the speaker taps on the back of the box and directly to the Stax socket on the front, completely bypassing the bias board and the loudspeaker switch. Those mods have done great things in terms of sound quality, but what I'm interested in now is modifying the bias circuit to operate as a self biasing one. As I understand it, Stax accomplishes this by tapping some of the output signal from one of the transformers, then passes it through a small transformer to step it up some more before sending it to, more or less, the same bias circuit as in the standard models. 

This seems pretty straightforward, but in my search for information, I've been unable to track down solid details about what type/values of transformer is used, and if there are any other important components in the self bias circuit (resistors, capacitors, diodes, etc.) that I'm not aware of. Any advice would be greatly appreciated. My ultimate goal is to have a system that runs solely off of 12v dc so it can be run off a battery if need be.

Thanks!

[The Headcase Stax thread]

I wonder if the L-700 pads will fit older Lambdas. The L-500 pads look pretty much identical to legacy lambda pads, and since the L-500 and L-700 share the same frame the pads should interchange. I'm guessing the L-700 pads will provide a better seal than the legacy lambda pads, and I'm curious how that would alter the sound of other Lambdas.