Pavel's Auto-Bias Board

Peter W. wrote:

erhard-audio wrote:

then we need some dimensions to make sure that enough of the pcb is removed to make it fit with the stepped attenuator. Can somebody here on the forum please measure how far the stepped attenuator stick into the chassis, then Pavel can see if the  AB pcb can be accordingly modded, thanks.

It is more than just that. There are very nearly as many stepped attenuators as there are flavors of ice-cream. I would suggest that Pavel determine the largest unit that may be accommodated safely in the available vertical space (from the top plate to the bottom plate, horizontal space (to the Octal plug) and work to that dimension. Allow a few millimeters for clearance. The longitudinal dimension is determined by the driver board, and so not something that is affected by the AB board.

This is a work-in-progress managed by a few individuals 1/4 world apart using its customers as Beta Testers. Not the entire Dynaco, Heath, Allied or Scott skunk-works. Not offered as an excuse, but as a possible reason why all these modifications are taking such time. Those years I spent as a machinist taught me one thing, if nothing else - the last 5% of the design process takes 80% of the total elapsed time.

tubes4hifi wrote:not much to reply to, no, the AB board will not install if there is a volume control in the way.
Since the bias pots are removed on the VTA driver board, the connection to the AB bias can be made from the center hole of the old trim-pots,
if that isn't  obvious (follow the circuit trace for 1/2" or look at the schematic!)  So makes soldering a wire much easier!
This is exactly why I HATE written instructions.   There are too many ways to interpret written instructions, so new instructions have to be written 2-3 times
for each person that doesn't interpret them the way that most people do.   Learn DIY !!   If you use the simple wiring diagram I can supply
you can see ALL of the connections on one page instead of reading thru 10 pages of instructions subject to your own level of understanding.
BTW, I'm no longer selling the AB boards, not enough demand, not enough understanding.   Available direct from Pavel at
ST70/120   https://www.audioamp.eu/en-detail-901899177-modules-for-to-optimize-bias-with-an-supply-of-bias-ab-q-st70-st120-v2.0-with-isolation-tr.html
MK3/M125   https://www.audioamp.eu/en-detail-901899178-modules-for-to-optimize-bias-with-an-supply-of-bias-ab-q-m125-v2.0-with-isolation-transfor.html

erhard-audio wrote:further to the above photo's, Pavel is looking into modding the AB module pcb's to remove some material off that corner where the transformer is.

pavlikkkk wrote:

erhard-audio wrote:further to the above photo's, Pavel is looking into modding the AB module pcb's to remove some material off that corner where the transformer is.

let's try this

Pavel

erhard-audio wrote:

pavlikkkk wrote:

erhard-audio wrote:further to the above photo's, Pavel is looking into modding the AB module pcb's to remove some material off that corner where the transformer is.

let's try this


that certainly will give the stepped attenuator more room to breath and is about as much as can be done with that pcb, thank you Pavel.

Glad to help :-)

This is exactly why I HATE written instructions.

New2Tubez wrote:Here's one of several pictures to come. Erhard's photos don't illustrate the attenuator clearance with the VTA board underneath. I'm barely able to insert a business card between the AB and the attenuator. And yes, the PIOs have plenty of clearance.

More explanation later but wanted to get this one out to really show the fit.

New2Tubez wrote:Not trying to throw you under a bus.
Roy showed me a similar picture and I waited until I saw a couple installed. The photo was just to show close things are.
About to fire it up for the first time- more pics and video to come.

erhard-audio wrote:

New2Tubez wrote:Not trying to throw you under a bus.
Roy showed me a similar picture and I waited until I saw a couple installed. The photo was just to show close things are.
About to fire it up for the first time- more pics and video to come.

no buses involved here :D
The important thing is that corrective action is being taken and that future ST70/120 AB modules should be easier to fit with the optional stepped attenuator installed.
Mind you, had the initial design been correctly carried out taking into account the possible use of the stepped attenuator, we would not have had to go through all of this.

New2Tubez wrote:

erhard-audio wrote:

New2Tubez wrote:Not trying to throw you under a bus.
Roy showed me a similar picture and I waited until I saw a couple installed. The photo was just to show close things are.
About to fire it up for the first time- more pics and video to come.

no buses involved here
The important thing is that corrective action is being taken and that future ST70/120 AB modules should be easier to fit with the optional stepped attenuator installed.
Mind you, had the initial design been correctly carried out taking into account the possible use of the stepped attenuator, we would not have had to go through all of this.

Agreed. I was about to install my v1 and the isolation transformer update happened so I put it off and and waited for v2. A work in progress... next one should be the charm!

Ernstmach wrote:

This is exactly why I HATE written instructions.

That explains a couple of things.

erhard-audio wrote:

pavlikkkk wrote:

erhard-audio wrote:further to the above photo's, Pavel is looking into modding the AB module pcb's to remove some material off that corner where the transformer is.

let's try this

Pavel

that certainly will give the stepped attenuator more room to breath and is about as much as can be done with that pcb, thank you Pavel.

Ecce novi infantem

erhard-audio wrote:very nice Pavel! That should eliminate any space issues when using the optional DAC style 24 step attenuator!
AND the larger pad holes so that 18gauge wire can be soldered through too!!!!

BryceJ wrote:The manual for the AB module states the following:

Should any of these blue LED’s go out or not go on after power up, means that here is an issue with that
given output tube and that the tube in question needs to be immediately replaced.

I seems that the blue LEDs should be always be visible to take advantage of this feature and to get full value out of the AB module.

BryceJ wrote:The manual for the AB module states the following:

Should any of these blue LED’s go out or not go on after power up, means that here is an issue with that
given output tube and that the tube in question needs to be immediately replaced.

I seems that the blue LEDs should be always be visible to take advantage of this feature and to get full value out of the AB module.