7 hours ago
Hi Guys
Everything old is new again.
The first DC Power Scaling kits were the SB Super Budget kits: SB1 for fixed-bias amps and SB2 for cathode biased amps. These had a very economical circuit and were problem-free to install. Many techs and amp builders still use them and we supply PCBs for them.
The simple circuit required the use a potentiometer with special characteristics, and the only way to attain that was to use a mil-spec pot. "Mil-spec" is a misunderstood term inasmuch as most people believe that the part is going to be better and/or last longer than an average part. That can be true but is not always the case. Mil-spec merely means that there is an official description of the part so that parts procurement can be uniform. In the case of the pot, its special characteristic is not contingent on it being mil-spec; rather, it just fell out this way as it was the only part available with the given parameter rating.
When I began using that pot style, I was getting an extremely good deal on the pricing. I ended up using a few different values and standardised the use of them in my early production amps. But then the prices went up precipitously. "Shock shock horror horror", as the song goes.
I designed out the expensive pots, which was fine for all the traditional control positions in an amp, but more complicated for Power Scaling. I needed an "amplified pot" and began on a path of designing many different solutions, each with its benefits and pitfalls, with each successive design aiming to improve on what came before. The final solution turned out to be great on paper but fragile in some installations. It eliminated the pot value as a variable in the control range and when I test the circuits here it always works for me. But I'm always lucky
A couple of very experienced Power Scale installers encountered issues with the latest circuits and I made a decision to go back to the SB approach. It is fail safe. It always works. No one has ever had a problem with it as long as they mount the mosfets in a location where air moves over that part of the chassis. Even while the latest-greatest was going out, I was researching the expensive pot options to see what the impact would be on kit pricing.
One of the issues with the SB approach was that the Power Scale pot did not physically match the Drive Compensation pot. The expensive pot had far fewer options than standard pots do, requiring different knobs, or ending up with the knobs sitting at different heights. The solution is to get a dual version of the expensive pot, which is even more expensive and larger, making finding place for the two controls more difficult on some chassis. The dual could be used for a single-pot Power Scale solution in some circuits.
Along with looking into the pot availability, I worked on the Automatic Drive Control issue which resulted in two kits to perform the drive compensation automatically. This means there only needs to be one panel control. There is a thread about that on this forum.
All of the PCBs for the new kits have been ordered.
Where the SB module boards carry a single mosfet and its related components, the new SBX module has all of the high-voltage circuitry as one module. The Power Scale control ties to this, and there are pads to tie into the ADC and TREM controllers, as required. There is also a provision to change the effective taper of the Power Scale pot to tailor the sweep of loudness to the individual player or amp designer.
The circuit is still economical in complexity by being very simple and not needing too many parts. None of the parts are critical yet the end result is precise. The expensive pot has its one special characteristic but is otherwise as imprecise as every other kind of potentiometer, but the circuit designs makes that not matter.
SB1 is an SBX + TBS, and only requires the addition of RBX and ADC-L or ADC-H as needed.
SB2 is an SBX + VCK, and only requires the addition of TREM and ADC-L or ADC-H as needed.
I'm considering including the ADC in the SB1 and SB2 package.
Everything old is new again.
The first DC Power Scaling kits were the SB Super Budget kits: SB1 for fixed-bias amps and SB2 for cathode biased amps. These had a very economical circuit and were problem-free to install. Many techs and amp builders still use them and we supply PCBs for them.
The simple circuit required the use a potentiometer with special characteristics, and the only way to attain that was to use a mil-spec pot. "Mil-spec" is a misunderstood term inasmuch as most people believe that the part is going to be better and/or last longer than an average part. That can be true but is not always the case. Mil-spec merely means that there is an official description of the part so that parts procurement can be uniform. In the case of the pot, its special characteristic is not contingent on it being mil-spec; rather, it just fell out this way as it was the only part available with the given parameter rating.
When I began using that pot style, I was getting an extremely good deal on the pricing. I ended up using a few different values and standardised the use of them in my early production amps. But then the prices went up precipitously. "Shock shock horror horror", as the song goes.
I designed out the expensive pots, which was fine for all the traditional control positions in an amp, but more complicated for Power Scaling. I needed an "amplified pot" and began on a path of designing many different solutions, each with its benefits and pitfalls, with each successive design aiming to improve on what came before. The final solution turned out to be great on paper but fragile in some installations. It eliminated the pot value as a variable in the control range and when I test the circuits here it always works for me. But I'm always lucky
A couple of very experienced Power Scale installers encountered issues with the latest circuits and I made a decision to go back to the SB approach. It is fail safe. It always works. No one has ever had a problem with it as long as they mount the mosfets in a location where air moves over that part of the chassis. Even while the latest-greatest was going out, I was researching the expensive pot options to see what the impact would be on kit pricing.
One of the issues with the SB approach was that the Power Scale pot did not physically match the Drive Compensation pot. The expensive pot had far fewer options than standard pots do, requiring different knobs, or ending up with the knobs sitting at different heights. The solution is to get a dual version of the expensive pot, which is even more expensive and larger, making finding place for the two controls more difficult on some chassis. The dual could be used for a single-pot Power Scale solution in some circuits.
Along with looking into the pot availability, I worked on the Automatic Drive Control issue which resulted in two kits to perform the drive compensation automatically. This means there only needs to be one panel control. There is a thread about that on this forum.
All of the PCBs for the new kits have been ordered.
Where the SB module boards carry a single mosfet and its related components, the new SBX module has all of the high-voltage circuitry as one module. The Power Scale control ties to this, and there are pads to tie into the ADC and TREM controllers, as required. There is also a provision to change the effective taper of the Power Scale pot to tailor the sweep of loudness to the individual player or amp designer.
The circuit is still economical in complexity by being very simple and not needing too many parts. None of the parts are critical yet the end result is precise. The expensive pot has its one special characteristic but is otherwise as imprecise as every other kind of potentiometer, but the circuit designs makes that not matter.
SB1 is an SBX + TBS, and only requires the addition of RBX and ADC-L or ADC-H as needed.
SB2 is an SBX + VCK, and only requires the addition of TREM and ADC-L or ADC-H as needed.
I'm considering including the ADC in the SB1 and SB2 package.