"4A of total bias on the A3 by the way will take you to 30Wrms pure Class A into a 4-ohm load. No need to raise the rails...that's A3 on top fuel!"
Yea, I know what you mean... sure it can be done and the fact that there are only two devices may also sound better than more piled on....
I was just testing and finding the bias point on my DIY KSA-50 clone and found out from another member that I had biased it as a KSA-100 and also had my rails too high! BTW: this is the effect of not reading ALL the posts for a project! I was at +/- 43 and sholda been at +/- 36. Still works just fine as it was caught in time. I had this thing up to about 3.5 amps per rail with just three MJL devices per rail! You'da probably seem me on the 5:00 news standing by the fire trucks had it not been caught in time........ If you're going to attempt to build what you've calculated then water cooling might be the most practical thing to consider.
Mark
Yea, I know what you mean... sure it can be done and the fact that there are only two devices may also sound better than more piled on....
I was just testing and finding the bias point on my DIY KSA-50 clone and found out from another member that I had biased it as a KSA-100 and also had my rails too high! BTW: this is the effect of not reading ALL the posts for a project! I was at +/- 43 and sholda been at +/- 36. Still works just fine as it was caught in time. I had this thing up to about 3.5 amps per rail with just three MJL devices per rail! You'da probably seem me on the 5:00 news standing by the fire trucks had it not been caught in time........ If you're going to attempt to build what you've calculated then water cooling might be the most practical thing to consider.
Mark
I would like to share my continuing exploration of taking the venerable Aleph 3 to extreme performance without moving away from its simplicity and hopefully keeping its signature Nelson Pass sound. I would like to christen this top fueled Aleph 3, the “Aleph 3SC”…SC of course is for SuperCharger
The measured power in simulation is what I think to be pure Class A 30W into 8 ohms and 4 ohms. This requires an increase in total DC bias to almost 4A. I chose 4A to bring each output and CCS Mosfet to its field-operating limit (50W) without reliability issues. Of course proper heatsinking goes hand-in-hand to achieve this goal. The +/- 25V of supply voltage will remain but transformer power should be at least 500hp…I mean VA. I am also adapting the Aleph 30/60 front-end circuitry for higher input impedance and what seems to be better looking simulated waveforms.We keep the 20dB of gain, we keep it single-ended input to output, we increase the negative going signal cut-off to 8A and we strap in NP’s nitrous oxide tank to get additional boost just like the stock car…I mean amp. Okay, here’s the summary of hardware revamp per channel: (Refer to both A3 and A30 circuit diagrams)
1. Power Transformer 500VA, 21V-0-21V/8A secondary
2. Wire input circuit like Aleph 30 but without –IN branch. Hang a 10k resistor to Ground between R7 and R10. Replace 10k R104 feedback resistor with 100k to keep the circuit gain at 20dB.
3. Top fuel economy is achieved by replacing Source resistors R120 to R123 with two 0.51ohm in parallel for a total of 0.255ohm Source R. This translates to almost 2A of bias in each output circuit branch with 0.5V of reference voltage. Scale it down to just below 2A with a different resistor combo in case you find your reference voltage is 0.55V or more.
4. For the purist in you disconnect R114 and you have 0% AC current gain. Our new hardware is now capable of 30W of pure Class A into 4 and 8ohms.
If you feel you need more boost at low impedances, let us strap on the Aleph nitrous oxide tank in the form of the CCS feedback.
5. First increase the cut-off current to about 8A. Based on the new Source R value, replace R110 with 215ohms.
6. For nitrous oxide to mix with top fuel, replace R114 with 1.82kohms. With 0.255ohm of Source resistors and the original 4 Sense resistors the AC current gain is pegged at 50%. Peak voltage in 4 ohms is about 22V and peak current is about 5.5A for a 60Wrms of power.
If you go through to number 4, the final power specifications will be 30Wrms into 8ohms and 30Wrms into 4ohms both pure Class A power figures. Completing number 6 will yield 30Wrms/8ohms pure Class A and 60Wrms/4ohms Class AB beyond 30Wrms.
Hopefully, this racetrack dragster if ever somebody completes it will be bulletproof enough to make it far beyond the quarter mile and sound excellent too. Thanks for reading. I enjoyed comparing amps to racecars. I can only dream of building a real top fuel dragster…meanwhile top-notch extreme audio is within reach. Just make sure you include an air intake on your chassis
The measured power in simulation is what I think to be pure Class A 30W into 8 ohms and 4 ohms. This requires an increase in total DC bias to almost 4A. I chose 4A to bring each output and CCS Mosfet to its field-operating limit (50W) without reliability issues. Of course proper heatsinking goes hand-in-hand to achieve this goal. The +/- 25V of supply voltage will remain but transformer power should be at least 500hp…I mean VA. I am also adapting the Aleph 30/60 front-end circuitry for higher input impedance and what seems to be better looking simulated waveforms.We keep the 20dB of gain, we keep it single-ended input to output, we increase the negative going signal cut-off to 8A and we strap in NP’s nitrous oxide tank to get additional boost just like the stock car…I mean amp. Okay, here’s the summary of hardware revamp per channel: (Refer to both A3 and A30 circuit diagrams)
1. Power Transformer 500VA, 21V-0-21V/8A secondary
2. Wire input circuit like Aleph 30 but without –IN branch. Hang a 10k resistor to Ground between R7 and R10. Replace 10k R104 feedback resistor with 100k to keep the circuit gain at 20dB.
3. Top fuel economy is achieved by replacing Source resistors R120 to R123 with two 0.51ohm in parallel for a total of 0.255ohm Source R. This translates to almost 2A of bias in each output circuit branch with 0.5V of reference voltage. Scale it down to just below 2A with a different resistor combo in case you find your reference voltage is 0.55V or more.
4. For the purist in you disconnect R114 and you have 0% AC current gain. Our new hardware is now capable of 30W of pure Class A into 4 and 8ohms.
If you feel you need more boost at low impedances, let us strap on the Aleph nitrous oxide tank in the form of the CCS feedback.
5. First increase the cut-off current to about 8A. Based on the new Source R value, replace R110 with 215ohms.
6. For nitrous oxide to mix with top fuel, replace R114 with 1.82kohms. With 0.255ohm of Source resistors and the original 4 Sense resistors the AC current gain is pegged at 50%. Peak voltage in 4 ohms is about 22V and peak current is about 5.5A for a 60Wrms of power.
If you go through to number 4, the final power specifications will be 30Wrms into 8ohms and 30Wrms into 4ohms both pure Class A power figures. Completing number 6 will yield 30Wrms/8ohms pure Class A and 60Wrms/4ohms Class AB beyond 30Wrms.
Hopefully, this racetrack dragster if ever somebody completes it will be bulletproof enough to make it far beyond the quarter mile and sound excellent too. Thanks for reading. I enjoyed comparing amps to racecars. I can only dream of building a real top fuel dragster…meanwhile top-notch extreme audio is within reach. Just make sure you include an air intake on your chassis
Should have some finished pcbs for the Hot Rod very soon.
I've been playing my retro Aleph 60 and measured the current gain last night at about 61 % using the schematic values.
Adjusting back to 50% does provide a subjectvie taste change, a crisper, more transparent but perhaps thinner sound.
Ian
I've been playing my retro Aleph 60 and measured the current gain last night at about 61 % using the schematic values.
Adjusting back to 50% does provide a subjectvie taste change, a crisper, more transparent but perhaps thinner sound.
Ian
Hi Ian,
It's good to know you're making quite a progress with your boards. I have made some more changes from the board design I sent you. It now has Q1 and Q2 also back to back on the other Board I and ready for heatsink HS131 or 132 (Digikey Thermaloy Fig 19). I also resized the cap going across Z5 on the CCS of the diff pair to fit a 6mm x 20mm film cap.
Less AC current gain I think will lessen Class AB power capability and you keep the original pure Class A power value at your bias setting. If your heatsinks can take some more heat, increase your bias for more pure Class A. I think this will sound much better with less ACIG.
Thanks for taking on the challenge of the HRA boards!
Cheers mate,
Allan
It's good to know you're making quite a progress with your boards. I have made some more changes from the board design I sent you. It now has Q1 and Q2 also back to back on the other Board I and ready for heatsink HS131 or 132 (Digikey Thermaloy Fig 19). I also resized the cap going across Z5 on the CCS of the diff pair to fit a 6mm x 20mm film cap.
Less AC current gain I think will lessen Class AB power capability and you keep the original pure Class A power value at your bias setting. If your heatsinks can take some more heat, increase your bias for more pure Class A. I think this will sound much better with less ACIG.
Thanks for taking on the challenge of the HRA boards!
Cheers mate,
Allan
Allan,
I am looking forward to the HotRod project.
At the moment I am just enjoying my Aleph 60 (downsized from an Alpeh 2) using in my system with the MOX High Low Pass crossover.
Nelson has mention the tendancy for owners of the X Series to bi amp their systems with the Aleph on the top end. I agree the Aleph excellent in this application.
I prefer to calculate the bias for the Aleph for the correct amount of peak current required for the impedance (the lowest impedence point) and power level of the speaker system at hand.
Then manually adjust the AC current gain to 50% for whatever your preference and taste desires.
This way your Aleph is optimised for your speakers and power requirement. The patent details the function of the Aleph current source quite clearly and 50% current share appears optimum.
Regards the 60% current gain in some respects I think the smaller commercial Aleph were setup in anticipation of market requirements for more power into lower impedance loads while still delivering a rated power into a nominal 8 ohm load for a given total power dissipation.
However, as mentioned above (and as outlined by Grey Rollins) the bias is best set for a given speaker and power level. More is better provided you don't mind the power bill and have sufficent heatsink real estate. The more bias, the more gain the design has and care must be taken to ensure stability by adding the correct capacitance to Q5 and negative side if required.
Ian
I am looking forward to the HotRod project.
At the moment I am just enjoying my Aleph 60 (downsized from an Alpeh 2) using in my system with the MOX High Low Pass crossover.
Nelson has mention the tendancy for owners of the X Series to bi amp their systems with the Aleph on the top end. I agree the Aleph excellent in this application.
I prefer to calculate the bias for the Aleph for the correct amount of peak current required for the impedance (the lowest impedence point) and power level of the speaker system at hand.
Then manually adjust the AC current gain to 50% for whatever your preference and taste desires.
This way your Aleph is optimised for your speakers and power requirement. The patent details the function of the Aleph current source quite clearly and 50% current share appears optimum.
Regards the 60% current gain in some respects I think the smaller commercial Aleph were setup in anticipation of market requirements for more power into lower impedance loads while still delivering a rated power into a nominal 8 ohm load for a given total power dissipation.
However, as mentioned above (and as outlined by Grey Rollins) the bias is best set for a given speaker and power level. More is better provided you don't mind the power bill and have sufficent heatsink real estate. The more bias, the more gain the design has and care must be taken to ensure stability by adding the correct capacitance to Q5 and negative side if required.
Ian
My double sided pcb materials will arrive tomorrow so I will be able to develop the boards.
Fingers crossed my trace of the layout is correct.
I have played with the bias and current share some more.
I have changed back my Aleph 60 to the schematic values for the current share and added the other capcitors for the negative side.
I prefer the sound this way!
One thing I realised is perhaps my Aleph is not running hot enough, this can effect the settings.
Ian
Fingers crossed my trace of the layout is correct.
I have played with the bias and current share some more.
I have changed back my Aleph 60 to the schematic values for the current share and added the other capcitors for the negative side.
I prefer the sound this way!
One thing I realised is perhaps my Aleph is not running hot enough, this can effect the settings.
Ian
Keep us posted Ian. Just make sure you solder together some of the traces going from bottom to top side of your pcb labeled "V".
"I have changed back my Aleph 60 to the schematic values for the current share and added the other capcitors for the negative side." -Ian
BTW, what caps are these?
"I have changed back my Aleph 60 to the schematic values for the current share and added the other capcitors for the negative side." -Ian
BTW, what caps are these?
Okay,
I am going to have to start over on my observations.
During my evaluations I had the Mox incorrectly adjusted for 12 db instead of 18 db slopes, the subjective result is night and day..too many jumpers can be confusing.
So, over the weekend I will revert back to a full passive system and have another listen.
About the boards I could build for a Alpeh 5/60 with the transformers I have.
Does anyone have a preference for which Aleph to trial the HR boards?
Ian
I am going to have to start over on my observations.
During my evaluations I had the Mox incorrectly adjusted for 12 db instead of 18 db slopes, the subjective result is night and day..too many jumpers can be confusing.
So, over the weekend I will revert back to a full passive system and have another listen.
About the boards I could build for a Alpeh 5/60 with the transformers I have.
Does anyone have a preference for which Aleph to trial the HR boards?
Ian
Nelson Pass said:
If the current source gain is set to 50%, then the static bias
can be set anywhere above 1/2 the peak current value. If you
bias at the peak output current value, you then have the luxury
of setting the gain anywhere between 0 and 100%.
Now that's a Coooool idea
Better find wide open space, somewhere with plenty of ventilation.
I would love to re visit this place(under Passlabs superision of course!)
Ian
Attachments
Give each pcb holds 6 power fets, one of the fun things I would like to try is a highly biased A30 to 3 amps or an A30 turbo biased with 12 fets to 6 amps.
This would allow adjustment from 0~60+ % current share and evaluation of subjective performance.
Ian
Ps When I was over there I drove through MS to Boston in a V8 Audi, very nice.
This would allow adjustment from 0~60+ % current share and evaluation of subjective performance.
Ian
Ps When I was over there I drove through MS to Boston in a V8 Audi, very nice.
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