Also, the feedback connection points are different. The ground lift was just extra insurance against hum from ground loops. There is an extra diode to protect the input stage as well. Mostly though, the PCB was designed with a wide variety of interface bolt holes for all the popular and low-cost Intel/AMD CPU coolers that use heatpipes/radiator/fans.
Whereas the Alpha 20 was designed to be UMS compatible.
Whereas the Alpha 20 was designed to be UMS compatible.
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Ok, so I did the test with my Alpha 20 running 1.35amp bias with R131=0.47R and R132= 0.22R.
I used two 270ohm (5W) resistors in series for the high impedance case for 3.52vrms or 9.96vpp.
Then with a 10.0ohm 2% 10W resistor I measured 3.39vrms or 9.59vpp.
So (1-9.59/9.96)=0.0368 or 10ohm/0.0368=27.2 DF - fairly close to the 30 DF Hugh predicted for the Alpha 20 running 1.93amps bias.
So one thing that is important is to use very low impedance speaker cables. They do make a difference. 16ga stranded copper zipcord is not as good as solid copper 12ga Romex. So back goes the Romex into the speaker setup.
I forgot that Hugh designed the Alpha to have higher damping factor at low frequencies where you need the bass cone control. Less at higher frequencies where you want less global feedback for better imaging. I ran my test at 1kHz. Maybe I should try redoing it at 55Hz kick drum center frequency and see what t is?
And maybe take 8 ohm load, Danny's sym shows the higher low frequency damping seems to disappear a little too ???I forgot that Hugh designed the Alpha to have higher damping factor at low frequencies where you need the bass cone control. Less at higher frequencies where you want less global feedback for better imaging. I ran my test at 1kHz. Maybe I should try redoing it at 55Hz kick drum center frequency and see what t is?
Well I am curious about the 0.11R, 36V, 200W+ per low cost cooler. Chinese watt specs can be funny
Dissipation per mosfet is bias x 36v rail = 100w ea. Hence ea channel has 2 CPU coolers.
I just read an interesting post about damping factor.
See the post of atmasphere.
I copied a part of it:
Amps that exhibit 'tight' bass often have lots of feedback, which is there to reduce distortion.
Unfortunately a price is paid: loop feedback at low frequencies can behave as a sort of dynamic compression,
and has the ability to cause the amplifier to loose soundstage definition (the 'air' around instruments that flesh out the body of the instrument as well as its ambient signature).
Often 'tight' bass is as a lack of definition at low frequencies.
IME, when you start to loose definition, the of the first things to go is the low frequency ambiance in the recording.
Further reduction of definition results in 'poster board' images of instruments in the soundstage.
Initially, this might sound as if the amp is more focused, but after a while the lack of ambient signatures (hall reflections and the like) let you know what is really going on.
See also the post from folkfreak:
As the owner of a pair of VTL MB 450 III with adjustable damping factor (4 settings) I can attest to the fact that damping factor matters.
Obviously it's an interaction with the rest of your system but as I got my room resonances under control I could lower the DF on my Magico Q3s and now have it at the lowest setting.
The effect of lowering DF is to lose some immediate "punch" in the bass but replace it with greater air, scale and overall body which is much more preferable.
My suspicion would be that too many amps (especially solid state) are over damped but that's just my preference and I'm surprised more manufacturers don't offer adjustable DF
See the post of atmasphere.
I copied a part of it:
Amps that exhibit 'tight' bass often have lots of feedback, which is there to reduce distortion.
Unfortunately a price is paid: loop feedback at low frequencies can behave as a sort of dynamic compression,
and has the ability to cause the amplifier to loose soundstage definition (the 'air' around instruments that flesh out the body of the instrument as well as its ambient signature).
Often 'tight' bass is as a lack of definition at low frequencies.
IME, when you start to loose definition, the of the first things to go is the low frequency ambiance in the recording.
Further reduction of definition results in 'poster board' images of instruments in the soundstage.
Initially, this might sound as if the amp is more focused, but after a while the lack of ambient signatures (hall reflections and the like) let you know what is really going on.
See also the post from folkfreak:
As the owner of a pair of VTL MB 450 III with adjustable damping factor (4 settings) I can attest to the fact that damping factor matters.
Obviously it's an interaction with the rest of your system but as I got my room resonances under control I could lower the DF on my Magico Q3s and now have it at the lowest setting.
The effect of lowering DF is to lose some immediate "punch" in the bass but replace it with greater air, scale and overall body which is much more preferable.
My suspicion would be that too many amps (especially solid state) are over damped but that's just my preference and I'm surprised more manufacturers don't offer adjustable DF
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Just an idea:
Now there are 2 options for the Aleph damping factor, depending on where the fb is taken: before or after the sensor resistor.
If you "split" the sensor resistor in 2 or more resistors in series, you get additional DF options or you can customize the DF to the value that you want.
I did some simulations and this works, I can customize the DF
Now there are 2 options for the Aleph damping factor, depending on where the fb is taken: before or after the sensor resistor.
If you "split" the sensor resistor in 2 or more resistors in series, you get additional DF options or you can customize the DF to the value that you want.
I did some simulations and this works, I can customize the DF
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The bigger mosfets behave so differently ? I mean for the smaller mosfets 0.22R would be around 100W ?Dissipation per mosfet is bias x 36v rail = 100w ea. Hence ea channel has 2 CPU coolers.
The dissipation would be the same - the smaller TO-247 packages simply cannot handle more than 35w each. They would melt at 100w. The bias current is pretty much function of the R131 (on Alpha 20 board) source resistor on the CCS. The big TO-264 packages handle more dissipation but have about three times the capacitance. So there is a difference there but Hugh’s circuit takes all of that into consideration and has been optimized (recall it was modeled as three pairs of IRF240/9240 for good reason).
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I received 3 boxes from Mouser today. All parts for Alpha BB are in my hands, now to find time... I have a business trip overseas to Germany this weekend so will probably not have enough time to build one before I go. However, will meet up with JPS64 and hand deliver some Alpha 20 and BB PCB's
Yes, Danny, use a 100R pot across the 0.12R output resistor and take the fb from the wiper, no change to the 22k fb resistor.
Yes, good idea, that will be the best and easiest way to try the different damping factors.
If I settle for one I can change the pot to two resistors (100r total), values determined by the pot.
This opens back the option for the 4R to go for 0.18 sensor and 0.33 source resistors to have less heat dissipation.
I can still adapt the damping factor if it gets too low.
X, a proposal for future PCBs: place for two extra resistors in series, parallel to the sensor resistor.
At the junction you can take the fb.
Regards,
Danny
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Danny,
On the 4R you can reduce the output sensor from 0.18 to the original 0.12 and restore the standard R17, which is 865R. Increasing it over 0.12 whilst still working well at the fixed figure does not give any advantage; it just increase Zout needlessly. You don't want DF less than about 27. Many SET tube amps have a Zout of around 4R, and their bass is less than optimal, so I feel high Zout is not a good idea.
Cheers,
HD
On the 4R you can reduce the output sensor from 0.18 to the original 0.12 and restore the standard R17, which is 865R. Increasing it over 0.12 whilst still working well at the fixed figure does not give any advantage; it just increase Zout needlessly. You don't want DF less than about 27. Many SET tube amps have a Zout of around 4R, and their bass is less than optimal, so I feel high Zout is not a good idea.
Cheers,
HD
The dissipation would be the same - the smaller TO-247 packages simply cannot handle more than 35w each. They would melt at 100w. The bias current is pretty much function of the R131 (on Alpha 20 board) source resistor on the CCS. The big TO-264 packages handle more dissipation but have about three times the capacitance. So there is a difference there but Hugh’s circuit takes all of that into consideration and has been optimized (recall it was modeled as three pairs of IRF240/9240 for good reason).
The IRFP240/9240 can't dissipate much more. But 0.33R on Alpha is around 1.9A, 0.27R in 4R version 2.4A, 0.22 would be around 3A, and then at 24V.
Now we have 36V, with around 3A (0.22R) that would be 100W+ ??? WIth 0.11R as in schematic that would be around 6A and 200W+??? So where do I go wrong ?
Hi Hugh,
Yes, the optimal values for 4R are 0.12, 0.33, 865
I did some simulations near clip level (16.7Vout) and only these values still gave a nice FFT.
Before I did simulations with only 9Vout and those FFTs also looked good with other values, but not anymore at 16.7Vout
Regards,
Danny
Yes, the optimal values for 4R are 0.12, 0.33, 865
I did some simulations near clip level (16.7Vout) and only these values still gave a nice FFT.
Before I did simulations with only 9Vout and those FFTs also looked good with other values, but not anymore at 16.7Vout
Regards,
Danny
Here the results of my long reflection about I2C VU-METER:
- THAT 4301 dynamic processor and adjusted AN119 (needs +/-15V signal ground referenced)
- low cost 8bit I2C ADC (needs +5V analog and +5V digital signal ground referenced) - ADC121 is 12bit, SOT23-6, only example
- ADuM1250 I2C isolator (needs +5V digital signal ground referenced and +5V digital ground referenced)
- to avoid ground problems by isolating dirty digital ground.
- I2C connector supplied today on ALPHA BB boards
- replacing OLED 1.3 inch with 4.2 inch three colour e-paper display
This need a complete redesign of the actual solution!
IMHO, this could be a standalone developpement (I2C today supplied on ALPHA BB boards) then not only for ALPHA amps!
JP
THAT Corporation 4301 Analog Engine - Dynamics Processor IC
http://www.thatcorp.com/datashts/dn119.pdf
4.2inch e-Paper Module (B - Waveshare Wiki)
YouTube
- THAT 4301 dynamic processor and adjusted AN119 (needs +/-15V signal ground referenced)
- low cost 8bit I2C ADC (needs +5V analog and +5V digital signal ground referenced) - ADC121 is 12bit, SOT23-6, only example
- ADuM1250 I2C isolator (needs +5V digital signal ground referenced and +5V digital ground referenced)
- to avoid ground problems by isolating dirty digital ground.
- I2C connector supplied today on ALPHA BB boards
- replacing OLED 1.3 inch with 4.2 inch three colour e-paper display
This need a complete redesign of the actual solution!
IMHO, this could be a standalone developpement (I2C today supplied on ALPHA BB boards) then not only for ALPHA amps!
JP
THAT Corporation 4301 Analog Engine - Dynamics Processor IC
http://www.thatcorp.com/datashts/dn119.pdf
4.2inch e-Paper Module (B - Waveshare Wiki)
YouTube
But don´t forget, vintage VU-METER are not really cheap!
SIFAM AUDIO LEVEL METER AL20SQ-Retro
SIFAM AL20-7 Retro Audio Level VU-Meter (Chandler replacement Instrument Meter) | eBay
SIFAM AUDIO LEVEL METER AL20SQ-Retro
SIFAM AL20-7 Retro Audio Level VU-Meter (Chandler replacement Instrument Meter) | eBay
12v Analog Panel VU Meter Audio Level Indicator Meter for Amplifier Speaker Sale - Banggood.com
How about this, Jean-Paul?
HD
How about this, Jean-Paul?
HD
Hi Hugh,
thank you. Yes, cheap chinese one. Or this one?
2Pcs VU Meter Warm Backlight Recording + Audio Level Amp With Driver Board Sale - Banggood.com
But the requirement is to visualize on display when using ALPHA BB CONTROL board.
It´s MMI, a never ending story!
JP
thank you. Yes, cheap chinese one. Or this one?
2Pcs VU Meter Warm Backlight Recording + Audio Level Amp With Driver Board Sale - Banggood.com
But the requirement is to visualize on display when using ALPHA BB CONTROL board.
It´s MMI, a never ending story!
JP
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