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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
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Old Yesterday, 06:19 PM   #2871
bk856er is offline bk856er  United States
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
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Originally Posted by xrk971 View Post
Although I have not tried it directly with the Alpha yet, the fact that the voltage rises slowly should eliminate the turn on thump. The ramp up rate can be adjusted with the RC time constant of the cap multiplier. If it is made slower than say 5 seconds, it should eliminate it.

Looking at the schematic above, it seems the time constant on this system is only 0.15sec - too fast. We would probably have to play with some simulations to slow the DC chargeup. If I look at it on an Oscope during turn on I can verify this. Probably even a DVM can see that it may be too quick in stock form.
I'll be watching for this and appreciate any input, sounds like a useful tweak for my upcoming alpha.

BK
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Old Today, 06:43 PM   #2872
jwjarch is offline jwjarch  United States
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I posed the question about the RC time constant in the Juma Easy Peasy CapMx thread. In the meantime, any idea which values to tweak X?
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Old Today, 08:21 PM   #2873
xrk971 is offline xrk971  United States
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Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Quote:
Originally Posted by jwjarch View Post
I posed the question about the RC time constant in the Juma Easy Peasy CapMx thread. In the meantime, any idea which values to tweak X?
https://www.diyaudio.com/forums/atta...son_sch_r1-png

Hi Jwjarch,

I think it is R2/C3 and R6/C7. Currently, it is 150R/470uF combo. On the Juma Easy Peasy, this main R/C combo is 10k/220uF which has a 0.7RC time constant of 1.55 seconds. For 150R and 470uF the 0.7RC time constant is 0.05 seconds, that's 31x faster and too fast to provide a slow ramp up. I connected a DMM to the output and switched it on, and sure enough the voltage jumps up to the nominal output value almost instantaneously. This will not work for turn-on thump reduction.

If we switch the RC combo to something similar like the Juma Easy Peasy, we could simply use something like 4k7 for the R2 and R6 value. However, I am not sure how that will affect the rest of the circuit in its ability to provide the ripple reduction over the bandwidth of interest.

Let me ask Mark Johnson in other thread as he is the designer.
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