Hybrid ZEN Amplifier + LM317 = Efficient and simple

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#221
diegomj1973 said:
I share a simple guideline table (elaborated from simulation) for those who wish to adapt the scheme of the first post to different voltage gain needs. It states that one of the resistors of the feedback loop remains unchanged (R6), while different values are given for R5. For each value of R5, we will have different voltage gains, the upper cut-off frequency of the circuit will also change and the distortion will be altered somewhat and possibly its profile somewhat (all these parameters should be properly checked under real operating conditions). In the table we can compare the total distortion at 1 W over 8 ohms and 1 KHz, for different preset gains, to compare similar operating conditions on the load.

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Best regards
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My Arta measurement is fully in line with Diego's table above: I used a 3K3 R5 feedback resistor and at around 1Watt/1,100 Hz) I get some 0.5% THD.
 
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#223
Of course it seems ultra low, but for my (below depicted) CD Audiophase walkman bought from Houston TX, 23 years ago, it is the perfect fit. Everyone is using different sources with different output Z, thus different impedance schemes have been put on the table by our 'audio' friend: Diego. Thank him and of course Mr. Nelson Pass - a lot !

Cheers,
Radu
 

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#224
I've tried to improve a bit distortion figures while trying not to change cadence of THD: H2, H4, H6, higher than H3, H5, 7, 9, 11.

So, I changed R2/R1 ratio from 0.8 to about 0.4... the result ? THD levels at 0.2 Watt, 1 Watt and max power have all halved, with no nasty H5, 7, 9, 11. For instance, THD at 1 Watt was about 0.25%. Overall, sound is very live, airy, very natural, I can describe it like this.

The only caveat: heatsink is now very hot, so that I can only keep my hand on it for max 10, 15 seconds...

I like the sound more than previously, so would it be a good idea to switch to a bigger heatsink/pc fan, or just simply revert to previous config? Is it healthy for the amp what I've done?

Diego, if you have time, what would you suggest ?
Many thanks!
 
#237
e_fortier said:
The ration of R2/R1 you found that sounds best, can I have your value of R2 and R1. I’ll definitely use your values.
Maybe Diego or Mr Pass can provide some feedback as I’m aware the value and ratio of R2 and R1 will change the harmonic profile.
Click to expand...

I originally used R2=1 ohm and R1=1.2 ohm so a 0.83 ratio.
e_fortier said:
Then, I paralleled R2 with a 1.2 ohm resistor giving me a new R2 value of 0.55 ohm. So, new ratio R2/R1= 0.55/1.2= 0.46.
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e_fortier said:
Originally I used R2=1 ohm and R1= 1.2 ohm, a 0.83 ratio.
Click to expand...
Plase note that I use a 20.4 volt laptop supply and that my 'setup' uses a 20W fullrange cheap Monacor speaker with a whizzer cone mounted on an improvised 25x35 thin plywood open baffle, so I cannot guarantee the sound I got will be the same in a different setup.
Also please note Diego warned that ratios lower tham 0.7 could produce a different harmonic cadence, resembling a single-ended ZEN design not anymore... however, I noticed that in my case it didn't impact my previous distortion profile, with H2 ruling across the spectrum.
Hope this helps,
Bests,
Radu
 
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