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About the Input / Output impedance

delta1

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About the Input / Output impedance

Postby obee » November 24th, 2017, 9:18 pm

Hi,
I read some post here when considering the input/output impedance, but I still have can't make a decision, could you help?

My plan is to have 6 inputs, 2 outputs like below:

dacs / tuners / phono -> delta 2 input -> delta 1 -> alpha24 -> delta2 output 1 -> beta22 -> headphone / beta24
dacs / tuners / phono -> delta 2 input -> delta 1 -> alpha24 -> delta2 output 2 -> beta24

What's the difference if I use 50k vs 25k as input impedance?
For output impedance, 1M is a good choice?

Thanks!
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Re: About the Input / Output impedance

Postby amb » November 24th, 2017, 11:12 pm

By "Input impedance" I think you mean Zatt. A good choice is the default of 25KΩ. Anything between 10KΩ and 50KΩ is OK. Much lower than 10KΩ then the attenuator might become a difficult load for some sources. Much higher than 50KΩ then resistor noise may affect the S/N ratio.

For "output impedance" if you mean Zload, and you're using the α24 after the δ1, then it should be set to 500KΩ.
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Re: About the Input / Output impedance

Postby obee » December 17th, 2017, 10:04 am

I have built the alpha24, delta1,2, LCDuino1. Basically, they work. However, I found that the volume control (delta1) is a bit weird that the loudness from 0.5dB to 0.0dB is much higher than other steps. I followed the calculator using 25k ohm Zatt and 500k ohm Zload.
Delta1_R2R.PNG


Unfortunately, I can't order exact resistance values. So I guess the weird behavior is due to the mismatch of resistor values. Does anyone know what resistor I should replace in order to fix the issue? Thanks.

Item=value (actual value bought) mouser parts number
--------------------------------------------------------------------
RS0=1.4k (same) RN55C1401BB14
RS1=2.71k (same) RN55C2711BB14
RS2=5.17k (same) RN55E5171BB14
RS3=9.2k (9.31k) RN55E9311BB14
RS4=15k (same) PTF5615K000BYEB
RS5=21k (same) RN55C2102BB14
RS6=24.3k (same) RN60C2432FB14
RS7=24.9k (same) RN55E2492BB14
RT=26.4k (26.25k) PTF5626K250BXBF
RP0=422k (same) RN60C4223FB14
RP1=205k (same) RN55C2053BRE6
RP2=96.5k (same) RN60C9652DB14
RP3=42.7k (same) RN55C4272BRE6
RP4=16.5k (same) RN55C1652BB14
RP5=4.7k (same) RN55E4701BRE6
RP6=642R (649R) RN55C6490FB14
RP7=16R (16.4R) RN55E16R4BB14
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Re: About the Input / Output impedance

Postby amb » December 17th, 2017, 4:07 pm

Is it every time it makes a -0.5dB to 0.0dB transition? I.e., from -20.5 to -20.0, from -12.5 to -12.0, etc.? Or is it only certain transitions?
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Re: About the Input / Output impedance

Postby obee » December 17th, 2017, 4:19 pm

amb wrote:Is it every time it makes a -0.5dB to 0.0dB transition? I.e., from -20.5 to -20.0, from -12.5 to -12.0, etc.? Or is it only certain transitions?

I think it only happens at -0.5dB to 0.0dB transistion, I can't feel big change of sound level at -20.5->-20dB or -12.5->-12dB
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Re: About the Input / Output impedance

Postby obee » December 17th, 2017, 4:22 pm

My current configuration is:
single delta 2 -> single delta 1 -> alpha24 -> SE output to 32ohm headphone.
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Re: About the Input / Output impedance

Postby amb » December 17th, 2017, 4:27 pm

obee wrote:I think it only happens at -0.5dB to 0.0dB transistion, I can't feel big change of sound level at -20.5->-20dB or -12.5->-12dB

OK, in that one case the only change would be a relay state change for K0, involving shorting RS0 and opening up RP0. But you said that you used the correct value resistors for these. Can you verify that? Does the resistors have labels (e.g., Vishay-Dale RN or CMF) or color bands?
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Re: About the Input / Output impedance

Postby obee » December 18th, 2017, 5:52 am

amb wrote:
obee wrote:I think it only happens at -0.5dB to 0.0dB transistion, I can't feel big change of sound level at -20.5->-20dB or -12.5->-12dB

OK, in that one case the only change would be a relay state change for K0, involving shorting RS0 and opening up RP0. But you said that you used the correct value resistors for these. Can you verify that? Does the resistors have labels (e.g., Vishay-Dale RN or CMF) or color bands?

The two resistors are:
RS0=1.4k (same) RN55C1401BB14
RP0=422k (same) RN60C4223FB14
I think they are correct.
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Re: About the Input / Output impedance

Postby amb » December 18th, 2017, 12:59 pm

Indeed they look correct. Are the resistors' and relay's solder joints good? If they are, then there shouldn't be this problem unless the relay itself is defective.
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Re: About the Input / Output impedance

Postby obee » December 18th, 2017, 9:23 pm

amb wrote:Indeed they look correct. Are the resistors' and relay's solder joints good? If they are, then there shouldn't be this problem unless the relay itself is defective.


That's what I think.
I checked many times the resistor values and the placements, all looks fine. For the relay, I don't know how to check, I can just hear tick sound and LED flash when there's change in volume. However, unlike delta2, the change of relay is very complicated that every change of volume may involve multiple relays.
May be the workaround is to define the maximum volume to -0.5dB to avoid turning up the volume too high at 0.0dB.
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