If you come up with a board including similar changes you better believe I will build it Salas. I believe your buffer is very good but you have to see it from my point of view to... if I can dial in the perfect impedance I dont need a buffer. Now, if I can dial in perfect impedance, use a buffer and get improved bass and none of the bad effect, yep, I would be all over that.
impdance matching
..my test setup is running with the 300R source (PLAYER) and the 10k7 load (Linkwitz Orion active crossover).
According to manufacturers info, the player is able of driving low impedances.
"Variation in load impedance is generally less of a problem as the op-amps in the (PLAYER) can drive loads down to 300 ohms without any appreciable increase in distortion. However, potentiometer values of less than about 10k will start to modify the high frequency roll-off of the output stage and may allow more RF noise to enter the power amplifier...
At low values of attenuation, the modified source impedance will be close to that of the original source, but as the attenuation is increased, the impedance seen by the load will increase and peak at about -6dB,
before falling to zero at infinite attenuation. This peak in source impedance may cause noise problems at certain attenuation values, especially if there is a significant cable run between the attenuator and the amplifier...
A good compromise potentiometer value would probably be 5K.
Now, I tracked the R seen by the source (curves at the bottom) and R seen by the amp (curves above).
In a second round I simulated, that each LDR is paralleled by a second LDR, which halves the resistance of the attenuator. Here, one might try to lower the supply voltage and increase the total impedance a little bit, as needed.
But I wonder what the effect on system THD would be when paralleling the LDRs / lowering the supply voltage?
Any predictions?
Frank
..my test setup is running with the 300R source (PLAYER) and the 10k7 load (Linkwitz Orion active crossover).
According to manufacturers info, the player is able of driving low impedances.
"Variation in load impedance is generally less of a problem as the op-amps in the (PLAYER) can drive loads down to 300 ohms without any appreciable increase in distortion. However, potentiometer values of less than about 10k will start to modify the high frequency roll-off of the output stage and may allow more RF noise to enter the power amplifier...
At low values of attenuation, the modified source impedance will be close to that of the original source, but as the attenuation is increased, the impedance seen by the load will increase and peak at about -6dB,
before falling to zero at infinite attenuation. This peak in source impedance may cause noise problems at certain attenuation values, especially if there is a significant cable run between the attenuator and the amplifier...
A good compromise potentiometer value would probably be 5K.
Now, I tracked the R seen by the source (curves at the bottom) and R seen by the amp (curves above).
In a second round I simulated, that each LDR is paralleled by a second LDR, which halves the resistance of the attenuator. Here, one might try to lower the supply voltage and increase the total impedance a little bit, as needed.
But I wonder what the effect on system THD would be when paralleling the LDRs / lowering the supply voltage?
Any predictions?
Frank
I'm doing a sound card mod. The card has a headphone amp stage that I want to remotely control the volume on (attenuating signal before amplifier stage). Remote means a cable from the PC to the desk. But I don't want to pull a cable all the way up and back with the signal in.
Will an LDR volume control do the job? In this case I only have to wire a potmeter without the signal to the desk.
I can get 5V from the computer but it turns off when the computer is turned off.
Will an LDR volume control do the job? In this case I only have to wire a potmeter without the signal to the desk.
I can get 5V from the computer but it turns off when the computer is turned off.
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Can't draw at the moment, but can explain:
Forget that it is a sound card.
There is an opamp output (from datasheet the ouptut resistance is 80 ohm).
Vout is ~3V.
This is followed by an opamp headphone amplifier stage, so the input resistance of this stage is quite high. Cant find datasheet yet.
It is possible to condition the computer supplied voltage..
I have 3 choice:
1) use the supply of the card itself, I thinc the dac needs as good supply as an optocoupler... this way I have (+-)9V
2) use the PSU 5V output
3) use the PSU 12V output and make a regulated psu from that.
Forget that it is a sound card.
There is an opamp output (from datasheet the ouptut resistance is 80 ohm).
Vout is ~3V.
This is followed by an opamp headphone amplifier stage, so the input resistance of this stage is quite high. Cant find datasheet yet.
It is possible to condition the computer supplied voltage..
I have 3 choice:
1) use the supply of the card itself, I thinc the dac needs as good supply as an optocoupler... this way I have (+-)9V
2) use the PSU 5V output
3) use the PSU 12V output and make a regulated psu from that.
All sound fine as far as the impedances go, give your supply a go, if noisy just use a 5v reg and a couple of caps with this.
12V Lithium-ion Li-ion Rechargeable Battery for CCTV - eBay (item 380219619869 end time May-03-10 21:00:17 PDT)
Cheers George
No, I have not. I don't have a need for a buffer right now although I have one as a jfet input stage of my Zen amp.
Hi George,
Yes, it is extremely silent now. The sound is absolutely mind blowing. Fabulous stuff for an audiophile. Thanks a lot for the find.
Best regards,
Bins.
Yes, it is extremely silent now. The sound is absolutely mind blowing. Fabulous stuff for an audiophile. Thanks a lot for the find.
Best regards,
Bins.
Hi Bins,
Did you notice any difference between 9V and 12V batteries? While both were quiet I noticed better dynamics with a 12V SLA into the 7805. Also, I've been comparing it to the linear regulated wall-wart suggested by George way back in this thread (from RP elec) and I doubt I could reliable tell the difference with the 12V battery I use.
Hi All,
Is there anyone in Sydney with a batch of LDRs that I can use to test my matching process? I could handling about 50 (maybe 100 at a pitch) before going mental. I'll return the LDRs with data and a couple of reports.
I would ask that each LDR have a label with number on it (I use masking tape). This would ensure you get your LDRs back and not my bad ones.
regards
Is there anyone in Sydney with a batch of LDRs that I can use to test my matching process? I could handling about 50 (maybe 100 at a pitch) before going mental. I'll return the LDRs with data and a couple of reports.
I would ask that each LDR have a label with number on it (I use masking tape). This would ensure you get your LDRs back and not my bad ones.
regards
Hi,
12V seems having better dynamics. I am not sure why it behaves so. Maybe George or Udailey can help.
Best regards,
Bins.
12V seems having better dynamics. I am not sure why it behaves so. Maybe George or Udailey can help.
Best regards,
Bins.
A 9v transitor battery like the Duracell copper top is only good for around 2-3hrs if fresh, it will fade very quick. Where a 12v SLA the smallest one I know will give around 20hrs before it starts to die.
The rechargable Lithium-Ion one I recommend will give around 12hrs and comes complete with cables pugs and charger with a switch in a nice compact package it's a no brainer for $9.00. Don't know why you would look at anything else.
12V Lithium-ion Li-ion Rechargeable Battery for CCTV - eBay (item 380219619869 end time May-03-10 21:00:17 PDT)
Cheers George
The rechargable Lithium-Ion one I recommend will give around 12hrs and comes complete with cables pugs and charger with a switch in a nice compact package it's a no brainer for $9.00. Don't know why you would look at anything else.
12V Lithium-ion Li-ion Rechargeable Battery for CCTV - eBay (item 380219619869 end time May-03-10 21:00:17 PDT)
Cheers George
Ok , now for the dumb question.. I use mine on 4 x 1.2 volt NiCads AA cells and no regulator.
Just direct to the ldrs via pots and recharge them about every 3 Months. (and that is 'cause I feel I should not because they need it)
So what am I doing wrong ??.
The wall wart (not switching) I first used through a 7805 just got worse and worse with the sound ending up congested and harsh.
Having no spare 7805 to substitute I just used the AA cells to see and all was restored.
.So what have I done and what am I missing ??.
Oh, and I like the Pugs too. We've only got foxies.
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Nothing wrong with what your doing there, probally the cleanest power one could get, just that when you have a full charge all is ok, but as the charge goes down you'll have less and less span between min and max volume nothing wrong with that if you keep adjusting the volume accordingly to suit your level. You should remember also that a 7805 regulator has an output noise of no more than 40uV, I very much doubt that this is detectable in this case, maybe something else was amiss, bad caps before or after maybe.
Cheers George
Cheers George
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