Andrew beat me to it - and he actually knows - not just assuming like me. But it's nice to see we agree... 😉
It would seem to me that at least one more requirement must be added and that is that the noise is not worse than that of a top quality resistor. Given that LDR's are usually made of some composite material their noise level may potentially be worse than that of a plain resistor. This characteristic should therefore be investigated before applying them.
I would be interested to hear if such tests have been applied.
Regards,
koest31
Yes,
we have used some of the best instruments we can find to do the tests you have mentioned.
We call them ears.
we have used some of the best instruments we can find to do the tests you have mentioned.
We call them ears.
The devices aren't opto-couplers, they're LDRs and they don't "follow" the audio signal. The signal passes through the LDRs only, not through the pot or across a coupler.
The volume pot regulates how much current passes through the LEDs and thus how bright they are. The LEDs in turn change the resistance of the LDRs. Once set, that resistance doesn't change until you turn the pot again.
The circuit is configured so that turning the pot CW lowers the value of the upper (series) resistor and increases the value of the lower (shunt) one, thus raising volume. Turning it CCW does, well, the opposite.
Hope that clarifies things . . .
My Tektronics scope has a visable noise floor of 200uV (micro-volts), I cannot see if the shorted input Lightspeed Attenuator measured at it's output at any level adds to this noise floor.
Cheers George
Cheers George
In regards to Koest's post about measureing noise floor on resistors: I have to say I have only done so with the LDRs, never messed with other resistors. I have a decent Tektronix. Did not see any additional noise. That solved my curiosity and I havent hooked them up again since then. The only other comparison I can offer is this:
I demo'd a LDR attenuator at a friends house. It smoked his Placette Audio - The best pre amps, preamplifiers, volume controls and that was his own admission. I certainly didnt say anything but he emailed me later about how amazed he was that it beat it, let alone even stood a chance. He figured, until that moment, that he had the best passive out there.
Of course this was, as Andrew stated, just our ears telling us the difference. We didnt whip out the AP to see what was going on, the choice for sonics was obvious.
When you do your resistor test dont forget to include the noise introduced by your relays and remember we dont use relays or any other contact when choosing volume with these LDR resistors.
Uriah
I demo'd a LDR attenuator at a friends house. It smoked his Placette Audio - The best pre amps, preamplifiers, volume controls and that was his own admission. I certainly didnt say anything but he emailed me later about how amazed he was that it beat it, let alone even stood a chance. He figured, until that moment, that he had the best passive out there.
Of course this was, as Andrew stated, just our ears telling us the difference. We didnt whip out the AP to see what was going on, the choice for sonics was obvious.
When you do your resistor test dont forget to include the noise introduced by your relays and remember we dont use relays or any other contact when choosing volume with these LDR resistors.
Uriah
Hi,
For my First Watt F5 I replaced the amps R9 & R10 with optocouplers. Since R9 is in series with the input and R10 goes to ground and is parallel to the shunt it made sense to just eliminate/replace them. My case is pretty open so no worries about heat. One caveat, make sure the optocouplers are powered first before the rest of the amp circuit or you will get a nasty ground hum.
I would monitor your dc offset at the speaker terminals first with the Lightspeed at all different levels before hooking it up to your speakers. As I have a feeling you will get some dc fluctuations at different levels, hopfully not too large to cook the voice coils of the divers.
Cheers George
I have wanted to build an amp with LDRs in it for a long time. Dont know whats slowing me down except matching LDRs for you guys. I think even in a chip amp it would be an improvement. Nice going Alazira. Did you appreciate the difference in sound?
Hi George,
Yes, the DC offset varies with diff volume settings, but no more than +/- 20mV, so well within the safety range. However, it also did that with standard LSA setup.
Udaily,
There was some improvement, probably from simply eliminating resistors in the signal path.
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That's good, means it has most probably a fet input stage like most of his amps. Just to be careful I would also monitor the dc switch off and on thumps at different Lightspeed settings, to make sure they are not too savage either.
Cheers George
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Maybe I'm crazy but I just did the LED bypass with some vishay/oscons and I swear the noise level dropped way down (I am using the optical volume control board).
Anyways I've only had this up and running for a day. Here's some of what I posted at audiocircle:
Okay, so how does it sound? It sounds really, really, really good. I can't really describe it. Honestly. Not because it's the second coming or anything. Just not really sure how to translate the difference. I have listened to it coming straight from my DAC (470R ouput imp and low-ish voltage) and also after my Aikido. The only word that comes to mind is 'pure'. Like spring water. Neutral, nothing is really emphasized. Low-level detail. No glare. Kind of relaxed, warm-ish even which was a surprise. I don't know. You just have to hear it. I I do think for some people it will be an eye-opener. Here's another word: high-end. That's what I kept thinking while listening. It makes my speakers sound really expensive. Weird thought, but that kept popping up. I felt like I owned really expensive gear and was hearing pure, unsullied, no colouration music. Even with the Aikido, you hear the Aikido contribution but it's cleaner and clearer. I know none of that sounds exciting, but I guess that's because in a way it doesn't sound like anything. It's not what it's doing that's impressive. It's what it's not doing. Anyway, you just have to hear it.
Big thumbs up!
Anyways I've only had this up and running for a day. Here's some of what I posted at audiocircle:
Okay, so how does it sound? It sounds really, really, really good. I can't really describe it. Honestly. Not because it's the second coming or anything. Just not really sure how to translate the difference. I have listened to it coming straight from my DAC (470R ouput imp and low-ish voltage) and also after my Aikido. The only word that comes to mind is 'pure'. Like spring water. Neutral, nothing is really emphasized. Low-level detail. No glare. Kind of relaxed, warm-ish even which was a surprise. I don't know. You just have to hear it. I I do think for some people it will be an eye-opener. Here's another word: high-end. That's what I kept thinking while listening. It makes my speakers sound really expensive. Weird thought, but that kept popping up. I felt like I owned really expensive gear and was hearing pure, unsullied, no colouration music. Even with the Aikido, you hear the Aikido contribution but it's cleaner and clearer. I know none of that sounds exciting, but I guess that's because in a way it doesn't sound like anything. It's not what it's doing that's impressive. It's what it's not doing. Anyway, you just have to hear it.
Big thumbs up!
You must have had a noisy/faulty power supply or smp to start with. As a good linear regulated power supply as what comes with the production Lightspeed Attenuator gives at its output with the input shorted 100-150uV (that's micro volts not milli volts) of noise, which only a good cro and probes can pickup because of the cro's inherent noise floor.
Cheers George
Cheers George
Very possible as I am using a cheap 12v linear I picked up from Amazon a while back.
Question: It seems that I have to have my pot turned to 2 or 3 o'clock before I get enough volume for moderate listening levels. I wasn't too surprised by this coming from my DAC which is low voltage, but my HT receiver is also patched in and the result is the same. Is this normal?
Hopefully adding the oscon bypasses didn't screw with the values... 🙁
Hopefully adding the oscon bypasses didn't screw with the values... 🙁
Not to worry, the only negative the Os-Cons will show is a slowed down response to volume control settings, probably not noticeable.
The 2:00-3:00 pot position is not unusual if your system does not have excessive gain. As long as wide open you have sufficient gain to drive your amp to full output.
Stuart