If you use a 1M pot its gonna be trouble. Just throw a 1M resistor on one of your spare LDR and see how high that sucker gets. Your volume doesnt change much because the LSPD is still a voltage divider and we can get the same voltage with a 1k pot as we can get with a 1M pot because 1x/2x is the same no matter what x equals.
I think you should check your impedance when using that 470k pot. What I found after recommending using a 500k pot is that when you test LDRs you get X resistance and when you insert 3 LDRs into a LSPD circuit you get X resistance from them but when you insert LDR #4 all resistances increase to around 3X, so now the 500k pot is not as necessary to increase the impedance as it is already done for use by inserting that 4th LDR and getting a significant voltage drop that gives us increased resistance on each LDR.
I wonder what would happen if you stuck another resistor of X resistance parallel to one gang of the pot..
I think you should check your impedance with a 100k dual pot. Just a suggestion and maybe you wont like it as much but in my experiments a few weeks ago it was the best solution still, even on the 500k LDRs because they increase so much in resistanc on the 4th LDR. BTW I was using a LM7805 with .1uf and .33uf caps in the regulator circuit driven by a 20VDC laptop computer supply and the 7805 and LDRs were on protoboard when I was messing with different pots.
Uriah
I think you should check your impedance when using that 470k pot. What I found after recommending using a 500k pot is that when you test LDRs you get X resistance and when you insert 3 LDRs into a LSPD circuit you get X resistance from them but when you insert LDR #4 all resistances increase to around 3X, so now the 500k pot is not as necessary to increase the impedance as it is already done for use by inserting that 4th LDR and getting a significant voltage drop that gives us increased resistance on each LDR.
I wonder what would happen if you stuck another resistor of X resistance parallel to one gang of the pot..
I think you should check your impedance with a 100k dual pot. Just a suggestion and maybe you wont like it as much but in my experiments a few weeks ago it was the best solution still, even on the 500k LDRs because they increase so much in resistanc on the 4th LDR. BTW I was using a LM7805 with .1uf and .33uf caps in the regulator circuit driven by a 20VDC laptop computer supply and the 7805 and LDRs were on protoboard when I was messing with different pots.
Uriah
no,
the 1M (in lieu of 500k) will set either the shunt LED or the series LED current very low (~3uA cf ~6uA).This will set the corresponding LDR resistance very high. The LEDs are current devices with a near constant Vf. The pairs of LDRs are voltage dividers and increasing one while holding the other low will change the ratio. As a result, using a 1M pot will increase the ratio of attenuation AND will also increase the load impedance.
This is conjecture based on an inadequate understanding of what currents the LEDs are drawing when your parallel circuit is supplying an unknown current. Do not base any conclusions on what you have not yet understood.
Well, here are the results from the Irish jury....
1. Adding an extra cap in parallel with the ones already in the DAC (increasing size of output cap to ~10uF made no difference. This should be the same as what you suggested Andrew about removing the output cap from the source and putting an input cap in front of the LS?
2. So I then went to plan B. Found a 1meg lin pot and fitted that. Straight away, the bass was back. So in my sertup at least, a 1meg pot was needed. A good benefit is that the range on the pot is much more. So I'm very happy. I did have to use a trimmer on the left channel as I had some imbalance, but that seems sorted now.
So increasing the pot size seems to have sorted this out.
Fran
1. Adding an extra cap in parallel with the ones already in the DAC (increasing size of output cap to ~10uF made no difference. This should be the same as what you suggested Andrew about removing the output cap from the source and putting an input cap in front of the LS?
2. So I then went to plan B. Found a 1meg lin pot and fitted that. Straight away, the bass was back. So in my sertup at least, a 1meg pot was needed. A good benefit is that the range on the pot is much more. So I'm very happy. I did have to use a trimmer on the left channel as I had some imbalance, but that seems sorted now.
So increasing the pot size seems to have sorted this out.
Fran
Obviously I am suprised that this worked. I will have to try it. Strange that with a 500k pot many people ended up with impedance of max 400k and min 70k but that 1M is working better. The higher in resistance the LDRs go the less they act in a similar fashion to each other. Meaning that I have noticed that, batch dependent, but around 25k they start to act quite differently from each other even if they matched all the way to 25k. This is why my instinct would tell me to stay away from 1M pots which are going to send that particular LDR to easily +10MOhm or more or Off for a good portion of the pot.
Uriah
True enough Andrew, but these are not conclusions and are conjecture. I have to resort to conjecture at this point because it is necessary until someone tells us exactly how they work. They dont work exactly the same as an LED even though we are using an LED to power them. The resistive material on the other side doesnt act the same way the LED does and gets finicky at that ~25k mark.
Uriah
no a series pair of capacitors ahs a combined capacitance that is less than either.
If one were 4u7F and the other were 2u2F and they fed 20k then the RC of the original would be 15ms
Doubling the 4u7 to 9u4 increases the RC to 17.8ms.
That is a change of approximately one third of an octave.
Try shorting out the smaller of the two coupling caps. Compare one DC blocking cap to the previous set up.
Now treble that single DC blocking cap and compare that to the original set up.
Have you heard any differences?
Here is the B1 schematic:
The caps I am referring to are C200 and C100. In the text he says:
"C100 and C200 are there because the Gate of the JFETs needs to be set at half the DC voltage of the power supply - a voltage delivered to the buffer inputs by R2, R3, and C2 through R103 or R203."
So maybe I have that wrong earlier about the 1uF in the B1.
In any case.... I must have it wrong because on listening last night, all the bass is back. So for me at least, this is fixed by your suggestion of the 1meg pot. Uriah, if you get time, you should try it out if you have any of those 500K LDRs left. I would be interested to see if anyone else sees (hears?) the same thing.
Fran
The caps I am referring to are C200 and C100. In the text he says:
"C100 and C200 are there because the Gate of the JFETs needs to be set at half the DC voltage of the power supply - a voltage delivered to the buffer inputs by R2, R3, and C2 through R103 or R203."
So maybe I have that wrong earlier about the 1uF in the B1.
In any case.... I must have it wrong because on listening last night, all the bass is back. So for me at least, this is fixed by your suggestion of the 1meg pot. Uriah, if you get time, you should try it out if you have any of those 500K LDRs left. I would be interested to see if anyone else sees (hears?) the same thing.
Fran
Attachments
I just got back from my weekend in Austin and am on the computer for the first time in days. Wow, thats a nice thing 
You know, to NOT be on the computer for nearly 3 days.
So the audio get together went great. The best setup was a Rega Planet, some RIAA tube pre, Lightspeed, Oddwatt Class A PP KT77 25W mono blocks, Audio Nirvana 12" Bass Reflex. One of the best sounds I have ever heard. Strangely it sounded like really incredible solid state. The clarity was so incredible it was unnerving. One guy jumped up and went to the hallway to text his wife. Something similar to "OMFG I have never heard music like this in my life!". So, yeah we all just sat there and listened to Alison Krauss on LP for a few songs before talking again. It was incredible.
I have to try this 1MOhm thing. I think I have a 2M pot and just 1M trimmers. I have to look around.
Uriah
You know, to NOT be on the computer for nearly 3 days.So the audio get together went great. The best setup was a Rega Planet, some RIAA tube pre, Lightspeed, Oddwatt Class A PP KT77 25W mono blocks, Audio Nirvana 12" Bass Reflex. One of the best sounds I have ever heard. Strangely it sounded like really incredible solid state. The clarity was so incredible it was unnerving. One guy jumped up and went to the hallway to text his wife. Something similar to "OMFG I have never heard music like this in my life!". So, yeah we all just sat there and listened to Alison Krauss on LP for a few songs before talking again. It was incredible.
I have to try this 1MOhm thing. I think I have a 2M pot and just 1M trimmers. I have to look around.
Uriah
I just got back from my weekend in Austin and am on the computer for the first time in days. Wow, thats a nice thing
So the audio get together went great. The best setup was a Rega Planet, some RIAA tube pre, Lightspeed, Oddwatt Class A PP KT77 25W mono blocks, Audio Nirvana 12" Bass Reflex. One of the best sounds I have ever heard. Strangely it sounded like really incredible solid state. The clarity was so incredible it was unnerving. One guy jumped up and went to the hallway to text his wife. Something similar to "OMFG I have never heard music like this in my life!". So, yeah we all just sat there and listened to Alison Krauss on LP for a few songs before talking again. It was incredible.
I have to try this 1MOhm thing. I think I have a 2M pot and just 1M trimmers. I have to look around.
Uriah
Hi Uriah,
Was that your LSA & AN 12"? Were there any other speakers tried with this setup? Sorry if a bit off topic.
different sound over LDR impedence?
I am using 1543 DAC with 910R I/V and 4.7uf Blackgate as output cap, now I set the VCCS LDR Zin to be around 100-200K, Zout 20-30K, it sounds better than original 10-20K Zin range, can not tell much difference over the bass. By the way, my tube amp has 750K input impedence, my IC is VH-lab design with very low capacity. With 100K+ Zin I can afford 0.1uf V-CAP now to replace the BG.
Not sure if others has experience over different LDR impedence range.
I am using 1543 DAC with 910R I/V and 4.7uf Blackgate as output cap, now I set the VCCS LDR Zin to be around 100-200K, Zout 20-30K, it sounds better than original 10-20K Zin range, can not tell much difference over the bass. By the way, my tube amp has 750K input impedence, my IC is VH-lab design with very low capacity. With 100K+ Zin I can afford 0.1uf V-CAP now to replace the BG.
Not sure if others has experience over different LDR impedence range.
Last edited:
There were some dayton line array that were built to prove budget is still soundworthy and there were some aperiodic but otherwise sealed cab Visaton 200B. Those last ones sounded real nice but the clarity went to the AN12's.
Puffin. With two monos:
If you have A W B for posts to solder to on the pots then go from A to W on one pot and W to B on the other. One controls the shunts and one controls the series. Why would you do this? To control impedance but man this is a painful exercise and I would recommend dual pot.
You could use matched Dual 100k pots and you could wire them as has been show but only control one side with each pot. Each pot would then be controlling one Series and one Shunt. This would give you complete stereo control and be a bit fiddly but still nice.
Best is to do it the way George shows and then stick a small 5k panel mount pot in series with the louder side of your Lightspeed and this will control balance just fine.
Uriah
Why do you want 2 mono pots?
EDIT: Do'h - you want one for left and one for right, correct? Got so wrapped up in adjusting series and shunt with respect to one another missed that!! So all you do is bring the 5V supply to the wiper and then one of the other pins goes to series and the other to shunts. Make both sides the same and then you have it. In my pots, I bring the 5V to the centre pin and then the feeds out to the LDRs are from the other 2.
Fran
EDIT: Do'h - you want one for left and one for right, correct? Got so wrapped up in adjusting series and shunt with respect to one another missed that!! So all you do is bring the 5V supply to the wiper and then one of the other pins goes to series and the other to shunts. Make both sides the same and then you have it. In my pots, I bring the 5V to the centre pin and then the feeds out to the LDRs are from the other 2.
Fran
Last edited:
You could take one of the single gang pots and control the left side if you wire the 5V to the wiper and then take shunt from one side and series from the other. But I dont think its the best solution given the problems we had using a single gang pot earlier.
Problems included way high impedance and fast impedance swings.
Uriah
Problems included way high impedance and fast impedance swings.
Uriah