Silonex LDRs for Lightspeed Attenuator

[chatziva]

go on then, i'll give it a go

do you want me to send you a paypal payment directly? or email?

[udailey]

email me your name/address/paypal email/DIYID/QTY and TYPE (single ended or balanced) and I will then send you an invoice.
This way I can look up your emails if I lose any info by using mail search functions.
Uriah

[cloudniner]

In for 25 unmatched LDRs. PM sent.

[chatziva]

email sent for 1 matched SE stereo set

[AlanElsdon]

Originally posted by udailey
I have heard that the Lightspeed will smoke a TVC so I am VERY interested to hear your reports on your Lightspeed build.
I sent your invoice.
Uriah

Uriah - I have a Promitheus Dual Mono TVC, a B1 Buffer and a Lightspeed (as you know) - I would rate them in the reverse of that order.

They all are fine devices and I will keep all three of them so that ocassionally I can get a different perspective on my system, plus there is the matching issue especially with the LS which means that with certain amps (Nelson Pass for instance) I will need to use the B1 as a true buffer after the LS.

Possibly the only way to improve the LS would be to remove it from the chain and let the system run flat out, assuming that impedances match.

I have already ordered one more set of matched LDR's - I think I will need another set (playing around with some ideas - like building a music centre!!

Having seen your recent postings about costs could you please adjust the cost of this new set to reflect the increases in the previous set- cannot have you losing money doing us all a favour.

Regards

Alan

[Telstar]

Originally posted by AlanElsdon


Uriah - I have a Promitheus Dual Mono TVC, a B1 Buffer and a Lightspeed (as you know) - I would rate them in the reverse of that order.

They all are fine devices and I will keep all three of them so that ocassionally I can get a different perspective on my system, plus there is the matching issue especially with the LS which means that with certain amps (Nelson Pass for instance) I will need to use the B1 as a true buffer after the LS.

Regards

Alan

Very useful post, Alan!

The only missing thing to the list would be the JBOZ
http://www.diyaudio.com/forums/showt...63#post1834363

[udailey]

AlanElsdon,
Sorry, I have been gone for about a week and didnt see this post. Can you shoot me an email about what you need?
Thanks alot.
Uriah

ps I have used the F5 with the LS and found no problems. Was an excellent match. Have you tried this and had issues?

[AlanElsdon]

Originally posted by udailey
AlanElsdon,
Sorry, I have been gone for about a week and didnt see this post. Can you shoot me an email about what you need?
Thanks alot.
Uriah

ps I have used the F5 with the LS and found no problems. Was an excellent match. Have you tried this and had issues?

Uriah - I have not finished building the F5 - all the boards are done it is just a question of mounting the devices on the heatsinks and wiring everything up etc.

When that is ready, installed, run-in I will let you know.

pm sent re more LDRs.

[pchw]

Slightly off topic, I was attempting to set up a matching jig for the LDRs and can echo Uriah's comment about these were the poorest devices being manufactured

I have been trying to "perfect" my matching process, but matching these devices is really hard. These devices are very sensitive to the power supply. Even with 2 regulators (7812 and then 7805), I could still measure the voltage varied by 10mV during the day, and 10mV will make a big different in the measurement, no kidding!!

I set up a 100K pot + 200K pot in series so that I could adjust the voltage for matching easier and also see the range of resistance when such pots are used. I found out that when the pots were fully attenuated, I could get a reading of 1.2M to 600K through out the day. This is the difference the 10mV can make!!! IMHO, to match these LDR's, it is very important to use the same voltage across the devices (LED pins) unless you have a very very precised power supply that can be accurate and stable down to 1mV because a series of fixed resistors will still vary the voltage.

So far, I am still playing with the first 12 LDR's. If matching means within 20%, then I have found 2 candidate LDR's. With another 38 to go, I have no doubt to find more to make a quad. Since I plan to use 2 pots, one per channel, perfect match isn't really that important, but I do want to know the painstaking of dealing with these devices. Seriously, if you are not prepared to spend hours and hours to do the matching, buy from Uriah, these little devils can drive you nuts :-)

[udailey]

Thats the truth.
I have a helpful tip that I have not yet tried. Pick a single LDR. Label it. Measure it and record room temp at time of measurement. Measure as many LDRs as you can right now when room temp is same. When you go to measure again try to get room temp the same then get your labeled LDR and measure it again. Does it measure the same as it did when you first measured it and all your other measured LDRs? If so then commence with measuring your LDRs again. If not then you will not find true matches.
I am quite skeptical that 20% is anything worth calling a match. If we are talking about resistance of 80 and 100R then maybe because it wont A: effect overall impedance and B: it will be so loud you wouldnt hear it anyway. If we are talking about 5K and 4K this is no good and you will need a very large multiturn trimmer to bring channels to balance.

edit: Fred I see what you mean. After 12 the closest you have is 20%, not that 20% was good enough. Still figure I should leave the post so others get an idea of good/bad matching. Also for anyone wondering, I think Fred is going to 1.2M and 600k more out of curiosity than anything. You dont need to do this. See below...

Another tip.. my measurements produce good matched pairs. I measure at 1k, 10k, 20k, 40k. I dont go all the way up to 80 or 100k. Have not needed to. But I did just get some 100k 25turn trimpots I would like to try out and will probably use them in matching this batch. What I am saying is its not necessary to go to extremes if they are tracking well along this set of 4 measurements.
Uriah