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Old 5th January 2010, 08:21 PM   #801
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Hey, I just got a pair of 20k smt attenuators from gigaworks on ebay in the mail today.

They're pretty smooth compared to the other 'normal' attenuators I've used in the past. I'll have to give them a try in the dcb1. Pretty good deal @ $10 each.
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Old 6th January 2010, 01:42 PM   #802
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Is wirewound potentiometer good for shunt regulated B1 buffer audio? Someone offers me a Cosmos Tokyo RA25Y B20K. It's wirewound.
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Old 6th January 2010, 05:04 PM   #803
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Quote:
Originally Posted by sutantoroy View Post
Is wirewound potentiometer good for shunt regulated B1 buffer audio? Someone offers me a Cosmos Tokyo RA25Y B20K. It's wirewound.
No, wirewound potentiometers are for power applications and not for volume control.
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Old 6th January 2010, 10:44 PM   #804
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Thanks Paul.
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Old 7th January 2010, 06:46 AM   #805
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Anyone knows MUR 860 has 3 legs? I buy these diode and it has 3 legs, fake one? Searched everywhere but still not finding any info about it.

Click the image to open in full size.
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Old 7th January 2010, 06:47 AM   #806
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http://www.fairchildsemi.com/ds/RU/RURP860.pdf
I guess the middle leg is the fake one, but this is easily measured with a multimeter.

Last edited by R-K Rønningstad; 7th January 2010 at 06:51 AM. Reason: wrong
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Old 7th January 2010, 09:47 AM   #807
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After having the valab 20k stepped pot in for a while, I subbed in my lightspeed 2 nights back. The set up is AC shared with 1 of the DCB1 supplies, after rectification into a teddyreg (gyrator based reg) and then 500k dual pot. My batch of LDRs needed 500K to get them to work...

So initial impressions are that this change is all about the soundstage and clarity. The LS does have more clarity than the stepped pot, but also seems a little dryer, if that makes sense to anyone. In my earlier B1 build I had a lightspeed but in the early stages the LS impedance was too low and I ended up with the bass being cut. It is possible that some of that is going on here too and I would need to go to a 1meg pot rather than 500k. But its not like I'm loosing any bass, just that its not full or warm as before (sounds like a contradicition, I know).

However, the soundstage is quite remarkable. Front to back depth is really very very good and vocals etc are frighteningly real. It scores a lot of points on that score - It would seem that the DCB1 and LSmkII is a pretty unbeatable combination. Now I don't have any fancy stepped pots to try, only the ebay ones, but the LSmkII beats them, and even they sounded good.

Very positive result I would say, and I would encourage anyone thinking of going this route but is undecided to not delay and fire ahead!

BTW, just so no misunderstanding - that issue with the 500K/1meg pot is peculiar to my lot of LDRs, and if you have bought other ones, and especially matched sets from Uriah, you won't see this. Also, I have kept my output caps in the source equipment fairly small, maybe too small so this may also be in play.

Fran
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Old 7th January 2010, 02:02 PM   #808
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Fran,
You like to tinker so try this.
Use a 100k pot or any other value. Put a 100R multiturn trimmer in series from power source positive to the 100k control pot. Now, with DMM attached to Series LDR and pot turned down all the way, turn on power to LDRs and turn the 100R from 0R up slowly and watch DMM. I think you will find a value that suits you. Then you can get rid of that 500k pot which is quite a hassle to many people. I wish I had known more about the interactions of the 500k pot when those LDRs were matched to provide a better suggestion. When I tested my own pair with the 500k it worked fine and I didnt test further. Seems a lot of people had trouble with 500k and I think this little work around will be fine.
Another option would be to use LM317 and adjust the voltage to LDRs down. Do the same thing... Put in LM317 and turn down voltage while watching value of the series LDR when its turned all the way down. Its going to be really touchy most likely but you will be able to find a resistance you like and will get away with using 100k. If you have 100R in series with LDRs like in George' schematic these values might change your low volume point if you use lower voltage, or they might not. Another experiment.
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Old 7th January 2010, 04:47 PM   #809
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Thanks uriah, I will try this ASAP.

I can vary the feed voltage out of the regulator so most likely that's what ill do.

What was the hassle with the 500k pots? Was it just availability issues at the time?

Fran
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Old 7th January 2010, 05:07 PM   #810
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Just a weird batch of LDRs that were way more efficient than any others I ever tested. So with much less current they would show low resistance than normal. This might be nice as they will get quieter with less current than what the average LDR will. So, with 100k they only got down to about 2k. With 500k they got more desirable resistance. A better value would have been 400k but who sells a 400k dual audio pot? No one I know of.
I agree that the DCB1 helps the bass with the LDRs a lot. Love it for this reason.
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