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Old 24th November 2012, 09:32 AM   #4861
freax is offline freax  Australia
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love this idea.
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Old 24th November 2012, 08:02 PM   #4862
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Quote:
Originally Posted by udailey View Post
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You can purchase LDRs anytime to build a standard LDR attenuator or to build my new LDR Attenuator "A Lighter Note". Email me. diyldr@gmail.com
Are you still taking orders through your website? I put one through a few weeks ago but have had no response.
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Old 25th November 2012, 11:40 PM   #4863
udailey is offline udailey  United States
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New Zealand is easily 3 weeks but please contact me by email. This is not my thread.
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Old 4th December 2012, 10:54 AM   #4864
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got my LDRs thanks Uriah!

another power supply question to clarify. After a brief glance on similar topics:
-7080 reg + bc550
-Salas mini shunt idea
-wall wart + 7805 comparison

I've decided to go for REG 1 + REG 2 (7805), hence the questions:

1. it is specified here that 470uf cap should be placed before the reg2 and vice-versa here. What would be the best option? Also may I use 0.1uf mkt cap for bypassing?

2. Will original (not mini) Salas shunt reg be kind of an overkill as a reg1? Would it be enough to use mini shunt or some alternative shunt reg on LM317 +BD139?

3. If Salas shunt will be used, what is the best sequence of caps here?
ex.: PS 2200uf (4700 ?!) -> Salas 100uf (output) -> 7805 470uf + 0.1 mkt (output)

4. This one is the most important that doesn't allow me to sleep at nights
Will I reduce PS noise by adding another voltage regulation circuit over existing one? The answer is yes as George's solution (wall wart + 7805) confirms, but if I add 10 more regs after the last one, will that bring more noise or there is some general rule here?

In many DACs and preamps the following scheme is used:
LM317 (alone or with some transistors/ zeners) -> 7805 (or any other fixed voltage reg),
so if I want to tune such or similar circuit should I replace it completely with Salas reg, for instance, or add Salas before the last 7805 reg or add Salas before LM?
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Old 4th December 2012, 12:51 PM   #4865
AndrewT is offline AndrewT  Scotland
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A 7805 or 317 is perfectly good enough for the LDR supply.
You may find that making the supply slightly adjustable, say from 3Vdc to 6Vdc will make the volume adjustment "feel" more to your liking. This would suit the 317 reg. This voltage also changes the input impedance seen by the source.

The lower adjustment leg of a 317 can have a LED inserted instead of a resistor. The output voltage is then 1.25V+Vf of LED. i.e. about 3V1 depending on Vf.

MKT=MKS=PES=polyester has a slightly higher esr than the "high quality" caps normally used for audio. This higher esr makes them ideal for decoupling. It reduces the risk of ringing on the supply rail due to the damping of the resistance element in the esr.
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Last edited by AndrewT; 4th December 2012 at 12:53 PM.
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Old 4th December 2012, 05:31 PM   #4866
udailey is offline udailey  United States
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You're overthinking it. The supply needs to be dead quiet is all. Improvement would be using a current source but after that put caps on the led side and be done with
it.
Read Walt Jung's "Sources 101" papers. Especially part 2. Note that a great solution would be lm317 voltage reg followed by two series lm317 ccs. That and caps. 100uf and .1-.47uf in parallel with it on each led. Oh, use 1-10uf tantalums on each lm317 leg.
I have been using 10-13v. I like it. Will be trying 3.3v in a new design because of cheap low noise surface mount parts designed to supply CPUs. Plus better caps in lower volts.
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Old 4th December 2012, 10:33 PM   #4867
wlowes is offline wlowes  Canada
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Default voltage regulator

For what it is worth I have played around with some simple alternatives for powering the light speed.
After using a 7805 regulator, I found that a simple and inexpensive diy regulator described in TNT audio resulted in an improvement. The Zener + emitter follower can be built very easily with a parts cost well below $10.
Simple Voltage Regulators Part 1: Noise - [English]
A well filtered linear power supply before this also makes a measured improvement.
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Old 5th December 2012, 05:52 AM   #4868
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Quote:
Originally Posted by AndrewT View Post
A 7805 or 317 is perfectly good enough for the LDR supply.
I also back AndrewT on this as well.
What I've always said after conducting a 20+ group of "Golden Ears" blind A/B test, is that no one could pick the difference between a linear wall wart + regulated 7805 based supply against battery power. It comes down to a psychological difference to the individual.
One needs to look at the big picture. The LDR's are for want of a better word "self regulating" because the reaction time is so slow to the LED variations, that any noise and spikes on the power supply to the LED's are mostly invisible to LDR's themselves, in other words they cannot react fast enough to these abnormalities "if any" to have an effect on their resistance once set by the led "volume" control.

Cheers George
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Last edited by georgehifi; 5th December 2012 at 05:54 AM.
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Old 5th December 2012, 01:08 PM   #4869
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thanks for clarification!
will stay with something simple then (TNTs reg + 7805)
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Old 5th December 2012, 10:38 PM   #4870
udailey is offline udailey  United States
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The ldrs "speed" has nothing to do with noise though. Awful regulations would change the volume and a 7805 is good enough for that cure. Noise from a poor supply couples to the signal. There is a capacitive coupling between led and resistor. Noise transfers over this.
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