Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 17th January 2013, 01:52 AM   #4911
diyAudio Member
 
georgehifi's Avatar
 
Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Send a message via MSN to georgehifi
Quote:
Originally Posted by studiostevus View Post
I have been using the lsa in my aikido preamp for a year now, but i am getting increasingly frustrated with tracking. I had ordered ldrs from uriah (2 matched pairs) but always had channel imbalance.

Yea, the lsa is in the same cabinets as the tubes (maybe 15 cm away). But i would assume the ambient temperature is the same for each ldr.

In your experience:
1. Is it possible to get perfect tracking channels?
2. How many Ldr's does roughly one need to buy to get a perfectly matching quartet (not 2 pairs)? (in your experience)
I've always said not to put them into an evironment like this, as you can change the resistance of them just by touching them, or even blowing on them, this is why in the production Lightspeed Attenuator the transformer is outboard and the LDR's are in their own little safe environment.

Cheers George
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
  Reply With Quote
Old 17th January 2013, 02:20 AM   #4912
diyAudio Member
 
Join Date: Oct 2009
Location: Brunei
That's useful feedback george... At least no need to order more ldr's.

On the other hand, i am not touching nor blowing on the ldr's, and i would think that the air inside the cabinet is quite static (the ldr's are positioned quite close to one another)
__________________
--------
TDA1541a-S2 / 6072a / MediaplayerDac -- Michell Gyrodec -- Aikido Preamp -- Pass F5 -- Audio Physic Tempo 2SE -- Yamamura Cabling
  Reply With Quote
Old 17th January 2013, 03:09 AM   #4913
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
I have been using the lsa in my aikido preamp for a year now, but i am getting increasingly frustrated with tracking. I had ordered ldrs from uriah (2 matched pairs) but always had channel imbalance.

Yea, the lsa is in the same cabinets as the tubes (maybe 15 cm away). But i would assume the ambient temperature is the same for each ldr.
Quote:
Originally Posted by studiostevus View Post
That's useful feedback george... At least no need to order more ldr's.

On the other hand, i am not touching nor blowing on the ldr's, and i would think that the air inside the cabinet is quite static (the ldr's are positioned quite close to one another)
What? Really? Ever heard of "convection"?

Sorry but your estimations about the temperature variations were actually quite unrealistic, to put it mildly. Then George informed you that your mounting location was contrary to long-standing recommendations from the designer himself, and that the LDRs are in fact extremely sensitive to temperature changes, and you brushed him off and made another wildly-unrealistic assertion about the temperature inside your tube preamp.

Therefore, throwing Uriah under the bus by attribution was unconscionable.

Here's a suggestion: Whenever you hear yourself thinking or saying "I would assume..." or "I would think...", maybe you should mentally translate it to "I actually have no idea", and then at least consider not resting your entire argument on it, especially when you should probably be going into learning mode instead of offensive mode.

The other obvious consideration, which could apply in many diferent types of situations over the course of one's life, would be to realize that when one is one of the very few having a problem, among hundreds or thousands who are not having a problem, the first person one should consider blaming is oneself.
  Reply With Quote
Old 17th January 2013, 03:58 AM   #4914
diyAudio Member
 
Join Date: Oct 2009
Location: Brunei
Quote:
Originally Posted by gootee View Post
What? Really? Ever heard of "convection"?

Sorry but your estimations about the temperature variations were actually quite unrealistic, to put it mildly. Then George informed you that your mounting location was contrary to long-standing recommendations from the designer himself, and that the LDRs are in fact extremely sensitive to temperature changes, and you brushed him off and made another wildly-unrealistic assertion about the temperature inside your tube preamp.

Therefore, throwing Uriah under the bus by attribution was unconscionable.

Here's a suggestion: Whenever you hear yourself thinking or saying "I would assume..." or "I would think...", maybe you should mentally translate it to "I actually have no idea", and then at least consider not resting your entire argument on it, especially when you should probably be going into learning mode instead of offensive mode.

The other obvious consideration, which could apply in many diferent types of situations over the course of one's life, would be to realize that when one is one of the very few having a problem, among hundreds or thousands who are not having a problem, the first person one should consider blaming is oneself.
Sorry my friend, but please read my posts carefully.

I have never "asserted", "brushed off", even "estimated", but certainly not "thrown under a bus".

I understand it may be late where you are, although i would recommend staying off the booze on wednesday nights.

Anyway, definately no harm intended by my INQUIRIES, certainly not to George.
__________________
--------
TDA1541a-S2 / 6072a / MediaplayerDac -- Michell Gyrodec -- Aikido Preamp -- Pass F5 -- Audio Physic Tempo 2SE -- Yamamura Cabling
  Reply With Quote
Old 17th January 2013, 06:20 AM   #4915
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Originally Posted by studiostevus View Post
Sorry my friend, but please read my posts carefully.

I have never "asserted", "brushed off", even "estimated", but certainly not "thrown under a bus".

I understand it may be late where you are, although i would recommend staying off the booze on wednesday nights.

Anyway, definately no harm intended by my INQUIRIES, certainly not to George.
Wow. You are simply providing examples that reinforce the need for you to heed the advice that I gave you

Implying that someone's mind must have been affected by booze in an attempt to discredit their observations is a form of ad hominem personal attack, and is also considered to be just a dirty tactic, in general. (And I haven't had any alcohol since Christmas. But even if I had, there would still be no contest.)

Anyway, that's no big deal. Actually, it's kind of humorous, I guess. And perhaps you meant it in a good-natured, friendly sort of way.

And I do see your point. You were inflicting potential harm to someone's livelihood without intending to, and apparently also without realizing it. But that's perfecly understandable, if you don't even know the meanings of words like asserted, and estimated.
  Reply With Quote
Old 17th January 2013, 06:48 AM   #4916
DRONE7 is offline DRONE7  New Zealand
diyAudio Member
 
Join Date: Aug 2008
@studiostevus

George has indicated the thermal requirements numerous times in this thread, as recently as post #4911 in reply to your query.

In addition, I believe the production Lightspeed has the LDRs potted in a block of hard wax to ensure they remain thermally linked to promote optimal tracking and minimal channel drift.

George has advised against mounting the Lightspeed within other electronics (solid state) and mounting within tubed equipment is simply inviting the troubles you are experiencing.

Last edited by DRONE7; 17th January 2013 at 06:55 AM.
  Reply With Quote
Old 17th January 2013, 06:50 AM   #4917
diyAudio Member
 
Join Date: Feb 2003
Location: West Coast of Norway
BTW: I am using kits from udaley.
  Reply With Quote
Old 17th January 2013, 01:55 PM   #4918
wlowes is offline wlowes  Canada
diyAudio Member
 
wlowes's Avatar
 
Join Date: Mar 2007
Location: Toronto
Blog Entries: 9
Default Another approach to Potting and balance tracking

For what it's worth, I took another approach to mounting that has worked very well over time.

I wired the LDRs tight together and in fact glued them together with silicon cement. Then they were encased in some shrink wrap. This allowed me to put the attenuator right on the amp circuit board making for very short signal path. The voltage side of the LDR was run via CAT5 cable to the light speed power pcb where the pots for volume and balance reside.

Result? Perfect tracking. Despite having a balance control, I have never needed to touch it for changes in balance due to volume setting. I do have to touch up the balance for some CD's that simply are out of balance on the recording, so the balance control is simple and worthwhile.

I built this in August 2007, and it is running perfectly providing amazing music ever since. My only changes to my implementation over time was to improve the power supply which does improve the SQ.

I am now building an second lightspeed to serve my new amps.
Cheers
Attached Images
File Type: jpg lightspeed.jpg (79.4 KB, 211 views)
  Reply With Quote
Old 18th January 2013, 03:16 AM   #4919
gootee is offline gootee  United States
diyAudio Member
 
Join Date: Nov 2006
Location: Indiana
Blog Entries: 1
Quote:
Originally Posted by wlowes View Post
For what it's worth, I took another approach to mounting that has worked very well over time.

I wired the LDRs tight together and in fact glued them together with silicon cement. Then they were encased in some shrink wrap. This allowed me to put the attenuator right on the amp circuit board making for very short signal path. The voltage side of the LDR was run via CAT5 cable to the light speed power pcb where the pots for volume and balance reside.

Result? Perfect tracking. Despite having a balance control, I have never needed to touch it for changes in balance due to volume setting. I do have to touch up the balance for some CD's that simply are out of balance on the recording, so the balance control is simple and worthwhile.

I built this in August 2007, and it is running perfectly providing amazing music ever since. My only changes to my implementation over time was to improve the power supply which does improve the SQ.

I am now building an second lightspeed to serve my new amps.
Cheers
You have touched-on some implementation details that are very important. (And it sounds like you did an excellent job implementing yours.) [The following is just general informaion and is not necessarily directed at only you.]

A short signal path IS important. It helps in not making an antenna. And it helps in minimizing the conductor's self-inductance. It's even more important to be absolutely sure that NO GAP is left, anywhere, between each signal conductor and its corresponding ground, on their way to and from the attenuator. Otherwise, you've made what's called "enclosed loop area". Another name for that is "antenna".

Any time-varying magnetic or electromagnetic field will induce a corresponding time-varying current in the loop (See Faraday's law.), in proprtion to the geometric area enclosed by the loop, and the strength of the field.

So twist the signal and ground wires tightly together, with at least four turns per inch, or, better yet, use shielded twisted pair, with the shield connected on one end only, to chassis ground (NOT to signal ground!). Hopefully, the AC Mains pair will be tightly twisted, as well as the secondary pairs, and the pairs connected to the inputs and outputs of rectifiers, and the output pairs, and the heater pair if it's a tube amp, and even the DC power and ground pairs, because all of those can and will act as transmitting (and receiving) antennas! (With PCBs, either use a ground plane everywhere possible, or put the pair's traces exactly overlapping on opposite sides of the PCB, or, if single-sided, keep them very close together, everywhere. RF (Radio Frequency) signals can also cause insidious effects, which are sometimes very subtle, which can make them very difficult to even identify, much less determine their source or eliminate them.

Your idea to have close thermal bonding of all four LDRs is a very good one. Encasing them then helped greatly, too. They could even be surrounded by a small metal box, perhaps with a resistor to act as a heater, so that the little oven's internal temperature would swamp-out any changes in the temperature outside the box. But you correctly understood that the main important factor is to not have changing differences between the temperatures of the LDRs, i.e. relative to each others' temps. Combining them all into one physical mass, with large contact areas between them, gets you most of the way there. Also then wrapping or potting or boxing them all inside of a single enclosure gets you almost all of the rest of the way there (and is probably more than good-enough). Doing that well-enough would enable you to place them almost anywhere, and there would be definite advantages to having them located as close as possible to the original signal path.

I wonder if anyone has ever played around with using "trimmer" LDRs, putting one in series with each of the main LDRs. Of course, you'd have to run them wide open (max current, to give lowest resistance) and then adjust a multi-turn trimpot by some hopefully-small amount, to reduce their LED current slightly to increase their resistance "offset" slightly. So the adjustment could only be upward in resistance. Assuming the first trimpot was fed from a separate fixed DC feed, they could optionally also receive some fraction of the main LDR's control current, which might enable better matching overall. But using them at all might also be a way to be able to use somewhat-unmatched main LDRs while still ending up with well-matched responses. I guess maybe it would be too complicated or too expensive.

Cheers,

Tom

Last edited by gootee; 18th January 2013 at 03:20 AM.
  Reply With Quote
Old 18th January 2013, 04:38 AM   #4920
soongsc is offline soongsc  Taiwan
diyAudio Member
 
soongsc's Avatar
 
Join Date: Mar 2005
Location: Taiwan
Quote:
Originally Posted by studiostevus View Post
I have been using the lsa in my aikido preamp for a year now, but i am getting increasingly frustrated with tracking. I had ordered ldrs from uriah (2 matched pairs) but always had channel imbalance.

Yea, the lsa is in the same cabinets as the tubes (maybe 15 cm away). But i would assume the ambient temperature is the same for each ldr.

In your experience:
1. Is it possible to get perfect tracking channels?
2. How many Ldr's does roughly one need to buy to get a perfectly matching quartet (not 2 pairs)? (in your experience)
I am curious, did you measure an imbalance or did you just use listening?
__________________
Hear the real thing!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 11:32 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2