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Old 13th November 2012, 05:48 AM   #4851
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Thanks,

I will order some and give both a try to understand the ldr behaviour. The single pot I will test is a 5 watt wirewound.

Alfredo
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Old 16th November 2012, 03:59 PM   #4852
KT is offline KT  United States
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Hi,

This is my very first post in this thread and I am very excited.

I've been wanting to try the Lightspeed for some time now but was put off by the process of matching the LDRs. After a hiatus of several years from DIY, I decided to take the plunge and I just put in an order for Uriah's DIY kit at Build An Amp.

I understand the circuit is a bit different from George's Lightspeed. For those who have tried both, what should I expect from this LDR premap? I am currently using a modded Cary Audio SLP-94 featuring 12au7 tubes, Shinkoh tantalum signal resistors, VTV Ultratone and Dynamicap signal caps, and a PEC carbon potentiometer. It's very musical. I do have very high expectations for the LDR preamp, however, after hearing all the positive buzz for many years. It'll probably be another ball of wax sonically, but I'm really looking forward to it.

One question I had was that I, too, am running a few variations of tripath amps. Currently I'm using a home modded amp based on the original Sonic Impact amp from several years back. My other amp in an original Charlize from diyparadise.com , and I will be finishing up a 41Hz Amp 11 at some point in the future.

I understand the LDR preamps are not a good match for these Tripath amps because of impedance incompatibilities. Because of this I am thinking of putting a version of Nelson Pass' B1 buffer directly after the LDR controller. It will be the Mesmerize, whose board can be purchased at the DIYAudio store.

Has anyone done this and would you recommend it? Are there any pitfalls to be aware of? After reading a little about the B1, I get the sense that it can run a little hot. Will this be a problem if I put both the LDR controller and the buffer in the same chassis? I understand the LDRs are affected by heat. What is your recommendation for this pairing?

As others have commented, this thread is very long. I'm in the process of working my way through it. I'm very excited about finally putting one of these preamps together.
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Old 16th November 2012, 05:38 PM   #4853
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The B1 doesn't get hot. The DCB1 can run hot if "hotrodded".
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Old 16th November 2012, 05:49 PM   #4854
Dimitris
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The mesmerize boards are actually DCB1

It can get hot if you increase its PSU current. But its up to you how hot you want it. I don t even know how high the mesmerize can go in terms of hotrodding. In any case, the benefits from higher current are big, so if you want to try an ldr pot with it, I would suggest getting it as high as your chassis/heatsinks can handle and then isolate the LDRs and keep them well ventilated and isolated from the rest of the DCB1.
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Old 17th November 2012, 11:33 AM   #4855
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I am currently working on a remotely controlled, motorized-potentiometer version of the Lightspeed-Attenuator (see attached images).
The additional PCB contains a stepper-motor H-bridge and a PIC µProcessor to implement the RC5 - remote-control software and to
drive the stepper-motor H-bridge.

The hard- and software - design is based on an idea / project, presented by FOTIOS.

The prototype - as shown on the images - works flawlessly.
I have re-worked the layout of FOTIOS' original PCB and added a transformer for +5VDC supply and a ICSP-header
to interact with the PIC µProcessor. (This interaction is not necessarily needed!)

I want to order professionally etched PCBs soon.
If somebody of you likes this idea and wants to have as well: please send me a PM.

Best regards - Rudi_Ratlos
Attached Images
File Type: jpg LS 002.jpg (216.4 KB, 358 views)
File Type: jpg LS 008.jpg (270.8 KB, 352 views)
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Old 17th November 2012, 03:38 PM   #4856
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Is the expression "Stepper-Motor - H-Bridge" familiar to everybody or is it restricted to German language only?
I don't know.

Please refer to the attached image.

Best regards - Rudi_Ratlos
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File Type: png Image1.png (12.6 KB, 337 views)
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Old 17th November 2012, 11:07 PM   #4857
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Hi Rudi,

Are all of the build/components shown in the photo make up the remote control, or what parts, and pcb design, is the remote control part of it?

And yes, I'm definitely interested but not sure what's involved here.
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Old 18th November 2012, 02:07 AM   #4858
Nanook is offline Nanook  Canada
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Default Another question regarding the impedance of the Lightspeed attenuator

Hi all.

George had suggested that as long as the attenuator sees an impedance of at least 20kΩ, then the Lightspeed should not cause any problems with T-amps. So I am assuming the load that the sources see is the impedance of the 100 kΩ poteniometer used.

I have sent an email to the amplifier manufacturer and await his reply for verification regarding this question. Just trying to stay in the loop.
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Old 18th November 2012, 03:03 AM   #4859
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No the 100kohm potentiometer will not isolate the Lightspeed from seeing the input resistance of the T-amp. In Eeffect you will now be even less than the 20kokm It now becomes 16.6kohms the Lightspeed is seeing. And then the source sees this 16.6kohm with the 10kohm of the Lightspeed which becomes 6.2kohms the source sees total.

Cheers George
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Old 19th November 2012, 06:19 PM   #4860
udailey is offline udailey  United States
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Guys be real real careful. Use gloves and good ventilation when handling or soldering LDRs.
http://ntp.niehs.nih.gov/ntp/roc/twe...es/Cadmium.pdf
The cadmium in/on them can cause Leukemia/other cancers.
Also see the bottom of the silonex.com page.
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