A brace of LDR passive preamps.

[Firebottle]

I have been asked to assemble a couple of the LDR board sets, one into an existing case and one as a miniature preamp.

The existing case has been updated to have 3 inputs and 2 outputs, both preamps are battery operated.

http://i66.tinypic.com/hvcg83.jpg


The top one is the miniature using a NiMH battery, also 3 inputs.

http://i63.tinypic.com/b82yop.jpg

http://i66.tinypic.com/312778i.jpg


The larger is using an SLA battery.

http://i65.tinypic.com/11llb7l.jpg

http://i65.tinypic.com/1538vo8.jpg



Side by side internal view.

http://i64.tinypic.com/4v37ro.jpg


The sound is very transparent however neither unit will go down to zero volume.

Chris LDR do you have any advice to get down to zero volume?

[Bigman80]

Look tidy Al.

[Marra]

The LDR pre-amps cannot be turned down completely to silence I seem to remember reading on diyaudio.

They do sound pretty good though.

[Light Dependant Resistor]

I have been asked to assemble a couple of the LDR board sets, one into an existing case and one as a miniature preamp.

The existing case has been updated to have 3 inputs and 2 outputs, both preamps are battery operated.

http://i66.tinypic.com/hvcg83.jpg


The top one is the miniature using a NiMH battery, also 3 inputs.

http://i63.tinypic.com/b82yop.jpg

http://i66.tinypic.com/312778i.jpg


The larger is using an SLA battery.

http://i65.tinypic.com/11llb7l.jpg

http://i65.tinypic.com/1538vo8.jpg



Side by side internal view.

http://i64.tinypic.com/4v37ro.jpg


The sound is very transparent however neither unit will go down to zero volume.

Chris LDR do you have any advice to get down to zero volume?

Nice work, the start volume point is fully adjustable to get silence

With voltage at the lower end of recommended range using battery power, easiest is to wire the end LDR board blue block white wire straight to your
battery positive. This will provide needed voltage difference to create silence at lowest volume.

With the later main board build it looks like you have the white wire connected to the lower top receptacle rather than the top receptacle of
that same blue block. Moving that wire should fix but otherwise wire to the battery positive

The start circuit and volume commencement point has two ways of being changed:
1. that the voltage be higher to the LDR board end blue block than the voltage feeding the anodes....
with your multimeter measure between LDR board end blue block with positive probe
and negative probe to the anode that is powered. With volume at minimum there should be 4.2v difference or more.

2. that there is suitable resistance placed on the LDR board prior to the blue block which is usually 47k. If needed it can be adjusted
as follows: where volume commences too early ( in this example ) its value can be lowered by soldering a parallel resistor -NOTE Under the LDR board
to make resistance suggest 27k

OR in the case where volume already has silence but is commencing too late add resistance from the end LDR board blue block to the main board top receptacle.
typically 22k-33k

Let me know how that goes, but you should be able to get silence at zero volume and volume commencing nicely at 7-8am
just in this case, by changing the end LDR blue block white wire to be at a higher potential. Either method though is very effective
and will give the needed result.

[Light Dependant Resistor]

The LDR pre-amps cannot be turned down completely to silence I seem to remember reading on diyaudio.

They do sound pretty good though.

No this incorrect, they can be made to be fully silent at zero volume by having the volume adjustment between shunt and series cathodes and the cathode always at a higher potential than ground typically 2.6v, and arranging
the cathode output to connect to a LM317 device Vin - from there resistance is placed from the 317 Adj terminal to a higher potential than the voltage measured at the anode.

[Edward]

Looking good Alan. :youtheman: Thanks for doing the work.

Hopefully you can have a bake off and give this a go against the dcb1 and other preamps.

Did you try the LDR before you replaced it with the new boards? Interesting to hear your views on the difference - if any.

[Marra]

No this incorrect, they can be made to be fully silent at zero volume by having the volume adjustment between shunt and series cathodes and the cathode always at a higher potential than ground typically 2.6v, and arranging
the cathode output to connect to a LM317 device Vin - from there resistance is placed from the 317 Adj terminal to a higher potential than the voltage measured at the anode.

Thanks for putting me right Chris. Could have sworn I'd read it somewhere:doh:

Nice work Alan.

[martian sunrise]

My little LDR pre sounds ace. Really impressed so far.

Playing through a pair of Alan’s miniblocks. Big, wide sound that is clear and sharp.

Lovely!

[Edward]

Good to hear Martin. Clear, wide and sharp are definitely the words I would also use.

Looking forward to mine which I will get at Kegworth. I'm hoping that the sq will be even better than it was before. Chris Daly assures me there is a noticeable lift in sq, but let's see. Also having remote control will be very useful. Looks like Alan has done things very neatly.

[Edward]

So I got my LDR pre back from Alan at Kegworth. Alan has done a fantastic job sorting it with the new LDR boards that Chris sent to me. The pre now includes a remote as well as two variable outputs so makes for a super friendly pre.

Am outputting to the Radford STA25 and the Nelson Pass Aleph clone amp (from Tom). From there to the Tannoy Eatons.

It's been a while since I used the LDR pre (with its old boards) as it was out on loan so difficult to ascertain if much improvement but I would say yes.

The LDR presents an open platform (inky black background, pure white - take your pick) on which music flows through with an unrestrained ease and fluidity. Massive amounts of detail comes through and presented in a highly coherant way. Very linear regardless of attenuation. Basically an open window that does not take or give.

Love it.

The volume control circuitry does a really neat thing. Not sure if you noticed this Alan. Essentially when you turn the preamp on, the volume control automatically goes to zero and then comes up to about 25% (that is about 75% attenuation) . Nice protective measure.

Anyway well pleased with this. Thanks Alan for doing such a grand job and thanks Chris for the updated boards.

Now we are all looking forward to Marco's uber review of his recently built LDR pre. :)


https://uploads.tapatalk-cdn.com/20190322/805d4043a6ba50ebf8ceb53d969c916f.jpg

§

[WESTLOWER]

Waiting for the invite to come and listen Edward!

[martian sunrise]

i tried to fit two knobs from a guitar to mine, but they wouldn't fit. (i thought teles had 1/4" knobs?!?) so i used a couple of chicken head knobs...

the volume is a bit looser that i would like, but it sounds ace

https://farm8.staticflickr.com/7916/47388525872_292302fe75_k.jpg (https://flic.kr/p/2fcyzKw)Untitled (https://flic.kr/p/2fcyzKw) by Richard Howard (https://www.flickr.com/photos/11052398@N04/), on Flickr

[Edward]

Waiting for the invite to come and listen Edward!


Oh does it have to be official Adam? Pop over now. Or whenever. :)

Actually come to think of it, as you know I will be away for a couple of weeks soon, so borrow the pre whilst I'm away if you want. Or perhaps there is a risk of putting your existing pre to shame? :eyebrows:

[Edward]

i tried to fit two knobs from a guitar to mine, but they wouldn't fit. (i thought teles had 1/4" knobs?!?) so i used a couple of chicken head knobs...

the volume is a bit looser that i would like, but it sounds ace



Why did you need to change the knobs Richie?

[WESTLOWER]

Oh does it have to be official Adam? Pop over now. Or whenever. :)

Actually come to think of it, as you know I will be away for a couple of weeks soon, so borrow the pre whilst I'm away if you want. Or perhaps there is a risk of putting your existing pre to shame? :eyebrows:

nice offer, cheers Edwardo

David Coe shall be along shortly to comment on your current deluded state regarding his outstanding Satchmo pre..;)

[WESTLOWER]

Or perhaps there is a risk of putting your existing pre to shame? :eyebrows:

you must leave the Ganja alone in the afternoon, it's sending you a bit gaga! :lol:

[Edward]

Innovation through competition. :cool: