Lightspeed Attenuator a new passive preamp

Jump to Latest
#2,505
dannybeckett said:
sweet =D
Click to expand...

Before doing this try to get all 4 LDR's touching each other and pot them in hard wax, this keeps them thermally balanced.

You only need the 1k calibration trimpot on the louder of the two channels, omit the trimpot on the lower level channel and direct couple it still leaving in the 100ohm resistor, do a fine calibration balance between the two channels so you can get them to track equally and have the imaging centered for all levels of playback.

There are 3 ways of doing this from most accurate to least accurate.

1: I do this using a 1khz sine wave from a audio signal generator with a good dual trace oscilloscope.

2: It can be done if you don't have these by using test disc that has a
-20db 1khz sine wave and then use a digital multimeter set at 2vac to do the calibration.

3: Then the really ruff way if you have non of these is to use a mono recorded cd of voice and adjust the 1k trimpot so you have a central image.

4: Always do this calibration after the Lightspeed Attenuator has been on and warmed up for at least 15mins at half volume.

Cheers George
 
Last edited:
#2,508
PJPro said:
Has the OptiVol kit been discussed in the depths of this thread? On the face of it, it would seem to be a lightspeed attenuator for $40AUS/$34US/£21 (including postage).

SKA Audio OptiVol

This was pointed out to me over the Chip Amp forum. I have posted a similar query in the Group Buy thread.
Click to expand...

Yes if you care to read or search the earlier threads this was discussed at length, it is my Mk1 Lightspeed Attenuator cloned and copied which a fellow Australian countryman decided to make a quick buck on and does not come close to the sound and performance of the MkII
1 does not sound as good as the MkII (dynamics especially)
2 does not go down as low in volume as the MkII
3 does not have the volume range
4 does not have as stable input/output impedance as the MkII
the list goes on.

One thing it has in it's favour the MkI was simple to build, sometimes I wish I'd stayed with it for sanity purposes.

Cheers George
 
#2,509
My Lightspeed was born today!!!

Thanks!!:spin: 😛 :cloud9: 😀 Lovely~~
 

Attachments

  • IMG_9779.JPG
    IMG_9779.JPG
    33.9 KB · Views: 796
  • IMG_9782.JPG
    IMG_9782.JPG
    21.4 KB · Views: 766
  • IMG_9787.JPG
    IMG_9787.JPG
    21 KB · Views: 768
#2,512
George,

I am new to the LDR preamp idea so bear with me on this. You say that it is preferable to have an amp with 100Kohm input impedance but how would I get around the fact that mine is only 22K. Would using a buffer help this situation.
Where can I find your pricing and delivery costs (to the UK) for your Lightspeed.

John
 
#2,513
Hi George,

it sounds wonderful after burn-in, yes, they needs 😎 very dynamic sounds, clear & fresh😀

I am using a soundcard(EMU1212M) & Tripath Ta2020, I haven't parallel any resistor to the LDR.

I just get the box in the local component store:spin: I like it so much too, even I am a exquisite taste guy 😉


udailey,

Yes, they are Sala mini shunt idea, easy to bulid, as I am using the trimpot to adjust the current.


I am going to bulid a remote control version:cloud9:, let see~~
 
#2,514
jaydeecee said:
George,

I am new to the LDR preamp idea so bear with me on this. You say that it is preferable to have an amp with 100Kohm input impedance but how would I get around the fact that mine is only 22K. Would using a buffer help this situation.
Where can I find your pricing and delivery costs (to the UK) for your Lightspeed.

John
Click to expand...

I have since a while back, revised this down to more than >50Kohm, we did an experiment with a few audiophiles at one of our meetings and kept changing the input impedance of an amp driven by the production Lightspeed Attenuator, we started at 130kohm and came right down to 33kohm before anyone heard a difference, so I now state more than >50kohm is ideal the more the merrier but after 50kohm you probably will not notice the difference. Yes at your 22kohm you may need a buffer, maybe, just listen to it as it may be system dependent, it cannot hurt anything to try.

Cheers George
 
#2,515
jaydeecee said:
George,

I am new to the LDR preamp idea so bear with me on this. You say that it is preferable to have an amp with 100Kohm input impedance but how would I get around the fact that mine is only 22K. Would using a buffer help this situation.
Where can I find your pricing and delivery costs (to the UK) for your Lightspeed.

John
Click to expand...

John,

I have a similar problem with input impedance so I put a Nelson Pass B1 buffer after the LSA - it replaced the pots on the B1 - it works very well. But as George suggests try it without a buffer first - it may work.

Alan
 
#2,517
AlanElsdon said:
John,

But as George suggests try it without a buffer first - it may work.

Alan
Click to expand...

Yes, if you have a CDP something like some Krells that have very low output impedance like 1-10ohm with good drive, then it is possible that a 22kohm input power amp will be fine. As the 22kohm of the power amp and the 7kohm of the Lightspeed will be seen to the CDP as approx 5kohm load and this should not worry something like the Krell CDP above.
Cheers George
 
Last edited:
#2,518
georgehifi said:
Yes, if you have a CDP something like some Krells that have very low output impedance like 1-10ohm with good drive, then it is possible that a 22kohm input power amp will be fine. As the 22kohm of the power amp and the 7kohm of the Lightspeed will be seen to the CDP as approx 5kohm load and this should not worry something like the Krell CDP above.
Cheers George
Click to expand...

Hi George

I have an old Pioneer PD93 feeding a DIY TDA1541 x 4 NOS DAC and I don't have any info on either of these as to what their impedance values are so I guess I will have to, as you suggest, try without a buffer first
 
You must log in or register to reply here.
Top Bottom