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Old 11th July 2006, 10:24 PM   #101
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Very nice Panelhead, if ever I decide to do dual monos or balanced instead of a single ended stereo, I'll go for a larger width chassis, as The one I use is very cute but would end up a PITA to build.

Cheers George
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Old 12th July 2006, 12:38 AM   #102
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Default Further comments

The unit has been on for more than 12 hours with music running through it. The sound should be close to settled in.
The unit preserves some edges and flaws in source material that my previous pre homogenized. Listening to Black Cadillac the first few cuts are edgy and close miked. The middle cuts are ballads and are presented with bloom and sweetness. This is how the CD is recorded.
I have to give this thing a real thumbs up. Comes across like an active unit as far as dynamics and frequency extremes.
If diy is not your thing contact Georgehifi and get him to build you one. The sub 400.00 price makes it a steal. Some pay that much for a power cord. This design rocks!
If building your own, a couple tips.
1. Order a dozen graded LDR's and match up at several current points. I used 0.1 ma, 0.5 ma ,and 1.5 ma. This was done with a 15 volt regulated supply and a dropping resistor. Measured the voltage across the resistor to dial in current then measured the other side of the LDR to get resistance. Plotted it out and it is an exponetial decay. It is easy to spot trends and find close matches.
2. Try to find a dual linear pot. Mine are 50K Alps located in a surplus shop. Picjked four by matching end to end, then picked the two that tracked the closest. A log pot will work fine also, but tracking with most is much worse than the linears. A poor tracking pot will negate the LDR matching.
3. A wallwart works great to power. Use the dual regs like the Lightspeed and do not connect the power supply ground to the signal ground. The are optoisolated!!
4. Try diddling with the current limiting resistors. I used 121 ohm instead of George's 100. If you never completely close the pot or open it up this is not critical. My selector is wired up with mute positions so there is no reason to ever close, and the level gets crazy loud before the pots are half open.

Like George mentioned earlier in this thread, the unit seems to work best with low output impedance sources and high impedance amplifiers. My 30+ year old Pioneer 9100's work, but not as well as my SA-8260's. I would guess that transformers and tubes are out. Thnk this is true with any passive attenuator.
Guess Melos knew what they were doing when they used these a decade ago. Too bad their implimentation lead to high failure rates.
Badge, let us know how yours pans out. My pots ate me up too. I still do not understand why they work as they do. Still learn something everyday.

George
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Old 12th July 2006, 12:50 AM   #103
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Ok either im really not getting this or this passive word has been described to me as something different.


passive means caps resistors / volume pot. I have been experimenting with my Alephs. I have 3 devices.

One, a passive Alps pot.
Two, A Buffer
Three, Bosoz Pre-amp In Single Ended / Balanced Mode.

Now to me honestly i have spent a-lot of money on all these devices except the alps pot. Now guess what one sounds the best. ?

The alps pot passively in Single Ended Mode. Now the only problem with this is that the alephs like a little bit of gain my Sony ( 6 or more years old ) has lots of gain so it works really really well.

Right now i am working on a project to build a simple Op-Amp Buffer to work with this.. Simple as in hardly and parts with out ruining the sound. So far it is a hard challenge as I'm trying to do this on my own.
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Old 12th July 2006, 04:24 AM   #104
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Quote:
Originally posted by jleaman
Ok either im really not getting this or this passive word has been described to me as something different.


passive means caps resistors / volume pot. I have been experimenting with my Alephs. I have 3 devices.

One, a passive Alps pot.
Two, A Buffer
Three, Bosoz Pre-amp In Single Ended / Balanced Mode.

Now to me honestly i have spent a-lot of money on all these devices except the alps pot. Now guess what one sounds the best. ?

The alps pot passively in Single Ended Mode.

Any opamp no matter how good, how expensive, how exotic will ever sound as good as a good quality passive pot properly impedance matched. And the only thing that sounds better than a good quality pot, is no pot at all, hence that's why I developed the Lightspeed Attenuator, it is straight in straight out without being corrupted by any form of contacts or switches, it's as though the cd or dac is fed directly to the amp.

Cheers George
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Old 12th July 2006, 04:28 AM   #105
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If i was to use no pot at all ID have a problem of being deaf I guess i could use passive cables with resistors in them Now that would be a idea
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Old 12th July 2006, 05:05 AM   #106
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Quote:
Originally posted by jleaman
If i was to use no pot at all ID have a problem of being deaf I guess i could use passive cables with resistors in them Now that would be a idea


If you say you could go deaf, that means you have got enough gain, so you can build a Lightspeed. And if your Adelph needs more gain, you could always lower the global or local feedback a little to give more gain.
And when you say use interconnects with a resistor in them, this is exactly what the Lightspeed does, except that resistor can have it's resistance varied acording to the volume you want.
So you can have your cake and eat it too.


Cheers George
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Old 12th July 2006, 05:23 AM   #107
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Quote:
Originally posted by georgehifi




If you say you could go deaf, that means you have got enough gain, so you can build a Lightspeed. And if your Adelph needs more gain, you could always lower the global or local feedback a little to give more gain.
And when you say use interconnects with a resistor in them, this is exactly what the Lightspeed does, except that resistor can have it's resistance varied acording to the volume you want.
So you can have your cake and eat it too.


Cheers George

Ok so can i buy all the parts to build one of these from you will it do balanced and Single ended ? Pm me please.
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Old 12th July 2006, 05:48 AM   #108
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Quote:
Originally posted by jleaman



Ok so can i buy all the parts to build one of these from you will it do balanced and Single ended ? Pm me please.


Sorry, you can build one yourself, I've given now all the info to do it circuit and parts you need in previous posts, it's not hard, just time consuming.
Panelhead and a few others have done it, or buy a complete one with power pack from me as other are doing that aren't confident in DIY. Stereo single ended only.

Cheers George
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Old 17th July 2006, 10:10 AM   #109
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Default More thoughts on mine

The one I built is a little different than the Lightspeed. It uses 50k limear pots instead of the 100K log. The pots used track extremely well. This has caused an issue with resulting attenuation taper for the unit.
Initially it was used with a borrowed First Watt F1. The amplifier benefitted significantly when coupled with the Lightspeed clone. Sound had more like, was a little leaner and faster. The sensitivity of this unit is low. The pots were normally opened about 25% of rotation. Drunken listening maybe 40% at most.
Switching to a My_Ref Rev C, the increased sensitivity is a liability. Normal listening is about 10% of rotation. Loud is 15%. Spectral balance is efected also. Sound is leaner, the low end is rolled off. This did not seem to be true with the F1 as the amp. Bit the bottom of the F1 is so fat, it might have not been noticed.
Overall, it is an excellent unit. Just as noted by George, it has a few system matching limitations.
If I can find some 100K log pots that track well, it will be my next project for this unit. Right now this is effectivily an 8K-9K pot. Using a 100K pot should increase the impedance. This may bring the low end back up. My normal preamp has 25K input impdeance.
So overall, it worked better than my usual preamp with one amplifier, and the results reversed with another. I will keep trying to get more out of it. Maybe my system limitations it is exposing, not an issue with the unit.

George
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Old 17th July 2006, 12:32 PM   #110
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Quote:
Right now this is effectivily an 8K-9K pot. Using a 100K pot should increase the impedance.
Hi George. What exactly do you mean with the 100k pot increasing the impedance?
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