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Old 6th August 2007, 07:45 PM   #1821
wlowes is offline wlowes  Canada
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Default Final version with lightspeed attenuator

I worked all day Sunday on the lightspeed attenuator. It was pretty tedious work to test couplers to come up with two pairs with matching specs across the attenuation range. I installed it all and took a leap of faith by hard wiring onto the chipamp pcb without first testing the circuit.

Got a good night's sleep and then double-checked all my work with a clear head. With some trepidation, I hooked it up and powered up... whew. It came to life and sounds glorious.

I'm not an experienced audiophile, so I don't pretend to have all the critical vocabulary to describe the results, but my impressions follow so many other posts I have read but never personally experienced. There is a whole new level of sound on all my CDs. Soloists take a breath between notes. It's like they are alive and in the room with me. It's up close and personal now. At even modest volume I got a spooky feeling in my spine as notes kind of startled me. Bass is fully extended but controlled.
Drums are drums. Cymbals decay in the background as the music carries on. Bells and triangles ring as if they are in the room.

I played Dianna Krall. The placement of instruments is precise. Her voice is up higher than the piano and comes from deep BEHIND the stone wall of the fireplace that the amp is sitting on.

Again, hearing her breath is spooky.

The mechanical sound of the digital source has left. After an hour or so I realized that I was not listening to the stereo any more but was listening to the music. I figure this is what the whole goal is.

Here is a picture of the finished amp. The optocouplers are at the end of the blue cable and their signal leads are soldered to the input spots on the chip amp board. Their input leads go to the CATV via 3 fine silver wires on positive and one 24 gauge copper on negative. The blue cable goes to a separate power supply and cheap pot that acts as a dimmer switch for the LED’s to control the resistance of the photodiode. It was easy to wire in a balance control without losing any quality as it is not in the signal path, its in the dimmer circuit. So Cool!
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Old 6th August 2007, 07:45 PM   #1822
wlowes is offline wlowes  Canada
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Default optocoupler attenuator

Here is the final pic. It's the attenuator under construction. A simple design following the design by georgehifi on this forum. Thanks George!
I used the version modified to include a balance control.

Lightspeed Attenuator a new passive preamp

My innovation was to wire it directly to the chip amp board. To facilitate this approach I simply glued two sorted couplers together rather than putting them on a separate board. I guess it reduces the flexibility of having a separate passive attenuator component, but my design goal is to produce a single integrated unit with all the characteristics of the best preamp, amp and DAC I can build on a budget. I don't plan to be changing components a lot, and I like the idea of one compact unit without a bunch of interconnects. I also came up with a rig to do the testing of all the optocouplers at once which took hours off the project. I'll post pics if anyone is interested.
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Old 8th August 2007, 03:18 AM   #1823
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Where did you get the optocoupler for the lightspeed attenuator. Last time I check, they were very hard to get.

Thanks...
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Old 8th August 2007, 03:32 AM   #1824
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Quote:
Originally posted by BNK
Do you sell chassis (+connectors) only or chassis+transformer (+connectors)?
I have an old BrianGT 3875 kit that I never used because of missing the above.
I have no problem assembling/soldering so I don't need it assembled.
Thanks.
The chassis pictured here: http://audiosector.com/chassis_integrated.shtml is available as a kit at $250. All accessories are extra:

Brass cones $15/set
Knobs $18 ea.
Wooden sides $10 unfinished, $20 finished maple, $40 exotic wood
Shaft extenders $10/set
RCAs $3.50 ea
Cardas patented binding posts $35/set
Noble pot $22
Source selector $8 (different than pictured)
AC module $3
Plitron 300VA toroid $85
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Old 8th August 2007, 03:46 AM   #1825
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Default Re: CD Pro2 LF

Quote:
Originally posted by jeffry_widjaja
So peter ... would you like to build another DAC,
use Excellent board, best component (maybe opa 627bp,
BGN, low jitter cristal, best resistor, etc) and the board can
be place it in CD casing or separate
I don't feel like changing anything in an existing DAC. It is complete product in a class of its own, and as such it's hard to improve any further.

There are certain mods that can still elevate performance, but that brings the price substantially higher: one can substitude Rikens for Caddocks TF020, use small value V-caps with a simple buffer at the output, and upgrade main filter caps to BG N or BG FK.

The DAC board can be placed in a CD player and some people actually do that.
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Old 8th August 2007, 03:48 AM   #1826
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Default Re: Another Peter Daniel amp springs to life

Quote:
Originally posted by wlowes
Peter,
I am pleased to report that another of your kits has sprung to life and you have another very happy customer.
Great work with quite unconventional approach
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Old 8th August 2007, 04:41 AM   #1827
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Default Re: Re: CD Pro2 LF

Quote:
Originally posted by Peter Daniel


There are certain mods that can still elevate performance, but that brings the price substantially higher: one can substitude Rikens for Caddocks TF020, use small value V-caps with a simple buffer at the output, and upgrade main filter caps to BG N or BG FK.

What would be the main advantage of adding a buffer to the output, other than lowering the output impedence from 3K (it is 3K, right ?) to something much smaller ?

My current amplifier has an input impedence of 100k, so I figure a buffer wouldn't help much. However, I do plan on building an F3 soon, and since that has an impedence of about 10-20K, there may be some issues (I plan on using a passive preamp, probably a TVC, or something ...).
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Old 8th August 2007, 04:52 AM   #1828
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is there no way to get the DAC as a kit now? I was suggesting it to a friend as a first little project and then went and looked and they were all assembled? Is there any particular reason for this?
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Old 8th August 2007, 05:54 AM   #1829
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Default Re: Re: Re: CD Pro2 LF

While the pictures show the DAC assembled, it's mostly available as a kit, when one does assembly himself. On special requests, assembled version is available as well.



Quote:
Originally posted by lordvader
What would be the main advantage of adding a buffer to the output, other than lowering the output impedence from 3K (it is 3K, right ?) to something much smaller ?

My current amplifier has an input impedence of 100k, so I figure a buffer wouldn't help much. However, I do plan on building an F3 soon, and since that has an impedence of about 10-20K, there may be some issues (I plan on using a passive preamp, probably a TVC, or something ...).
The main advantage of a buffer is lowering output impedance which may work better with following stages, especially when those have low input impedance.

The buffer will also allow to use smaller value of coupling caps. This matters mostly in case of premium parts, like teflon V-Caps. So instead of using $300/pc 2uF cap, one can get away with 0.1uF cap that costs "only" $50/pc
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Old 8th August 2007, 06:17 AM   #1830
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Well on the site it only shows assembled prices? And when will they be available again?
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