CF Linestage Mods

8th Anual CarverFest. September 10th - 24th
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radioeng2
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CF Linestage Mods

Post by radioeng2 » Mon Sep 07, 2015 4:36 pm

The factory has today released an official pair of modifications. These two modifications are to help lower audio output noise of the linestage as built.

In the last couple of months I finally had forced in the time to investigate the greater than desired noise floor on the CF14 Linestage. I found two things that really helped. One is to fuss with the filament supply area. And the other is to add another filtering stage to the power supply.

Mod 1

The first is adding a ground to a center tap position of the filament supply. The original transformer has two 6.3v windings. We added those together in series to get a 12.6 supply. And like most all power transformers, if you're not loaded right up to maximum current draw on it, the windings run a little higher in voltage than the specified number. In this case, if I'm remembering right, it was a little over 13 volts. So rather than leaving it be and shortening tube life, the design had a single resistor inserted between the windings. We have that junction on the end of the power supply board.

So to effect the mod, we take out that .82 ohm resistor and instead insert a pair of .47 ohm. We drop from a single 5 watt resistor to a pair of smaller 2 watt. This pair gives us the ability to access a center tap point and ground it. This removes a little spike shown in the output audio. To physically accomplish this pair of resistors, we move over one filament wire one post and then run one resistor from each wire to the immediately adjoining ground.

OK...then on to Mod 2.

In poking at the noise, I was looking at the original idea that a voltage regulator, here a OD3, trims down the DC voltage to the regulation point and in taking off the "top", also trims right off noise that's riding along on the DC. Well, in this implementation, it does reduce ripple from around 160mv AC to about 30mv. A pretty decent number. Well, by adding another filtering section to the supply, we can better this. Out of the simple addition of another R and C element, we can drop the regulator input noise to about 70mv (from 160mv) and coming out of the regulator down to about 6mv from the 30mv. Which is a really tiny amount on 150vdc.

Implementing another section without a lot of trouble was worrisome. But it turned out to not be too bad. We have a red wire jumpering down the outside of the supply bringing the DC from the post below the original second cap down to next to the end where we have output + and - side by side. What we do is remove that red jumper and sub in a 30 ohm 2 watt resistor. We go past in input AC on the diodes etc, so we have to insulate the resistor legs and route it with care but that's not too hard by just looking at what's in front of you and bending parts to slightly different elevations. Then with the resistor in place, you drop a third power supply cap into those last two terminal posts, as that's the + and -. DONE!

Image

This picture shows the two resistors in the filament supply to the right. Then towards the other side, the added resistor with red heat shrink down low going towards the left end where the added cap is.

I've put together a bag with each persons name that bought a LS kit. It has in it, line by line specific info and pictures showing you in detail these two mods.

Image

It also has a new full schematic showing the additions. Then, there is two small plastic bags with the parts. The first, is the two resistors for the filament center tap addition. Second bag is for the PS additional filtering and has the resistor with heat shrink and the cap. Also, three people were gone last year before we had the CF LS14 badges on hand, and those three also have those in their mod kit bag. Thanks again to Eric for those!

Tools you need...fine needle nose pliers. Very important. Some small dikes to trim ends. And a soldering iron. Should be less than 30 minutes for most to do...an hour for Al and 10 for me to fix it. :lol:

On four Linestages here, this mod puts the A weighted noise figure down about 80db and results on pretty highly efficient speakers with no noise audible until you stick your ear into the driver and then only barely there. I'm hoping this works well for everyone and is easy to get implemented.

Mark
I was there "At the Fest!" Hope you were too!

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Zoot Horn
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Re: CF Linestage Mods

Post by Zoot Horn » Mon Sep 07, 2015 5:22 pm

Just loaded mine,,thanks for doing this Markie,,guess I will have to be nice to Harry,,as my depth perception ain't so good anymore.

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Magnaryder
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Re: CF Linestage Mods

Post by Magnaryder » Mon Sep 07, 2015 5:27 pm

I was bringing my LucasLabs LS anyway so this is a great time to do the mods under your tutelage Markie! Maybe I'll put in the Obligatto caps too.

ray
Magnaryder

Its going to be used equipment when I sell it, so it may as well be used equipment when I buy it.

"Racing is life, the rest of the time you're just sitting around."-Steve McQueen

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Zoot Horn
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Re: CF Linestage Mods

Post by Zoot Horn » Mon Sep 07, 2015 5:36 pm

Mark,, please put me in the same class as Al! I got my Obligattos in Ray! If anyone wants a pair I have one pair left.

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Magnaryder
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Re: CF Linestage Mods

Post by Magnaryder » Mon Sep 07, 2015 6:29 pm

Zoot Horn wrote:Mark,, please put me in the same class as Al! I got my Obligattos in Ray! If anyone wants a pair I have one pair left.
gotta remember to remember to pack the caps

ray
Magnaryder

Its going to be used equipment when I sell it, so it may as well be used equipment when I buy it.

"Racing is life, the rest of the time you're just sitting around."-Steve McQueen

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MRHP
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Re: CF Linestage Mods

Post by MRHP » Mon Sep 07, 2015 6:41 pm

Are the Obligattos really that good. Do they make a significant change in sound. How much?
TFM-75 serial #0001
PT-2400 serial #0001
Baby Black Magic serial #0001
Baby Black Magic serial #0002
Cherry/260wpc Mono Blocks
Lightstar Reference
Sunfire Series II 625x2
Carver 490t
OPPO-103
Lucas Labs CF-14
Sunfire Tube pre
DENON DP-62L TT
DUAL CS 5000 TT
DQ-20's
Tesla CF-15 speakers
Douglas Cables
OK ERIC, LET GO OF THE MOUSE AND BACK AWAY FROM YOUR PC WITH YOUR HANDS IN THE AIR. NOW SLOWLY LAY FACE DOWN ON THE FLOOR!!!! - Snoop65

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Zoot Horn
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Re: CF Linestage Mods

Post by Zoot Horn » Mon Sep 07, 2015 6:48 pm

Nothing wrong with the clarity caps that Mark provided,, just a matter of taste/preference,,I think the obligattos offer a tad more flavor/ smoothness ,maybe a smidge more detail

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frenchguy
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Re: CF Linestage Mods

Post by frenchguy » Mon Sep 07, 2015 7:24 pm

A hour for Al? Guess maybe I should just save time then & have you do it Markie!! :lol:
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radioeng2
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Re: CF Linestage Mods

Post by radioeng2 » Mon Sep 07, 2015 7:39 pm

frenchguy wrote:A hour for Al? Guess maybe I should just save time then & have you do it Markie!! :lol:
Had to poke ya Al! Ha...ha...ha...

These are right there at the edge of the supply like the picture shows. Needle nose are the key...really is. Nobody has small enough fingers to do anything in and around those areas. And were talking the tweezer end kinda ones too Ray...not some plumbers ones! :rolleyes:

Mark
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Magnaryder
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Re: CF Linestage Mods

Post by Magnaryder » Mon Sep 07, 2015 7:43 pm

I brought the needle nose pliers last year Markie! It was plumbing solder for the amp build. You might notice it has NOT come apart....yet \:D/

ray
Magnaryder

Its going to be used equipment when I sell it, so it may as well be used equipment when I buy it.

"Racing is life, the rest of the time you're just sitting around."-Steve McQueen

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Re: CF Linestage Mods

Post by MRHP » Mon Sep 07, 2015 8:06 pm

Zoot Horn wrote:Nothing wrong with the clarity caps that Mark provided,, just a matter of taste/preference,,I think the obligattos offer a tad more flavor/ smoothness ,maybe a smidge more detail
Maybe we could work up a trade.....hotrodded caps for some ummm high octane race fuel :-"
TFM-75 serial #0001
PT-2400 serial #0001
Baby Black Magic serial #0001
Baby Black Magic serial #0002
Cherry/260wpc Mono Blocks
Lightstar Reference
Sunfire Series II 625x2
Carver 490t
OPPO-103
Lucas Labs CF-14
Sunfire Tube pre
DENON DP-62L TT
DUAL CS 5000 TT
DQ-20's
Tesla CF-15 speakers
Douglas Cables
OK ERIC, LET GO OF THE MOUSE AND BACK AWAY FROM YOUR PC WITH YOUR HANDS IN THE AIR. NOW SLOWLY LAY FACE DOWN ON THE FLOOR!!!! - Snoop65

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Zoot Horn
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Re: CF Linestage Mods

Post by Zoot Horn » Mon Sep 07, 2015 8:40 pm

Sounds good to me!

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engtaz
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Re: CF Linestage Mods

Post by engtaz » Tue Sep 08, 2015 3:03 am

Ill take that pair of obligattos if no one at fest wants them.
engtaz


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radioeng2
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Re: CF Linestage Mods

Post by radioeng2 » Tue Sep 08, 2015 7:01 am

And BTW, after the fest I'll ask for everybody that has a Linestage and didn't get to the fest for their address, and I'll send out their mod packet.

Mark
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Zoot Horn
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Re: CF Linestage Mods

Post by Zoot Horn » Tue Sep 08, 2015 7:21 am

radioeng2 wrote:And BTW, after the fest I'll ask for everybody that has a Linestage and didn't get to the fest for their address, and I'll send out their mod packet.

Mark

You are a prince Markie

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