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Old 20th July 2011, 03:24 PM   #1131
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I think both intact and Promitheus Audio could supply a kit
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Old 20th July 2011, 05:05 PM   #1132
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Besides the TVC route, check out the LRD volume control kits. Reputedly they sound as good as TVCs.

[Review] Paul Hynes Design LDR volume control kit review - [English]
DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers)
Lightspeed Attenuator / Audiohm Optocouplers / LDR • DIY Audio Projects Forum
all about volume control...

The above should make a start. Anyone built one?

andy
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Old 24th July 2011, 06:24 PM   #1133
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hi Andy

i have built DIY "Lightspeed Attenuator" - Passive LDR Volume Control (audio optocouplers) but with the buffer, it sounds superb. however with buffered its been coloured by some active stage. but it still very nice. its one of best passive preamp imho.

Hi Thomas

i got question about TVC, why we use it on output instead of input of the preamp as the resistive volume pot? so you recon that 10k:600 would be suitable for AVC/TVC?

ps: i still cant differentiate the differences between TVC and AVC. need more research

thanks in advance

regards,
Erwin
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Old 24th July 2011, 10:10 PM   #1134
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Hi Erwin,

TVCs need a low source impedance to perform best. If all your sources have low output impedance, you could place it at the input as well. However I found that solid state sources even with low Zout offen sound poor when they are inductively loaded.

TVC stands for transformer volume control. That can be with a separate primary and tapped secondary, or in form of an autoformer which just consists of a single tapped winding. The latter is appreviated AVC for autoformer volume control

Best regards

Thomas
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Old 7th August 2011, 07:52 AM   #1135
Richard is offline Richard  Australia
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G'day All,

Geez this thread has progressed a lot since I finished my 26 pre. I've recently updated my preamp using some Hashimoto Hl-20K transformers. I was using 2 Hammond 150 chokes in series with a FT-3 0.1uF & 1M RC output, for over a year.

The transformer out did bring a lot of improvements to the sound. Clarity is something that stands out the most, I'm not good at using audiophile words but it sounds much more natural now with the Hashimoto's in there. I've been running them in and the bass is also improving. Still not quite as good as the 300H plate choke, but it seems to be getting there in time.

The rests of the system uncludes a 2A3 PP amp and Philips AD5200M in JE labs open baffles, with Saba black cone tweeters. One thing that was also evident, was the sound of guitar. The notes seemed to have more weight to them.

The next stage is to add a TVC and do away with the pot and input cap. I'm using battery grid bias as per schematics in the this thread. I'll post my findings when I get around to this upgrade.

Cheers,

Rich
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Last edited by Richard; 7th August 2011 at 07:56 AM.
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Old 7th August 2011, 01:06 PM   #1136
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you were using exactly what I use - 2 Hammond 150 chokes in series, with a FT-3 0.1uF & 1M RC output. It's not bad isn't it!

I'm going to get some better plate chokes and see what that does. I use filament bias which means no input cap - sounds better too, but needs a choke input and a Rod Coleman supply or equivalent. Hammond do suitable chokes - 159ZA, 300mH, 1A, or 159ZC, 60mH, 2A if you prefer.

The 300H inductance with the two 156C does make the 26 feel very happy!

Andy
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Old 8th August 2011, 12:15 AM   #1137
Richard is offline Richard  Australia
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Hi Andy,

I've been following your posts in interest. The 2 plate chokes are a very good option and are fairly close to the transformer output. I got the idea from Gary Pimm's 26/56 preamp, I also like his use of VR tubes. It's the best option for the price.

Schematics

I've got Rod's filament supply and still am yet to install it. I was also considering trying filament bias but will need to upgrade the transformers. It's a choke input with locally wound 60mH 2A chokes, with 7V before the regulator.

Could you elaborate a bit more on why you found filament bias better than battery grid bias?

Also, have you used the Hammond 300mH 1A choke in your 26 filament supply?

Quote:
The 300H inductance with the two 156C does make the 26 feel very happy!
They were indeed, but I'm happer with 'Japanese steel' in their place.

Rich out
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Old 8th August 2011, 06:42 AM   #1138
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My filament supply uses 18v secondaries - it's just a 18+18v toroid. I then have a small cap - 220uF - and in my case my chokes are 280mH at 2.7A. Pretty big. Follow that with 30,000uf of caps or so and then Rod's supply.

Sound was just generally better - cleaner and more focussed.

Andy
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Old 8th August 2011, 07:39 AM   #1139
massimo is offline massimo  Italy
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Quote:
Originally Posted by andyjevans View Post
My filament supply uses ...
... also some special Dale power resistor, selected for sound IIRC.
2nd option?
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Old 8th August 2011, 08:43 AM   #1140
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10 Ohms 5% @ 95 Watts WW POWER RESISTOR (4 pcs) | eBay

The above are overkill, but the supplier has various values to make up 10 ohms at about 50 watts.

eBay - The UK's Online Marketplace

The above can be used in series parallel. These were the best sounding resistor types for me. Equivalent types tend to be harder to find or out of stock e.g.

MULTICOMP|MC14655|RESISTOR, 10 OHM 25W | Farnell United Kingdom
MULTICOMP|MC14663|RESISTOR, 10 OHM 50W | Farnell United Kingdom
http://uk.farnell.com/vishay-sfernic...10r/dp/1141252

I didn't like the alu clad ones and the thick film types were the worst sounding of all. Needs some kind of wirewound.

Andy
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