205D Phono pre.

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dave slagle
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205D Phono pre.

Post by dave slagle »

Out from the email and into the fire.
I'm thinking about building a 205D Phono with a combined line stage. I'm possibly interested in some nickel or amorphous core chokes, output transformer, and maybe the transformer volume control
Mmmm lots of tasty iron.
Do you also do a RIAA equalizer out of chokes?
I can do chokes for both LC and LR riaa, but the high Rp of the 205 will not make it easy.
Anyway could you give me any recommendations? There would
probably be a total of 3 205D tubes per channel, two phono and one for line
on each channel.
Iirc, the 205 only has a gain of ~8, so my guess is three of them will not get the job done. With an input step-up, 3 of them might get you close to .25V output, but then you will need another stage to get that to the 2V "standard". Thomas Mayer did a all DHT phono stage and used 4 stages of 801's and I think it was an article in sound practices, maybe you could dig that up for a starting point. I must admit the idea of 8 205D's in a phono stage would surely get some attention :-)

Tossing a high mu DHT in the mix like a AV-30 or 841 sure would help keep it to three stages, but you still have the high impedances to deal with.

dave
Guest

Post by Guest »

Great to hear from you again. Ya I've been concerned about enough gain, I would for sure be useing a step up transformer for the moving coil cartridge. My speakers being 106 DB also helps! I just finished building a 205D line stage on Monday so I'am in the process of listening right now for a while to see if it is worth all the effort and money. So if you don't hear from me for a few days you will understand why. I probably should have listened before I contacted you, but I have been thinking of a 205D phono ever since I started the line stage! Anyway I will be back in touch as I listen a little more and figure things out, thanks Kevin
dave slagle
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Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
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Post by dave slagle »

hey kevin,

Thank god there are no rules. Luckily we can draw on our collective experiences to define our own rules and take it from there. Whenever the 205D is mentioned i remeber one of the early NYnoize shows at JC's loft and Stuart's 250TL amp. He used the 437 for gain, the 205 for flavor and the 250TL for power. Since the main concern of a phono stage is gain, i'd be a bit concerned about using too much flavor. Let me rephrase that, I'd rather mix flavors than use the same one over and over. Building amps is like cooking and you need to know what flavors suit your audience. I personally hate ginger in large doses, but a slight hint of it really wakens my taste buds.

Common wisdom says the first tube after the MC stepup must be high gain. Why not sprinkle a 205D there? Place a 1:26 stepup feeding a 205D and you have a good start. Then couple that (through a 1:1) to a resistive loaded 841 and you have someting that could be stepped down to drive the EQ circuit... whatever that may be :-)

dave
Ed Sawyer

all DHT phono

Post by Ed Sawyer »

Dowdy and I have a plan to build an all DHT phono stage, will be 3 or 4 gain stages... maybe he can post the details sometime soon. offhand it will be something like

1:20 stepup -> EML AV-30 -> AV-30 -> 316A ->10k LCR RIAA -> 2A3 -> 1:1 IT

or something like that. ;-)

if the AV30 isnt' quiet enough, alternatives we considered were WE 416A/B or WE 437A .

Dave is working up the special 1:1 IT I believe, with some current-cancel windings.

205D's are sweet though. I have an amp in the works using those.. but only 1 per channel, not 4. (how cool would that be! ;-)

FWIW
-Ed
JeffreyJ
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Western Electric Phono...

Post by JeffreyJ »

Not that I was asked, but if I were building this bad boy full of tennis balls, I would go:

mc step-up > 102d > 205d > riaa > 205d > out...

that one section of 102d should get you the gain you need.. I am getting away with two 6c45 stages and no cathodes bypassed.. I think a key is no capacitors at these low signal levels.. they really rob the life... and I also don't like the big series R's... same reason..

and yeah.. horns definitely help... I'd love to see someone with 106dB horns design "by the rules" for an amplifier.. build a 304tl that is half volt sensitive for full power and put the typical audiophile preamp in front of that... stand back as the hiss will likely be deafening... :)

that said, I certainly am all for DHT phono stages..

Peace,
Me
slowmotion
Posts: 20
Joined: Wed Mar 09, 2005 7:04 pm
Location: Norge

Post by slowmotion »

or directly heated pentodes....

cheers ;)
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