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Old 8th April 2004, 12:36 AM   #11
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Hi,

Quote:
How I wish I have a schematic
Nothing special about it....
I don't know why it's said to sound so good, I suppose it all depends on what you're used to.

Technically speaking it's about the only topology I'd avoid using, the whole thing works like a badly balanced see-saw.

Sorry, if you want a really good preamp it'll have to be a little more than just that one.

Cheers,
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Old 8th April 2004, 02:20 AM   #12
s2kov is offline s2kov  Canada
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Jojo,

I just choose 12AU7 for my try on tube preamp design. That's why i'm collecting opinions from tube gurus here to let me know if indeed i'm doing my homework right.

Salamat kabayan!

Andy


Quote:
Originally posted by JojoD818
Kabayan s2kov!

I see you are using 12AU7, the foreplay preamp of bottlehead uses 2 of those. Unfortunately, I think it is copyrighted so no DIY!

Regards,
JojoD
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Old 8th April 2004, 03:35 AM   #13
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Quote:
Originally posted by fdegrove
Hi,



Nothing special about it....
I don't know why it's said to sound so good, I suppose it all depends on what you're used to.

Technically speaking it's about the only topology I'd avoid using, the whole thing works like a badly balanced see-saw.

Sorry, if you want a really good preamp it'll have to be a little more than just that one.

Cheers,

Nice way of putting that see-saw thing Frank. I have seen writeups about that preamp so many times and keep on wondering when can I try it.

Thanks Frank!

s2kov,

You're welcome kabayan!
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Old 8th April 2004, 03:38 AM   #14
Bryan is offline Bryan  United States
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I've been working on a 12B4A preamp, currently breadboarded. I've had LOTS of help from Frank and others. It is a work in progress, but this being said, it is by far better than anything i have owned to date....

I am very happy with this tube.

Bryan
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Old 8th April 2004, 07:02 AM   #15
s2kov is offline s2kov  Canada
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Quote:
Originally posted by fscarpa58
Hi s2kov,

if res and caps as to be put at each cathode (advisable thing) the value of res has to be doubled and the value of caps halved to retain the original characteristic.

Bye
Federico

Is this what you mean? Will i still get the an operating point right?....
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Old 8th April 2004, 03:29 PM   #16
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Hi s2kov

The resistor values I have suggested (ra about 15k and rk about 200) come from simulation
(I use Micro Cap 7 demo). These values allows for lower distortion.


Regarding the duplication of the resistance to assure more similar static current in case of badly matched tubes, the values are reported in the following pic.

Ciao
Federico
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Old 8th April 2004, 05:26 PM   #17
s2kov is offline s2kov  Canada
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Federico,

Thanks for the help! Sorry, i overlook the Rk connected in parallel and it should be 2*Rk....

Can you point me how to run the simulation in Microcap?

Many thanks....


Andy
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Old 16th April 2004, 11:48 AM   #18
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Hi s2kov

Quote:
Can you point me how to run the simulation in Microcap?
have you downloaded it?
if not try at


http://www.spectrum-soft.com/demodown.shtm

bye
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Old 20th April 2004, 12:56 PM   #19
billr is offline billr  New Zealand
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Quote:
Originally posted by JojoD818
Kabayan s2kov!

I see you are using 12AU7, the foreplay preamp of bottlehead uses 2 of those. Unfortunately, I think it is copyrighted so no DIY!

Regards,
JojoD

nonsense, this is a standard design, you cannot copyright something that has been in text books for at least 70 years. go ahead and build what you want.
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Old 20th April 2004, 01:39 PM   #20
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Quote:
quote:
Originally posted by JojoD818
Kabayan s2kov!

I see you are using 12AU7, the foreplay preamp of bottlehead uses 2 of those. Unfortunately, I think it is copyrighted so no DIY!

Regards,
JojoD



nonsense, this is a standard design, you cannot copyright something that has been in text books for at least 70 years. go ahead and build what you want.
Also I dont think anyone can stop you for copying a patented or copyrighted circuit for DIY purposes, what you are not allowed to do with a patented circuit is to build it and sell it . For copyrighted material you are not allowed to publish it without owners consent.

For DIY, use whatever patented or copyrighted circuit you want if you can find it!

Regards Hans
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