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Old 6th July 2008, 10:31 PM   #11
juma is offline juma  Germany
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Quote:
Originally posted by stefanobilliani

...
And of course it is a preamp . since it amplyfies the current of the signal .
No, it's not a preamp. Amplifiers are gain devices, determined by voltage amplification. Current amplification is something else - it's called impedance matching.
This can be argued but it's consensual definition.
BTW, F5 doesn't need impedance matching. Its' input impedance is the similar as B1's.
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Old 6th July 2008, 10:45 PM   #12
MEH is offline MEH  United States
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Quote:
Originally posted by juma

This can be argued but it's consensual definition.
Nice to meet you, Mr. Consensual.
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Old 6th July 2008, 10:47 PM   #13
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Quote:
Originally posted by juma


Amplifiers are gain devices
Infact the B1 is a gain device .

F5 needs a volume control


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Old 27th July 2008, 06:26 AM   #14
lineup is offline lineup  Sweden
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Quote:
Originally posted by juma
The one I attached will do nicely - it sounds very good and it's easy to build. F5 is very light load (100k).
R6/R1 ratio sets the gain (make them both 1k for the gain of 2V/V or 6 dB) and P1 sets the DC offset on output.
You can use F5's PS to make a regulated PS for this preamp.
Input pair of K170/J74 can be GR or BL ; output ones are BL or V.
Very good juma
I couldnt have made it better myself
.... I wish i had .. before you did juma
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File Type: gif juma_jfet_preamp_for f4_f5.gif (7.4 KB, 4704 views)
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Old 27th July 2008, 06:34 AM   #15
EUVL is offline EUVL  Europe
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If one needs no additional gain, I personally would just put an attenuator (or passive preamp, or whatever else you want to call it) right at the input of the F5, driven directly from the CD player. With 101k input resistance, there is no real need of a buffer stage if you use a 10k attneuator (which an avergae CD player will drive easily) and no long cables in between).

BUT personally taste. Everyone is entitled to choose his own favoured solution.


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Old 27th July 2008, 06:58 AM   #16
lineup is offline lineup  Sweden
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this may be the first option to try, EUVL

now i would use a volume pot of 22k/25k instead
as my CD-output is limited to minimum ~15 kOhm

good advice by EUVL:
- do not add things to your sound system signal chain '
.. that you do not really need

.. any addition will more or less make you signal worse
this is the hard facts!
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Old 27th July 2008, 10:51 PM   #17
juma is offline juma  Germany
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Quote:
Originally posted by lineup


Very good juma
I couldnt have made it better myself
.... I wish i had .. before you did juma

Sorry lineup, but I can not be credited for that circuit. I found it in one of the articles published on E. Borbely's site and it seemed to me a right preamp for F5. Most important drawback of this preamp is its inability to drive very low impedances, but it won't be the problem with F5 (101 k Zin). It produces 5V output (peak) with ease and it sounds lovely (no change in F5's sound character, only higher output) - that's all I need
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Old 27th July 2008, 11:33 PM   #18
lineup is offline lineup  Sweden
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Sound lovely!
I guess so

JFET output. JFET input is excellent. Many opamp use it.
Output, as you say can be a bit much distortion, if too much loaded.

But 100 kohm is perfect for JFET output.

Nelson Pass has been kind to us.
Setting input impedance high as 100 kohm in F5.

Means Tube or This JFET amplifier can be used for F5.
Of course JFET Op-Amps like OPA2134 would be another option.

Again .. very nice little amplifier. Thanks for publish here, juma.
Even if some other made this amp.


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Old 28th July 2008, 10:17 PM   #19
juma is offline juma  Germany
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Here is another idea that I've been playing with. It's based on J. Broskie's Aikido tube design. I used FETs that are cheap and abundant. Recorded values from simulation software are pretty much consistent with real life circuit (it's often true for simple circuits).
By listening to it I cannot find a fault, but it has certain drawbacks from designer's point of view:
- higher PS voltage (must be derived from separate transformer or by means of voltage doubler from F5's transformer)
- PS voltage must be very clean
- design uses a couple of coupling caps

OTOH, it's simple, easy to build, no hard to find parts, highly customizable (use of other FETs possible), no P-channel FETs needed, and IMHO, it sounds good
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Old 28th July 2008, 10:28 PM   #20
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by juma
Here is another idea that I've been playing with. It's based on J. Broskie's Aikido tube design. I used FETs that are cheap and abundant. Recorded values from simulation software are pretty much consistent with real life circuit (it's often true for simple circuits).
By listening to it I cannot find a fault, but it has certain drawbacks from designer's point of view:
- higher PS voltage (must be derived from separate transformer or by means of voltage doubler from F5's transformer)
- PS voltage must be very clean
- design uses a couple of coupling caps

OTOH, it's simple, easy to build, no hard to find parts, highly customizable (use of other FETs possible), no P-channel FETs needed, and IMHO, it sounds good

use fb arrangement as in inverted OP amp , then you'll loose one cap ;
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