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Old 7th February 2004, 09:37 AM   #11
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HI Dimitri!

Thanx for your nice reply. Godd company? Surtantly! I indeed need your help to develop my preamp, so please stay tuned

Before I comment your suggestions I would like you to elaborate and explain a little on the two GIF's your have attached.

Best,

Peter
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Old 7th February 2004, 10:54 AM   #12
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interesting thread...

jazzpeter, could I ask, what sort of the programme are you using to generate those freq pictures?

thanks.
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Old 7th February 2004, 01:03 PM   #13
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The program I used for the EQ curves are called Tone stack calculator found at http://www.duncanamps.com/tsc/

Great tool for trying all kinds of tonestack for guitar out.

Baxendale is there too - it's called "james".

- Peter
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Old 7th February 2004, 01:30 PM   #14
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Default Location of brightswitch...

Dimitri, you wrote:

>Use 10-47nF instead of C2 – it will be bright and shunt it by >switch with your 220uF – it will be normal.


Wouldnt it be easier just to move the bright cap and switch to the gain pot?

- Peter
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Old 7th February 2004, 03:37 PM   #15
dimitri is offline dimitri  United States
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>I would like you to elaborate and explain a little on the two GIF's your have attached.
Could you please ask what is incomprehensible?

>Wouldnt it be easier just to move the bright cap and switch to the gain pot?
Yes you can do it, you will get different sonic signature, so you can try what would you like best. In my preamps frequently I use both “bright” switches: in the source(cathode) of the first stage and by bypassing of the “gain” pot.
I try to explain. The second stage, being JFET or tube based, will have a substantial input current when being overdriven by positive half of waveform. The capacitor C3 will be charged by this current through part of R7+R1 and move the working point of the second stage to the negative gate-source voltages. This effect can be described like a small compression or sustain. If you use “bright” by bypassing of the “gain” pot this compression/sustain will not be pronounceable at high frequencies.
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Old 7th February 2004, 03:48 PM   #16
dimitri is offline dimitri  United States
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And Mr.Lund, on your site http://www.bossaboa.dk on the photo on the starting page – where are you – on the left?
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Old 7th February 2004, 09:21 PM   #17
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Yes, I must admit. I'm the guy with the guitar. Sorry, this site is only in Danish so far...;-)

- Peter
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Old 7th February 2004, 09:30 PM   #18
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Dimitri,

I get the point about the different placement of the bright switch. I never thought about it this way. Very interesting. I'll try both exsamples to see what I like the best.

It seems that you have designed quite a few guitar preamps yourself. Would you like to share some of them?

- Peter

PS: What I really like about desiging for instruments is that it's all about sound - not measurements....

If it sounds right...it is right!

- Peter
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Old 7th February 2004, 09:38 PM   #19
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Dimitri;

Concerning active guitar electronics:

I was just wondering why you brougt the two circuits of yours into this thread.

What has active guitar electronics to do with the preamp? What is the connection?

Best,

- Peter
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Old 8th February 2004, 07:38 AM   #20
dimitri is offline dimitri  United States
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The guitar amp must work in heavy conditions, say from +10C (club with bad heating) up to +60C (summer stage or when some stupid idiot put your amp on the top of tube combo ). When you open datasheet for 2N5457, you can find that drain current changes ~ 20% in that temperature range. The sound of your amp will change with temperature. I show my design which is actually the same common source JFET stage, then i/v converter with servo, no need for temperature compensation and no caps.
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