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Messages - zyggurat

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Preamps and Effects / Re: An universal guitar preamp
« on: January 27, 2009, 08:11:02 PM »
Awesome! That´s what I´ve been looking for ! It´s really UNIVERSAL  8| I´ve got only one question  - what opamps have you used ???

Preamps and Effects / Re: Help with making of a preamp
« on: September 26, 2007, 01:33:04 PM »
In my opinion, a parallel loop (which the "mixing" circuit mostly is) is not that great as one would initially think: It may turn into an oscillator if the effect in the loop causes enough phase shift, it is also less effective with equalizing effects.

Besides that issue, the circuit looks OK to me (assuming the circuit feeding it has proper output signal levels and buffering properties). Can you provide a brief description of what seems to be the problem?

I decided to rebuild fx loop to a simple fx loop consisting of two opamp buffers that you posted in this topic

but now I ´ve got a problem: preamp oscillates at frequency approx. 1khz - I hear it from the speaker.
After fx loop there´s low pass filter with gain=20 and another non-inverting opamp -I ´ve tried to change it´s gain but it doesn´t affect the oscillations. I haven´t got an idea where´s the problem. :(

Preamps and Effects / Re: Help with making of a preamp
« on: September 24, 2007, 01:52:55 PM »
My preamp is not complete yet, tonemender section works well, but I ´ve got some problems with effect loop section - I decided to use marshall valvestate effect loop:

I can´t find out what´s the problem , my pcb is ok and schematic looks ok too...

TO blindsjc:

If you connect first opamp as non inverting amplifier you´ll get more gain - gain of voltage follower is 1, but I think it doesn´t affect the tone too much.

Preamps and Effects / Re: Help with making of a preamp
« on: May 25, 2007, 03:20:51 PM »
Here´s a schematic of simple low pass filter, that I´m looking forward to use: 

Two resistors "R" and capacitors "C" set the cutoff frequency, but what I´ve to change in schematic if I want to adjust frequency by a pot? Is there need to substitute that two resistors by a double pot ? I think this is not very good solution ... Anyone got an idea?

Anyone has got sound samples of this circuit?

Preamps and Effects / Re: Need more sustain in my distortion
« on: March 22, 2007, 06:26:11 PM »
Post a sound sample, if you can  :)

Preamps and Effects / Re: Help with making of a preamp
« on: March 04, 2007, 07:33:45 AM »
Is it better to use active or passive low pass filter? I´d like to place it after tonemender, because freq. response of my speaker ends at 20kHz and I want to remove those horrible highs from 5kHz and higher. I know how to design it but don ´t know which type is better to use.

Preamps and Effects / Re: Help with making of a preamp
« on: February 27, 2007, 02:48:30 PM »
I ´ve got one question else, if a tonemender will be at input of this preamp, how I should design input section (I mean first opamp in tonemender wired as volt. follower), should I take a look of some ss preamp schematics and use it´s input buffer? How the design of the input buffer affect sound of preamp? And at last, how high should be input impedance of my preamp? I´ve read that manufacturers use something about 200 - 500 kOhms , but will it be bad if I use higher value , for example 1MOhm? Thanks for replies. ;)

Preamps and Effects / Re: Help with making of a preamp
« on: February 27, 2007, 10:34:03 AM »
Thanks a lot for your help.

Preamps and Effects / Help with making of a preamp
« on: February 26, 2007, 04:35:23 PM »
Hello. I ´m going to make my own preamp that ´ll use TONEMENDER (tone control) and FX loop called "splitter blend" from
The preamp will look like this:

Input  -> Tonemender -> FX loop -> Output (to poweramp)

1.In schematic of tonemender, why is the first opamp wired as a voltage follower? Isn´t  there any gain needed for input of my preamp? Can (should) I wire this as a normally non-inverting opamp to get bit of gain?

2.The "splitter-blend" is dual fx loop , but I´m going to use only the RED part of that loop, so I´ll get single loop. Is that right? Will it work?
Another question about this fx loop is same as about the tonemender, in this RED part of fx loop there are two opamps, both wired as voltage followers.

3.If I rewire this two circuits to feed they from dual power supply, can I feed poweramp from the single PS? If yes, how should I connect their grounds together? 0V (gnd) of dual PS with - (0V) of single PS ?

4.I ´ve read somewhere of adding a cap to paralel with volume pot, to avoid highs or bass loss at low volumes, is one cap enough for that ? How can I calculate it´s value?

Thanks for all replies. ;)

Amplifier Discussion / Re: Dual mono = dual transformer?
« on: February 06, 2007, 12:20:04 PM »
See the first figure in the article.

I think there is no need to use two rectifiers and double amount of filter caps, you only have to use caps with double rate of cappacitance and only one rectifier, but  with double current rate , so fo example if you use 3A rectifier and caps with total amount of capacitance 20000uF, for dual amp you´ve got to use at least 6A rectifier and total of 40000uF capacitance for filtering...
Good luck  ;)

Amplifier Discussion / Re: Dual mono = dual transformer?
« on: February 05, 2007, 05:24:40 PM »

LM3886 is a 70W amplifier IC, am I right?
So that means you need approximately 140VA transformer to run it , that´s for dual mono 2x140VA=280VA of power altogether. So you can split that power among 2 amps, on both amps there ´ll be same supply voltage in both amps as in the PSU , but  it´ll drain double current from the PSU. So it´s unnecessary to use 2 transformers when that one is powerful enough.

Sorry for my bad english, I still study it  0:)
By the way this forum is great, long time I looked for something like this...

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