Good evening to everyone,
I'm a beginner in the diy world but with a friend of mine (he's not a begineer) we decided to build this famous schematic of a guitar preamplifier :
As probably you've just noted, the fourth transistor from the left ( that in the right of the scheme) is without name. Do you think is of the type of the others ? Is the input of this transistor to be connected to the near 1M resistances ? I see cables crossing.
Thank you in advance
I'm a beginner in the diy world but with a friend of mine (he's not a begineer) we decided to build this famous schematic of a guitar preamplifier :
As probably you've just noted, the fourth transistor from the left ( that in the right of the scheme) is without name. Do you think is of the type of the others ? Is the input of this transistor to be connected to the near 1M resistances ? I see cables crossing.
Thank you in advance
I would think it is a typo and they forgot to add another of the same type. Also the mid pot is probably 20k.
So, do you recommend to use 20k for the mid potentiometer ? And please, what about the power supply ? A common 24 V dc is well fitted for this preamp or is it incline to introduce noise (i.e. ripple voltage noise) ?
Both the mid pot and presence (really treble cut) pots are 2k.
Randall means scooped, almost no mids sound; 20k will give you way too much mids and a nasal sound.
Marshall uses 25k mid, but together with 250k and 1M pots, here they are 50k.
Randall means scooped, almost no mids sound; 20k will give you way too much mids and a nasal sound.
Marshall uses 25k mid, but together with 250k and 1M pots, here they are 50k.
Mumble, so i think i'll go with 2k for the mid, thank you. Do you know what transistor can i use to replace the 2n5484 ? I need a transistor that is currently on sale.
Apparently only SMD versions are available of 5484 (MMBF5484) in an SOT-23 package.
http://it.farnell.com/search?st=mmbf5484
Farnell.it recommends a Fairchild J105 as a substitute:
http://it.farnell.com/fairchild-sem...dp/1471024?rpsku=rel3:2N5484E3&isexcsku=false
http://it.farnell.com/search?st=mmbf5484
Farnell.it recommends a Fairchild J105 as a substitute:
http://it.farnell.com/fairchild-sem...dp/1471024?rpsku=rel3:2N5484E3&isexcsku=false
I'll try researching it , Sir. My last doubt is about what type of power supply use, a power supply to buy from internet and not to build myself. I've read somewhat about noise induced by ripple voltage. Sorry, also i cannot find on internet a 4V zener.
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2v zeeners in series should allso sortha give you that.
allso i think it should work with 4.3 volt zeeners, those are more of a common sight...
as for the transistors...
2SK246 my corss-reference sheet says it should do it,
but i would wait for someone else to confirm it too.
as for powersupply..
i sortha think it would be perfectly okay to use 2x9v battery in series.
i fail to see why it should not work.
allso i think it should work with 4.3 volt zeeners, those are more of a common sight...
as for the transistors...
2SK246 my corss-reference sheet says it should do it,
but i would wait for someone else to confirm it too.
as for powersupply..
i sortha think it would be perfectly okay to use 2x9v battery in series.
i fail to see why it should not work.
Thank you for the trick. I found only 2V zener with 0.5 watt max power allowed ;3.9 V 5 watt zener (rare) or the more common 0.5 watt 3.9 V zener, i cannot choose beetwen them because i don't know what power will flow in that part of the circuit.
Fortunately finally i found a lot of 2n5484.
Excuse me, but in that manner i get 28 V dc,or not?
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18 volts you get, and i don't see why the circuit need 24.
maybe i'm missing somethng, but it may run properly even form 1 single 9 volt battery.
0.5 watt 3.9 V zener, i would give that a shot, i did not d any calculation but i fail to see why would it require more powerhandling than that.
maybe i'm missing somethng, but it may run properly even form 1 single 9 volt battery.
0.5 watt 3.9 V zener, i would give that a shot, i did not d any calculation but i fail to see why would it require more powerhandling than that.
Q4 is NOT critical. Any JFET is fine. Use another 2N5484.
The Gate has to be connected to the two 1Meg and the 0.005u, otherwise it won't work.
25V or 24V supply is utterly indifferent.
Power demand is 3mA. Two or three 9V (18V or 27V)will run many many hours, hum-free, and would be my choice for initial tests.
> it may run properly even form 1 single 9 volt battery.
It has no bias adjust. When the supply is not-large compared to the JFET threshold voltage, it tends to cut-off. The image does not say what the biases should be. So get too far from design voltage and it will work crappy, and you won't know why, and I sense that Rob is not yet seasoned enough to know what to do from there.
2N5484 is a very old type-number. Can you even get them today? (Edit... nevermind.)
3.9V Zener is same-as 4V for all practical purpose. Take 3.3V or 4.7V if that's all you can score. You want some more than 0.6V (the 1N914 breakdown) but some less than 10V (where the JFETs will clip). Power rating is unimportant (>0.01W).
> mid pot is probably 20k.
For 250K-500K Bass/Treb pots, yes. Here all impedances are scaled-down from Fender tube-amp custom. We need something with good pull-down on the 4.7K "slope" resistor, to make space for the Bass and Treb to put-back. 20K is not much pull-down. 0K-2K is more reasonable. 5K Audio would also be an interesting choice, since the "5" value of around 1K is similar in scale to the fixed 6.8K or 15K used in Fenders without a Mid-knob.
The Gate has to be connected to the two 1Meg and the 0.005u, otherwise it won't work.
25V or 24V supply is utterly indifferent.
Power demand is 3mA. Two or three 9V (18V or 27V)will run many many hours, hum-free, and would be my choice for initial tests.
> it may run properly even form 1 single 9 volt battery.
It has no bias adjust. When the supply is not-large compared to the JFET threshold voltage, it tends to cut-off. The image does not say what the biases should be. So get too far from design voltage and it will work crappy, and you won't know why, and I sense that Rob is not yet seasoned enough to know what to do from there.
2N5484 is a very old type-number. Can you even get them today? (Edit... nevermind.)
3.9V Zener is same-as 4V for all practical purpose. Take 3.3V or 4.7V if that's all you can score. You want some more than 0.6V (the 1N914 breakdown) but some less than 10V (where the JFETs will clip). Power rating is unimportant (>0.01W).
> mid pot is probably 20k.
For 250K-500K Bass/Treb pots, yes. Here all impedances are scaled-down from Fender tube-amp custom. We need something with good pull-down on the 4.7K "slope" resistor, to make space for the Bass and Treb to put-back. 20K is not much pull-down. 0K-2K is more reasonable. 5K Audio would also be an interesting choice, since the "5" value of around 1K is similar in scale to the fixed 6.8K or 15K used in Fenders without a Mid-knob.
Thank you, the 2n5484 is scarce on any electronic internet store but i found a lot of them from a private vendor. How do you know current an voltage inside the circuit so fast ? Pspice or a lot of experience ? And finally, i wish to insert also a led to indicate the on/off state of the sustain/boost switch and a led for the on/off state of the main supply, where I have to put them? I think in series whit the associated switch, but for the sustain/boost case the led will drain current and provide a voltage drop so it will modify the circuit.
The latter, though you don't need a lot.
Some clues: that's a small-signal JFET, which can only supply a few mA of current at most. A fairly small supply voltage. Source resistor value is thousands of ohms (meaning small currents). Coupling capacitor not big enough to flow large currents.
-Gnobuddy
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