Two versions of SS guitar power amplifiers

Original effect designs complete with schematics, layouts and instructions. Freely contributed by members or found in printed or online publications. Cannot be used for commercial purposes without consent of the respective owners of the copyright.
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KMG
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Post by KMG »

I would want to propose to your attention two versions of SS guitar power amplifiers 40W and 90W
In the proposed versions of the amplifiers used lateral mosfets because they have the transfer and output characteristics almost identical to pentodes that allows as close to a tube sound. They also have a negative drain current dependence on temperature, which eliminates the need for thermal stabilization. The amplifier is built on the classic "tube" schematics - differential stage and further push-pull output stage that drives the output transformer.
40 W (Primary coil impedance Ra-a = 200 ohms)
Schematics
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PCB (ready to transfer)
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Upper side assembly
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Bottom side assembly
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Assembled board
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Example of transformer windings for the 20x60 core:
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The windings 153 (0,6 mm) - 91 (0,6 mm) - 37 (0,6 mm) - 54 (0,6 mm) - 153 (0,6 mm) - 91 (0,6 mm) - 37 (0,6 mm) -- 54 (0,6 mm) - 153 (0,6 mm) - 91 (0,6 mm) - 37 (0,6 mm) - 54 (0,6 mm) - 153 (0,6 mm). 153 - the primary, all in series. Secondary parallel. 91 - 4 ohm, 91+37 - 8 ohms, 91 +37 +54 - 16 Ohm
Mouted on chassis
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90 W (Primary coil impedance Ra-a = 80 ohms)
Schematics
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PCB (ready to transfer)
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Upper side assembly
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Bottom side assembly
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Assembled board
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example of transformer windings for the 20x30 O-core:
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Each coil 232 (0,7 mm) - 217 (1,0 mm) - 90 (0,9 mm) - 127 (0,7 mm) - 232 (0,7 mm). 232 - the primary, all in series. Secondary parallel. 217 - 4 Ohms, 217+90 - 8 ohms, 217+90+127 - 16 Ohm

Assembled in 2U rack with three channel fet version of Ecstasy
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Some comments to the schematics:
Potentiometer "Symmetry" used to set equal amplitudes of signal halves.
Resistors R4, R7 (for 40 watts) and R5, R8 (for 90 watts) determine the sensitivity of the amplifier input. If they decrease the sensitivity increases and vice versa.
Resistor R25 (for 40 watts) and R1 (for 90 W) can be connected to the negative feedback from the output transformer with adjustable Presence. You only need to take into account that the resistance of the resistor 1,6 kOhm that is 3 times less than usual in the tube circuits (4,7 kOhm). To get the same frequency response capacitor in series with the control you need to increase by 3 times.
Example of "Presence" and "Depth" schematics:
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Output signal limitation
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meffcio
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Post by meffcio »

That's fantastic, even because changing the speaker cab won't limit/boost the nominal power! :D
But um... +/- 80V? Kinda big, but still lower than for valves. But winding transformers can be a pain in the a**...
Sorry, just thinking loudly..

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gnognofasciani
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Post by gnognofasciani »

Great project!
So great that I could give it a try! How many A should the transformer be? Does the mosfet have to be matched somehow?

Thanks again for your great contribution! :applause:
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tictac
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Post by tictac »

Do you have a recommended preamp to go along with this power amp?

Do you make PCB's for your projects?

Thanks,

TT

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KMG
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Post by KMG »

+/- 80V
Not the bipolar 2x80V, single 80V or 75V supply.
But winding transformers can be a pain in the a**...
Yes, this is the main disadvantage of the project.
You have to buld output transformer by your own hands, because there are no transformers with matching primary coil impedance.
Does the mosfet have to be matched somehow?
It`s better to use matched pairs, but latheral mosfets has less difference of characteristics. Randomly choosen pair gives difference about 5 mA at 100 mA of initial current.
Do you have a recommended preamp to go along with this power amp
I tested this amps with many different preamps tube and fet based.
Do you make PCB's for your projects?
In first post I place links to ready to transfer PDF`s for Laser-Iron technology.
Initially PCB`s designed in Ultiboard. If anyione intrested in this, I can upload Ultiboard files too.
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gnognofasciani
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Post by gnognofasciani »

What about Amperage or Wattage of the transformers?

Thanks again :thumbsup
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KMG
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Post by KMG »

Efficiency of amplifier at full power is about 60%, so the best choice for power transformer is 2x of output power.
For output trnsformer calculation you can use one of the programs for tramsformer calculation for tube power amps.
Simply enter the corresponding primary coil impedance. All other parameters are the same as for the transformer for tube amp.
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file1
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Post by file1 »

Dear All,

I want to build 90W PA version , but I have a huge problem with output transformer. Plase could somebody provide me some more information about it? Link on internet where it could be bought also can be usefull. Does it someone tried to build it with EI core and could provide parameters for 90W version? Which type of tpk-190, exactly could be used for rewinding ? Thank you in advance, Igor

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