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Epic Polar Boost v1.0 

 

Manufacturers and product names are mentioned solely for circuit identification, and where applicable their trademarks are the 
property of their respective owners who are in no way associated or affiliated with the author. No cooperation or endorsement 

is implied.

 

10 

When you switch the bright switch on (

SW1B

) the resistance is cut to 1k since the switch bypasses 

R6

. So the cutoff frequency changes to:  

𝑓

𝑐

=

1

2𝜋𝑅𝐶

=

1

2𝜋 ∙ 1000 ∙ 3.3 𝑒

−9

≈ 48𝑘𝐻𝑧

 

So now the signal cuts off in the 

very high treble

 section which is almost not audible, but something 

else also changed. 

By lowering the resistance the gain of Q2 also changed! The effect is now brighter and also a bit 
louder (approx. 3db). 

By adding a tone control to the effect you can change the bandwidth of the cut off frequency. 

Mark Hammer introduced the “

Stupidly Wonderful Tone

 

Control

 (

SWTC

in 2005 which combines a 

simple adjustable RC filter with the ability to keep the gain constant. This is done in the optimized 
version of the boost by introducing 

P2

 (B50k). If you want to remain close to the original boost but 

still want to be able to change the cut off frequency, I changed 

R6

 to 22k.  

This way the 50 pot and 22k resistor in parallel give 

𝑅

𝑡

=

1

1

50000

+

1

22000

≈ 15𝑘

 which is about the same 

as 

R6

 in the original. Now the tone control gives you a sweep between 3kHz and 48kHz while not 

changing the level of boost while turning the knob! The bright switch (SW1B) will act a bit different 
than the original as is will take out R6,P2 and C5 all at once, just leaving 

R5

 in the circuit. This way 

there is no RC filter left, just a small extra boost. Changes are that high frequency interference is 
more audible when you switch 

SW1B

 on. 

If you use a jumper in 

J1

 the filter will act more like the original and will cut some volume when you 

turn it up (=cut highs). However the bright switch will function exactly as in the original. To end this 
lecture, some suggestions to make the tone control even more usable: 

Author 

R5 

R6 

P2 

C5 

fc

 min 

fc

 max 

LG 

1k 

22k 

B50k 

3n3 

2,9kHz 

48kHz 

LG 

1k 

NC 

B25k 

3n3 

1,85kHz  48kHz 

LG 

1k 

NC 

B50k 

3n3 

945 Hz 

48 kHz 

LG 

1k 

NC 

B100k 

3n3 

477 Hz 

48kHz 

F Briggs  470R 

NC 

B10k 

10n 

1,5kHz 

33,8kHz 

NC= not connected 

NB. When using J1 “jumped”, the higher P2 the bigger the 

volume drop when turned down. 

Transistors 

The original uses a 

2N5457

 as 

Q1

 and 

2SC1815

 as 

Q2

. A lot of people prefer a 

J201

 as 

Q1

 since it has 

a bit more gain and a 

2N5088

 as 

Q2

. Check the pinout of your transistors before you solder them! 

The correct pinout is printed on the PCB and insert the transistors accordingly. You can always 
experiment with other types of transistors and if you find better combinations, please let me know! 

Summary of Contents for Epic Polar Boost

Page 1: ...Epic Polar Boost Building instructions v1 0...

Page 2: ...ed 2 Table of contents PCB layout 3 Components 4 Original configuration 4 Optimized configuration 5 Build sequence 6 Drill template 7 Switch 7 Off board wiring 8 Modifications 9 Charge pump 9 Tone sec...

Page 3: ...ly for circuit identification and where applicable their trademarks are the property of their respective owners who are in no way associated or affiliated with the author No cooperation or endorsement...

Page 4: ...R7 1M 1 metalfilm C8 100u Electrolytic 25V R8 10k 1 metalfilm C9 100n SMF MKT Wima R9 47k 1 metalfilm C10 10u Electrolytic 25V R10 100R 1 metalfilm C11 47u Electrolytic 25V R11 33k 1 metalfilm C12 47...

Page 5: ...7 1M 1 metalfilm C8 100u Electrolytic 25V R8 3k3 1 metalfilm C9 100n SMF MKT Wima R9 NC C10 10u Electrolytic 25V R10 Jump C11 47u Electrolytic 25V R11 4k7 1 metalfilm C12 100u Electrolytic 25V R12 390...

Page 6: ...The original version puts a 8k2 resistor in VR1 For this there are 2 special pads X and Y marked on the PCB which will fit this resistor Next comes the diodes If you want to experiment with another t...

Page 7: ...ll be the status LEDs Hammond 1590B case or similar in your favorite color This case will fit tightly and leaves no room for error If you need more room you could consider using a Hammond 1590N1 125B...

Page 8: ...istors You can change the value depending on the type of LED you use but 4k7 is safe enough for almost all LEDs 9V Note that the diagram is using star wiring for the ground connection The sleeve of th...

Page 9: ...s You could also change D1 back to a 1N4148 like the original D1 has no tonal function so it would be for optics purism only Tone section This is the interesting part and yes we are going to get a bit...

Page 10: ...bout the same as R6 in the original Now the tone control gives you a sweep between 3kHz and 48kHz while not changing the level of boost while turning the knob The bright switch SW1B will act a bit dif...

Page 11: ...bs to max boost and when applicable volume and tone and turn VR1 until you get to the spot that you like best as maximum boost This is up to personal taste and I always prefer to set it by ear but you...

Page 12: ...t you oriented the capacitors IC s transistors and diodes the right way SMF MKT and ceramic capacitors as well as resistors do not need to be oriented A likely sign of incorrect capacitors and or orie...

Page 13: ...ames are mentioned solely for circuit identification and where applicable their trademarks are the property of their respective owners who are in no way associated or affiliated with the author No coo...

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