Silent tuner with boost (solved)

[Michael68]

Hi all,

I am new in the forum and bought a Silent Tuner kit.
I read that it has a gain x2 by default and it is mentioned that it can be changed, especially by using a pot that allows for a « boost » feature.
is anyone did that modification and if so what are the right value for the pot and the resistor C4, R8 and R7 ?

many thanks.

[Playsforfun]

Welcome Michael68. Glad to help. So in a nut shell what is going on in this case is that the gain of the second half of the Opamp is set by the relationship of the values of R7 and R8. C4 is provided for a bit of frequency manipulation fun with R8. The math formula is provided for the gain calculation. Keep note of it for the next however many years you plan to build these circuits. It’s important. Keeping it simple today, if you keep R8 and C4 as is, and increase the value of R7 you will increase the gain. Using the example given for increasing R7 to 220K for a gain of 3.2, what if you substituted that 220K for a 250K pot used as a variable resistor. So if you wire the pot with lugs 1 and 2 soldered to the pads for R7, you will create a variable gain control. Lug 3 can be connected to lug 2 on the pot. Let us know how you like it. Cheers

Let me add to Barry that this build doc has several mistakes in it, making the modifications hard to follow, so an update would be truly appreciated.

[Michael68]

Thanks! I will try this out and let you know how it goes.
Can we imagine to have a switch also that when off it goes to unity gain and when engaged with have this boost activated together with the variable resistor ? That would be pretty cool.
I am building up a full integrated pedalboard with several pedals including that one, the TwEQ, Cbuffer (that i already install on a cry baby wha) and some other pedals that I plan to rehouse (tube screamer, tube driver, large beaver triangle) – a project that will last this year ! So more to come

[Playsforfun]

Well you could turn it into this:

which just switches in and out the variable gain with the same values as above. Given that you have the gain calculation on the build doc, you can probably find just the right gain value for you by trying combinations of pots and resistors to ground. C4 was omitted for convenience.

[Michael68]

Hi Barry.

thanks again for you input few months ago.
I finally went on with the builting and follow your advice for boost. I used a 3pdt switch instead and add a LED that should show if the boost is on/off.
unfortunately this doesn’t work and no boost/influence of the pot is heard:

I attach few pictures of you can quickly figure out something, thanks

 

[Playsforfun]

I see some stray strands and slag and possible bridge within your soldering. I can’t distinguish your pot wiring to see if it is wired up as a variable resistor, where you would tie lug two with one of the outside lugs. And I wonder what happened to R8. R8 cannot be omitted. If you use my drawing and a footswitch then you will have to find a way to add R8 between the switch and ground as shown(or between the switch and C4 if using C4). With a higher resistance at R7 than R8 there will be gain as per the build doc.

As a note, the build doc references R4 and R5 within the Gain Mods paragraph, but should say R7 and R8. Also the section for R4 refences R1 mistakenly. R1 is necessary.

[Barry]

Thanks Playsforfun, I fixed the typo and replaced the pdf file.

If you download it again be sure to refresh first so you do not get a cached copy.

[Michael68]

Thank you playsforfun ! Much appreciated.
Indeed some connections are strange, will work on it.

not clear to me is where the C4 should be connected, still in the pcb ? Between R8 and ground ?
of not much to ask can you update your scheme ?

thanks.

 

[Playsforfun]

No problem. To simplify, just populate the board with R8 and C4 and leave your switch and the pot as is after you confirm they are free of defects. Ultimately you are just replacing R7 with a switch. It selects either unity gain or the gain pot, along with an led to light the way :). A 2-Knob Job board would get the work done nice and neatly.

FYI. If you populated R8 and jumpered C4 you would be following my drawing.

As a note, C4 eliminates bass notes to ground that we can’t hear. R8 at 100K and C4 at 220n will yield a 7 Hz. cutoff frequency.

Enjoy!

[Michael68]

Hi.
I worked on it and all is fine by now. Thank you for you support.

Mick.

 

[Michael68]

Hi all,

just a follow up question, when I activate/deactivate the boost with the switch, I have a huge pop that can be heard.
any idea on what I can do to get rid of it ?

thanks again and have a great day.

[Playsforfun]

Alot of times the led is the reason for the pop. See if it goes away without the led being lit while activating the boost.

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