Valv-e-tizer 1.5 needs some tweaks!

[Tom Lauten]

Got my Valvetizer 1.5 boards on the weekend and built a pedal today....LOVELY! The board takes solder so well!

I did notice that the output is a bit boomy. Does anyone have any suggestions to get a wider tonal range? Could use a LOT more in the brighter range.

[WormBoy]

Which version did you build?

[Tom Lauten]

I built up the distortion version of the v1.5.

[WormBoy]

There is nothing in the schematic that suggests boominess. I have built one, but deviated quite a bit from the BOM (and used a 12ax7). You could try another tube (or different type of tube) before you start desoldering/resoldering. If there is nothing wrong in your build, you still have an option to use cathode bypass caps ... (the distortion version leaves C15/C17 open). Lower cap values will increase treble content, so you could install sockets and experiment with values between 0.1 and 1 uF.

[Tom Lauten]

I'm rocking the AX7 myself at the moment. Sockets aren't a problem. Never really fully understood cap values vs tone and where to put them etc.

Do you think trying low (?) cap values in any particular position c15 vs c17 (?) would result in ....something (?)

[WormBoy]

Yes, it will result in something  . Google for 'cathode bypass caps' and you get all you've ever wanted to know. Basically: these caps boost the gain of the tube section. Large values (say >10uF) will provide a full-range boost. Smaller values progressively boost less of the low frequencies, so you get a treble boost. More boost with higher values of cathode resistance, so the settings of the trimmers will also effect this. Personally, I would start with experimenting on C15 with smallish caps; probably most effective to boost highs early in the circuit. Of course, assuming that there is nothing wrong with your build.

[Tom Lauten]

What would you say the value range we are talking about here say, smallish to large-ish?

[WormBoy]

There's probably some math out there to calculate the exact frequencies, but my guess is that you want to be between 0.1 and 1 uF, for extreme to subtle treble boost, resp. But let your ears be the guide.

[Tom Lauten]

Thanks very much for all this help...I shall be "cap in hand" today...sorry... 

[WormBoy]

 

If you still have room for a (trim) pot .... another cool trick is to make the bass continuously adjustable. I found this in a tube-amp schematic by DvNator: http://www.chasingtone.com/dvnator/wp-content/uploads/sites/3/2013/03/Junior_Delinquent_schem_v1.jpg (look at the first tube stage). You might want to go smaller than the 0.68 uF, to get more range on the dial. I have not tried this trick myself yet, but am urging to use it in a tube pre-amp I am planning to build.