BAJA Ampeg SVT bass amplifier pedal 9v 010418  [documentation]

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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bajaman
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Post by bajaman »

One question though: is this supposed to distort very early?

remove the clamping diodes on the output ;-)
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Post by mcrowe »

I mean...I'm completely okay with it distorting where it does. Mostly curious whether I screwed something up. Good to know about removing those diodes in case I change my mind though.

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Post by jeepe »

hi, Bajaman,

thank you for this wonderful project!

what classification of the ksk117 would you recommend? GR or BL?
Idss: GR: 2.6~6.5 mA, BL: 6~14 mA
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Post by asbestosaurus »

jeepe wrote: 09 Jan 2022, 22:42 hi, Bajaman,

thank you for this wonderful project!

what classification of the ksk117 would you recommend? GR or BL?
Idss: GR: 2.6~6.5 mA, BL: 6~14 mA
not bajaman but otherwise happy to help.

because of the 100k source resistor, the 2sk117 is running at such a low current that any classification is suitable.

the differences would matter in a much higher current application, closer to Idss.

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Post by Paul_5 »

mcrowe wrote: 19 May 2021, 23:12 I mean...I'm completely okay with it distorting where it does. Mostly curious whether I screwed something up. Good to know about removing those diodes in case I change my mind though.
I dropped the value of the gain pot to something tiny (I think 5 or 10k) and compensated by increasing the gain between pins 6&7 on the output opamp stage.
The sounds in my head don't match the sounds from my amp, I guess that's why I'm here...

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I want to end up strumming some strings at the end of the day, whatever the sound

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I'm so sad that this beautiful culture (and freedom movement) is totally ephemeral
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Post by jeepe »

thank you, asbestosaurus! :)
pedal building, tracing and sharing is such a beautiful freedom movement... If only it could be viewed as a future heritage, but it really is ephemeral, as it seems

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Post by Matybigfro »

I'm eyeing this up as something to give a try as I have a Behringer BDI currently that I'm reasonably pleased with but has a bit of noise with the treble all up and lack of control of the mids. Looking into the documentation I have been wondering how similar the ever increasing number of SVT in box style pedals out there are.

I see that this and the sansamp bass driver both make use of TL072 op-amps how similar are the circuits and sounds?

I noticed that the controls exactly match those available on the Master Effects Super 300, elsewhere on their website they mentioned using jfets in their other amp in box pre-amp pedals but don't specifically mention this in relationship to this pedal. I know RoG have a whole host of pre-amp modelling circuits using jfets so I was interested to know if anyone wondering how related it might be to those circuits.

Which has left me wondering how different other popular Ampeg SVT style pedals like the Broughton SV Pre and new Origin Bassrig and how much is pedal marketing bumph.

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Post by Paul_5 »

TL072s are a JFET based opamp, so they've got the box ticked. The mids control on this makes ll the difference between the and lots of other 'SVT style' preamps.
The sounds in my head don't match the sounds from my amp, I guess that's why I'm here...

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Post by pedrocucaracha »

I love this pedal! Works like a charm, but to me the mida and 5 point switch are doing nothing…. Am I missing something? I triple-checked my build….
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Post by bajaman »

check again ;-)
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Post by pedrocucaracha »

bajaman wrote: 29 May 2022, 12:36check again ;-)
Touche.. will do, hehe! Thanks!
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Post by pedrocucaracha »

bajaman wrote: 29 May 2022, 12:36check again ;-)
Well, there's a reason why you're Bajaman and I'm just... whatever I am.

I quad-checked it, and I made a huge mistake. I feel so dumb, hahaha!! It works like a charm.

Having solved that issue, I have to say this is the most beautiful pedal I've even built. I will put it to very good use. Thanks a lot!

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Post by tuck »

Please excuse my lack of knowledge on electricity but if I substitute the 3u3 in the Mid Freq control with a polarized Tantal, where would the + leg go?

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Post by deltafred »

tuck wrote: 27 Oct 2022, 11:37 Please excuse my lack of knowledge on electricity but if I substitute the 3u3 in the Mid Freq control with a polarized Tantal, where would the + leg go?
The easiest way if it is not immediately obvious from looking at the schematic is to fit a capacitor and measure the voltage across it with a multimeter.

I would use a normal electrolytic for this as tants don't like having reverse voltage on them. Once you find the correct orientation then swap it for your polarised tant.
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Post by Paul_5 »

Would I be ok to take a feed to an active (TL072) DI circuit at the point just before the last gain stage?
Baja%20Ampeg%20SVT%20bass%20amplifier%20pedal%209v%20rev%201%20050418.gif
I’m thinking of taking a feed from in between the 2n2 and IC2b.
The sounds in my head don't match the sounds from my amp, I guess that's why I'm here...

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Post by okwestern »

I would like to build this and add an output stage to drive my headphones. Any tips on how to do this? And any good available schematics on amplification that works for headphones, and doesn't ruin the beautiful Ampeg tone?

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Post by alexdepaulo »

Good afternoon! Do you happen to have this project in PCB with printing? Thanks.

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Post by bajaman »

sorry - i do not have a pcb for this project
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Post by tuck »

Hi Bajaman,

this is now a bit embarrasing because I think I did everything right to wire a 3PDT as bright switch.
But I think I don't get the sonical function of it or I messed it up but I don't understand how.
brightswitch.jpg
brightswitch.jpg (61.01 KiB) Viewed 36168 times
Pin 8 & 9 are connected to an led.

If bright is on 2->3 and 5->6 then the sound is a tad lower in volume and slightly darker.
That should be the opposit, right?

And what would be the way to make the effect of the ultra high switch more prominient? I don't hear any difference with the 5nF capacitor.

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Post by bajaman »

Hello Tuck
The way you have wired the switch is correct BUT, it has been so long ago that i designed this pedal and upon investigation of the Ampeg SVT schematic the 220n capacitor is far too large to be effective - it should 4.7nF !
Also i would suggest changing the 330k for a 560k resistor, although the capacitor change will make the most noticeable difference ;-)
The Ultra High switch is mostly effective at low gain settings and becomes decreasingly effective at higher gain levels :-)
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ps: check my latest post in the Bass Butler thread ;-)
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