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Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 06 Apr 2019, 12:03
by bajaman
jhergonz wrote:bajaman wrote:zyu wrote:drd wrote:Hi Baja,
A great one, thanks a lot! Some questions though... Is there a reason you made the input buffer out of a jfet instead of using IC1b for this? Also I'm thinking about making this one the preamp of a Class D poweramp I've seen on ebay. I would use a switching powersupply for it (again from the evilbay) and those have +/-15V outputs too. Do you think I could adapt this one to bipolar powersupply? I think I would only need to remove the vref connections from the inputs of the opamps and change all other vref connections to ground instead. And I wouldn't need a vref at all in that case I guess... Or am I wrong here? Thanks!
By the way, the question is really interesting. I also wonder why not use IC1b for the buffer.
Very interesting to know the thoughts of the author.
Simple answer: because IC1b is already being used as a low impedance vbias source. However most any small signal njfet could be used as the input buffer, or you could simply omit using the buffer at all if you like. The 2SK117 100k source resistor could be reduced as low as 10k if desired. If using a bipolar power supply (+/- 15v), yes your assumption is correct.
cheers
bajaman
it provides a very low impedance path to ground - isolates the many stages to avoid interaction
I think this is a perfect timing to ask this... What is the advantage of having a buffer in vref? Or low impedance vref?
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 06 Apr 2019, 12:06
by thetragichero
keeps Vref at a constant point, whereas with a simple voltage divider that midpoint can go up or down depending on the demand of the rest of the circuit - that's at least what I've read
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 06 Apr 2019, 16:39
by zyu
I have one more question.
I understand it is true that at the output of the IC1A there is always a bundle of 22n 22n 6.8k and 15k 15k 22n?
Is this link always parallel to the gain resistor?
That is, this circuit always affects the tone?
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 30 May 2019, 07:25
by tommymariotti
Somebody tried to run it with 18V? It works better than 9v?
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 09 Jan 2020, 23:34
by Iosutxoo
Hello, I am a beginner in the construction of pedals, and besides that I am a bass player.
I am not yet able to read these schemes, ...
I still ask too much
Could you make a PCB in this format?
Thx.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 10 Jan 2020, 04:20
by soulsonic
Iosutxoo wrote:Hello, I am a beginner in the construction of pedals, and besides that I am a bass player.
I am not yet able to read these schemes, ...
You should use the stripboard/vero layout posted at the beginning of this thread. It is very easy for beginners.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 10 Jan 2020, 11:17
by Iosutxoo
Yes, that stripboard could solve it, although I usually do the pcb with a face plate and acid.
the parts not vero , is where I have more problem.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 10 Jan 2020, 19:42
by soulsonic
Iosutxoo wrote:
the parts not vero , is where I have more problem.
Learning to read the schematics should be no problem. It takes the average person about 5 minutes to learn and understand. It's only a matter of knowing what the symbols mean and how to know the way they are connected. There's nothing the least bit esoteric or hidden about it. You need this skill. I mean it in all sincerity when I say you can learn it in about 5 minutes.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 16 Nov 2020, 17:43
by x-tn
bajaman wrote: ↑05 Apr 2018, 06:48
...
and the updated parts not on vero
Looks like the same file from the first post is attached by mistake.
I believe it should look like this
Maybe a moderator can edit the second post if bajaman approves.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 27 Nov 2020, 14:36
by JiM
It means that it will be very stable, over a wide range of current drawn.
On the contrary with a simple resistor divider, the actual bias voltage will depend on the current consumption at this point. You can look at it as a (possibly variable) impedance in parallel with the lower resistor, changing de divider ratio.
An opamp will provide the bias voltage from the main power rails, with larger current available, and the divider only serves as a reference here with very little current drawn.
BAJA Ampeg SVT bass amplifier pedal 9v 010418: weak output
Posted: 23 Feb 2021, 19:54
by R2Bass
Hi! I am new in this forum (but not new in diy fx building) and the first thing I want to do is thank @bajaman for posting this and other incredible contributions for this community.
I built this circuit on a veroboard, without success: The output sound is weak and distorted, independently of the position of all pots and switches. The only pot that do something is Level...
I reviewed several times the vero and wiring and everything seems OK. Nevertheless, I noticed that a 2u2 capacitor placed between the positive input of IC2b and v_bias in the schematic, is missing in the vero. Could it be the cause of my problem? Any suggestion is welcome.
Thank you in advance!
and hello everyone in this wondeful community!
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 23 Feb 2021, 21:58
by The G
That is a 2n2 (2.2 nanofarads) capacitor. It is part of a bandpass filter with ~720Hz as center frequency, which means that the further from 720Hz are the frequencies of the filter input signal, the harder are they attenuated.
Now, change it with a 2u2 (2.2 microfarads) capacitor. The center frequency moves to ~23Hz. As you can imagine, there's not much audio signal passing to the output.
So, first thing I'd do would be to check that I really have the same values as in the schematic.
If everything checks,
audio probe the circuit and you'll be able to locate the problem.
One can play with the nice filter calculator on the
Okawa Electric Design's site, look at the bottom of the page (
there are heaps of calculators there). I'm not affiliated in any way with them.
Also, we have a forum dedicated to debugging and troubleshooting, try to use it. Reference in your post the schematic you used and the details of your build, so potential helpers would not be forced to hunt for information.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 23 Feb 2021, 22:14
by R2Bass
Sorry, my mistake in the value. I meant that 2n2 capacitor (not 2u2). I understand that it is part of a bandpass filter.
What strikes me is that it is in the schematic but not in the veroboard layout. Indeed, I checked the photos in the first post by bajaman and I can't find this capacitor there.
I will try to add this capacitor in my build and check if the problem is solved.
Thanks for the links. They seem nice to have handy.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 23 Feb 2021, 22:25
by The G
The absence of that capacitor would make the signal stronger, not weaker, so the problem is most likely elsewhere.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418: weak output
Posted: 24 Feb 2021, 22:48
by R2Bass
R2Bass wrote: ↑23 Feb 2021, 19:54
Hi! I am new in this forum (but not new in diy fx building) and the first thing I want to do is thank @bajaman for posting this and other incredible contributions for this community.
I built this circuit on a veroboard, without success: The output sound is weak and distorted, independently of the position of all pots and switches. The only pot that do something is Level...
I reviewed several times the vero and wiring and everything seems OK. Nevertheless, I noticed that a 2u2 capacitor placed between the positive input of IC2b and v_bias in the schematic, is missing in the vero. Could it be the cause of my problem? Any suggestion is welcome.
Thank you in advance!
and hello everyone in this wondeful community!
Problem solved. A capacitor was in a wrong place. Thanks for your help.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 06 May 2021, 23:48
by mcrowe
Apologies for bumping an old thread, but I'm embarking on this build, and as I always do, I screwed something up on my Mouser order. This time I accidentally bought the SMD version of the TL062 instead of the through-hole. Tried to make a go of soldering leads onto the pins so I could use it anyway, but ended up breaking one clean off. Anyway...I was poking around the junk pile and found an old Ibanez pedal with a Toshiba TA75558P in it. Any thoughts on what would happen if I put that in place of the TL062? I'll probably try it just to see, at least until I have an excuse to put together another Mouser order.
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 07 May 2021, 06:42
by R2Bass
mcrowe wrote: ↑06 May 2021, 23:48
Apologies for bumping an old thread, but I'm embarking on this build, and as I always do, I screwed something up on my Mouser order. This time I accidentally bought the SMD version of the TL062 instead of the through-hole. Tried to make a go of soldering leads onto the pins so I could use it anyway, but ended up breaking one clean off. Anyway...I was poking around the junk pile and found an old Ibanez pedal with a Toshiba TA75558P in it. Any thoughts on what would happen if I put that in place of the TL062? I'll probably try it just to see, at least until I have an excuse to put together another Mouser order.
I have never tried the TA75558P but it is a dual op amp with the same pinout than TL062, so I bet it will work. In my build, I used some TLC2262 because I didn't have TL062/72 in that moment and it was OK. Good luck!
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 08 May 2021, 15:00
by The G
One way to make an adapter at moment's notice is this (
DIY Guitar Stuff - SOIC Adapter for the monetarily impaired, be sure to read the original article):
- SOIC_ADAPTER_socket-trimed2.jpg (16.12 KiB) Viewed 2765 times
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 10 May 2021, 07:38
by JiM
Re: BAJA Ampeg SVT bass amplifier pedal 9v 010418
Posted: 19 May 2021, 02:34
by mcrowe
I just powered this pedal up for a preliminary test, and so far I'm impressed. Even just through a cruddy solid state amp, it's instantly recognizable as *that* sound. I have a couple of mistakes to fix and some functions to investigate that don't seem to be working right, but so far so good. One question though: is this supposed to distort very early? I start to hear distortion once the gain dial hits 9:00, and I'm wondering if that's intentional or a side effect of my opamp substitution.
