The Vox AC15C1 is their reasonably priced ($800) current production 15W circuit board based version and I
finally found a schematic for it here: I'll also try to attach the .pdf in case that source is lost.
https://www.tdpri.com/attachments/ac15c1-schematics-rev-2-pdf.291408/
Posted in this thread: https://www.tdpri.com/threads/vox-ac15c1-no-sound.570181/
There's at least one error in the reverb driver, perhaps more but overall a good job, by inkomodo.dragon
not sure who this is or if they are on here or not.
I've looked at the vintage 60s AC15 and thought that the Tremolo is way too complicated and it
would be a major cost savings to make it solid state which they've done in this design.
The Reverb driver and recovery is done with OP amps for another cost savings.
There's one OP amp in the main signal path that it looks like there's no need for, or it could at least
be moved so that it is in the Reverb path only.
Here's a discussion about this amp including some mods:
Remove the 330K in front of the volume pot in the Normal channel.
Change the tone stack values to those used in the JMI version.
He does one more that adds a "mid shift" switch but not sure how that's done:
finally found a schematic for it here: I'll also try to attach the .pdf in case that source is lost.
https://www.tdpri.com/attachments/ac15c1-schematics-rev-2-pdf.291408/
Posted in this thread: https://www.tdpri.com/threads/vox-ac15c1-no-sound.570181/
There's at least one error in the reverb driver, perhaps more but overall a good job, by inkomodo.dragon
not sure who this is or if they are on here or not.
I've looked at the vintage 60s AC15 and thought that the Tremolo is way too complicated and it
would be a major cost savings to make it solid state which they've done in this design.
The Reverb driver and recovery is done with OP amps for another cost savings.
There's one OP amp in the main signal path that it looks like there's no need for, or it could at least
be moved so that it is in the Reverb path only.
Here's a discussion about this amp including some mods:
Remove the 330K in front of the volume pot in the Normal channel.
Change the tone stack values to those used in the JMI version.
He does one more that adds a "mid shift" switch but not sure how that's done:
Last edited:
This schematic has a switch in the tone stack and it is called "Mid Shift" in the text:
http://www.runoffgroove.com/tonemender.html
http://www.runoffgroove.com/tonemender.html
The NJM2147D is a very high voltage OP amp rated for +/-30V supplies but is no longer available (NLA).
Does anyone know what the zener voltage is in the power supply for the OP amp rails in this thing?
Does anyone know what the zener voltage is in the power supply for the OP amp rails in this thing?
Reverb Drive redrawn with correction and signal flow left to right, ground current down:
Note that feedback is taken from 47R in ground path of tank.
Note that feedback is taken from 47R in ground path of tank.
It says that the time limit to edit the last post has expired.
I forgot R30 330K from the output buss to U1B neg input in the previous post.
I forgot R30 330K from the output buss to U1B neg input in the previous post.
Thanks for the schematic! Can you explain to me how the tremolo works? I'm trying to design a pedal version of it. What's the VCC going into the circuit? Where are the input and output? What's the voltage of B+2? Is Q2 only there for switching purposes?
@artofharmony Sorry I don't come on here often.
You need to look at the full schematic, in the .pdf and for the FET MF1.
First notice that the circuit connection C goes to the grid bias of the output tubes indicating
that this is the bias shift type of tremolo. The output stage is cathode biased but it is still
possible to shift the bias by altering the bias voltage on the grids.
MF1 the LND150 is a phase shift oscillator with the phase shift provided by the Rs and Cs in
front of the gate. B+2 has and RC filter and then a 100K to the drain of the FET, just as with
a 12AX7. The output is AC coupled (C47) to the depth pot.
Q2 shorts the DC bias voltage across R69 in order to stop the oscillation.
You need to look at the full schematic, in the .pdf and for the FET MF1.
First notice that the circuit connection C goes to the grid bias of the output tubes indicating
that this is the bias shift type of tremolo. The output stage is cathode biased but it is still
possible to shift the bias by altering the bias voltage on the grids.
MF1 the LND150 is a phase shift oscillator with the phase shift provided by the Rs and Cs in
front of the gate. B+2 has and RC filter and then a 100K to the drain of the FET, just as with
a 12AX7. The output is AC coupled (C47) to the depth pot.
Q2 shorts the DC bias voltage across R69 in order to stop the oscillation.
Revisiting this and looking at the reverb driver they are obviously using multiple small OP amps
to try to serve as a power amp and these are a high voltage type for +/-30V that are no longer
available. So, why not just use a single power amp chip such as the LM1875 which is in a TO220
package and also has a +/-30V rating. This came up quickly with a search, I'm not up on these
and not sure if there's a better one.
to try to serve as a power amp and these are a high voltage type for +/-30V that are no longer
available. So, why not just use a single power amp chip such as the LM1875 which is in a TO220
package and also has a +/-30V rating. This came up quickly with a search, I'm not up on these
and not sure if there's a better one.
Nah. That would be too easy.
I have not done more than see it work, got pushed to the back burner for a while.
Link doesn't work for me, what is the main site for this or is it your hard drive?