Xotic - AC Booster [ goop-alarm ]  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
cAMPus
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Post by cAMPus »

... eeeeehm forgot to say:
it includes R.G.Keens mosfet polarity protection and millenium bypass

cAMPus
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Post by cAMPus »

... and another pcb layout switchable AC <> RC Booster - not verified yet !!!

Use a 6P2T rotary switch for switchen AC <> RC

Both layouts can be used as a model for a perfboard layout.

U.

cAMPus
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Post by cAMPus »

....
Attachments
xotic-ac-switch-to-rc-booster_schematic_v1.png
xotic-ac-switch-to-rc-booster_layout_v1.png

cAMPus
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Post by cAMPus »

... the zipped eagle files cause someone asked for
Attachments
xotic-ac-switch-to-rc-booster_v1.zip
(61.24 KiB) Downloaded 219 times
xotic-ac-or-rc-booster.zip
(57.8 KiB) Downloaded 204 times

sjwebb90
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Post by sjwebb90 »

Reference Low pass filter in diagram R8 (10K) and C4 (0.1uF)
https://www.freestompboxes.org/viewtopic.ph ... r&start=40

The corner frequency for these combined values is 160Hz. This doesn’t look right and is probably accounting for the muddy sound as the treble is being attenuated.
You can check this yourself using the following link:
http://www.muzique.com/schem/filter.htm

If the 0.1uf cap (C4) is regarded as correct then ideally this should paired with a 1K (R8) to give a corner frequency of 1.5Khz, this should correct the problem.

cAMPus
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Post by cAMPus »

sjwebb90 wrote:Reference Low pass filter in diagram R8 (10K) and C4 (0.1uF)
https://www.freestompboxes.org/viewtopic.ph ... r&start=40

The corner frequency for these combined values is 160Hz. This doesn’t look right and is probably accounting for the muddy sound as the treble is being attenuated.
You can check this yourself using the following link:
http://www.muzique.com/schem/filter.htm

If the 0.1uf cap (C4) is regarded as correct then ideally this should paired with a 1K (R8) to give a corner frequency of 1.5Khz, this should correct the problem.
Hi,

it seems that this is a reply to my question at german diy forum https://forum.musikding.de/vb/showthread ... post312502 :secret: :applause:

Thanks lot ... and I am ashamed wondering why I didn't realize this by myself

Greets U.

Colca
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Post by Colca »

hello, someone have any idea how to do the mod compressor as they do in the custom shop?

MullisMan
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Post by MullisMan »

I've taken the AC Booster schematic from madbeanpedals.com and breadboarded it, but I removed the input and output buffers. I've verified the wiring and checked all my voltage levels, but I'm getting a very low output signal. At full volume there's still a slight volume boost, but it's not like the actual AC Booster, which I own. I've tried three different IC's, the 4558, TL072, and the OPA2134, and all have the same volume issue. The tone stack works like it should, and I know that tone stacks can cause loss, but if the original works just fine why shouldn't this one? I've included the schematic to show what i'm working with. Any suggestions?

I can include voltage readings on the IC as well.

On pins 3 and 5 i'm getting 6.8 volts
Pin 8 I'm getting 9.46 volts
Pin 4 is 0
On the output pins and pins 2 and 6 I have 6.8 volts as well.
I want to build it all.

cAMPus
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Post by cAMPus »

Hi,
MullisMan wrote:I've taken the AC Booster schematic from madbeanpedals.com and breadboarded it, but I removed the input and output buffers. I've verified the wiring and checked all my voltage levels, but I'm getting a very low output signal. ...
1. the gain potentiometer of the ac-booster should be a 500k log
2. VB is 4.5V so your RBIAS2 has to be a 22k

http://www.madbeanpedals.com/projects/Q ... Quasar.pdf
or my schematic there (R7 must be 1k):
https://www.freestompboxes.org/download/fil ... &mode=view


U.

MullisMan
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Post by MullisMan »

My mistake, I have a 500k potentiometer for the gain pot, that 100k pot was left over from a different schematic. I'm not sure what you mean when you say the Vbias is 4.5 volts, in your schematic and in the actual pedal there's a 22k and 6.8k voltage divider for the first stage of the Vbias. That works out to around 6.8 volts.

Also in your schematic, R7 should be a 1K, the 10K resistor is used in the RC Booster I believe, not jumpered. The capacitor C4 (0.1uF) creates a really low corner frequency with R7 when using a 10K that causes a lot of muddiness in your signal. The 1K resistor would make it around 1.5Khz.

I've corrected and re-uploaded my schematic, if a mod would like to delete my previous schematic post go ahead.
Attachments
TSBAXbare.png
I want to build it all.

cAMPus
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Post by cAMPus »

MullisMan wrote:... in your schematic and in the actual pedal there's a 22k and 6.8k voltage divider for the first stage of the Vbias. That works out to around 6.8 volts. ....
... and from the 6.8k another 15k is connect to ground so that you have 22k to +9V and 6.8k + 15k to ground for VB - makes +9V / 2

R7 10k was not correct in the original schematic that ranmusic84 postet a few sides before in this topic:
https://www.freestompboxes.org/viewtopic.php?p=22674#p22674

Here you can read about the correct value (1k) for R7 (R8): https://www.freestompboxes.org/viewtopic.ph ... 70#p141270
For the RC-Booster R7 is jumpered.

MullisMan
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Post by MullisMan »

Ok thanks I see now. I was disregarding the 15K resistor from the original bias. The original is a split Bias for the input buffer transistor and the opamp. My mistake. Now i'm getting a volume boost, but it still is bunched up at the end of the volume pot taper, past 1 o clock. On the AC Booster that I have, the volume knob is unity at around 10:30 or 11. :scratch:
I want to build it all.

cAMPus
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Post by cAMPus »

Hi,

where is the input of the circuit, the inverting opamp, connected to.
Maybe the load of the input (~10k impedance) is to much?!

U.

MullisMan
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Post by MullisMan »

Well I tried that, I tried different resistors all the way down to 3.3K, and didn't have much of a change. But that was before I fixed some other problems, so maybe i'll try that again.

Thanks.
I want to build it all.

TheLemon
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Post by TheLemon »

Youll need a 470k resistor connected between C2(.022) and R5(10k) to Vb (4.5v) for it to work properly. Im suprized you have gotten any signal.

jymaze
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Post by jymaze »

No, a resistor between C2 and R5 is not needed since it is an inverting opamp configuration. It would be needed in the non-inverting configuration though.

MullisMan
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Post by MullisMan »

jymaze wrote:No, a resistor between C2 and R5 is not needed since it is an inverting opamp configuration. It would be needed in the non-inverting configuration though.
Yeah this isn't a standard TS configuration. The other input pin of the IC is already biased. I haven't had a chance to mess around with the circuit anymore and correct the Vbias network yet. Hopefully tomorrow i'll get to it.
I want to build it all.

fretzburner
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Post by fretzburner »

MullisMan wrote: Also in your schematic, R7 should be a 1K, the 10K resistor is used in the RC Booster I believe, not jumpered. The capacitor C4 (0.1uF) creates a really low corner frequency with R7 when using a 10K that causes a lot of muddiness in your signal. The 1K resistor would make it around 1.5Khz.
I beleive using 10k resistor makes the sound muddy.Just converted my RC booster to AC specs with few parts replaced and before conversion sounds ok,after it is very muddy and very low output.Will try to change 10k to 1k.

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Post by IvIark »

Forgot this too, I need to keep things more uptodate!

Image
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP

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Post by blakbeltjonez »

built it on vero, sounds pretty good to me! only a couple of things, and it's probably outside the realm of what the original could provide, is a bit more gain/drive. also, i'm using it with a Fender Champion 600 at a fairly low volume, the bass control has a lot of range but the treble doesn't seem to get as bright as it seems like it should..... have to try it out on another amp.

is there anything i can do to get a bit more distortion?

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