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

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

ranmusic84 wrote:i'm really sorry for my mistakes.

Mr.gori told them and i've fixed them.

-add 10uF in bias circuit
-change emitter of output transistor to GND

Image
C1 = 47nF
C2 = 1uF / NP
R8 = remove and bridge
C4 = remove
R5 = 22k
R7 = 250k
Clipping-Diodes = 3x 1N4148 each side

that is the RC-Booster :wink:

regards, kusi

tlpruitt
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Post by tlpruitt »

Maybe its me but I always thought the AC Booster sounded a bit too "wooly" in the low end and it lacked enough mids to make it really "sing". Right now I have 4 clipping diodes (2 pairs of 4148 diodes) in mine and a OPA2134PA opamp and I think it is an improvement over the stock sound but the low end still seems a bit "muddy".

Anybody have any suggestions on mods to clear up the wooly low end and also improve the mids? I was thinking about swapping the electrolytics in the signal path with metal film caps and maybe lowering their values a notch.

Roa
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Post by Roa »

Hi guys, I have to say that I degooped my AC and RC boosters and my pcbs are not like the one Rota has published, but the AC and the RC PCBs are just the same thing with some different components. I will leave three picture here of both units. Mi IC was sanded to, but I can perfectly read the transistors. I will post the exact kind tomorrow, and if you need any values let me know and I´ll post them.
Image
Image
Image

:thumbsup

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The Rotagilla
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Post by The Rotagilla »

Transistor numbers would be nice, thanks!
The television will not be revolutionized.

gtrwrks
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Post by gtrwrks »

Roa - The pics you posted are of the latter-day layouts by Xotic - the pics/layout-version earlier in this thread are of the older type - there are at least three, with the first two layout/versions being single board, most similar to the first one in this thread.

It's the same circuit, just a diff layout/configuration to take advantage of the small/board-mounted pots, et al.

A little OT - one of my fave RC Booster tweaks is to add yet another pair of diodes to the FB loop - small but noticable diff @ stage volume.

tlpruitt
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Post by tlpruitt »

ranmusic84 wrote:i'm really sorry for my mistakes.

Mr.gori told them and i've fixed them.

-add 10uF in bias circuit
-change emitter of output transistor to GND

Image
Are the + and - on the opamp correct in the schematic or should they be reversed?

gtrwrks
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Post by gtrwrks »

They are correct, Pruitt - opamp input is into the inverting input - hence the 10K res just prior.

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Post by sadrew »

is the 4557D lot different than the 4558D?
I've never tried one...

gus
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Post by gus »

Vref setup I would build it different. A NPN EF transistor buffer can "turn on" more than the 10K can pull down and you have the VBE drop that is a good fraction of the 9VDC supply. I would offset Vref 1 more to +9 in other words flip the resistors Vref 2 would still be about 1/2 and Vref 1 would be at the two resistor node but closer to 9Vdc.

How stable is the input buffer bias with a 2SC1815 and a 1meg R3? If I wanted a 1meg R3 I would use a higher hfe transistor in that section or make R3 a 470K and R1 a 10meg.

Is R2 as 10K in the circuit just to add noise?

The output buffer goes to Vref 2? If both go to Vref2 as drawn I would get rid of C10 and R16 and wire the base to the volume wiper but you could have wiper noise when adjusting the circuit.

Look at the 3 tran the input buffer is offset more to +9

I do like the inverting gain stages.

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gori
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Post by gori »

I think that ACBooster is an idea from FA -1 of BOSS
http://www.freeinfosociety.com/electron ... ossfa1.png

gus
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Post by gus »

gori

Thanks for the link. Now the vref makes sense MAYBE they copied it from the BOSS FET input for a 2sc1518. Changed a couple resistors and caps in the tone section and added clipping diodes.

The stock boss circuit looks very good, well thought out IMO.

nooneknows
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Post by nooneknows »

Hi,
it could be one of my dumb questions: is C9 useful? There's C10 to decouple the dc from VRef

audioguy
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Post by audioguy »

Is there a PCB floating around for the RC Boost yet?

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Post by lynessmy »

What is the purpose of the tranny (MOSFET?) nearby the clipper diode?
It was not presents in the older board.

gtrwrks
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Post by gtrwrks »

lynessmy wrote:What is the purpose of the tranny (MOSFET?) nearby the clipper diode?
It was not presents in the older board.
LED

pbblues
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Post by pbblues »

hi .... Is there a pcb for the RC Boost ??? please ...... :oops: .... maybe someone can make it .... :horsey:

quaternotetriplet
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Post by quaternotetriplet »

here is a layout for ac booster not yet verified.
Attachments
ac booster layout.png
acbooster pnp 2.png
acbooster pnp 2.png (8.47 KiB) Viewed 1231 times

quaternotetriplet
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Post by quaternotetriplet »

here are the parts list

pbblues
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Post by pbblues »

tnx .... big quaterno !

quaternotetriplet
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Post by quaternotetriplet »

+9V1 +9V(T) +9V(T) SQUARE gm-supply 1
C1 10u 0503 050_020_3 gm-caps-electro-pol 1
C2 10u 0501 050_020_1 gm-caps-electro-pol 1
C3 .02u 075X0304 075X030_4 gm-caps-film-chicklet 1
C4 .1u 080X0503 080X050_3 gm-caps-film-chicklet 1
C5 150pf 050X030_0501 050X030_050_1 gm-caps-ceramic 1
C6 .1u 080X0504 080X050_4 gm-caps-film-chicklet 1
C7 .0047u 050X030_0253 050X030_025_3 gm-caps-ceramic 1
C8 .033u 075X0352 075X035 gm-caps-film-chicklet 1
C9 .033u 075X0352 075X035 gm-caps-film-chicklet 1
C10 1ufnp 0501 050_020_1 gm-caps-electro-pol 1
C11 .0047u 050X030_0252 050X030_025_2 gm-caps-ceramic 1
C12 .1uf 080X0504 080X050_4 gm-caps-film-chicklet 1
C13 10u 0501 050_020_1 gm-caps-electro-pol 1
D1 1N4148-2 1N4148-2 DO35-2 gm-diodes 1
D2 1N4148-2 1N4148-2 DO35-2 gm-diodes 1
D3 1N4148-2 1N4148-2 DO35-2 gm-diodes 1
GND8 GND(T) GND(T) SQUARE gm-supply 1
GND9 GND(T) GND(T) SQUARE gm-supply 1
GND10 GND(T) GND(T) SQUARE gm-supply 1
IC1 LM4558N LM4558N DIL08 gm-ics 1
IN1 IN(T) IN(T) SQUARE gm-supply 1
OUT1 OUT(T) OUT(T) SQUARE gm-supply 1
POT1 500kb POT POT gm-pots 1
POT2 50kb POT POT gm-pots 1
POT3 50kb POT POT gm-pots 1
POT4 100k POT POT gm-pots 1
Q1 2N5089 2N5089 TO92- gm-trans 1
Q2 2N5089 2N5089 TO92- gm-trans 1
R1 22k 6MM.4 R0207/4 gm-resistors 1
R2 6k8 6MM.3 R0207/3 gm-resistors 1
R3 15k 6MM.3 R0207/3 gm-resistors 1
R4 1m 6MM.5 R0207/5 gm-resistors 1
R5 10k 6MM.4 R0207/4 gm-resistors 1
R6 1m 6MM.3 R0207/3 gm-resistors 1
R7 10k 6MM.3 R0207/3 gm-resistors 1
R8 10k 6MM.3 R0207/3 gm-resistors 1
R9 47k 6MM.3 R0207/3 gm-resistors 1
R10 10k 6MM.5 R0207/5 gm-resistors 1
R11 4k7 6MM.4 R0207/4 gm-resistors 1
R12 4k7 6MM.4 R0207/4 gm-resistors 1
R13 33k 6MM.3 R0207/3 gm-resistors 1
R14 10k 6MM.4 R0207/4 gm-resistors 1
R15 470k 6MM.4 R0207/4 gm-resistors 1
R16 10k 6MM.3 R0207/3 gm-resistors 1
R17 470r 6MM.3 R0207/3 gm-resistors 1

partslist i forget where the non pollar electrolitic is.
R18 100k 6MM.3 R0207/3 gm-resistors 1

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