Vox / Orange / Apollo - Treble and Bass Booster  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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Electric Warrior
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Post by Electric Warrior »

any news, pedalman?

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Post by RnFR »

i don't think it would be that hard to figure it out from the pics, with a bit of patience.
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Post by Electric Warrior »

I tried once, but it wasn't easy. I'll see what I can do..

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Post by drewl »

I didn't read through all 5 pages, but is this the same treble/bass boost found in Vox guitars?
If so I think I drew it out as I've had to fix a couple of those.
Like a Lynx 12string with built in fuzz, wah, repeat percussion, tuner and of course T&B boost.
that was a pain in the rear.

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Post by DiscoFreq »

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Post by RnFR »

drewl wrote:I didn't read through all 5 pages, but is this the same treble/bass boost found in Vox guitars?
If so I think I drew it out as I've had to fix a couple of those.
Like a Lynx 12string with built in fuzz, wah, repeat percussion, tuner and of course T&B boost.
that was a pain in the rear.
i believe it is. a schematic would be great as the owner seems to have gone AWOL. :D
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Post by drewl »

I'll see if I can find my notes from when I worked on it.....that's the hard part....finding my notes...

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Post by tonefree »

HELP -

I have the later Vox box version - Made in Italy. (twenty 25 years ago I had the skinny chrome version).

But the box version came in the mail, and after hooking up the 9volt battery, I noticed one of the wires is off where it's supposed to connect to. It's coming off the 9V power and is supposed to run, I guess, onto the board part.

Picture is here:


Image



So where does the red wire go to? I am guessing to the area of the brownish circle. Someone please help confirm!

Thanks. :?

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Post by Electric Warrior »

analogguru wrote:
I don´t have a schematic or good guts, the onlything I gathered is this inside-photo:
http://analogguru.an.ohost.de/temp/Vox_ ... acks_c.jpg

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Post by tonefree »

Electric Warrior wrote:
analogguru wrote:
I don´t have a schematic or good guts, the onlything I gathered is this inside-photo:
http://analogguru.an.ohost.de/temp/Vox_ ... acks_c.jpg
Thanks for showing where that red one goes.

Looks like the white wire and yellow wires in the two different pictures are going two different places. Odd.

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Post by gigelmargel »

Woooow!!!
Thank you very much Pedalman!

I hope to see a correct schematic soon :horsey:

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Post by gigelmargel »

I didn't understand the input network from the description... :hmmm:

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Post by Pedalman85 »

soooo sorry folks! forgot pw and forgot that i made this enjoy. Note: S1 and S2 is a DPDT slide switch.
Attachments
apollo treble bass booster.png
apollo treble bass booster.png (4.48 KiB) Viewed 4510 times

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Post by Pedalman85 »

so where do i find those 2SB175's or a Low Hfe equivalent? I thought i had found some once but i've forgot where.
I'd like to do some mods but i need a clone first, cuz i ain't chopping up this unicorn. :lol:

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Post by Electric Warrior »

ebay for instance: http://cgi.ebay.de/2SB175-Transistor-x- ... 588c323337
http://cgi.ebay.de/8-x-Matsushita-2SB17 ... 588c778c99

These were available in different gain groups, marked A (55-130), B (85-220) and C (150-360). What type is the one in your booster?

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Post by acidfuzz »

Jus in case anyone wanted to know, the treble/bass booster found in 60's Vox guitars such as the Starstreamer and Ultrasonic, etc... is basically the same as the Vox Treble-bass booster V8401 schematic Ron Neely posted earlier in this thread. You can use the same schematic + just change the resistor values + omit R5.

The differences are as follows:

-R1 is 56K, not 36K
-R2 is 150K, not 430K
-R3 is 22K, not 220K
-R4 is 68K, not 180K
-R5 is omitted entirely
-R6 is 560K, not 1meg

Q1 is a BC109b with Hfe of ~250 and biases up to ~4.8v at the collector with the above changes.

The above was traced from a 1968 Vox Ultrasonic guitar. :D

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Post by LucifersTrip »

acidfuzz wrote: Q1 is a BC109b with Hfe of ~250 and biases up to ~4.8v at the collector with the above changes.
How sure are you about the 4.8v? I built it and so did a bunch of others and if wired properly with a 200+ hfe transistor, the C voltage is ~ 1.6-1.8

When I built it, I did a test with various transistors:

hfe/ C voltage
42 / 2.20
70 / 1.88
200 / 1.72
228 / 1.56
304 / 1.62

...using 1M, not 560K, but that shouldn't do it.

calculations can be found here:
https://www.diystompboxes.com/smfforum/ ... #msg815603

Image

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Post by acidfuzz »

I'm sure I got 4.5v @ the collector. Did you also omit R5?

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Post by LucifersTrip »

acidfuzz wrote:I'm sure I got 4.5v @ the collector. Did you also omit R5?
We built is by the schematic above...and it sound killer. the only thing I changed was the 500K pot to 50K, whcih gave me a far better sweep.

Did you check out the link above. I don't understand the calculations, but one of the really good guys figured it out. It would be nearly impossible to get 4.5v if wired as the schematic shows.

================================================================================
"> where do i take the calculations from that point

It is a 430K:220K voltage divider, probably.

IF the amp has a bias-point (if it "works"), we know the tap is 0.55V.

What voltage do we need at the top of 430K:220K to get 0.55V?

0.55V * (430K+220K)/220K

I work it out to be 1.625V.

This assumes the Base draws ZERO current from the voltage divider.

There IS base current. How much? Do we have to account for it?

2N5232 spec is given as "beta: 250-500". This is similar to 2N3904 beta. But such numbers are usually at 1mA. Beta may be less at the low 0.025mA here. The 2N3904 data shows hFE "typical" very flat from 0.1mA to 10mA. It may be (must be) down some at low-low current (and the hard-data says so), but maybe not by much. Let us take "250" as the current gain. If collector current is 0.025mA then base current is 0.025mA/250= 0.000,1mA. This must flow in the 430K resistor. 0.000,1mA*430K is 0.043V added drop.

So now the collector voltage which makes the base happy is 1.625V+0.043V or 1.668V. If hFE were higher, it would be less. But even if hFE were infinite we'd be back to the 1.625V assumption. (Base current is much less than divider current.) So collector voltage CAN'T vary by much. It has got to be in the 1.6V-1.7V range.

(I musta counted too fast when I figured 1.5V-1.6V.)

OK if collector is near 1.6V and supply is 9V, then there is 9V-1.6V= 7.4V across the 180K collector load. This current must be 7.4V/18K= 0.04mA. That's somewhat higher than our "in the middle" estimate. Go back and squint/extrapolate Vbe for 0.04mA. Might be nearer 0.58V. Voltage-divider means to get 0.58V at base the collector must sit near 1.69V. The base current is higher but still small compared to divider current. We might pencil 1.7V as our expected voltage.

EDIT: Oh!! I forgot the 100K collector to ground! This is an odd feature (it makes the clipping less asymmetrical). There's a couple ways to account for its effect. Obviously if collector is anywhere near 1.6V, then there is 1.6V/100K or 0.016mA in the 100K. That means 0.016mA less in transistor. So the "0.04mA" is more like 0.024mA. Vbe is lower, maybe 0.056V. Collector may be 1.65V, or a wee bit more. No big difference. "

================================================================================

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Post by sinner »

Based on AG schematic I did this

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