Analogguru - SDD-preamp  [verified]

Original effect designs complete with verified schematics, layouts and instructions. All project were freely contributed by members and cannot be used for commercial purposes without consent of the respective owners of the copyright.
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Post by analogguru »

So folks,
too often I heard the rumours about the "fabulous" Korg SDD-3000 preamp which a guitarist used one time.

So I took the SDD-3000 schematic and drew out the relevant part, which can be found here:
Korg SDD-3000 preamplifier schematic

I added a footswitch. This circuit is supplied with +/- 15V in the SDD-3000.

Since this is a horror for battery-junkies, I adapted this circuit for use with a battery. The schematic can be found here:
Analogguru SDD-preamp schematic

There shouldn´t be any difference in sound, only in the maximum headroom is smaller.

Some remarks to the circuit:
R2, D1, D2 are for protecting the TL 072 from static discharge by plugging in the guitar. Marshall omitted them on the valvestate series and had a lot of problems with broken TL072 - they become noisy.

Since the next stage is inverting, D3 and D4 do: simply nothing.
The 3k3 resistor from the +input to Vref is there to minimize offset problems by keeping the input current the same. Since this stage is the second half of the TL072 (high-z FET-opamp) it wouldn´t be necessary to use it.

The coupling capacitor of 10µF (C7) is not necessary to be so high in the "standalone" application. 470n is far enough. With that value you will have a lower corner frequency of -1,5 dB at 20 Hz. For guitar application 100n would do it too, but too keep the original design intact as far as possible I used 470n.

The rest of the adapted values will not have any difference to the original circuit - it´makes it only easier to build.

Since there is a half of a dual op-amp unused I made with it a buffered reference voltage around IC21-1.

I won´t do a pcb or stripboard layout for this, maybe somebody else.
Dirk Hendrik has made a pcb layout (23/08/2008)

enjoy building and use of this preamp,
analogguru
Last edited by modman on 23 Aug 2008, 17:39, edited 2 times in total.
Reason: added link to DH's pcb layout
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Post by Dirk_Hendrik »

First remarks/requests:
- May I have a cap in parallel to R9 to keep that voltage divider clean?
- I'd prefer R1 at the switch side of R2
Sorry. Plain out of planes.

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Post by analogguru »

Dirk_Hendrik wrote:First remarks/requests:
- May I have a cap in parallel to R9 to keep that voltage divider clean?
yes, but not really necessary. The opamp gain is (only) one, so any "noise" there wil not be amplified. There shouldn´t be much "noise" cause of the power-supply filter-cap. Even if there should be some, this would not appear at the output of the op-amp, since there is an additional 47µF cap.
- I'd prefer R1 at the switch side of R2
Hey.... then it would not be like the original... you could probably loose a lot of mojo... :roll: :wink:

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Post by soulsonic »

Thanks! I always learn something new when I see your designs. :wink:
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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Post by Cow4prez »

i think i will give this a try, Thanks

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Post by JimiB »

this is awsome I am gonna try it. Anybody do a board or a vero yet?

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Post by JimiB »

would this work to get both a +15 and a -15 VDC supply for this?

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Post by JimiB »

oops :oops:
https://www.mouser.com/Search/ProductDet ... 9-TC962CPA

if I fed it with a 15VDC supply

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Post by analogguru »

If you connect it to a +/-15V supply you dont need the Vref circuit. Instead all what is connected to there should be conected to ground (like in the original).

You can use a single supply with higher voltage than 9V (eg. 18V or 24V) but the capacitor voltage ratings - especially in the power-suply section - should be able to handle this higher voltage.

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Post by JimiB »

do you think it would have the same headroom if I used a 24V supply?
I don't know if using the original +15 -15 Vdc power supply would make a difference but I would really like it to sound and operate like the original - since it would be the last thing in the chain the likelyhood of it getting slammed hard is high - therefore it seems that the headroom would make a difference. Am I mistaken here?

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Post by analogguru »

JimiB wrote:do you think it would have the same headroom if I used a 24V supply?
Nearly.... only missing 1,5 dB or so....
I don't know if using the original +15 -15 Vdc power supply would make a difference but I would really like it to sound and operate like the original....
You are free to use a +/- 15V DC....
- since it would be the last thing in the chain the likelyhood of it getting slammed hard is high - therefore it seems that the headroom would make a difference. Am I mistaken here?
Maybe....... did you ever feed a guitar amp with a 8Vpp signal (instead of the original 100mVpp from the guitar itself) ?

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Post by JimiB »

Maybe....... did you ever feed a guitar amp with a 8Vpp signal (instead of the original 100mVpp from the guitar itself) ?
Sorry, not sure what that means. If I am chasing my tail here and overcomplicating things please tell me and I will just build it to use a 9V supply.

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Post by JimiB »

:D

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Post by analogguru »

JimiB wrote:
Maybe....... did you ever feed a guitar amp with a 8Vpp signal (instead of the original 100mVpp from the guitar itself) ?
Sorry, not sure what that means. If I am chasing my tail here and overcomplicating things please tell me and I will just build it to use a 9V supply.
A guitar normally delivers only about 100mVpp (pp = peak to peak) of signal level. The guitar-amps are designed to deliver full power with this 100mVpp. With 9V the booster will start clipping at about 8 V - so 80 times more signal level. So the amp gets a 80 times higher level at the input as expected....

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Post by JimiB »

I guess I am thinking about the headroom of the preamp not the amplifier. I have no doubt that it will have plenty of output. Will it make much difference to when the preamp begins to clip?

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Post by Dirk_Hendrik »

4 page PDF with board layout (verified):
http://www.dirk-hendrik.com/SDD3000_preamp.pdf

(and especially mentioned for AG, the layout may be made with a PCB CAD program but no autorouter was used :wink: )
Sorry. Plain out of planes.

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Post by JimiB »

wow awesome, thanks!

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Post by kyle31 »

On the schematic what does the 'E' stand for in 220E. Ohm?

I know what k and m etc mean. I've just never seen E.


Also I don't have a way to etch pcbs so if anyone would like to do a 1 off board or 2 i'd make it worth your while. I could build it on perf or those radioshack ic boards, but i'd like to keep it clean and simple.

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Post by analogguru »

On the schematic what does the 'E' stand for in 220E. Ohm?
yes.....

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Post by ryanuk »

Hi

Just found this thread and thught I'd have a go at building this to see what all the fuss is about.

I've been looking at the original SDD3k schematic.

Can someone explain the function of the 2 pole, 3-way switch at the input?? I.e. what componments are switched in/out in order for the unit to attenuate the input signal?

I've tried to figure it out - but am getting confused. :oops:

It appears from the schem provided by Analogguru that the switch somehow bypasses 2 resistors (130k and 30k??)??

However, I can't see how the switch does this on the original schematic??!!

Analogguru - can you shed any light?

RyUK

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