Skrydstrup R&D - Overdrive ODR2

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Skrydstrup R&D - Overdrive ODR2

Postby CableBling » 30 Nov 2012, 00:39

Hi,
Just acquired a Skrydstrup R&D ODR2 of eBay and thought you'd apprechiate some gut shots.
Amazing build quality.... if it had any warrenty left, its gone now! :shock:
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Re: Skrydstrup R&D - Overdrive ODR2

Postby atreidesheir » 30 Nov 2012, 01:11

nice. Looks like the adults built that one :applause: .
How does it sound. I've never heard of it.
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Re: Skrydstrup R&D - Overdrive ODR2

Postby bajaman » 30 Nov 2012, 01:17

Oh NO :shock:
It's got those "essential" Finnegan Klon diodes too :lol: :lol: :lol:
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Re: Skrydstrup R&D - Overdrive ODR2

Postby Intripped » 30 Nov 2012, 03:26

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Re: Skrydstrup R&D - Overdrive ODR2

Postby tube-exorcist » 30 Nov 2012, 11:21

Nice build, but from a technical viewpoint only a POS. Here are only a few points:

Input/output wires are screened, but the same length pot wires are not ?
Constant 51k load on the pickups ?
Always a buffer in the signal path ?
No pulldown resistor at the input-cap (after the footswitch) ?
9-pin footswitch soldered to the pcb ?
....
....
....
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Re: Skrydstrup R&D - Overdrive ODR2

Postby Bernardduur » 30 Nov 2012, 13:48

Output ground is lifted through a 10n cap......... does that work??

(never tried)

And I like those WIMA MKS4's caps in amps........ but in pedals?? 400V is a bit overrated!!
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Re: Skrydstrup R&D - Overdrive ODR2

Postby tube-exorcist » 30 Nov 2012, 16:06

Correction:
The 51k is at the output. The input is via a "Cornish-Buffer". Rest appears to be a Cornish SS-2 derivate/clone.

Output ground is lifted through a 10n cap......... does that work??

It´s not the "output ground", it is the chassis which is "lifted".
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Re: Skrydstrup R&D - Overdrive ODR2

Postby Dirk_Hendrik » 30 Nov 2012, 19:51

tube-exorcist wrote:Nice build, but from a technical viewpoint only a POS. Here are only a few points:
....
....
....


ok, let's turn this around,
If one person/company makes a design there's always the option to be critical on decisions this person made based on personal experiences. That's an easy thing.

Now, let's put the question, in general, different,
Would it be possibe to develop a set of guidelines that, if followed correct, could be used not only as a guide in "how to do it" but even as a standard? Effectively taking the wind out of the back and forth arguing if something is acceptable based on "personal" opinions?
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Re: Skrydstrup R&D - Overdrive ODR2

Postby tube-exorcist » 30 Nov 2012, 20:40

Would it be possibe to develop a set of guidelines that,....

That´s not really necessary, there exists engineering schools where you can learn that (since at least more than 50 years).

For example:
"The higher the impedance, the more the circuit will be sensitive to hum."

Now let´s apply this rule:
The buffer output impedance is less than 1kOhm. The distortion op-amp output about the same. Therefore the wire carrying the output signal is ALWAYS low impedance (< 1k).

The wire to the potis carrys an impedance between 25k and 100k.

So which wire is more important for screening ? The wire to the output jack, or the wire to the potis ?

So to use a screened wire to the output jack is pure mojo when the poti wires are not screened too.

"If a capacitor is left floating (on one side), it will cause a pop noise when connected to a potential"

Now lets have a look:
Does the input capacitor (left to the footswitch) of the distortion circuit have a definite potential ?

Let´s go further - The schematic of the Cornish Buffer should be well known:
A resistor from emitter to ground, followed by a cap a 20k pulldown resistor (in this case 18k), followed by an (unnecessary) 51 Ohm series resistor (right down corner).
Now please tell me for what do you need after a 51 Ohm resistor a pulldown-resistor of 1M ?
The cap already has a pulldown of 18k BEFORE the 51 Ohm resistor.

And for what do you need an RF-cap to ground in parallel to the 1M resistor ?
If there would be an RF-signal at this place, it would be rectified long before by the diode-junction of the transistor. An educated and skilled technician should know that.

Footswitch:
Did you ever have to replace a 3-pole footswith soldered into a double-sided pcb with lead-free solder ?

Case lifting:
There is no reason to lift the case with a cap. This is only done in AC-powered units (transformer inside) to avoid hum loops because a metal case has always to be connected to earth. To avoid hum loops, sometimes the earth is separated with a 100 Ohm resistor or a capacitor (or combination) from the audio ground.

Now please tell me: Where is this (DC-powered) case connected to an AC-mains-earth ?

This are basic rules every educated technician should have learned in school, so why explain them extra ?
I expect from everybody who want´s to earn some money, that he has a proper education for his job and understands what he/she is doing. In this case - building electronic pedals - the job is electronics.

Alltogether it appears, that Skrydstrup has only the skills of a solder jockey and a lack of understanding what´s going on electronically when he is cloning Cornish stuff. And as every skilled EE-expert will acknowledge the same, my statement is not only an "opinion" instead it has the value of an expertise because I can justify my judgement with facts and rules.
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Re: Skrydstrup R&D - Overdrive ODR2

Postby Dirk_Hendrik » 30 Nov 2012, 20:59

Since I'm not able to edit my above post anymore, the answer is a partial yes. The partial because these standards do exist and are used extensively throughout the engineering world. Following these standards avoids shitloads of common mistakes, hearsay and ill-founded assumptions (assuming board mounted switches are always bad for instance). The odd thing in this case is that as soon as one enters a discipline where these standards are less common, let's take the effects boohtheek industry as an example, suddenly people start to resort back to poor or unfounded opinions, hearsay and other misconceptions. Why? Lack of knowledge that these standards exist and therefore dseclaring personal experiences as the thruth.

An example of this that crosses my mind right now happened a few years back when a forummember posted an early '70's handmade PCB layout and described it as "when PCB design was still an artform". In another topic the same member referred to one of my layouts as "autorouter"and the source of the oscillation problem I ran into. Wether or not the problem was in the PCB layout or not the PCB layout was definitely not autorouted. The forummember seemingly thought that if a CAD system was used for PCB design it must be autorouted. Anyone with a little experience in PCB CAD systems and autorouters will know that autorouters will add little to nothing to the miniature analog effects circuits we play around here and it all wil come to handwork. That in turn means that the member who decladed the handmade PCB layout "artwork", showed, with his/her remarks, not to have any practical experience with CAD based PCB design and was therefore completely unable to judge if using a CAD system does not require the same skills to get the required results as the handwork does. Lack of knowledge on the subject and therefore assuming personal experience as the judge.

Odd, isn't it?
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Re: Skrydstrup R&D - Overdrive ODR2

Postby Dirk_Hendrik » 30 Nov 2012, 21:01

T-E
Please take note my above post was written while you posted yours.

As for the replacing of the 9 pole switch the answer is yes. Tens of times, including RoHS compliant soldering. Doing this requires the right tools, skills, and insight in the material. If these are in place, there's absolutely no problem doing this job. Same way there's no problem replacing a multipin integrated circuit from a multilayer PCB. Since the Skydrup servicing most likely needs to be done by "qualified" service personell there's no reason not to mount it on the dual sided PCB.

If you would have brought up the question why the skypdrip gents chose to resort to using the switch as a PCB mount, with no other means of mechanical strain relief I would have agreed with you.
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Re: Skrydstrup R&D - Overdrive ODR2

Postby tube-exorcist » 30 Nov 2012, 21:18

Dirk_Hendrik wrote:Since the Skydrup servicing most likely needs to be done by "qualified" service personell there's no reason not to mount it on the dual sided PCB.

Now let´s assume, that there exists other than bedroom guitarists (who buy a € 400,-- unit) which are on tour or want to avoid the time and to pay the expensive shipping costs to the manufacturer. What do you think is easier, faster and therefore cheaper: To replace a switch (maybe mounted on an seperate single-sided pcb) with a multipin-jack to the main-pcb - as even Behringer can do (see picture) - or the way it is mounted here directly in the main pcb ?

Don´t forget: We are talking about a € 400,-- unit....

And BTW, yes, agreed, a 3-pin-only potentiometer can be board-mounted and this sometimes is even better....
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Re: Skrydstrup R&D - Overdrive ODR2

Postby Dirk_Hendrik » 30 Nov 2012, 21:30

Simple,
I said qualified. I did not say Skydrup. Therefore there's no need for shipping. There's the need to fing a local repair guy. Any experienced TV repair shop can replace that swith (BYO though) in a matter of minutes.

How long does it take to get Behringer to ship one of those PCB's to a end user? :scratch:
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Re: Skrydstrup R&D - Overdrive ODR2

Postby tube-exorcist » 30 Nov 2012, 21:33

Did you never see a shitty autorouted pcb in audio stuff ? Then have a look here:
viewtopic.php?f=7&t=850

This insanity only an autorouter can do. But I have to agree, in audio-design it is much better to switch off any autorouter, but how many of the bootweak solder-jockeys are than able to finish a pcb ?
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Re: Skrydstrup R&D - Overdrive ODR2

Postby tube-exorcist » 30 Nov 2012, 21:38

Dirk_Hendrik wrote:How long does it take to get Behringer to ship one of those PCB's to a end user? :scratch:

No need for shipping, because the pcb is single-sided, the switch is only 6-pin and you can take it out from every consumer-electronic-stuff (or buy it new everywhere) :wink: :

Behringer_Footswitch_2.jpg


And on a single sided-pcb you don´t need a special tool - even for the 9-pin footswitch....
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Re: Skrydstrup R&D - Overdrive ODR2

Postby theehman » 30 Nov 2012, 21:52

:popcorn:
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Re: Skrydstrup R&D - Overdrive ODR2

Postby tube-exorcist » 30 Nov 2012, 22:03

theehman wrote::popcorn:

And BTW, you can replace the 2P2T with 4P2T if you need more than 2 poles (4P2T on the right) :wink: :
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Re: Skrydstrup R&D - Overdrive ODR2

Postby steve440 » 30 Nov 2012, 22:40

Should the screened wire be grounded at both ends? I always thought not, just one end, maybe I'm wrong.
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Re: Skrydstrup R&D - Overdrive ODR2

Postby CableBling » 01 Dec 2012, 01:00

Glad my pix have stirred up some interest!

Case lifting:
There is no reason to lift the case with a cap. This is only done in AC-powered units (transformer inside) to avoid hum loops because a metal case has always to be connected to earth. To avoid hum loops, sometimes the earth is separated with a 100 Ohm resistor or a capacitor (or combination) from the audio ground.

Now please tell me: Where is this (DC-powered) case connected to an AC-mains-earth ?


I've wondered before about the case lifting, having seen it on the Cornish (Work In Progress) pedalboard builds and also on another Skrydstrup pedal I had a few years back - the BF2MFD Buffer (picture below).
They only ever seem to fit the case caps (10nF 1kv I think) to output sockets..... never to the Input socket which is wire grounded as normal.
Is it really just some misguided mojo?.... ie. Cornish did it (for whatever reason) and Skrydstrup followed suit?
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Re: Skrydstrup R&D - Overdrive ODR2

Postby silverface » 01 Dec 2012, 18:55

Could you post the capacitor values and transistor type? Not all are visible in your pictures. Thanks
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