Solo Dallas - SVDS Replica  [traced]

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moonshiner
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Post by moonshiner »

caspercody wrote:Just a reference point for voltage contacts. so if I needed to connect to a specific voltage, I know where they are located on the board. As for building the vero, it means nothing.
Thanks . I have made several hundred vero pedals . That was messing with me a tad ha ha . My parts come Tuesday . I’m excited . Ha ha

madras
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Post by madras »

Hi there!

As I mentioned before in this topic I have already build mine one based on original schematic:
https://www.freestompboxes.org/viewtopic ... 60#p277360

I found out major part of the schematic around LM380 seems to be useless. I am talking about the part marked in red circle:
Image

1. First of all R10 and C15 creates low-pass filter with roll-off above 72.3 kHz (C15=1nF) or 15.4 kHz (C15=4.7nF). In case of guitar signal it does nothing except atteuating signal in linear way and adding noise.
2. Next we have R11 and R12 making pure voltage divider which attenuates signal and adds more noise.
3. Next we have LM380 power amplifier which was originally purposed for driving XLR transformer. It amplifies already attenuted singnal by 34 dB and adds a lots of noise!! Attenuation and then amplification of a signal does not make any sense.
4. R13 and C20 is just a Zobel network originally introduced to neutralize the effects of the XLR transformer inductance load. In our case there's no transformer anymore! So no need for Zobel circuitry, becasue it does not changes anything which would be audible. For reference see - https://trueaudio.com/st_zobel.htm

Based on my analysis, I removed all the mentioned part. Thanks to removal of mentioned low-pass filter and voltage divder I gained quite a lot of signal signal level and now no need for additional amplification with LM380. So the amp was also removed together with Zobel circuitry. NE570 compander output has built-in opamp / buffer which is strong enough to push Marshall Plexi pre-amp really hard!

Thanks to the modification I reduced noise a lot! SVDS sound characteristics remains the same as before. The only difference is now I have significantly less noise and a little less gain, but it is not a disadvantage for me, because the highest levels are unusable in original Schaffer Replica, becasue in my testing a signal started to clip with default 15 VDC power supply.

I hope some people find it helpful. If someone thinks the thing is different, then please explain why the part of circuit I am talking about is important. I am looking for interesting discussion :popcorn:

Best regards!

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EddieTavares
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Post by EddieTavares »

madras, Great job!!!

There is some components in that circuit that does not affect the tone like l1, LM117, D1, D2, C34, R14, R15, C27, C31, C32, the LM380 does a little overdrive but is almost irrelevant.

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ppluis0
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Post by ppluis0 »

Hi madras,

OK to discard the LM380 and associated circuitry. There was implemented to drive an transformer to have a true floating XLR.

I'm in doubt about the need to process the signal using a compander, since this operation was due to establish an RF link between the instrument and the amplifiers.

Please try to extract the signal right at C5 -avoiding the compander chip- and tell us if you hear any difference.

Cheers,
Jose

madras
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Post by madras »

ppluis0 wrote: I'm in doubt about the need to process the signal using a compander, since this operation was due to establish an RF link between the instrument and the amplifiers.

Please try to extract the signal right at C5 -avoiding the compander chip- and tell us if you hear any difference.

Cheers,
Jose
Jose, you may be right. I have also wondered how compressing 2:1 and then expanding 1:2 may affect the sound. In theory it should do nothing. In practice companders wasn't perfect those days, so it is possible it adds some harmonics. What I obsered NE570 starts to clip itself when input potentiometer set to around 60-70% on 15VDC power rail. I have also obeserved NE570 boosts signal noticeably, so getting signal straight from C5 will effect with less gain :D

What shapes the tone for sure IMO is preemphasis circuirtry at the beginning and linear boost in NE570 (and LM380 ofc) pushing preamp tubes to distort.
EddieTavares wrote:madras, Great job!!!

There is some components in that circuit that does not affect the tone like l1, LM117, D1, D2, C34, R14, R15, C27, C31, C32, the LM380 does a little overdrive but is almost irrelevant.
It is power supply so this is obvious. Let's focus on signal path.

Best regards.

caspercody
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Post by caspercody »

I put a SPDT switch in and connected one side to normal output and the other side connected after C5 and I did not notice much if any tone change.

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ppluis0
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Post by ppluis0 »

caspercody wrote:I put a SPDT switch in and connected one side to normal output and the other side connected after C5 and I did not notice much if any tone change.
I always believed that the use of a compander was not justified and it was just a sales pitch. :roll:

In other words, this results in a bad reproduction of an old device, as been proved with the elimination of the LM380

If any other member of the forum that has build a replica of this "replica" can do the same test with a spdt switch I would like to hear his results in this thread.

After all, one of the reasons for this forum to exist is to break down myths, isn't it ? 8)

Cheers,
Jose

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Post by caspercody »

Here is a vero layout with out the compander and beyond.
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SVDS small.png

rcflyinghokie
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Post by rcflyinghokie »

patricef wrote:Attached the latest schematic. Enjoy !
Hello all!

So I put this wiring together a year or so ago and never finished. I am back to trying to complete this board and my LM380 gets very hot and my signal out is very weak.

Was this schematic shown to be working? Any help would be greatly appreciated!

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Post by madras »

The schematic you mentioned is electrically correct. Also I've built one. It looks like you made some mistake. I guess you have circuit accidentially shorted somewhere near LM380.

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Post by rcflyinghokie »

madras wrote:The schematic you mentioned is electrically correct. Also I've built one. It looks like you made some mistake. I guess you have circuit accidentially shorted somewhere near LM380.
Yeah I found a ground short before (with the 380 installed) but all shorts are now resolved. Is it possible I fried my 380? It only gets hot with the signal pins attached. If I lift pins 2 and 3 no heat is generated.

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Post by madras »

It may be possible it has been broken. But in order to rule out other possibilities make voltage measurements (referenced to ground) of LM380. And then let's compare it to IC3 measurements made by patricef: https://www.freestompboxes.org/viewtopi ... 46#p268246

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Post by mictester »

FFS!!!

You've all missed the obvious. I put a circuit up here several years ago, using the halves of an NE/SA 570/571 as a compressor first (actually as an ALC circuit - see the datasheet) and as a noise gate second. Set up correctly, this gives plenty of clean sustain, but shuts off the objectionable noise when the input becomes too quiet and the ALC gain reaches maximum. The ALC gain is limited to prevent it becoming a radio receiver or picking up the cries of distant seabirds.....

https://www.freestompboxes.org/viewtopi ... =13&t=5504

The circuit can be thrown together in minutes on a scrap of Veroboard (if you have the compander IC). It sips current from a 9V battery, and I've built these into guitar bodies for people who seek lots of sustain. The circuit works really well with single coils, but needs a little attenuation of humbuckers - unless you run the circuit at 18V......
"Why is it humming?" "Because it doesn't know the words!"

rcflyinghokie
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Post by rcflyinghokie »

mictester wrote:FFS!!!

You've all missed the obvious. I put a circuit up here several years ago, using the halves of an NE/SA 570/571 as a compressor first (actually as an ALC circuit - see the datasheet) and as a noise gate second. Set up correctly, this gives plenty of clean sustain, but shuts off the objectionable noise when the input becomes too quiet and the ALC gain reaches maximum. The ALC gain is limited to prevent it becoming a radio receiver or picking up the cries of distant seabirds.....

https://www.freestompboxes.org/viewtopi ... =13&t=5504

The circuit can be thrown together in minutes on a scrap of Veroboard (if you have the compander IC). It sips current from a 9V battery, and I've built these into guitar bodies for people who seek lots of sustain. The circuit works really well with single coils, but needs a little attenuation of humbuckers - unless you run the circuit at 18V......
This isnt helpful at all.....

rcflyinghokie
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Post by rcflyinghokie »

madras wrote:It may be possible it has been broken. But in order to rule out other possibilities make voltage measurements (referenced to ground) of LM380. And then let's compare it to IC3 measurements made by patricef: https://www.freestompboxes.org/viewtopi ... 46#p268246
Yeah I popped in a new 380 same issue...do you want the measurements with the chip in place?

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mictester
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Post by mictester »

rcflyinghokie wrote:
mictester wrote:FFS!!!

You've all missed the obvious. I put a circuit up here several years ago, using the halves of an NE/SA 570/571 as a compressor first (actually as an ALC circuit - see the datasheet) and as a noise gate second. Set up correctly, this gives plenty of clean sustain, but shuts off the objectionable noise when the input becomes too quiet and the ALC gain reaches maximum. The ALC gain is limited to prevent it becoming a radio receiver or picking up the cries of distant seabirds.....

https://www.freestompboxes.org/viewtopi ... =13&t=5504

The circuit can be thrown together in minutes on a scrap of Veroboard (if you have the compander IC). It sips current from a 9V battery, and I've built these into guitar bodies for people who seek lots of sustain. The circuit works really well with single coils, but needs a little attenuation of humbuckers - unless you run the circuit at 18V......
This isnt helpful at all.....
Why not? You're all chasing your tails over an NE570 feeding an LM380 amp chip. Stop believing the hype. It's nonsense!

There is no point whatsoever in putting your guitar signal through a compressor stage then through an equivalent expander unless they're either side of a noisy wireless link or a noisy effect. Angus' guitar sound isn't anything special! The "effect" is 99% hype.

The mod that I made to a few wireless guitar rigs (for some very well-known guitarists) was to disable the expander on the receiver - they preferred the compressed output from the receiver. That's all that was done to Angus Young's gear. I frequently modified the expander in the receiver to be a noise gate. Trivial.

I sometimes can't believe the stupidity of people in the music business. No wonder the Boutique Boobs are still raking in the cash......
"Why is it humming?" "Because it doesn't know the words!"

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Post by madras »

mictester wrote:Why not? You're all chasing your tails over an NE570 feeding an LM380 amp chip. Stop believing the hype. It's nonsense!
Yes, in general I can agree with you. I have built one. Above you can see my post with analysis I made above. I have shown at least 1/3 of schematic does nothing except adding noise to the signal (circuitry around LM380). And I am taking into account NE570 compander. If we take into account it would mean 2/3 of Schaffer Replica's does nothing except clean signal booster with some EQ. The only part of circuit which actualy affects the sound is pre-emphasis circuitry which make boost of trebles.
mictester wrote:The mod that I made to a few wireless guitar rigs (for some very well-known guitarists) was to disable the expander on the receiver - they preferred the compressed output from the receiver. That's all that was done to Angus Young's gear. I frequently modified the expander in the receiver to be a noise gate.
Ohh, wow. I haven't known it before. Do you have information Angus also modded his wireless system this way? Or you personally modified it for him? You really interested me on this. Could you elaborate more on it?
rcflyinghokie wrote:Yeah I popped in a new 380 same issue...do you want the measurements with the chip in place?
Yes, please make measurements when LM380 in place and also when it is unplugged. I mean voltages referenced to ground on all LM380 pins (in two cases when LM380 is in place and voltages on corresponding board pins when it is unsoldered.

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Post by mictester »

madras wrote:
mictester wrote:The mod that I made to a few wireless guitar rigs (for some very well-known guitarists) was to disable the expander on the receiver - they preferred the compressed output from the receiver. That's all that was done to Angus Young's gear. I frequently modified the expander in the receiver to be a noise gate.
Ohh, wow. I haven't known it before. Do you have information Angus also modded his wireless system this way? Or you personally modified it for him? You really interested me on this. Could you elaborate more on it?
I'm sure that Geoff Banks would tell you if you asked!

The NE570 (series) is quite widely used in higher priced guitar pedals. It works well at voltages from 9 - 18V (the higher end is better), and it's trivial to make 2 : 1 compressors for the input of a noisy effect, and 2 : 1 expander for the output. This was commonly done with BBD-based effects, since the BBDs (particularly the Reticon ones) used to hiss so badly.

There are other interesting effects possible with the 570 - ALC mode gives great sustain (look at the datasheet for the configuration), and if you make the timing capacitor deliberately too small, you can get some nice second harmonic (and a really ghastly fuzz on chords!). These ICs can be configured as VCAs - I used to build a stereo panner / tremolo based on this approach - it's useful that the 570 and 571 have two complete channels. The 572 was used by Peavey in a really good sustain unit, and the 575 is frequently used in wireless rigs.

My "standard" clean sustain uses an NE 571, NE5532 (because the op-amp inside the 571 is not great), and an LM324 for the "variable capacitor" trick (it's in the datasheet) to give really fast attack and a slowed decay. It doesn't pump, and is really nice before some distortion effects, so that you hit them at exactly the "sweet spot" all the time. I also provide a buffered, non-compressed output, to be used as the feed for the sidechain of Mutron or other envelope-driven effects. I run the circuitry from 17.5V, and it doesn't contribute any noise of its own, because the 5532 is so quiet. The distortion is also vanishingly small, so it doesn't colour the sound of the instrument. I have added optional tonal shaping - it's sometimes a good thing to roll off the top end when going into a Fuzz or other distorting effect, because the effect will "paint in" the missing upper harmonics.....

The clean sustain is designed to be the first device in an effects chain. This spoils the interactivity of effects like a Fuzz Face, but if you want that, you can put one before the sustain unit....

The genesis of the design was given in the thread I referred to in a previous post. The circuit given is perfectly useable - especially with single-coil equipped guitars. I've even built it into the body of Telecasters - it really helps country players! In that case, I used a push-pull switched pot to enable or bypass the sustainer. If you want to use it with humbuckers, you need a higher supply voltage if you are to completely avoid clipping.
"Why is it humming?" "Because it doesn't know the words!"

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Post by tbsfx »

Hi guys, this in my version about the Schaffer preamp, and works very well, like the original , all info below. :wink:

Images
Image
Image
Image

Video
https://youtu.be/6AapZWDFiYE

See Ya :)
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Storm Replica schem.zip
Schematic
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Thefamilycurse
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Post by Thefamilycurse »

There is a re-housed Schaffer replica EX Tower on Reverb right now and the guy selling it has posted a bunch of guy shots. I hope this helps you guys! Might find some new information there.

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