1981 - Inventions DRV  [traced]

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

I was thinking about it, i guess I assumed the voltage doubler does not "double" perfectly due to the diodes and vref=v_supply wouldn't be exactly half of v_double.

So if my supply is 9v and my voltage doubler puts out 17v, v_ref is only 8.5v. It probably doesn't make a difference in operation.

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Seiche
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Post by Seiche »

The schematic is available now, a few differences
- the DRV uses non-inverting opamps throughout
- there are feedback caps on all stages and on the rat stage its much bigger than a normal rat
- not true bypass, bypass buffer and effect inputs are always in circuit and in parallel, while the outputs are switched
- the voltage doubler also builds a 2x 10k VRef as discussed above, presumably to get a true center voltage.
- it's kind of ruetz modded as there is only one cap and resistor combo from fb loop to gnd, but it's 470R + 220nF (instead of 47R + 2u2).

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Seiche
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Post by Seiche »

I wasn't completely wrong, though that bypass style is interesting. It's kind of like a vintage pedal. But with a relay (which is omitted from this project).
Screenshot_20190620-213820__01.jpg

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Groovenut
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Post by Groovenut »

I find SW2 on the input of the LT1054 to be interesting :hmmm: . It's not mentioned in the documentation and is not on the pcb.

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Post by aion »

Seiche wrote:I wasn't completely wrong, though that bypass style is interesting.
Straight up Klon buffer! Only differences are the 10k input resistor changed to 1k, and the 560R output resistor changed to 470R.

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Seiche
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Post by Seiche »

Groovenut wrote:I find SW2 on the input of the LT1054 to be interesting :hmmm: . It's not mentioned in the documentation and is not on the pcb.
I'm pretty sure that is the pad that needa to be connected if you're using other charge pumps. This is mentioned on page 2 of the docu. 7660 and 1044 charge pumps always want pin 1 and 8 connected (compare my "inspired by" circuit).
aionios wrote:Straight up Klon buffer! Only differences are the 10k input resistor changed to 1k, and the 560R output resistor changed to 470R.
The klon buffer in the klon is at the beginning of the effect though and always in signal.

Edit: I guess this is kinda always in signal, too. I'm wondering about tone suck. Wasn't that what we were always told about the vintage pedals with spdt switches on the output?

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Post by plush »

Seiche wrote:I'm wondering about tone suck. Wasn't that what we were always told about the vintage pedals with spdt switches on the output?
Oh yeah, I'm feeling the vibes of early 200s, when all boss pedals "had bad bypass", 3pdt mod was pretty much mandatory circlejerk on each gear-wank forum and so on.

We have a signal load in bypass, which is solved due to buffer. So, no tone suck occurs.

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Seiche
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Post by Seiche »

plush wrote:We have a signal load in bypass, which is solved due to buffer. So, no tone suck occurs.
So even though it looks like the vintage MXR bypass, it's solved by having a buffer in bypass (vs just a wire)? Why didn't they think of that back then?

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Post by plush »

Seiche wrote:
plush wrote:We have a signal load in bypass, which is solved due to buffer. So, no tone suck occurs.
So even though it looks like the vintage MXR bypass, it's solved by having a buffer in bypass (vs just a wire)?
Yep.
Seiche wrote: Why didn't they think of that back then?
[smilie=a_whyme.gif]

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Seiche
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Post by Seiche »

So I built the informant and while it sounds good at some settings, I think overall it's quite bright/thin and probably more suited to bigger rigs that are already breaking up. I'm playing it with a tele through a tweed champ clone at a bit over bedroom volume and it's a bit tinny.

It also doesn't let signal through when no power is applied, and high pitch whines when there is no cable in the input. I also don't really get why it needs a voltage doubler as the circuit doesn't seem to take advantage of higher headroom, maybe when running it like a boost (but with gain all the way down it doesn't really have that much volume reserves).

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Post by bool »

This circuit definitely looks like it comes from "more is more" philosophy.

Maybe try it with some humbuckers?

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Post by LaceSensor »

I built the vero - I like it actually!
I think Rats are kinda cool but I always felt mine sagged a lot and had this compression that I just didnt like.

I sold that one (80s RAT2) for a small song a while back, and this is a nice replacement of sorts.

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Seiche
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Post by Seiche »

Sounds much better (to me) when doubling the 220nf cap to 440nf or 470nf. More girth, more low end, better range of the cut knob.

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Post by Barcode »

I'm about to test out a build on this, but wanted to point out that the 2.2M resistor on the output stage seems nonsense. Has anyone validated that value? I was looking at this circuit with another builder as it is laid out in the build docs for both Express Layout and PedalPCB versions, and both have that 2.2M, but it seems bonkers to us. That whole stage seems a little pointless at that value, unless I'm missing its purpose. Is the expectation that it's a unity buffer? If so, then ok. If it's supposed to be gain recovery, shouldn't it be more like 2.2k or so?

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Post by Whoismarykelly »

That's almost surely a typo on the schematic. Like whoever drew it needed another vertical orientation resistor and they just copied the bias resistor and forgot to change the value before publishing.

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Barcode
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Post by Barcode »

So I got one, and did a trace, and I'll be damned. They actually did use that value there. Pointless.

So.... I modded the circuit to include a cap and a pot on a switch, which provides for a nice boost mode!

This is a great circuit but could benefit from some tweaks for sure.

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