Drewtronics Sherlock

[Guest]

Hi, I know that many of you have built Drew's Shure Level Loc clone, the Sherlock. I'm curious about a mod that I know I read about somewhere (possibly the TapeOp board, which has been down) to convert the mic level unit into a line level unit to be used as an insert/aux send for mixdown. I'd love to mod mine to have and XLR input on the front for mic level and 1/4" on the back for line in/out.

I emailed Drew, but he's not longer giving out those instructions. Just hoping someone here knows how to do it.

My guess is that on the input side of things I would have to pad down the line level input somehow because the unit is expecting mic level, right? On the output side, I would have to add some gain somehow to get it from mic level to line level. And would there be some impedence issues? Again, I have no idea...just thinking out loud.

Thanks.

 

[Guest]

OK, I could keep the output at mic level and just use a pre to bring it to line level, but can someone tell me how to pad down the line level input so that I can feed it off the board?

Is is as simple as adding a resistor or something? A VCA? Xfmr?

 

[smilinfu]

I just put some of the Shure pads in front of the inputs. For me it was easier than adding switches and/or extra inputs to my already cramped box.

However I know it was not a very DIY solution but... :sad:

It has been a while but I belive the AUX outputs are at line level already.

 

[gyraf]

IIRC, the level-loc uses two mic input transformers - one to convert mic signal to something approaching line level, and another one at the output to convert line'ish level back to mic level.

A guess could be that you could simply omit the transformers for something like a line-level (don't expect high-level +4) in and out.

Jakob E.

 

[Guest]

OK, so far I?ve been told of 4 different approaches to this problem, and I?m not sure which is the best way to go, but maybe someone can help me sort it out.

1. Gyraf suggested that since the LL used an input and output transformer to take the mic level to line level, and line level back to mic level, that I bypass them to utilize the line(ish) level. The LL schematic corroborates this, and the Sherlock BOM indicated a pair of 10:1 transformers. I?m going to reopen it (I did it a while ago) and see what?s going on in there (after my Trig final next week ? gotta put off the DIY to study?). And I just found a schematic for the Sherlock (which doesn?t indicate the XFMRs because they?re off-board ? but I?m sure they?re in there.

2. Some info I found on the web said that to take balance line level down to mic level the input just needed to be padded down about 50db and that this could be accomplished 2 300 ohm resistors in series on both pins 2 and 3, and a 4 ohm resistor in parallel connected together between each pair. From what I can gather, this is the mod that was originally suggested by the Sherlock designer, Drew (drewtronics).

3. I spoke to Bill Whitlock, president of Jensen Transformers, and he suggested that I use their JT-DB-E transformer (12:1) to convert an (unbalanced) line level to balanced mic level. Since I want to use this with a line level feed off the board, it?s already balanced, but I think it?s still the same. Maybe not? Maybe Gyraf?s suggestion is better since I?m working with a TFMR already in there instead of adding another one.

4. The original Shure Level-Loc literature says that the unit can be used with line amplifiers by turning the ?Input? on the Level-Loc down, and that the ?AUX? out is +60 or +80, depending on if the mic is high or low impedence. When I last used the Sherlock, the aux signal much louder, but I can?t remember if approached line level.

 

[leigh]

[quote author="gyraf"]IIRC, the level-loc uses two mic input transformers - one to convert mic signal to something approaching line level, and another one at the output to convert line'ish level back to mic level.

A guess could be that you could simply omit the transformers for something like a line-level (don't expect high-level +4) in and out.[/quote]

Yeah, that's how it's set up. It's already got a line-level Aux out, and I think for an input you could just bypass the input transformer.

Actually, check the original schem for line-level input circuitry:

http://www.shure.com/pdf/discontinued/m62v.pdf

Cheers,
Leigh

PS: Whoops, this crossposted with your last one, Twitch....

 

[soundguy]

if you want to keep the input transformer, just put a line pad in front of it. Other than that, Id bypass the transformer and see where you are at. What are you feeding it? If you are sending an aux to it that has a level control for the output, you'll probably be fine by just bypassing the input transformer, you'll have to try to know either way though.

dave