mic preamp / delay project

[bladerunner]

Hi,
A vocalist friend has asked me if i could make him a combined mic preamp and delay unit for use onstage, and i could really use some help with the design!

For the delay portion of the unit i was planning on using the innards of an old electro-harmonix memoryman delay that i have lying around, which is powered by +24V single-rail AC supply:-

http://mysite.wanadoo-members.co.uk/deltaharmonic/schems/EH_delux_memoryman.gif

(link from murk burnley post - cheers mark!)

Looking at the schematic it seems the 24V AC is then rectified becoming single -15V DC. i hope this is right!!

I would like to ask is any advice or recommendations for a suitable mic preamp circuit that might fit the bill - i suppose ideally the mic pre would run off the same +24V single supply as the MM circuit. although if i was to do something like a very basic version of the green pre, would it then be feasible to run the MM circuit from the - rail of the +/-15V supply?

The unit would always be used with an SM58, so no phantom power is needed...

The input and output of the memoryman is unbalanced instrument-level, so i suppose i would need level/impedence matching between the two circuits... and also would need to add balanced output stage or buffer of some kind - the ultimate output of the unit would be line level via XLR to front of house..

i have some surplus bits lying around which it would be great to incorporate - a sowter 9820c input transformer (API input replacement), and some unidentified input transformers from an old mic mixer (marked 32246F). the sowter transformer is 1+1 : 3.54 but im not sure about the ratio of the other transformers..

any help would be greatly appreciated!

 

[StephenGiles]

Remember that the Memory Man was designed for instrument level input. Also that is a redraw of the EH circuit, so there may be mistakes. I'll dig out the original if you would like it.
Stephen

 

[NewYorkDave]

Rat Shack useta make an analog echo unit (bucket-brigade type) with a mic input. I used one back in the '80s :wink:

Schematic

Here's someone on evilBay trying to sell the same unit at a ridiculous price. Nice photos, though :roll:

http://cgi.ebay.com/Realistic-Electronic-Reverb-Vintage-Analog-Sliders-OB_W0QQitemZ7390746263QQcategoryZ64382QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[EZ81]

There is a the PT2399 IC which just needs some caps/resistors for audio in -> delayed audio out. It is for example used in the Danelectro BLT slap echo (one of their cheap crappy plastic guitar FX) (which i hacked years ago to make the delay time adjustable :roll: ). Far from studio quality, though...

;Matthias

 

[bladerunner]

Thanks very much for the replies guys! Stephen i would definitley appreciate that original MM schematic if you have it to hand, cheers mate!

I am still planning on using the memoryman for the delay part of the circuit, especially as the guy im building this for loves the MM sound and is really into the idea of incorporating it.. maybe this is actually making problems for myself, as it means i have to fit internal levels/power supply voltage around the MM circuit, but i think the time and effort it would save using the MM rather than building a delay circuit from scratch makes it worth doing, especially as i have a MM already sitting here to use as a donor. surely there is a simple, halfway-decent sounding mic-pre design that would fit the bill? either a single 24v type or maybe a simple version of the green pre? still wondering whether i could run the MM off the -15v side of the supply, or just use a 24v transformer with a +/- 15V supply fro the green, and take the MM 24v from the secondary of the trf..

Thanks a lot for the ratshack link NYD - what do u reckon about using the mic-pre part of this circuit? can you remember if it sounded ok? also, what exactly is going on with the power supply part of the circuit? are the opamps getting 9v from it or is Q6 changing the voltage in some way?

Sorry if my questions are showing my almost complete ignorance!! also i'm rubbish at writing posts that get across what i want to say so please forgive my vagueness!! i think i could learn quite a bit from doing this project, and hopefully fill in some of the important gaps in my knowledge - eg interfacing levels/impedence and power supply issues... its so frustrating when you are trying to study this stuff without having done a basic course in electronics, essentially teaching yourself - you end up understanding some really quite complex stuff, but missing some of the real basics...

Thanks once again for the help so far - any more input would be really great. cheers!!