building an external spring reverb, more questions then answers

[tonym645]

Hi

I found this cool schematic of a external spring reverb. my problem is i dont know if this will work on a electric guitar?



thx to Dödgenigt's Lab (http://www.dogenigt.com/2013/08/spring-reverb-module.html)

To be honest, today became my first day to really dig into electronics, especially for audio.
the only thing that ever came close was putting new pickups & potentiometers in my guitar and building a radio when i was 10( from a children s learning kit)


At first i thought it needed a buffer for guitar because of the high impedance levels
then i found out the ic's do just that, but there are a few differences between the guitar schematics iv'e seen using the same ic's and this one.
every time i tried to edit it i found out i was playing for a fool, you can maybe learn to build it from a schematic in a day certainly not edit it

also i have no idea if it will work with my spring reverb tank

Input Impedance 150 Ohms, Output Impedance 2250 Ohms

I hope someone can help get me on track because ive got my mind set on building it
otherwise its gonna take me a lot of time.

Lots of thanks in advance

Tony

[amptramp]

Your input impedance is very low for guitar work.  Guitars like to see a load of 500 Kohms and up.  The input impedance of this in the midband (where the coupling capacitors can be neglected) is the 10 K pot for dry volume in parallel with the 1 Kohm input resistor for the first stage amplifier.  The input amplifier on the left is an inverting amplifier where there is a virtual node at the inverting input caused by the amplifier trying to drive this point to the same 4.5 volt voltage as the non-inverting input.  Thus, the input sees an immovable voltage on the op amp end of the 1 Kohm resistor at the input.  If it was a non-inverting stage, you could raise the impedance to 1 megohm easily.

I am curious why dual op amps are used because one side of each op amp is driven by the Vcc/2 voltage. and the output goes nowhere.  Some pedals use the output of a Vcc/2 buffer to reduce the output impedance of the Vcc/2 level, but this does not.

You have a gain of -100 on the spring driver and spring receiver stages.  I am sure you don't need that much.  It looks like this circuit was designed to operate from low-impedance, low-level sources and the guitar is a high-impedance high-level source.

Your 150 ohm input to the tank will load the input stage severely and the 10 Kohm input gain pot is totally mismatched to the job, as is the TL082 op amp.  You need a power driver stage here and the TL082 with some transistors around it can serve as that stage or you could add an LM386 stage although this may introduce more complexity and distortion.  There are several types of power stage you can design around an op amp.  One uses transistors driven from the output in a complementary emitter follower configuration.  Another uses resistors in the op amp power leads to bias transistors on to various levels, adding to the current output.  If this is not clear, I can find some examples of each.

[garcho]

To be honest, today became my first day to really dig into electronics, especially for audio.

i would start with buying a breadboard, a few of the basic components you need for a guitar pedal, and try to make a simple, single transistor circuit first. there are many options, feel free to ask. or, buy a 'kit'. there are many to choose from, including reverb units. again, just ask (or do a search like this). you can learn the basics of audio electronics (at least enough to build with) quickly but you have to start at the beginning.

spring reverb is a little harder than it might seem to DIY. you need the right drive/recovery for the right transformer, if you're not sure what that means, there is a lot of good reading online you can find through a search engine. Here are some things you should read:

http://www.accutronicsreverb.com accutronicsreverb.com go to "how reverb works" at the top. also see "application" at the top and then look at "schematics".

more reading:

rod elliot

[tonym645]

Thanks to you both,

indeed it turns out to be a lot more complex than i realized.

amptramp, thanks for your reply, although i (roughly) understand 40% of your reply, i realized (at least) that i should have learned a lot more before even starting this post. i will read your reply again someday into the future.

garcho, its indeed better to start at the beginning, just like learning guitar, you cant just jump on stage the first day you hold one
i will search for something simpler.

thanks for the info!

when i get a little more educated ill be sure to post my questions, thoughts, and working schematics on this forum. (if i create a schematic and get it working )

Have a great day