How does send and return really work?

Manfred-Klose · 2008-08-28T22:14:46+00:00

How does send and return work on a full valve amplifier? No one gave ever gave me a straight answer, i'll guitarforum a try. All i want to know is when the...

How does send and return really work?

Manfred-Klose

right on rene!!

FenderBender

Hi Manfred,

My apologies for taking so long to get back to you. I had a long look at the specs of the pedals and the diagram of your amp.

The levels we have to consider in your setup are:

-6dBV (amp effects loop) = 0.501Vrms = 0.706Vpeak
-20dBu (DD-6 pedal cct) = 0.077Vrms or 0.108Vpeak

We can more or less calculate the peak instantaneous power dissipated by the input stage of the pedals when fed by the amp using Ohm's law:

P=V2/R = (0.7062)/1000000 = 5*10-7W or 0.5 microwatts, of little threat to your pedals input stage.

The impedance of the amp's "effects return" input stage is (you guessed it!) 1Mohm. Although the signal level sent from the pedals is a lot less than specified in your manual, the amp is equipped with feedback from the output transformer's secondary winding that is used to regulate the bias on the cathode of the first valve in the main amp circuit. This should take care of varying signal levels.

IMO you are ok electrically, but you will have to listen to it and decide if works for you or not.

FenderBender

Take a look at http://www.sengpielaudio.com/calculator-db-volt.htm for a signal conversion calculator and tips.

Manfred-Klose

Hey graeme its not the end of the world, seems we are the only ones scrolling the internet at 2 in the morning.

lucky me i studied Electrical engineering at shcool, so know know a little bit about these things.
How did you get all your knowledge about electrical circuits? library,internet,college......

Thanks for the time you took.

How would the send and return differ for say a marshall jcm900?
I just went and looked at the circuit, and the send and return configuartion seems similar.

GO check out some of these sites for Schematics on almost everything:
http://www.schematicheaven.com/index_HTML.htm
http://www.freeinfosociety.com/electronics/schempage.php?cat=1

I gave the shcematics of the jcm800 to one of my buddies, and he is building his own marshall, thats intense.

AlanRatcliffe

Good links guys, I'm bookmarking frantically here!

Manfred-Klose

One day when i have the knowledge, i'd rather build my own amp,than to pay R20 000+ for a boutique amp.

Anyone with me on that on?

MiKeZilLA

One day when i have the knowledge, i'd rather build my own amp,than to pay R20 000+ for a boutique amp.

Anyone with me on that on?

Yep i'd much rather have you build me one too... ?

FenderBender

Hey graeme its not the end of the world, seems we are the only ones scrolling the internet at 2 in the morning.

Yeah I'm really addicted! I only ever put my time into things I really enjoy....most of my time that is ?

How did you get all your knowledge about electrical circuits?

I started pottering around with electronics in 1983 and then studied EELC at CPUT in the late 80s. After that I worked in the consumer electronics sector repairing video cameras and then moved to the industrial sector in 1994. My last position was the electrical manager for a large packaging producer...until being retrenched at the end of July.

Thanks for the time you took.

Well thanks for giving me something to get my teeth into ?

How would the send and return differ for say a marshall jcm900?

I'll take a look and get back to you ?

I gave the schematics of the jcm800 to one of my buddies, and he is building his own marshall, thats intense.

Thats lekker!

One day when i have the knowledge, i'd rather build my own amp,than to pay R20 000+ for a boutique amp.

Anyone with me on that on?

Bring it on! I have plenty time on my hands lately, hence getting into guitar and related equipment. I'd be very game to put together a kickass amp project with any willing parties. I have a good gut feeling that I should be doing exactly what I am doing. It has already been far more rewarding in such a short space of time as opposed to 5 years in a (thankless) production environment ?

FenderBender

I reckon the specs on you amp being strange has less to do with the blues and more to do with grass.

The problem being? ?

Manfred-Klose

Awesome man.

I heard of a guy in paarl that builds boutique valve amps, i lost his contacts though, he had a website, but cant find it, will have a look around.

if you would build a amp, how much would you charge? and would you be able to do mods?
say it would be something like a jcm900 head for example.

My last position was the electrical manager for a large packaging producer...until being retrenched at the end of July.

was BEE involved ?

FenderBender

if you would build a amp, how much would you charge?

I would not be able to answer that as I am not up to date with current component costs, but will put some time into this and see what comes ?

would you be able to do mods?

Probably far easier than a build from scratch. What did you have in mind? ?

FenderBender

was BEE involved ?

I think BEE is a BEEG part of our lives in SA these days.

Manfred-Klose

i Dont have any mods want to do yet, just asking so i can keep you in mind when some day i need to mod something, or someone asks me for contacts.

I forgot to tell you, i also studied electrical engineering but only on a high school level, blown a few relays back in the days.....but it was fun, no one got injured though.

Anyway to get back to the topic, one of my projects i did was to build a Distorion pedal, i chose the mxr distortion circuit. did ever function correctly, but it was a great learning experience.

I bought the capacitors and resistors,jacks,potensiometers, and pcb for a R100 at Yebo electronics.
That is a big bargain if pay R100 for a custom made pedal than to R800 for something that has been assembeled by slaves in korea.

I takes a lot of your time though.

Here is the link to yebo electronics site, see you are cape town, so this could be close to your home:
http://www.fort777.co.za/

The have the prices of all of their products, and can be ordered through the internet.

Martyr

pedal order

Manfred-Klose

Where did you get that pic?

Martyr

got it LONG ago i found it like a hour ago on my pc and saw this thread so i posted it...

AlanRatcliffe

Martyr wrote: pedal order

That pic for me proves just how variable these things can be. There's quite a few things I would do differently, and even a few I would say are definite no-nos.

For instance:

- I'd never put a preamp pedal in front of a compressor, as every time you kick the preamp on, it would affect the compression and the compressor would bring the level down anyway, evening out any volume boost. For me, the only time I'd use a compressor anywhere other than first in the chain is if I were using it to even the varying output level of a modulation pedal like a chorus or flanger.

- The delay would be further along the chain, right in front of the reverb, as the digital delays I like are pretty neutral tonally, so the EQ could go on either side of it. They also have a negligible noise floor, so the noise gate works better in front of the delay but after the EQ. I'd also have the volume pedal before the delay so that volume changes don't affect echoes unnaturally (as mentioned before). Having the delay later also means that it's possible to use the stereo outputs into the reverb (which often have stereo inputs too) - then I could take the stereo output of the reverb into two amps if I wanted.

Manfred-Klose

Same here Alan.

Dont know why you would want to run delay, and then ad a noise gate to that?

Use this as a reference:
http://ratcliffe.co.za/articles/effectchain.shtml

FenderBender

Now where did u get that ? ?

AlanRatcliffe

Manfred Klose wrote: Use this as a reference:
http://ratcliffe.co.za/articles/effectchain.shtml

I do ?