Calling all who dare to explain

[vitalsigns65]

I have been learning all that I can for a few years now about vintage receivers while I try to understand how they work. I've replaced some caps, cleaned some pots, and adjusted some test points. I still lack the basic understanding of what I am working on when I open up a Pioneer SX-1250 for example, and a Sansui G-8000 for another example. It's the "Big picture" that I can't see, while I stick to a small task that must be done correctly or risk a step backwards.
I understand that when I take a line level input and send that signal out to the speaker posts there's a lot going on to make that happen that I don't understand.
What is meant by signal path ? Isn't the whole thing a signal path?
Is there an easy way to get my head around what's going on inside a receiver, such as a flow chart? How about a word or two from the people who find it easy to explain?
I'd really like this to turn out to be a enduring thread for the good of many others who have trouble with "The Big Picture".

:scratch2:

 

[dshoaf]

Here's a highly simplistic diagram to get you started: http://www.kpsec.freeuk.com/bdiags.htm

On those big receivers, there's a lot going on inside each of those blocks you see. For instance, inside the tuner block there are quite a lot of other circuit functions going on. Here's another simplistic diagram of what a tuner's block diagram looks like: http://www.radio-electronics.com/in...erheterodyne-radio-receiver/block-diagram.php. Those blocks show the parts of a tuner that takes a radio signal in, performs signal processing on it and produces an audio signal out of it, which then is fed back into the preamplifier stage you see on the other block diagram.

So, you can see that block diagrams are used to set the boundaries for certain functions within a receiver, amplifier or other piece of electronics. They don't worry about the details until you start drilling down into smaller blocks. Here's an example of the block diagram of an integrated amp with a bit more detail about how the switching interacts to allow you to control inputs: http://www.djerickson.com/pcpreamp/

What block diagrams do not show is how the amplifier or tuner actually works, though. I'd suggest your first step is to sit with your gear and see if you can identify which of those switches you see in that last diagram are present on your receiver or amp. Get comfortable with that first. Those big, monster receivers had lots of 'bling' switches to provide all sorts of little functions that don't actually get used much. Get used to the main ones first and the rest will come about in due time.

Hope that helps.

Cheers,

David

 

[vitalsigns65]

Now that's what I'm talking about! Thanks for those links!
Considering this simplified diagram how, if at all, does it translate to the topography of the Pioneer SX-1250?

 

[dshoaf]

Good catch. That's the overall block diagram of the power supply. On your Pioneer, there will be more than 1 regulated voltage output so think of more levels of voltage being regulated and you get the idea.

A regulated power supply supplies power to all the other blocks you see in the diagrams. So, this means that you don't see a line drawn to each of the other blocks that would indicate that the power supply is running them. Most block diagrams assume that you know that there's a power supply somewhere that is powering things.

Turns out that AK has a bunch of lit for the '1250, including the owners manual and the service manual. Start here: http://akdatabase.com/AKview/displayimage.php?album=44&pos=31. I suspect there's a block diagram one of both of those manuals.

Cheers,

David

 

[vitalsigns65]

Thanks again for the information!

 

[cfinchrist]

Thanks for posting this vitalsigns65. The same question has been in my mind as well for a little while now. When people say they "replaced the caps in the signal path" it was a little puzzling to me. Like you said, isn't it all in the signal path (at least in some capacity)?

 

[Hyperion]

Thanks for posting this vitalsigns65. The same question has been in my mind as well for a little while now. When people say they "replaced the caps in the signal path" it was a little puzzling to me. Like you said, isn't it all in the signal path (at least in some capacity)?

In my book only the parts of the circuitry intended to amplify or process the signal (in the audio sense) are in the 'signal path'.

So, PSU = no, Protection circuitry = no, Meter amplification/driving circuitry = no

 

[slowpat]

Now that's what I'm talking about! Thanks for those links!
Considering this simplified diagram how, if at all, does it translate to the topography of the Pioneer SX-1250?

As "dshoaf" mentioned, owner's manual and service manual are a must. Your goals have a slight conflict where you want to "big picture", and yet you got specific about the sx-1250. What I have found is that the diagrams provided by the other AK'er gives you an understanding of the building blocks of how the signal traverses different stages before getting to your speakers. That's the basic concept.

Now, each manufacturer tries to out do each other by tweaking one or more of those stages. Thus, you need to read through the operational theory provided in the service manual. The service manual will help you map that to the actual components in your receiver. Some are more helpful than others. Some of the Marantz service manuals explains how that particular model works, and I have seen a couple of Sony "theory of operations" manuals for their shortwave receiver. You need to have the patience to "connect the dots" from the conceptual reading to the manufacturer's implementation.

I would suggest picking up a lower end, more simple model and download all associated owner's and service manuals, and go through them. Then move up the chain.

Have fun..