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Old 11th November 2006, 09:06 AM   #1
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Default Determine the signal path ?

Hey all.

It's been a while since I've visit these forums (a long while methinks), but I'm ready to get back into DIY audio.

Question though, when looking at a schematic, how can you determine which components are in the signal path (besides the obvious components in the straight line from input to output), or strongly influence the signal, in order to determine where not to skimp on the components.

Ie, should components coming off the psu rails onto the signal path be high quality ? What about components going to ground (like in a zero feedback circuit) ?
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Old 11th November 2006, 11:50 AM   #2
lineup is offline lineup  Sweden
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Best is if all components, signal path and supply, are of high quality.

If you have not clean supply and may not help how good parts in signal part.

I usually compare an amplifier, with making a BIGGER PAPER Photo form a small (24x36mm) negative.

The copier machine is = the amplifier, to enlarge, amplify.

1. Do not have any dirt or scratches on the negative!
2. For copy paper .. do have it ALL WHITE, without dirt.
3. Make sure you have a good lens of high quality and keep it clean.
---------------


1. Input. Make sure you have good quality sound source before amp.
If your input signal is not good, you may put 1.000.000
and it will still deliver same quality output signal = not good.
For in a good amp: input = output.
---------------

2. Power supply. Copy paper - ALL WHITE.
This is the material used to create an amplified version of the signal.
Make sure you have clean DC to feed your amp.
Ripple, noise or too weak supply can often give bad result
even if your amplifier circuit is PERFECT with best possible components.
---------------

3. The lens - the amplifier circuit itself.
If this is not good, it does not matter how good source(1) and power supply(2).
---------------



The result from 1,2,3
will only be as good as the weakest point 1,2,3 allows, or worse.
A good hifi reproduction REQUIRES ALL of these:

1. good input signal
2. good adequate power supply
2. good amplifier circuit



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Old 19th November 2006, 08:48 AM   #3
Trebla is offline Trebla  United Kingdom
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No one seems to have answered this question. So i have resurrected this thread.
I would also like some ideas on how to trace the signal path components. I have a schematic for the Nad 7020, but it looks to be a different version to my amp. Therefore i need to find another way.
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Old 19th November 2006, 09:49 AM   #4
es44 is offline es44  Denmark
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If you have a decent copy of the schematic, then it's quite easy to determine the signal path. The lines are enhanced compared to voltage feed lines.
Hope that makes sense.

Best regards
Ebbe

Edit: this goes for the Nad 7020
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Old 19th November 2006, 10:24 AM   #5
lineup is offline lineup  Sweden
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Quote:
Originally posted by Trebla
No one seems to have answered this question. So i have resurrected this thread.
I would also like some ideas on how to trace the signal path components. I have a schematic for the Nad 7020, but it looks to be a different version to my amp. Therefore i need to find another way.
Trebla



My answer is in Post #2.
http://www.diyaudio.com/forums/showt...40#post1054040

************************************************** *****

I thought I had answered at least this question:

1. Should components coming off the psu rails onto the signal path be high quality ?
2. What about components going to ground (like in a zero feedback circuit) ?


Quote:
A good hifi reproduction REQUIRES ALL of these:

1. good input signal
2. good adequate power supply
2. good amplifier circuit

lineup
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Old 19th November 2006, 11:14 AM   #6
AndrewT is online now AndrewT  Scotland
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Hi,
the speaker gets it's current from the mains.
All the components between the mains and your speaker will to some extent (sometimes inaudible and sometimes unmeasurable) affect the output.
The PSU tries to provide a clean DC supply with no noise and low source impedance.
The amplifier can be thought of as a variable resistor that alternately connects +ve Dc and -ve DC to the speaker terminals.
All the components in these two major parts affect the quality of sound.

The exceptions are the components outside these two circuits.

eg. a relay to switch the "speaker delay on start up" and/or the LED to show "power on" and/or the other ancilliaries that are not between mains and speaker terminals.

BUT the other components must not modulate the clean DC that is vitally important to the overall sound quality. Some MUST get their power from else where.

The clever bit is recognising when compromise will least affect the sound quality. eg cheap and small electrolytics in some parts of the circuit. Eg. I have a Conrad Johnson pre-amp (the cheapest in the range) which has no electrolytics anywhere, not even in the PSU.
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Old 19th November 2006, 11:24 AM   #7
lndm is offline lndm  Australia
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In determining a 'signal path', some like to draw a line through an input coupling capacitor, through the transistor and out the output coupling capacitor, (for a simple single-ended example).

In fact, the signal could be imagined as stopping at the base, and being taken up again in the emitter-collector circuit, then being tapped out to the output coupling capacitor. In other words, the signal out is what is going through the emitter capacitor, transistor and collector resistor.

This signal then flows through the power supply. A supply rail should in theory be an AC short to ground. If it isn't, or more commonly, isn't consistently across the spectrum, it may introduce a signature.

Quote:
Originally posted by lineup Best is if all components, signal path and supply, are of high quality.
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Old 19th November 2006, 11:33 AM   #8
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by lndm
In determining a 'signal path', some like to draw a line through an input coupling capacitor, through the transistor and out the output coupling capacitor, (for a simple single-ended example).

In fact, the signal could be imagined as stopping at the base, and being taken up again in the emitter-collector circuit, then being tapped out to the output coupling capacitor. In other words, the signal out is what is going through the emitter capacitor, transistor and collector resistor.

This signal then flows through the power supply. A supply rail should in theory be an AC short to ground. If it isn't, or more commonly, isn't consistently across the spectrum, it may introduce a signature.

too simplistic and omits hundreds of components that seriously affect sound quality and show measurable degradation of output.
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Old 19th November 2006, 11:56 AM   #9
lndm is offline lndm  Australia
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Quote:
Originally posted by AndrewT
too simplistic and omits hundreds of components that seriously affect sound quality and show measurable degradation of output.
Hi AndrewT, we posted at the same time. So anyway, do you think lordvader was asking for a starting point, or a thesis?
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Old 19th November 2006, 01:23 PM   #10
lineup is offline lineup  Sweden
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hi

this is the compare, the analogy, I use to explain to non audio people
what signal amplification is about:

Quote:
Originally posted by lineup

Best is if all components, signal path and supply, are of high quality.

If you have not clean supply and may not help how good parts in signal part.

I usually compare an amplifier, with making a BIGGER PAPER Photo form a small (24x36mm) negative.

The copier machine is = the amplifier, to enlarge, amplify.

1. Do not have any dirt or scratches on the negative!
2. For copy paper .. do have it ALL WHITE, without dirt.
3. Make sure you have a good lens of high quality and keep it clean.
---------------


1. Input. Make sure you have good quality sound source before amp.
If your input signal is not good, you may put an 1.000.000 amplifier
and it will still deliver same quality output signal = not good.

Because in a good amp: input = output. Dirt in = dirt out!
---------------

2. Power supply. Copy paper - ALL WHITE.
This is the material used to create an amplified version of the signal.
Make sure you have clean DC to feed your amp.
Ripple, noise or too weak supply can often give bad result
even if your amplifier circuit is PERFECT with best possible components.
---------------

3. The lens - the amplifier circuit itself.
If this is not good, it does not matter how good source(1) and power supply(2).
---------------


lineup
I think it is not too bad analogy
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