It is currently Mon Mar 16, 2020 2:18 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 10 posts ] 
Author Message
Post subject: Fender 140 - help needed on signal flow.
Posted: Thu Oct 23, 2014 3:30 pm
Offline
Hobbyist
Hobbyist

Joined: Wed Aug 27, 2014 1:53 pm
Posts: 15
Hi,

I'm struggling a bit on how the signal flows through a Fender 140.

This is the schematic:
http://www.emerald-green.de/images/fender-140-schem.jpg

So far I understand as much as this:

- input signal, one channel, two equal inputs
- V1, first triode
- tone stack, mid boost, bright, volume control, lead control
- V1, second triode

[...]

- equalizer
- V5, phase splitter
- V6-9, output tubes

But I'm totally lost as regards what's going on in between.
How does the signal travel through the reverb section, and how's the
effects loop, the bass boost, treble boost, master and lead volume hooked on?

Also, in other fender schematics you'd normally find the 82 K-ohm and 100 K-ohm
resistors which in the fender 140 are placed after the phase inverter and before the
output tubes, in front of the phase inverter.
Does it make a great deal of a difference in any regard where those two resistors
are or have they been put infront of the output tubes because of the tube matching pot?

If anyone could possibly point me into the right direction, please.
I'm not asking for a detailed analysis of the schematic, I would just like to have a
clearer picture of the path the signal travels from input to output.

Any help would be highly appreciated.

Matt


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sat Oct 25, 2014 2:13 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Hi EmeraldGreen,

I traced the circuit path on your schematic, from input to the PI circuit. The red shows the main signal path, and the blue is the reverb path. The reverb signal path is parallel to the main signal, across the two 1.5 meg resistors.

Switching on the EQ basically puts that circuit in parallel across the V4A tube, affecting the frequencies passed through that tube.

If you switch the treble boost switch, the 10 meg resistor is shorted (bypassed), or left in the circuit, resulting in a higher or lower signal. The 10 meg resistor and 330 pF cap are parallel to the 470K ohm resistor, and shorting the 10 meg resistor leaves only the 330 pF cap parallel to the 470k ohm resistor, altering the frequency of the signal passed, effectively resulting in more or less treble sound.

The bass boost switch simply shorts out the .01 mF cap to ground, altering the frequencies bled to ground, effectively resulting in more or less bass sound.

The lead switch just connects another half of a tube into the signal path, for more gain (V3B).

The effects loop is created by inserting a TRS plug, which breaks the circuit and routes it through the effects connected and back into the amp at the point where the circuit was interrupted.

BTW, the resistors that you referred to, the 82k ohm and 100k ohm Plate resistors for the PI, are in the exact same place in the circuit as they are on other amps, this schematic is just drawn differently, so it looks like they are placed differently but they are really the same. These resistors are conneted from the high voltage supply to the Plates of the PI, as they always are. The signal comes out of the Plates, through the coupling caps, to the output tube control grids.

Hope this helps.
Image

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Last edited by shimmilou on Sat Oct 25, 2014 2:21 am, edited 2 times in total.

Top
Profile
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sat Oct 25, 2014 2:17 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
I wish to know how to do sketch like you do . Congrat.


Top
Profile
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sat Oct 25, 2014 2:39 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
I saved the schematic as a picture, and then opened with the "Paint" program in Windows, and traced colored lines along the paths. :)

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sat Oct 25, 2014 2:42 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Fri Feb 05, 2010 4:31 am
Posts: 14049
Location: Province de Québec, Canada
Thank's


I need more to do a good job like you do ; know how menues work .....and more ? And pratice practice


Top
Profile
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sun Oct 26, 2014 2:04 am
Offline
Hobbyist
Hobbyist

Joined: Wed Aug 27, 2014 1:53 pm
Posts: 15
shimmilou, thank you a million times !!!

this is exactly what I needed. It really helps a great deal and will make my
life so much easier once I start checking up on all the components in there.

Thanks again for taking the time and effort !

Matt


Top
Profile
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sun Oct 26, 2014 3:01 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
You're welcome. No problem, I enjoy this sort of thing. :D

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sun Oct 26, 2014 3:17 am
Offline
Hobbyist
Hobbyist

Joined: Wed Aug 27, 2014 1:53 pm
Posts: 15
and it sure helped me a great deal ...

while you are there, can I just ask one more thing:

you said, and because of the way you traced it I can see it clearly now,
that the reverb section runs parallel to the main signal. That would mean, that
once reverb is engaged via the pedal that the signal sum would carry both, the dry and
the damp portion from reverb.
If that is correct, is there any way to tap into the reverb to be able to check whatever
the reverb tank does on its own w/o the dry part of the signal?
I guess that would help to determine whether the result from reverberation is good or not.


Top
Profile
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sun Oct 26, 2014 4:42 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Hmmm, hadn't really considered that. I guess that you could unsolder one side of the second 1.5 meg resistor and see what happens. My guess is that it wouldn't sound good at all, but...... :?: Try it at your own risk, I can't say what would happen, and frankly, I wouldn't mess with it. Surely there is more than enough reverb in your amp as-is. The reverb is typically always parallel with the dry signal due to the type of the reverb circuit design. You can check out a separate reverb unit if you want to put the reverb in series with the main signal. Something like a '63 reverb unit, inserted into your effects loop as one option.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Fender 140 - help needed on signal flow.
Posted: Sun Oct 26, 2014 5:00 am
Offline
Hobbyist
Hobbyist

Joined: Wed Aug 27, 2014 1:53 pm
Posts: 15
That's not exactly what I meant.
I'm not really worried about the amount of reverb but the quality of the sound.
If I were able to isolate the damp signal that comes out of the reverb tank, I
could tell wether a bad reverb sound results from something wrong within the
reverb section or from anywhere else.

It's not that I have actually encountered the situation yet. I was just wondering because
of the parallel hook up of the reverb section. So, in the end it might not be all that important.


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 10 posts ] 

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: