Resistive dividers

[xtian]

I read Aiken's page on resistive and inductive dividers. It is true that resistive dividers do not affect AC, and that inductive dividers do not affect DC?

[Firestorm]

Resistive dividers don't care. Inductive dividers divide AC by induction, but divide DC resistively.

[JazzGuitarGimp]

Resistive dividers do not affect AC in terms of frequency response, because resistors are not frequency dependent like capacitors and inductors.

For capacitors, the formula for capacitive reactance is:

1
Xc = --------
2piFC

Where F is the frequency for which your seek the capacitor's equivalent resistance, and C is the capacitance in Farads.

For Inductors, the formula for inductive reactance is:

Xl (that's a lower case "L" [and should really be subscript]) = 2piFL

Where F is the frequency for which you seek the inductor's equivalent resistance, and L in the inductance in Henries.

[vibratoking]

You should know that an ideal inductor has zero DC resistance. It looks like a short, so be careful if trying to divide AC with inductors...if your AC is riding on some DC you may end up shorting your DC supply to ground. That ain't usually good.

As resistive divider will divide an AC or DC signal.

[xtian]

Do me a favor. Look at the schematic on page 1, after the "TONE" label (the treble pot) you'll see a voltage divider. From Treble wiper to 1M resistor on top, 56K on bottom to ground. This looks to me like it will reduce the volume to 5%. That's an error in the schematic, right?

[Firestorm]

Page 1?

[JazzGuitarGimp]

Which schematic?

[vibratoking]

I'm stumped...page 1 of what schematic?

1M on top and 56k on bottom is 5%, though

[xtian]

Guys, call me Duh. Was posting from hospital where my daughter was having her appendix removed. All went well.

Schematic attached.

[xtian]

Still hope someone peeks at the schemo and confirms the error.

[JazzGuitarGimp]

Still hope someone peeks at the schemo and confirms the error.

Yeah, I think I would agree with you. Perhaps it should have been 680K, rather than 68K. That would make more sense.

[xtian]

More to the point, R34 is 1M and is in series with the signal. Not much signal is going to pass through that 1M resistor, right?

[JazzGuitarGimp]

I'm pretty certain the input impedance of the following stage is determined by the value of R17. So if the 68K resistor were removed from the circuit, you'd wind up with a divider with 1M at both the top and bottom, yielding a voltage gain of 0.5x to the next stage. If R35 were 680K, then the divider would have 1M on the top, and 680K || 1M = 404.7 K. Gain to the following stage us now 0.288x. This seems plausable to me.

[VacuumVoodoo]

Take a walk backwards along the signal path:
EL84 in output PA need at the most 16V peak signal amplitude to go wild.
The LTPI has some 30-32db gain in each arm, 35x in amplification factor is just about it.
So, into the LTPI you need 16V/35=0.45V=450mV peak amplitude.
LTPI input impedance is several times higher than 1M because R17 is bootstrapped, it lands at roughly 10 to 15M.
Together with 100nF input cap this gives 0.16Hz low end -3db point - this, and another 100nF at the guitar input makes wonder what were they thinking...
No, the 1M/56k divider provides 18x attenuation,so you need 18 x 450mV = 8.5V peak from the tone stack.
The question is: is the preamp capable to put out sufficiently high amplitude to also overcome the 10-15db loss in the tone stack?
Hint: with Volume pot all the way up you amplify the input signal well over 2000 times before it hits the tone stack...and your guitar puts out at least 50mV.
Looking at the schematic I'd say this thing must have a big flabby bottom.
Changing C3 to 10nF and C15 down to 1nF setting low end 3db to 15Hz at LTPI input should do it good.
You can change that 56k R35 to 100k if it'll remove your doubts, and add a PPIMV while you're at it.

[gingertube]

VV's analysis (which I agree with unless I wanted to nit pick about the last 10-20% here or there) shows that the schematic is probabaly correct.

A quick look at other Trace Elliot schematics of similar models would also confirm this.
See this one for example:
http://www.webphix.com/schematic%20heav ... tte12r.pdf

Cheers,
Ian