Tube mods on solid state amps ?

[SpareRibs]

Hello,
      I have used Gerald Weber's books to modify tube amps. Most of the things worked. I am wondering if a
few of them would be applicable to solid state amps ?
1. In the preamp would it be possible to use the method of bypassing the cathode resistor with a capacitor ? 2. Is there a way to changing cathode resistor value, or is there even anything comparable in the circuit ?
3. Would reducing value of resistors divider coupling stages be possible, and if so how dramatic of an effect ?
      I would like to attempt these things on a Fender Squier 15 that I have. I have looked at the schematic and fail to understand what would represent a cathode in the little triangular amps on the diagram.
      Thank you in advance for any help or advice.

[Enzo]

You have discovered the problem.  The little triangles are op amps, not tubes, and there is no cathode.  Nothing to bypass.   Look up the basics of op amps, you will find the gain of a stage is set by the ratio of the feedback resistor and the input.  You can change that ratio and thus change the gain of the stage.  In fact many of them make the feedback resistor variable and use it as a volume control.  But that is totally unlike a tube.

[SpareRibs]

Hello,
      I looked up opamps. I gave the same information as you stated about gain set by ratio of the feedback
resistor. Then it was off to algebraic, mathematical, equations, that was mind  boggling. So I guess it is something I will never understand. Anyway thank you for your input. I was just looking for any obstructions
in the flow from the input jack to the speakers, or any possible enhancements.

[Roly]

that was mind  boggling. So I guess it is something I will never understand.

Don't give up the ship!

Most of the math in electronics is only multiplication and division, e.g. Ohm's Law.

Concept - an op-amp will always try to adjust its output to minimise the difference between its two inputs.


With the voltage follower (top-right) the output is directly connected to the inverting input (-), so whatever voltage is presented to the non-inverting input (+) will cause the output to change until the (-) and (+) inputs match, in this case the voltage on the (+) input, hence "voltage follower" or buffer.



Now if we look at the gain arrangement (lower-left) we have placed a resistive voltage divider in this feedback path.  If R1 is equal to R2 then the voltage at their join, the (-) input, will be half the output.  For equal inputs the output will now have to be twice the (+) input voltage, so we have a gain of x2.

In situations where the gain is high, say more than x10, and the application isn't critical, say a guitar amp, we can approximate the gain as the ratio of R1 and R2.  So if R1 is 100k and R2 is 1k we can approximate the gain to be ~x100 (it's actually x101, a 1% error).

Gain = (R1+R2)/R2 is only saying "the R2th part of the whole of R1 plus R2" and doing this in full normally only matters where the ratio, and therefore gain, is small.

[J M Fahey]

Agree and add: that Math, Calculus, Algebraic Equations, etc. , ARE ONLY REALLY NEEDED AT GAIN OR FREQUENCY EXTREMES, such as making an earthquake sensor (not kidding), a Radio receiver, an ultrasonic control, a Q>100 filter or a microphone preamp to record a cockroach singing 1 mile away, but for *normal* use:
audio, within 20Hz and 20KHz, gain 100X or less, the very simple "4 operations" (division/multiplication/adding/substracting) Math is all that's needed.
Yes, often there´s some error involved ... usually less than 1%.
Can you live with that?  :lmao:

[SpareRibs]

Hello,
      Thanks Roly. The information you provided narrows it down to the areas I may be able to deal with. The graphs you provided will go a long way in clarifying the explanation. I down loaded and copied them  to study in depth and compare then to the schematics I am currently trying to make sense of.
      The web sites I looked into at Enzo's suggestion (gain stage ratio of feedback and input resistor) starts with the presumption that someone is familiar with all of the terms being used. I am sure it would be very informative or maybe even common knowledge to you guys.           
       I want to see if I can milk a little more preformance and or clarity out of the Fender Squier 15. I am aware it is only 15 watts but I am going to look for ways to refine it if possible. I know if I increase any
values it will just be dampened by resistors further down the circuit. I have thought of just adding another 12" speaker. I think that would do more than anything else to really make it sounding bigger

   

[SpareRibs]

Hello,
     J.M.Fahey, I hadn't really entertained the thought of dog whistle frequencies in any recordings,however
the information I was reading did not make the distinction as plain as you have stated it. It just starts with a boat load of formulas and equations. They threw in a couple of references of things like Q and it just went on and on from there.
      Thanks for letting me know that what I was looking at was for the over the top stuff. All of that being as it is, don't you ever wonder what bugs sing about when they are a mile away from us ? 



 

[Roly]

Electronics for the most part isn't all that precise, ten, perhaps five percent at best, so you really only want to know what the first two or three digits are and where the decimal point is. And you don't actually want a number anyway, you want a result and the number is only a stepping stone to getting that result.

[phatt]

Hi SpareRibs,,FWIW,
I read a lot of books and built some disasters years back but over time I started to come to grips with all.
My biggest breakthrough was when One kind person gave me a copy of simulation software. (Bare in mind This was all before I had internet connection)

With what I had already learned it did not take long to catch onto what/how opamp circuits worked.
Simulation software put me leaps ahead in the first year,, many arrh-huh moments once I got the knack of using it.
To coin and old phrase, A picture paints a 1,000 words. <3)

My sim program came with a whole list of already functioning circuits so even us dummies can get some idea of how to make something work.
Quite a few come free with limitations but enough to get you started.

Most of the gear I've built and posted here has been with the aid of simulations which saved me hours and hours of building circuits that would have ended up as land fill.

I highly recommend it,, but do keep reading books. :tu:
Phil.

[SpareRibs]

Hello All,
       I found a tutorial on a Mouser Electronics page called, All About Circuits, Negative Feedback, op-amps.
It looks really cool because it starts with just a triangle and builds on it from there. I have downloaded the
first two parts which is eight pages. That should at least get me out of the fog, Wish me luck. Thanks guys.

[J M Fahey]

Cool  :dbtu:
Please link that page here, it will be useful to many.

[SpareRibs]

Hello,
      I don't know how to link to things but the top of the page says as follows (www.allaboutcircuits.com).  Hope that helps. It should help people to start from zero and come to grips with op-amps. It seems to me they act as a voltage regulators by balancing input to output. I am also almost understanding how to manipulate an op-amp circuit with resistors and capacitors. Anyway it is more informative than reading about someone doing
something and just glossing over the op-amp part presuming it is common knowledge.

I just used the link and it works.

[g1]

This is the article on negative feedback with op amps:
http://www.allaboutcircuits.com/vol_3/chpt_8/4.html
I don't think it appears on the mouser website although they may have a link to it.

[SpareRibs]

Hello,
      I am sure you are right, I just went there from searching on the web. The information I posted was on top
when I went there from my bookmark. Thank you for clarifying that so everyone else can find with no problems.
It is a lot of good information. There is also a homepage and menu to find lots of other things.

[teemuk]

Ron Mancini: Op Amps For Everyone - Design Reference (Rev. B)

http://www.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slod006b