is it worth it to replace caps in old equalizer??

the

I did read your original post, merely meant it as general comments on EQ in other setups. Yes, for guitar use it may matter less.

To the other poster: sorry I misspelled linear :) (as if it matters..)

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Kind regards,
Mogens V.

They are glued. Remember, this is the worst grade of mass-market trash available at the time; it's not designed to be actually repaired. Pry them off with a screwdriver.

I suspect you will find that there is a bunch of stuff on the board that you haven't seen yet.

--scott

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"C'est un Nagra.  C'est suisse, et tres, tres precis."

They are not glued, but about a decade or so ago when I was mucking around in one they were very difficult to get off. At this age the attempt may break the posts off the pots. It would still be useable but you'd need a key or a screwdriver or something to adjust it.

It may just be better to be glad the thing works. I know two people with that model, the one modified and the other stock.

But now that you got me started, that EQ is poor for music. IIRC those were actually discrete component OPAMPS and on the 60 HZ, which I would've liked to extend the response of down to DC, it simply isn't possible. That's OK, when they use like a 33uF and I replace it with a

470, it is close enough.

I have this old Soundcraftsman that I would really like to get a power transformer for. Now that's an EQ !. And it uses coils in the tuned circuit. Now that you got me started, the design of the old unity gain except for shunting either source or degeneration with passive tuned circuits has an advantage. The is when you use two adjacent controls in the same direction (boost or cut) the tuned circuits begin to act as if they are in paralell, giving less of a double hump in the response curve.

This is going to get deep, get your waders on. Decades ago there was a very accurate method of measuring frequency response. It fed a speaker a single tick, and through fast fourier transform it was able to plot the entire frequency response curve of a speaker. It was abandoned because it was too accurate.

For a couple of decades cheap speakers were being passed off as high fidelity and how they did it is simple. To make the response curve look better they began using bands of pink noise, and a wide spectrum mike. The problem was the bass, an FFT would accurately show the possible +-10db variations in the lower ranges.

Now remember that the cone is still moving, being an inductive load fed by a constant voltage, the problem is cancellation, and nonlinearity of the magnetic field and/or compliance or the woofer's suspension. This means that tons of THD are produced at the frequencies reproduced less efficiently by the system.

Now, abandoning the FFT method and going with the pink noise, they are checking for say 60Hz, but appearing in the output with this method are the distortion components, 120Hz, 180Hz, 240Hz and so forth. This all added up makes the curve look flatter, but it is not. I don't know about anybody else, but for a 60Hz input, for a frequency response curve, I would only want the 60Hz output to count in the results.

So anyway, back to the price of beans in Chile. This sparked my curiousity and I promptly got out the square wave generator and the oscilloscope. After some experimentation seeing what the controls did to a 1Khz square wave I understood how the FFT works. Not the complex math involved, but at least the concept. The FFT method was touted as having the great advantage of not requiring an anechoic chamber to take the test, true, a speaker would read pretty much the same in an open field or in a phone booth. That is an exageration though, the mike had to be a certain distance away.

Over the years I came to realize the one should just get good speaker if one can afford them, and that is what I did. I got the Boston A150s. This was over ten years ago and after all the abuse people with their own stereos still come to hear things on MY stereo. And I just found out recently that the midrange has the biggest magnet in the system, not the woofer. At $400 for the pair used, which was MSRP I whipped out the money after hearing them.And they were ten years old almost at the time !. Go ahead and think that I got fleeced, but come and listen to them first. We are talking 20-20,000 within 3db and 0.7% THD at one watt. Remember, one watt is pretty loud for most people.

Some purists shun tone controls altogether, but not me. In fact I designed but never built perhaps the best set of tone controls ever. Bass turnover continuously varible from 44-480 Hz and +- 18db range. Yes it is dangerous ! Midrange was pretty much standard but the treble was just as gnarly. Went from about 2Khz to 9Khz, and had the same range. No, you do not crank these up.

It was designed in response to the industry's propensity for not giving us the outer octaves. But I simply do not need it anymore.

At this point, even though I do use a boosted bass, when I run out of power it doesn't clip just the bass, all frequecies pretty much clip at the same point.

Now to the guitar. If you play an electric with distortion, with solid state you generally can't play G type or C type chords. The problem is that the second note in the chord is only 4 frets (=BD steps) away from the base, rather than 7. But it can sound good on tubes, or specially designed circuitry.

That old sweet sound was also due to interaction of the soft output stage with the output transformer as well as the speaker. They built power soaks for people who wanted that sound but wanted to practice at a lower level, but the results were not quite the same thing. Would've been better to regulate the B+ to the output stage.

I don't know if FETs would react the same, but they might, or at least be very close.

The best thing I did though, was to start using two amps. One clean and one all fuzzed out. You can just about make one guitar sound like two. If you place the amps across the room from each other, you actually get a sort of stereo image out of it.

Time marches on. I got ripped off and did not have a guitar for a while. Then I got so dismayed by the media that I not only stopped watching TV, I actually stopped listening to music for years. That's right, it is hard to fathom, but I did.

That had a very interesting result. I do not play copies or covers anymore. Period. I've written three songs, well one and two almost songs. I have switched to the acoustic, and use chordography that would never fly on an electric, even clean. It just sounds better on an acoustic. Mine even has a pickup, but I prefer to mike it.

My next step is to buy one of those newer ones with the advanced internal pickups. You can play it on a stereo and it sounds like an acoustic. I was very impressed the first time I heard one.

Good luck grinding the ax (a term we used to use for playing with distortion, heavy metal).

Ummm, BTW, something just cropped up in my memory. You got that old EQ which allows seperate adjustments for each channel, get two amps and set them inversely. Don't run them tandem, feed both via a splitter, then each out to it's own amp. Then you set, say the left 60, 1K and

10K down, the others up. On the right set the 250 and 3.5K down, and the others up. You might like the effect.

I am not too crazy about these new amps with all the digital effects. It is all taken out of my hands. I don't think that'll ever change.

Also sometimes I'll play on the old Fender amp and a bass amp at the same time. That sounds pretty good too.

Have fun with it.

JURB

youre probably not looking at quality then. The 70s was awash with grotty discrete kit.

NT

He did say it was Radio Shack !

Graham

Right. The performance of cheap equalizers actually went uphill when cheap ICs became available for implementing them.

To the best of my knowledge, this equalizer was not an RS design. It came from a little company called Metrotech, and appeared as a Popular Electronics construction project. The same circuit was later used by BSR for a 12-band equalizer.

It should be noted that, even in the '70s, IC designers were still "finding their way" with respect to op amps. And there are plenty of current designers who would not agree that ICs are inherently superior to discrete.

The problem is that active filters built on op-amps require lots and lots of gain.... as a consequence, discrete op-amps in active circuits tend to be problematic because really high-gain discretes are difficult to build and keep stable.

It's the one application where monolithic op-amps really _were_ a huge win, even back in the seventies when monolithic op-amps were... well... kind of nasty.

Then again, you will still find people who are huge fans of the old ITI equalizers, which are the typical four-op-amp parametric configuration built with video-amplifier-style discrete op-amps. Neutral they aren't. But some people like the interesting weirdness.

--scott

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"C'est un Nagra.  C'est suisse, et tres, tres precis."

In certain specific instances ICs are clearly inferior. Mic amps for example.

Graham

Depends. What is discrete and what is an IC?

Are large area transistor arrays discrete or ICs? They make great mike preamp front ends.

Hybrids aren't monolithic... but they aren't discrete either....

--scott

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"C'est un Nagra.  C'est suisse, et tres, tres precis."

The Metrotech's amplification was not op-amp based.

on

I can see most of what is on it from various holes around the side, and I can certainly tell there are no ICs from the back of the circuitboard, if that's what you were alluding to.

Yeah I will give that a try. I had been using both channels of the EQ with a splitter sending both to the two inputs on my amp, but that wasn't very interesting so I tried sending one to the amp then took the amp out, back into the other eq channel and out of the eq into the other amp input, which gave me some pretty good distortion and feedback...

Anyway thanks for the response, I didn't understand most of it but it was fun to read!