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

D

Derwin

Jan 1, 1970
0
Plus many/most inexpensive EQ's arent phase liniar anyways...
Mostly useless for high quality audio. Besides, problems with a hifi
setup is better addressed actually fixing those problems at the source,
not trying to EQ them out.

If you had read my post accurately you would have noticed that I said I use the
equalizer in a guitar effects chain, not to EQ a 'hifi setup'. I'm quite sure
the quality is no worse than a typical cheap equalizer guitar pedal. The
guitar signal goes through the effects chain, into the amplifier, and the
amplifier is miked. So 'phase linearity' of the EQ isn't all that important,
though I suppose it may color the effects in some way, which may be either
good or bad, but I'd have no way of determining that without a 'phase linear'
EQ to do an A-B comparison with. In any case, it's not something I'm concerned
about as it sounds fine to me.
 
M

Mogens V.

Jan 1, 1970
0
Derwin said:
If you had read my post accurately you would have noticed that I said I use the
equalizer in a guitar effects chain, not to EQ a 'hifi setup'.

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..)
 
S

Scott Dorsey

Jan 1, 1970
0
Derwin said:
But unfortunately it appears I won't be able to try them. The plastic ends on
the sliders don't come off the sliders, they're either glued on or were
manufactured that way, so it is impossible to take off the front panel to get
behind it where the circuit board is. Oh well.

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
 
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 (½ 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
 
Actually I opened it hoping I could replace an op amp but there are no ICs in
it at all. But I did eventually realize that the two big electrolytics are
probably part of the power supply.

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


NT
 
A

Arny Krueger

Jan 1, 1970
0
Eeyore said:
He did say it was Radio Shack !

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

William Sommerwerck

Jan 1, 1970
0
And even if you do, you're stuck with 1970's
You're probably not looking at quality, then. The 70s
was [sic] awash with grotty discrete kit.

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.
 
S

Scott Dorsey

Jan 1, 1970
0
William Sommerwerck said:
You're probably not looking at quality, then. The 70s
was [sic] awash with grotty discrete kit.

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
 
E

Eeyore

Jan 1, 1970
0
William said:
And there are plenty of current designers who would not agree that ICs are
inherently superior to discrete.

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

Graham
 
S

Scott Dorsey

Jan 1, 1970
0
Eeyore said:
In certain specific instances ICs are clearly inferior. Mic amps for example.

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
 
W

William Sommerwerck

Jan 1, 1970
0
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.

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

Derwin

Jan 1, 1970
0
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.

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.
 
D

Derwin

Jan 1, 1970
0
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.


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!
 
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