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Distortion (Clipping) when using equalizer

S

Swissknight

New Member
I am looking for advice on a distortion issue. I have acquired a Heathkit AD-1703 10-Band Octave Equalizer and am noticing heavy distortion when I boost the lower frequencies. I usually do not use an equalizer, but was testing this out.
If I boost the lower frequencies with the built in receiver equalizer only, there is no clipping or distortion.
The equalizer set up to the tape monitor 2 circuit.
The built in equalizer curve is set to flat and mid way.
If the music is played in "bypass" on the equalizer, all is fine.
If I set the EQ to "record equalized" or "equalize" the music distorts -just like heavy clipping if I boost up 3 or 4 of the lower end sliders on this external EQ
This distortion/clipping does not occur if the same frequencies are boosted on the built in EQ only
The distortion/clipping occurs at any volume level
I sprayed all of the sliders with Deoxit in hopes that may be the cure, however that did not change anything . . .

BTW - I am using a Sony STR-D1011 receiver for testing - but I do not usually use an external EQ. The Sony appears to be fine. Is there a problem with the external EQ or is this normal with external EQs boosted? I used to have a cheaper Fisher EQ a long time ago on a different system and never had distortion like this. I am wondering if there is another possible issue that I am overlooking. Any thoughts or similar experiences?
 
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EQ can take some fiddling if you have major excursions that need to be addressed. Sounds like you're overdriving part of the bandwidth trying to maintain the "smiley face" curve.

Try this - you get a curve that seems to work for you, but has the clipping issue. Move ALL the sliders down equally as much as you can - the goal is to maintain the curve, and still have the same output level you have with the EQ bypassed. This limits overdriving the system as much as possible and can help a whole bunch. If you end up bottoming a slider or two doing this, you're still better off in the long run.

Goes without saying, if you have a frequency that's giving that much trouble, you should first try to address that using hard treatments like baffles, absorbers, and such. The closer you get to flat without EQ, the better EQ can work for you.
 
Sounds like the amount of boost from the external eq may be overloading the receiver's input, since you say the distortion is independent of the volume control.
 
I find it better to cut out what I don't like with the EQ first before any boosting of what I do like.
 
If your using an external EQ, then the receiver's EQ should be set to flat. The external EQ is not a volume control after all, but rather an expanded bass and treble control. The distortion you experience is from over-driving the circuits on your receiver.

Wayner
 
Thanks for the link. What is weird is that the built in EQ is set to 0 flat curve. I can produce a sound/ curve with the built in EQ, but if I set it to 0 and try to reproduce the curve with the external EQ - it distorts. If I set most of the sliders to 0 and set two of the lower frequency sliders, the sound does not distort. I never experienced this before in the past with my other EQ (which died some time ago).

mfrench said:
I find that EQ is best when its used as a reduction, rather than as an addition.
Click to expand...
Good point - but I guess my question is - is this a problem with this EQ or is this the way some EQs are, especially since I have never seen this prior (and the internal EQ can perform the curve without the distortion)?
 
3 dB of bass boost requires double the amplifier power at that frequency range. Another 3 dB of bass boost requires another doubling of amplfier power and so on.
Its really easy to run your power amp out power using an equalizer.

Frank Van Alstine
 
keep the sliders below the zero point to start with ..then be gentle after that .
if you want more lows turn the highs down .. if you want more lows get a bigger amp ..
 
All of my Soundcraftsmen EQs have "Zero Gain" controls with lights to balance the output to make sure there's no boost in overall level. If you don't have such controls or indictors, simply do as other have mentioned and cut your high-frequencies rather than boost your bass to keep the output level down such that there's no increase in gain from the EQ.
 
avahifi said:
3 dB of bass boost requires double the amplifier power at that frequency range. Another 3 dB of bass boost requires another doubling of amplfier power and so on.
Its really easy to run your power amp out power using an equalizer.

Frank Van Alstine
Click to expand...

And all the while he has the loudness button on!:jump:
 
Missed that it is independent of volume. Now that I caught that and had a look at things, the problem is in the receiver, but not a fault, a design problem.

Looking at the EQ print, that thing should be able to put out 18 volts without clipping, so it is not the issue unless some source is out, and if that was the case it would not sound good flat. The receiver now, if you look at page 15 of the service manual you see that the tape ins from tape 2 go to the surrround board. No doubt, you are overloading that.

I do not want to put Sony down, but I have been consistently underwhelmed by their audio equipment. In this case, to get the S/N ratio they used up most of the dynamic range of the next stage. When you boost something by 10 dB, the voltage is 3.163 times what it normally would be. In my not so humble opinion, the receiver should be able to take that but it appears in this case it cannot. And I cannot excuse it because of the line levels changing.

Yes, sometime last millennium they went from like around a volt nominal to maybe a quarter volt. I do not see that as a valid excuse.

The problem is that in most things the tape two in goes right to the tone board which is usually fed by at least +/- 12 volts, giving it plenty of headroom. However in that unit it is further amplified and fed to an AD convertor (IC 301) which is obviously the source of the clipping. It also uses a shitty muting circuit and don't even try to troubleshoot that, the print is simply wrong. they got -7.2 volt on the base of an NPN transistor with both base and collector at zero DC. The audio is at the emitters, if there was -7.2 volts at the bases there would be over -6 volts at the emitters. There is a slight possibility that circuit is causing the distortion but it would have to be what drives it, or one of the transistors slightly leaky.

When the "standard" line level went down, most audio designers made their products to be able to handle the older equipment. In this case, I think Sony acted like Microsoft. Nup, go throw out your $$$$ Revox n ****, we got all the equipment you need, for a price.

That is my opinion on the subject. Disconnect the EQ and enjoy the dynamic range of the Sony brought to you by running the chips near max input level.

The thing probably sounds great, just bear in mind that they saved a little money on it. As such, the way to hook up an external sound processor like an EQ would be through the pre out main in, but it doesn't have that.

So screw it, just enjoy the sound. you were only testing the EQ right ? It tested good.

In fact, that is one of those good old fashioned EQs that have real coils in them. I think they sound better than those gyrator based jobs. Not sure why, maybe because the Q changes as you approach the ends of the range ?

I'd buy it.
 
Actually DO test it on something else to be sure. There IS a slight possibility of it being a fault in the EQ, albeit very slight.
 
JURB said:
Actually DO test it on something else to be sure. There IS a slight possibility of it being a fault in the EQ, albeit very slight.
Click to expand...
That ^^^^ is what I would've done,and if the EQ then worked as it should,and the reciever went back to working as it was supposed to,I would've just chalked it up to poor "synergy" between those two components,as I would've likely been too lazy/busy to dig thru the schematics trying to figure out the "why" of that situation.

I dont mess w/newer audio gear so this has never really happened to me,what I mostly meant to say was that the described symptoms were'nt a normal occurance when using an external EQ,and that there were a chance it could be the EQ to blame,but JURB's explaination makes far more sense than a bad EQ does,so it's a good thing he went thru the trouble to look thru the schematics and explain it all so well.

Bret P.
 
Will you find and try a 20 dB (10:1) or 15 dB (5.6:1) stereo signal attenuator inserted between the “TAPE 2 REC OUT” of your receiver and your EQ’s “line in” terminals?
 
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It should be fairly obvious to anybody that actually read the OP in it's entirety...................................... that the fault is within the Heathkit EQ which is likely 20 years past needing a re-cap and power supply rebuild.
 
I agree with JURB. Have a Kenwood VR-6070 that does not play nice with any external components in the tape loop. AV receivers with their dsp circuits do things a little differently than analog receivers. There are tradeoffs to produce their rated power. Gain in my Kenwood is purposely lowered internally when it's in surround mode. That's why i have an av receiver and analog receivers. I would use a powered sub woofer with the Sony if it was the lows i wanted to boost.
 
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