Helios type69 Veroboard vs Schematic. Narrow "Q" problem.

[Ted Krotkiewski]

As I said, the low cut consists of two components, the series capacitor and a resistor from the cap to 0V. I have attached a pic of the schematic for a simple low cut. I have used a single 27K instead of 22K + 5K1. Connect this from and to your soundcard and see what you get.

This became so obvious now after seeing this and trying it out.
I feel ashamed for taking your time with such basic matters.

So for this to make sense in my head: The low frequencies that are being filtered away needs another path to disappear to right? So those freq´s has to be led down to ground in order to "dissapear".
Is that a somewhat correct explanation for this?

Thank you!!!!!!

I am learning so much!  8) ;D 8)

 

[ruffrecords]

This became so obvious now after seeing this and trying it out.
I feel ashamed for taking your time with such basic matters.

So for this to make sense in my head: The low frequencies that are being filtered away needs another path to disappear to right? So those freq´s has to be led down to ground in order to "dissapear".
Is that a somewhat correct explanation for this?

Thank you!!!!!!

I am learning so much!  8) ;D 8)

Basically, all EQ is based on a potential divider. If you make a pot divider with just 2 resistors you drop the level the same amount at all frequencies. If you swap one of the resistors for a frequency dependent component like a capacitor then you still have a pot divider but the actual attenuation is frequency dependent.

In the simple HPF example the pot divider is the series capacitor and the R to ground. At high frequencies the capacitor is effectively a short circuit so there is no attenuation. As the frequency decreases the impedance of the cap begins to increase and hence so does the attenuation. It is a simple as that.

Cheers

Ian

 

[Ted Krotkiewski]

Basically, all EQ is based on a potential divider...
...It is a simple as that.

Fantastic!!
I get it! I get it!!
Makes me so happy.

Thaaank you!

 

[ruffrecords]

Fantastic!!
I get it! I get it!!
Makes me so happy.

Thaaank you!

That you understand makes me happy too!

I am lucky enough to be seen as pretty smart but I am not really. I discovered at a young age that if I could break down complicated things into a series of small easy to understands bits, I could suddenly understand the complicated thing. I wish more teachers understood this.

Cheers

Ian

 

[Squeaky]

OK, I think I need to explain it in general terms. A passive like the Helios EQ works by making an attenuator for the incoming signal. In the Helios it is basically the 22K pot and the 5K1 resistor to ground. This attenuator has a loss of about 15dB.

I would also like to express my appreciation for your contributions Ian, you help remove veils from people's eyes, including mine.

 

[Ted Krotkiewski]

Hi again.
After some further experimentation with trying out different transformers, buffer stages, tweaking frequency values, different HPF topologies etc. I have finally completed something that I really REALLY like and I am soon ready to test print some PCB´s for the first time in my life.

However, even though I think it sounds great as is, there is still one major thing that I cant get my head around.

OpAmp interference.
I have mentioned it in this thread before, but never found any way of solving it.
When having an OpAmp after the EQ to restore the gain, it affects the Q-width of the EQ and also, the amount of peak boost. (Please see attached pic with comparison) If you have the time you may also look at my attached schematic to see if I did something wrong in the Output buffer stage.
If you do look at the schematic, it might be confusing at first, because I have 2 different Opamps in the output buffer. This is only because I want to have both footprints in the PCB so that I can later choose either IC opamp or API 2520 styles. So, obviously only one of them will be in use.

In the picture I have max boost of 6K and 30Hz with both graphs normalized to same gain so comparison is easier.
The blue graph is WITHOUT Opamp
The Red graph is WITH Opamp.

Many thanks for your time and input.

 

[ruffrecords]

When you test with the output op amp, are you including the transformer?

Am I right in thinking the idea is to fir one or other of the two op amps not both together?

Cheers

Ian

 

[Ted Krotkiewski]

When you test with the output op amp, are you including the transformer?

Am I right in thinking the idea is to fir one or other of the two op amps not both together?

Cheers

Ian

Hi Ian.
The same result happens with or without the transformer Im afraid.
Same thing happens without the other Unity Gain buffers in the circuit.

I followed your simple TL072 Gain makup circuit that you provide.
Now, It just occurred to me that you also have a more complex TL072 Gain makeup circuit, wich I have not yet tried. Perhaps the circuit reacts differently to that one? hmm. Have to try it as soon as I get time.

Can it have something to do with the resistors leading to ground from the Opamp? I remember playing around with different values for the 3k3 leading to ground, and it did change the amount of boost and perhaps even "Q-Width" but I never found anything working "Better" in this scenario.

Regarding Multiple Opamps: Yes, you understood it right, it is only ONE Opamp that will be used, so the added 2520 is only so that I can add that footprint in the PCB if I want to swap out to that format at a later stage.

Thank you Ian!

 

[ruffrecords]

OK, just to be clear, when you test it without the output op amp, what do you connect it to?

Cheers

IAn

 

[Ted Krotkiewski]

OK, just to be clear, when you test it without the output op amp, what do you connect it to?

Cheers

IAn

From EQ OUT it goes straight back into the LINE IN on my Soundcard.
There is no hi-Z engaged.

So, to be clear. On the breadboard, when changing between Opamp and Without, I just move the positive wire leading to "Pin" on the 1/4 Output Jack between the two different paths.
The ground (Ring) wire always stays connected to the same ground.

Thanks!

 

[danalexanderaudio]

fyi - Helios never named anything type 69 . If you look at the Helios section of my book, you will find the original Helios module brochures and model types. The information came directly from Dick Swetenhams personal sales binder.

 

[ruffrecords]

From EQ OUT it goes straight back into the LINE IN on my Soundcard.
There is no hi-Z engaged.

So, to be clear. On the breadboard, when changing between Opamp and Without, I just move the positive wire leading to "Pin" on the 1/4 Output Jack between the two different paths.
The ground (Ring) wire always stays connected to the same ground.

Thanks!

OK, this sound a bit like the previous missing 5K1 resistor problem. The line in on your soundcard will probably have a 10K input impedance. This, in parallel with the 5K1 (if it is there) forms the bottom arm of the potential divider that is the basis of the EQ as I have explained before. Even if the 5K1 is missing or is fitted with 51K, the 10K inpout impedance of your sound card will give you some reasonable peaks in the EQ. If instead you connect it to a high impedance input like the op amp, there would be a much larger value resistance for the bottom arm of the EQ so you get hardly any peaks at all. This is exactly what you observe so it must be a problem with the 5K1.

Edit: Hang on a minute. I just took another look at your schematic. You have added an extra op amp after the the mid section. I think that is where you problem lies. Why is it there?

Cheers

Ian

 

[Ted Krotkiewski]

Ian!
I Found the problem!
There actually was no prolem to begin with. I just looked at it the wrong way around.
It was WITHOUT the Output buffer, that the results became OFF, resulting in a higher amount of boost and narrower Bandwidth.
So, WITH the buffer, the results are more or less exactly the same as your tests Ian.

However, I truly wish that I could have the BASS band become as narrow as without the Op Amp. I love that.
Also, the amount of boost (+19dB) wouldnt hurt either. Or perhaps the Q is actually the same, its just more amount of gain available, making it look more narrow? hmmm...
aaanyway. Im happy everything is as should. Sorry for taking your time with this. =)

I just took another look at your schematic. You have added an extra op amp after the the mid section. I think that is where you problem lies. Why is it there?

That extra Op amp acts as a Unity Gain Buffer, so that I can "Isolate" the Hi-Shelf to not interfere with Mid band. It gives me some +25dB of boost summed together. If that day will come when I actually need that.. =)
So, I basically created another 22K + 5k1 network for the HiShelf and then doubled the amount of Make Up Gain on the Final Output Op Amp.

All my best.
//Ted

 

[ruffrecords]

I am pleased you got it working. For a narrower bass oost you would need a higher value of inductor which would be something of a challenge. If you really need sharper bass peaking response you need to reduce the characteristic impedance of the EQ. To do this you would need to reduce the value of the 22K and 5K11 resistors that form the central potential divider of the EQ. For example, if you halve their values, you double the sharpness if you keep the same value inductors. But rememeber this means the driving circuit needs to be able to drive a minimum impedance of about 2K5 instead of 5K1.

Cheers

Ian

 

[Ted Krotkiewski]

I am pleased you got it working. For a narrower bass oost you would need a higher value of inductor which would be something of a challenge. If you really need sharper bass peaking response you need to reduce the characteristic impedance of the EQ. To do this you would need to reduce the value of the 22K and 5K11 resistors that form the central potential divider of the EQ. For example, if you halve their values, you double the sharpness if you keep the same value inductors. But rememeber this means the driving circuit needs to be able to drive a minimum impedance of about 2K5 instead of 5K1.

Cheers

Ian

Thank you Ian.
You have given me (us) so many parameters to play with based on you valuable shared knowledge.
This info right here gives me so many more possibilities to shape this into something else.

When you say "the Driving circuit" Could you please expand on what you mean by that? The source before the EQ?

T H A N K Y O U

 

[ruffrecords]

When you say "the Driving circuit" Could you please expand on what you mean by that? The source before the EQ?

That is correct.

Cheers

Ian

 

[Urskov]

Hey Ted
Would it be possible for you to share your final vero layout?

 

[capacitorless]

I know this is a bit of a necro-bump, but I too would love to see the final

(and huge thanks for everything you've done here, Ian!)

 

[Ted Krotkiewski]

I know this is a bit of a necro-bump, but I too would love to see the final

(and huge thanks for everything you've done here, Ian!)

Hi.
Please excuse my very VERY slow reply @capacitor @Urskov.
I would love to share it if only I had it as an updated version.
Ever since Ian and the other masterminds here helped me get everything in place, I just went on with it on my breadboard and only changed parameters in the Schematic.
So, my Vero layout has not been updated from whats already in this thread.

However, As soon as I find the time, I will do my best to create a new updated Vero Layout, so that you all can have it.
I would love to finally be of help to this forum and contribute something back after all the help I have gotten here.

Thank you for your patience!