Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #20 on: March 14, 2021, 06:04:18 PM »
The most likely reason for not enough boost is a wrong value pot or 5K1 resistor. These form the basic 14dB pad that defines the maximum boost.

Thank you so much for your help Ian! Cant thank you enough.

Quick report of my further findings.
Firstly, Indeed stupid me, forgot the 5k1 resistor in my breadboard. :o
The boost is now acting as should. (Yayy)  ;D

Regarding the non-linearity on FLAT setting:
It appears that it is the Bass section affecting the circuit. When I disconnect the Bass section, I do get a "Flat as a pancake" measurement. Even though it is set to zero boost, I get a veery wide (10Hz - 2Khz ! ) boost of about 3db.
Do you have aaany idea (again) what I might do wrong?
(Please see pictures)

Then I also discovered that the general boost specifically the MID was greatly affected with and without Opamp at EQ output. 
With Opamp +15dB
Without Opamp: +19dB
Is this normal? 

Thank you for your time!
//Ted


Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #21 on: March 14, 2021, 06:05:16 PM »
When putting in the Bass section it becomes like this...  :-\

dogears

Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #22 on: March 14, 2021, 11:26:53 PM »
That is not abnormal. You can recreate that in the sim - depending on the value of the gain pot you use in series with the inductor. Later Helios desks had an off switch built into the pot for that reason.

Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #23 on: March 16, 2021, 02:55:39 PM »
That is not abnormal. You can recreate that in the sim - depending on the value of the gain pot you use in series with the inductor. Later Helios desks had an off switch built into the pot for that reason.

Hi Dogears.
Thank you for your reply.
I tried putting a 500K pot instead of the 50K pot. and the unwanted (10hz - 5k-ish) boost went down to 0.5dBs wich is a great improvement,  8) :D although not Linear flat as Ian said it should be.

Can´t stop wondering though, what on earth makes Ian´s Freq response flat (with 50K-pot) and mine having this bump?

I am also currently reading up on how to determine "Q" factor value. But by comparing my Width to Ian´s Measurements. My seems to be quite a bit wider? Especially in bass band. Please see my attached very clumsy pics.

Except for recalculating and changing values for LC, is there something else that can be done to a circuit like this to make Q-width more narrow?

This is so much fun, and I am sorry for asking all this basic questions, but for me, this is such a success, making this circuit (almost) work from Ian´s circuit layout.
Can´t thank you peoples guidance enough!  :)
« Last Edit: March 16, 2021, 03:04:30 PM by Ted Krotkiewski »

Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #24 on: March 16, 2021, 02:56:46 PM »
..And here´s a comparison between my measurement and Ian´s for 6K boost.

dogears

Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #25 on: March 16, 2021, 08:59:59 PM »
It won’t be ruler flat with the inductor in the circuit.

ruffrecords

Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #26 on: March 17, 2021, 05:23:06 AM »
If you are using the usual switch to select bass boost/cut frequency then you should have a centre 'flat' position where the bass boost pot is disconnected. Once a bass boost frequency is selected there is a minimum  boost determined by the value of the pot. As has been mentions, in some versions of the Helios EQ, the bass gain pot was one with an integral switch to make it easier to turn it off.

If the OP amp after the EQ is affecting the amount of boost then its input impedance is probably wrong. If you are using the TL072 design shown in the Helios documentation on my web site them make sure the input resistor at the + input is 470K.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #27 on: March 26, 2021, 05:37:44 PM »
Hi.
Thank you everyone for all your wonderfull help.
My little EQ build is going really well and I am very happy how it comes out.
It sounds damn beautifull.

I have something I want to try, a little off topic and perhaps a "dumb" question, but thought I´d ask here before spending a lot of time finding it out the hard way myself.

I have a bunch of old Mullard/Philips Mustard caps lying around, that I always wanted to put on a switch together with other cap types to compare if there is an audible difference.

So, I thought that I could create a mirrored row of Mustards (with same values as my current WIMA caps in this circuit).
Lets say I create a duplicate row of all the caps that goes to 0.2H, on the mid band and I put a switch that can toggle between having the current go through WIMA´s or the Mustards.

So my question is, If I for example have the switch set to the WIMA´s, will then the xtra Mustard caps affect the circuit, even though they are switched off/have an open circuit (not leading any current through them)?

I am guessing NO since no current will flow through them and this is how the rest of the circuit switching works, but still. I know nothing, and expect the worst of my ideas, so I have to ask.

Hope what I am saying makes sense.

Having it this way, one could get an honest opinion from myself and other producer friends using it in real life instead of listening to A/B blind tests.
So I thought this would be the best way to do it.

Thank you so much for your time!!  :)
//Ted
« Last Edit: March 26, 2021, 06:16:06 PM by Ted Krotkiewski »

ruffrecords

Re: Helios type69 Veroboard vs Schematic. Narrow "Q" problem.
« Reply #28 on: March 26, 2021, 07:07:11 PM »
If the WIMAs have one end disconnected they will have no effect. It will be interesting to hear if you can detect any difference in the sound. I am not an advocate of using 'vintage' components of any sort and I suspect the sound of the Helios owes more to its design and the inductors than it does to the make of capacitor used.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

 

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