Picked up a 10 Band EQ called EQ210 from Ali Express.
I am looking for the schematic or even better if anybody has entered this up into a spice / Tina TI / Micro-Cap file.
The idea is to play with the Band Values. But all I really would like to do is just eliminate the need for a pre amp. The thought process is if I could use the first OP amp to boost the signal a bit. I wouldn't need a pre-amp. Would the idea work ?. Or would it fall flat i.e. the second I use the first opamp to boost signal Ill mess up the signal ?.
This is the link for the item.
https://www.aliexpress.com/item/1005003536983742.html?
There is a very low res image of the schematic I guess its better than nothing. But maybe somebody will recognise it and or have a clearer image. Ive given up with playing with Tone Control Boards. Plan to give this a shot.
I am looking for the schematic or even better if anybody has entered this up into a spice / Tina TI / Micro-Cap file.
The idea is to play with the Band Values. But all I really would like to do is just eliminate the need for a pre amp. The thought process is if I could use the first OP amp to boost the signal a bit. I wouldn't need a pre-amp. Would the idea work ?. Or would it fall flat i.e. the second I use the first opamp to boost signal Ill mess up the signal ?.
This is the link for the item.
https://www.aliexpress.com/item/1005003536983742.html?
There is a very low res image of the schematic I guess its better than nothing. But maybe somebody will recognise it and or have a clearer image. Ive given up with playing with Tone Control Boards. Plan to give this a shot.
Hi,
The first opamp is a buffer stage: it is there to isolate the circuit from preceding stage ( by presenting an high impedanceb to the circuits which will be connected to it, and a low output one to 'drive' the band of your circuit). This buffer stage are usually unity gain (gain of 1).
You could mess with it but it'll most probably induce headroom issue wiithin the circuit ( you don't have enough margin to boost a band and it'll overload with low amount of boost).
What do you want to mess with bands characteristics?
I want to mess with the band because the last band on this is 12Khz. I want it to be 16.
Anyway did some digging. Looks like this is a copy of this design.
https://www.rolls.com/product/EQ210
In this design. They have allowed you to increase the gain. Lets see if I can find the schematic for the Rolls board.
Another strange thing I noticed when I zoomed into each section. Is that around each opamp the the component values seem identical. At least the SMD resistors. So that means he must be only changing the smd caps. Guess I could start with pulling each of the SMD caps and measuring their values.
The other idea I had was maybe change the SMD opp amps. He has used 11 x 4558 op amps.
But based on what I have read and heard so far. The JRC 4558 SMD opp amps are pretty decent performers.
And for 10 bucks this is good value for money.
I will try and mod the buffer stage to give me a little gain. My P3a based amp is sounding a bit weak. With the present input from this.
Anyway did some digging. Looks like this is a copy of this design.
https://www.rolls.com/product/EQ210
In this design. They have allowed you to increase the gain. Lets see if I can find the schematic for the Rolls board.
Another strange thing I noticed when I zoomed into each section. Is that around each opamp the the component values seem identical. At least the SMD resistors. So that means he must be only changing the smd caps. Guess I could start with pulling each of the SMD caps and measuring their values.
The other idea I had was maybe change the SMD opp amps. He has used 11 x 4558 op amps.
But based on what I have read and heard so far. The JRC 4558 SMD opp amps are pretty decent performers.
And for 10 bucks this is good value for money.
I will try and mod the buffer stage to give me a little gain. My P3a based amp is sounding a bit weak. With the present input from this.
If you just move the last band center frequency from 12 kHz to 16 kHz there could be a dip in the response between the last two bands when their controls are set to zero, unless you increase the width of the last band. Why not just get the 15 band unit instead of the 10?
Attached is the section of National Semiconductor Audio Handbook for EQ circuits with a 10 band circuit and the supporting math.
Attached is the section of National Semiconductor Audio Handbook for EQ circuits with a 10 band circuit and the supporting math.
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Ok here is the deal. I want control over the band based on the drivers Im using. rather than spend a bomb and break my head on a cross over. I want the 10 or 15 or 32 band to control my problem spots with the drivers. These are very specific frequencies. I want that flexibility. before you say buy a parametric eq. I did got scammed it worked like crap. My budget is limited. Hence the DIY.
Thank you for your post.
Thank you for your post.
It seems they are using ceramic caps rather than film caps for the important frequency-setting ones, these will be a source of lots of distortion since many of the values are too large for NP0 or C0G types.
Yes the resistors are all the same since each node has to be at the same impedance (they are all in parallel).
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It seems there was an issue in your use of parametric rather than a scam: graphic eq are fixed Q and freq so can't be by definition as precise as a parametric ( and i can tell you by experience it's true as those was tools i used on a daily basis in a former job), so rather to blame the tool i would observe what you did and try to understand what happened.
If it sounded like crap maybe you tried to fix an issue an eq can't fix ( non minimal phase) or you didn't manage to setup the eq as it should had been ( which isn't easy with a parametric if someone did not taught you how to do so).
Given the frequency involved i bet you try to fix a breakup related issue on a fullrange: given it is a breakup related it is by definition a non minimal phase effect. Eq will more or less lessen the effect by lowering it's level but it won't make it disapear as there will be spot where it'll be more obvious than others ( when a membrane enter breakup there is place where the issue will be more directional than other spots, iow directivity are parts of the issue and this an eq can't fix).
Do you use a computer as source? If that is the case rather than spend money on a physical build or gear you can use software based solution to try if it is the answer you need or not. From there if this is what is needed and you want something physical then you will know on what spend money.
Could you describe more accurately what you face as it doesn't seems to be a 'typical' issue ( drivers mean you use multiple drivers and without crossover it'll be difficult to treat on issue on one of them without compromising the whole result...).
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The 10-band (or even 31 band - 1/3 octave) graphic is basically a very old, very out-moded tool. It made a little more sense when all we had was 1/3 octave spectrum analyzers. But those days are happily long gone. Now we can see all sorts of detail, is measurements are done properly, and that's a whole other subject. But if we see the detail, we need to be able to respond to it, and that takes a stack of parametrics. As someone who does system EQ as part of professional services, I look at a 1/3 octave EQ like trying to perform surgery with an axe. And that makes a 10-band brutal.
As to budget, will free software (REW), and a low-cost calibrated mic, and a bit of time and care, you can get good high res measurements in a cluster and average them so you're not chasing a single-point measurement error. If you buy a used digital EQ like a an FBQ2496 you can even develop the correct inverse filters from your measurements automatically and send them to the EQ from REW. It works, it's precise, and reasonably easy to do.
As to budget, will free software (REW), and a low-cost calibrated mic, and a bit of time and care, you can get good high res measurements in a cluster and average them so you're not chasing a single-point measurement error. If you buy a used digital EQ like a an FBQ2496 you can even develop the correct inverse filters from your measurements automatically and send them to the EQ from REW. It works, it's precise, and reasonably easy to do.
Most of the problems Im trying to fix are there in the drivers design from the factory. Like the nasty bump at 8.5 Khz On the 2002 CDs from eminence.
Thanks for your inputs. Yes on computers I use the Peace EQ wonderful software. But in my workshop I use mostly FM Radio or Bluetooth. Got all the info I need to mod the EQ on the PDF that was very kindly shared in post #5.
I blew my budget on test equipment buying a DatsV3 unit. As I felt that was more important than a calibrated mic at the time.
Now I have to figure out if I get the 20$ calibrated unit or wait some time and get a Umic 1. Or try building one myself.
The datsv3 has started acting up. And getting any kind of support sitting in another country is going to be hard.
At least it worked long enough for me to get my sweeps in for all the drivers involved. Now every time I try to calibrate it it gives me different results.
Thanks for your inputs. Yes on computers I use the Peace EQ wonderful software. But in my workshop I use mostly FM Radio or Bluetooth. Got all the info I need to mod the EQ on the PDF that was very kindly shared in post #5.
I blew my budget on test equipment buying a DatsV3 unit. As I felt that was more important than a calibrated mic at the time.
Now I have to figure out if I get the 20$ calibrated unit or wait some time and get a Umic 1. Or try building one myself.
The datsv3 has started acting up. And getting any kind of support sitting in another country is going to be hard.
At least it worked long enough for me to get my sweeps in for all the drivers involved. Now every time I try to calibrate it it gives me different results.
Well so far I have done 5 tone control boards. 4 of them are opp amp based PCBs I purchased most are rip offs from the original Rockola board. Low mid and high control.
This EQ outperformed all of them. The only thing better in terms of low distortion is an old single ended transistor only tone control board. But it has no control over the mids.
So of all the boards built this crappy 10 band EQ is the best I have right now.
I see no distortion. It does what it claims to do. I could look into replacing the ceramic caps at some point. But for now I think I will just figure out how to replicate the Rolls design where they allow you to change the gain on the buffer op-amp.
ps: I also got a parametric Equalizer based on op-amps from a local builder but it was a big disappointment. At some point I plan to make a schematic off it and try to fix it.
if you search the internet with the following:
1976_National_Audio_Handbook
and if you luckily find the pdf file in section 2-17 you'll come across completely theory of building an equalizer ground up, modifying it will be easier if the underlying schematic is solved.
This used to be my favorite book back my middle school time and I learned from it than the college courses.
Or you can find national Semiconductors linear Applications Handbook, much more detailed.
hope this helps.
1976_National_Audio_Handbook
and if you luckily find the pdf file in section 2-17 you'll come across completely theory of building an equalizer ground up, modifying it will be easier if the underlying schematic is solved.
This used to be my favorite book back my middle school time and I learned from it than the college courses.
Or you can find national Semiconductors linear Applications Handbook, much more detailed.
hope this helps.