3D "AIR" EQ - "Night EQ" PCB's Complete!

[earthsled]

Many thanks to khstudio, harpo, peterc, and everyone else who has contributed here!

I wonder if anyone is still keeping up with this 5-year-old post???

Okay - here goes -- I'm currently working on a two-layer PCB version of the EQ3D for a rackmount unit (non-500-series).

I've decided to include the clipping circuit on my PCB, and because of this, I've run into a few snags that I was hoping to get some help with...

1. What's the value of C200 and is it necessary? It's not on the schematic, but it appears to connect between pins 5 and 8 of U6... http://www.twin-x.com/groupdiy/albums/userpics/U-4-5-6.JPG Judging by the color, I would guess that it's the same value as C13 (22pF) -- can anyone verify this?

2. How many watts is R202? This resistor appears much larger than the surface-mount units, but it's difficult to tell if it's more than a 1/4W... http://www.twin-x.com/groupdiy/albums/userpics/Switch___Led.JPG

3. How many volts is C201? I'm assuming 25V or 35V - but the clipping circuit was omitted from the Nite PCB BOM - so, I just wanted to double check.

4. This is question about DC power (rather than the clipping circuit) -- The Nite PCB appears to split the +/-18V DC into 2 sets of rails -- one set powers U1, U2, U3 and the other powers U4, U5, U6. I'm wondering if there is an advantage to this setup versus having all ICs linked to a single +/-18V rail.

Thanks in advance for your help!

 

[Harpo]

1. What's the value of C200 and is it necessary? It's not on the schematic, but it appears to connect between pins 5 and 8 of U6... http://www.twin-x.com/groupdiy/albums/userpics/U-4-5-6.JPG Judging by the color, I would guess that it's the same value as C13 (22pF) -- can anyone verify this?

not verified, but 22pF should fit. Might be omitted, as voltage gain of NE5534 is set for 4.3, so opamp should run stable.

2. How many watts is R202? This resistor appears much larger than the surface-mount units, but it's difficult to tell if it's more than a 1/4W... http://www.twin-x.com/groupdiy/albums/userpics/Switch___Led.JPG

With +/-18V supply NE5534 might swing +/-16V. Subtract 2 diode drops from 1N4148 rectifier and maybe 2V forward voltage from a red LED / 680R, giving ~19mA current thru LED and a resistor rating of at least 0.24W needed for a worst case continuous constant overload scenario. 1/3W seems sufficient.

3. How many volts is C201? I'm assuming 25V or 35V - but the clipping circuit was omitted from the Nite PCB BOM - so, I just wanted to double check.

use 35V rating.

 

[earthsled]

Harpo -- thank you so much!

In fact, I've been looking at your spreadsheets and I'm planning to use rotary switches in place of the antilog pots. -- Could you tell me if the calculations from the 3D-EQ_Stepped_Pot.xls will work for the AIR boost control as well as the other frequencies? Also, it seemed like you were recommending 10K for R30 (and R48) when using stepped controls, is this correct?

 

[Harpo]

Could you tell me if the calculations from the 3D-EQ_Stepped_Pot.xls will work for the AIR boost control as well as the other frequencies?

simple calc of an inverting opamp stage. Be aware that the 'filter' stages aren't filters but bandwidth limited non-inverting gain stages, so voltage gain doesn't fall below 1.

Also, it seemed like you were recommending 10K for R30 (and R48) when using stepped controls, is this correct?

Could bring resistive noise down a little, but requires other changes as well. Finaly I modded mine for a non-inverting summing stage, resulting in a totaly different behaviour that was more to my taste.

 

[earthsled]

simple calc of an inverting opamp stage. Be aware that the 'filter' stages aren't filters but bandwidth limited non-inverting gain stages, so voltage gain doesn't fall below 1.

Hmmm... I'm a little confused what you mean about the voltage gain - the default spreadsheet shows the voltage gain ranging from 0.53 to 1.88 (for -5.5dB to +5.5dB).

I ask about the "air" band because it's only boosting - rather than cut & boost, yet it originally used the 500K reverse-log pot like the other bands. For instance, if I calculate resistances for -10dB to +10dB -- would this translate to a range of 0 to +20dB for the "air" band?

Could bring resistive noise down a little, but requires other changes as well.

Perhaps it would be best to stay with the original value of 56K2 -- just to keep it simple.

I appreciate your help!

 

[earthsled]

Would this circuit work for an alternative "pot-to-switch"?
(image attached)

Also - I'm still unsure if a rotary switch will work for the "air" boost control. Has anyone tried this?

Thanks.

 

[Nobru]

Hi there! Is there somebody who would share the schems for this unit with me or any pcb??? this eq can be magic  ;D I would love to play around it.
Thx

 

[earthsled]

This link should have all you need...
http://www.khstudio.us/EQ3D.htm

Cheers!

 

[Nobru]

Many thx! ;D

 

[earthsled]

If anyone is interested in using the "series-string" switch configuration (pictured above), here are my calculated resistance values for an 11-position rotary switch with 2 dB steps (+/- 10 dB for each cut/boost control) --

step 1 to 2 = 36k5
step 2 to 3 = 28k7
step 3 to 4 = 23k2
step 4 to 5 = 18k2
step 5 to 6 = 14k7
step 6 to 7 = 11k5
step 7 to 8 = 9k09
step 8 to 9 = 7k32
step 9 to 10 = 5k76
step 10 to 11 = 4k64
step 11 to sum = 17k8 (replaces R37,39,41,43,45)

Lorlin CK1589 switches...
http://www1.mouser.com/ProductDetail/Lorlin/CK1589/?qs=sGAEpiMZZMsqIr59i2oRcnKZ3G9keN4Q2tT6qRGPIX4=

From what I understand, using this switch configuration as the air-boost control will result in 1 dB steps -- but Harpo points out that the air-boost technically does not start with 0 dB because it sums with the 2.5k section once it's turned on.

Enjoy!

 

[ytsestef]

If anyone is interested in using the "series-string" switch configuration (pictured above), here are my calculated resistance values for an 11-position rotary switch with 2 dB steps (+/- 10 dB for each cut/boost control) --

step 1 to 2 = 36k5
step 2 to 3 = 28k7
step 3 to 4 = 23k2
step 4 to 5 = 18k2
step 5 to 6 = 14k7
step 6 to 7 = 11k5
step 7 to 8 = 9k09
step 8 to 9 = 7k32
step 9 to 10 = 5k76
step 10 to 11 = 4k64
step 11 to sum = 17k8 (replaces R37,39,41,43,45)

Lorlin CK1589 switches...
http://www1.mouser.com/ProductDetail/Lorlin/CK1589/?qs=sGAEpiMZZMsqIr59i2oRcnKZ3G9keN4Q2tT6qRGPIX4=

From what I understand, using this switch configuration as the air-boost control will result in 1 dB steps -- but Harpo points out that the air-boost technically does not start with 0 dB because it sums with the 2.5k section once it's turned on.

Enjoy!

Well done, erthsled, thanks for reviving the thread. I have left my build unfinished because of my lack of knowledge on how to make gainswitches work on the air-band. So with the above configuration the switch will be 1dB Boost to 11dB Boost, right?

I also wonder whether it would be possible to make "range switches" for the other bands so that each band would have a switch next to it that switches Rshunt and give less range, but more precise control (for example switch between +/-5dB in 1dB steps and +/-10dB in 2 dB steps)... Could be quite useful, but I don't know if it's possible.

 

[earthsled]

So with the above configuration the switch will be 1dB Boost to 11dB Boost, right?

To be honest, I'm not sure how many dB it will be. Perhaps Harpo would be kind enough to comment on this matter?

I also wonder whether it would be possible to make "range switches" for the other bands so that each band would have a switch next to it that switches Rshunt and give less range, but more precise control (for example switch between +/-5dB in 1dB steps and +/-10dB in 2 dB steps)... Could be quite useful, but I don't know if it's possible.

That's a great idea, but it won't work by changing 1 resistance value. Rseries (aka R37,39,41,43,45) sets the maximum boost level, while the total resistance of the pot (or series-string switch) sets the maximum cut. -- If you wanted to get fancy, you could use a switch with 2 decks (each with a different set of resistors) and another switch to select between the decks.

 

[ytsestef]

If you wanted to get fancy, you could use a switch with 2 decks (each with a different set of resistors) and another switch to select between the decks.

Yeah, I thought it wouldn't be that simple. Getting dual gand switches for all the bands of each channel and all those weird resistor values doubled would raise the cost much too high over the original revlog pots, plus the overwhelming amount of work to wire all this stuff...  :-\

 

[earthsled]

Hi all - Does anyone have recommended fuse values for 115VAC and 230VAC operation? Or, better yet, does anyone have a good way to calculate a mains fuse in general for audio equipment and linear power supplies?

I'm planning to use a 25VA toroid transformer with an LM317/337-based power supply to power 2-channels of EQ3d. The PSU will have a voltage selector for both 115VAC and 230VAC input.

khstudio mentioned this in November of 2007...

If my math is correct, each card should be drawing less that 100ma.
250 - 300ma TOTAL (LEDs & all) should be enough for a stereo unit.

There's some info here, but many of the links are inactive...
http://www.groupdiy.com/index.php?action=printpage;topic=27493.0

On a related topic - I noticed the LED for the Bypass circuit uses a 3K3 resistor for current limiting. -- This seems like a high resistance value to me - limiting the LED to about 5mA. Would using the same value be appropriate for a power-indicator LED connected to the +18VDC rail?

Thanks!

 

[ytsestef]

I think most transformers pretty much indicate the recommended fuse value and type straight away in their label or specsheet. Mine (50VA) uses T 315mA...

 

[earthsled]

Funny - I've used toroid transformers from Avel Lindberg, Triad, and Antek, and none of the spec sheets or labels seem to have fuse recommendations - just rated current on the secondaries. ???  Plus, I'd like to choose fuse ratings that will not only protect the transformer, but also the EQ circuit itself - so I'm thinking it would be a lower value than for the transformer.

Out of curiosity, what brand are you using? Do they have specs for 115V vs. 230V operation?

 

[ytsestef]

Funny - I've used toroid transformers from Avel Lindberg, Triad, and Antek, and none of the spec sheets or labels seem to have fuse recommendations - just rated current on the secondaries. ???  Plus, I'd like to choose fuse ratings that will not only protect the transformer, but also the EQ circuit itself - so I'm thinking it would be a lower value than for the transformer.

Out of curiosity, what brand are you using? Do they have specs for 115V vs. 230V operation?

I used to use Multicomp toroidals for the previous projects (gssl,ssl9k), but this time I bought one that is made here (Greece), the brand name is "T. Giatras". It is rated 225V / 50Hz.

 

[earthsled]

I decided to email Triad Magnetics and I'm glad I did. Their engineering manager responded quickly with this information...

"Since the VPT36-690 transformer is rated at 25VA (Volts times Amps), the theoretical input current would be 25VA / 115V = 0.217A or 25VA / 230V = 0.109A.  However, this does not include the magnetizing current or inrush currents – so we generally recommend the fuse be rated at 1.3 to 1.6 times the theoretical input current.  It is very important that a Slow Blow (time delay) fuse be used to allow for inrush currents that exceed the fuse rating to prevent nuisance fuse blowing."

This seems like a very good guideline for fusing the transformer.

Accounting for the actual draw of the DC circuit is considerably more complex -- I'm probably going to just stick with the guidelines above.

 

[ytsestef]

Finished mine  ;D ;D Thanks a lot everyone!
http://www.groupdiy.com/index.php?topic=43855.0

 

[sneakthief]

My minimalist user-interface approach: