[Anthropic]

Thanks for your responses and help.  I ended up grounding the PIN 1s of the XLR IN/OUT to chassis at entry.  I left the shields of the internal cables attached to the ground holes on the INs/OUTs of the EQ board.  I also grounded the -+18 ground on the EQ boards directly to star/chassis ground.  The ground hole on the "output" of the PSU board was left unconnected.  This seems to be the most effective grounding scheme so far. 

Unfortunately, I'm now realizing that the vast majority of the hum is coming from the toroidal power transformer (as it is almost twice as loud in the EQ board closest to it).  I've rotated the transformer to the position that produced least hum but, even there, it produces hum that makes the EQ completely unusable. 

The only real solution seems to be mounting the PSU outside the case, which becomes another pain.  Oh well...  I guess I'll have to put this project aside for a while.    

[Harpo]

..the vast majority of the hum is coming from the toroidal power transformer..

..that would have a VA rating and secondary voltages printed on its label as well as indicators to identify the start of each secondary winding, if you don't have the manufacturers part ID to look up the datasheet. Colour coding of transformer wires is not standarized. Source of your hum might come from an out-of-phase series connection of your secondary windings, if your transformer isn't already a center tapped transformer.

[Harpo]

when I connect output of EQ to input of my speakers with TS cables,I hear a little bit of distortion!!but when I connect the output to a headphone,there is no distortion.what is the reason for that?should I use TRS cable only??

Speaker?Headphone? This is an EQ, not a power amplifier. When using TS cables for an unbalanced connection to your assumed monitor- or headphone amplifier, set the jumpers on pcb for unbalanced connection, else you nearly short out the summing stage U5. This will cause more than 'a little bit of dirtortion'.

1.Is it possible to explain the AIR,VARY and SUB band of this EQ??when I change the VARY I can't understand exactly what happened.VARY and AIR are related to each other??I mean the frequency of AIR band choose by the VARY selector??or vary is a shelve??
2.and the sub band is a band under 40HZ??
3.It seems that the Q of this EQ is very wide, isn't it??

Already answered, just read this thread...

[Anthropic]

..the vast majority of the hum is coming from the toroidal power transformer..

..that would have a VA rating and secondary voltages printed on its label as well as indicators to identify the start of each secondary winding, if you don't have the manufacturers part ID to look up the datasheet. Colour coding of transformer wires is not standarized. Source of your hum might come from an out-of-phase series connection of your secondary windings, if your transformer isn't already a center tapped transformer.

Interesting.  I'll try swapping the connections and see if it has any effect.  Thanks for the tip!

[Harpo]

I'll try swapping the connections and see if it has any effect.

Didn't say so, but as long as you keep your transformer data and how you connected it a secret, noone could seriously help you.

[Anthropic]

Oops, sorry Harpo.  I'm using a Toroid-brand transformer, model #602.152.  It's 0-15V, dual secondary, rated for .80A per secondary.  Right now, I have it wired with BROWN and ORANGE together to the GROUND of the PSU (as a pseudo center tap)(with a third wire which goes to star ground), while the RED and YELLOW secondaries each attached to a respective AC input on the PSU.  Previously, I had RED and ORANGE twisted together and attached to the GROUND input on the PSU (also with a third wire to star ground) and YELLOW and BROWN each separately attached to one of the AC inputs on the PSU. 

Both configurations had a high level of stray field buzz injected into the EQ boards.  To confirm this, I unbolted the transformer and lifted it out of the chassis (as far as it could go with the wires still attached).  As I moved it around, I could find areas and positions where the buzz diminished considerably.  However, none of those positions lent itself to convenient mounting.  Furthermore, no position was able to diminish the buzz to a level at which the EQ could be usable. 

As an aside (due to other posts mentioning this), I've measured the resistance of each of the chassis panels to star ground and none measures more than 1 Ohm (most, if not all, were below 0.5 Ohms).  Accordingly, I'm doubtful that the Faraday-cage-like effect of the chassis is compromised in any way.

To further muddy the waters, another pair of Night EQs I am building at the same time used a different brand/model of toroidal transformer.  That transformer is an AMVECO 62063-P2S02 (25 VA, dual 15V secondaries).  This transformer has much less buzz induced in the EQ boards, but is still not quiet enough for use. 

Anyway, I hope this makes my problem a little clearer.  Thanks for the attempts to troubleshoot this one.

Dan

[Harpo]

The 'Toroid Corporation', model #602.152 should either have red+orange joined for the center tap or brown+yellow joined for the center tap connection. Rotating the toroid for least induced hum (50Hz/60Hz) should help a little. For usual the greatest radiated field is where secondary wires leave the toroid, so get this spot furthest apart from high impedance areas on EQ-pcbs. Distance is your friend. (If your induced hum is at dominant 100Hz/120Hz instead, source of hum mostly will originate from PSUs diode snap.) Bolting some vertical metal shield between toroid/psu and the eq-circuit and distant placing of AC-mains wires should further help.

[dogma]

Sorry about coming in late - I was hoping that someone might be Ble to confirm if this is the same as on gustav s site? I'm looking for a mouser bom for that build and can't locate one. Some assistance would be SO appreciated

[Harpo]

I was hoping that someone might be Ble to confirm if this is the same as on gustav s site?

Colins version (PCBs from Gustav) base on a partly similar circuit with different behaviour in a different format,
whatever the meaning of 'Ble' (bloody low educated?) might be.

[imloggedin]

Will this transformer: http://www.parts-express.com/pe/showdetl.cfm?partnumber=122-605 work with the power supply board? Its 30VA.

[peterc]

That transformer should be fine.

Peter

[imloggedin]

Thanks Peter,

Whats all this:  "Cbyp Cbyp Cbyp Cbyp Cbyp1 Cbyp10 Cbyp2 Cbyp3 Cbyp5 Cbyp6 Cbyp7 Cbyp8" in the parts list. I don't see any capacitors like that anywhere in the schematic.

[kooma]

almost ready

[kooma]

and finished:)

[peterc]

Whats all this:  "Cbyp Cbyp Cbyp Cbyp Cbyp1 Cbyp10 Cbyp2 Cbyp3 Cbyp5 Cbyp6 Cbyp7 Cbyp8" in the parts list. I don't see any capacitors like that anywhere in the schematic.

These are PSU bypass caps.

Peter

[frazzman]

Any prospect of another run of pcbs? I'm really keen to build one of these but can't track down any boards. Cheers

[seavote]

small bear (supplier in US) has rt angle pc mount 1000k reverse audio pots. no 500k as needed for nite EQ. is there any reason not to order 1000k pots and strap a 1000k resistor across the lugs of the 1000k pot to make my own 500K reverse pot. is there something im not thinking of . seems like a simple solution to me if not.

[Harpo]

small bear (supplier in US) has rt angle pc mount 1000k reverse audio pots. no 500k as needed for nite EQ. is there any reason not to order 1000k pots and strap a 1000k resistor across the lugs of the 1000k pot to make my own 500K reverse pot. is there something im not thinking of . seems like a simple solution to me if not.

The rheostats unity gain setting would be at about 65%, not 50% turns angle. You could use paralleled 1M stereo rev.log.pots instead, if avail.
Not that much redesign needed to use lower value pot/rheostat values than 500K.

[frazzman]

Thanks for your responses and help.  I ended up grounding the PIN 1s of the XLR IN/OUT to chassis at entry.  I left the shields of the internal cables attached to the ground holes on the INs/OUTs of the EQ board.  I also grounded the -+18 ground on the EQ boards directly to star/chassis ground.  The ground hole on the "output" of the PSU board was left unconnected.  This seems to be the most effective grounding scheme so far. 

Unfortunately, I'm now realizing that the vast majority of the hum is coming from the toroidal power transformer (as it is almost twice as loud in the EQ board closest to it).  I've rotated the transformer to the position that produced least hum but, even there, it produces hum that makes the EQ completely unusable. 

The only real solution seems to be mounting the PSU outside the case, which becomes another pain.  Oh well...  I guess I'll have to put this project aside for a while.   

Get a sheet of mumetal shielding, its self adhesive... cut a strip large enough to wrap around the whole toroid. The stuff is amazing, I had a strong hum on one of my g-pultecs, didn't matter where I put the toroid. Once the sheilding was there the hum was gone entirely.

[fazeka]

Hi,

Long time member only getting 'round to starting on this project now.

Question about the stepped Lorlins with this project and gain.

I am probably going to use the 12-position Lorlins as there is no seemingly affordable rotary switch readily available.

The gain of each frequency on the original is +/-15dB.

Using Harpo's stepped pot calculator, that means 3dB increments. Seems like more than I'd like per step.

If I go +/-10dB, I get 2dB increments per step. But is 10dB going to be enough? IOW, will I likely ever have a need for more than 10dB?

What have others found as the best compromise?

Thanks,
Chris

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