Barry Porter "Net EQ"

[petermontg]

Plus they are log pots. You can build the resistor chain the same. Check back through the thread for wiring.

 

[frazzman]

These -different project- posts from you might be related to your problem ...

Just have an issue with a the Calrec mini PSU board. Basically I etched one to use for another projector (2x net EQ). Anyway, I used alternate regulators to get a 18v supply. The only issue is on my 30VA toroid, the secondaries seem to be a bit hotter than normal. So I end up with about -/+ 20V rather than 18v.

20V at unload condition? That is OK in most cases, try that with some load and measure again, BTW if You use NE5532 op amp that's OK (+/-22V Max).

Thanks for the quick reply....yes at unload - actually closer to 21v

It turns out I'm an idiot and I accidentally ordered a 30va 2x25 instead of 2x18...
Will 7818 and 7918 regs play nice with this extra voltage ?
The net eq is jam packed with ne5532s so I'm glad to hear they will cope with the surplus voltage...

With your 2x25VAC secondaries unloaded and kept a secret mains transformer in front you operated the fixed voltage regulators above their abs.max. 35VDC input voltage (and as well maybe the storage caps), so these might be damaged and maybe still are with your now 2x18VAC transformer in front. If you once have connected this maybe faulty supply to your NetEq pcbs (from Gustav or self etched as well?), not all of the populated NE5532s might have survived. Just an idea.

Hey Harpo,

Thanks for the reply. I didn't actually connect the PSU to the mainboard at that stage. All I did was connect the (wrong) toroid to my self etched Calrec PSU.

When I measured the voltages and observed that they were too high, I stopped and replaced the toroid with the correct 2x18v one.

So all in all - the circuit never saw this increased voltage...

 

[biigniick]

Plus they are log pots. You can build the resistor chain the same. Check back through the thread for wiring.

Oh, I'll have to look at the schematic again. I thought the boost/cut, frequency and Q were all 10k linear. The HPF is 20k reverse log though...  I'll go double check

- Nick

 

[ruairioflaherty]

Plus they are log pots. You can build the resistor chain the same. Check back through the thread for wiring.

No.  The original circuit and notes from Porter are very clear that it was designed for all pots to be 10k linear for ease of sourcing, with center taps on the gain pots only.

Of course you can go log on the frequency pots/switches and remove the law bending resistors that Porter used to make linear work.

Log is not suitable for either Q or Gain switches.  I've never seen log used in either position in any SVF design,

 

[frazzman]

Good advice, thank you....

I'm regards to a signal probe - perhaps something like this :

http://web.archive.org/web/20050310014839/http://www.diyfactory.com/data/mbsignaltracing.htm

Mnats had a link on his site to this page and I made one of these probes but never had a need for it... (Until now)

I don't think you need to go that far.  Without a scope what you are looking to do is measure just parts of the circuit through RMA, first input stage, then after first eq bands, then after HPF, then after output stage.  It should help you find the area of the circuit that's oscillating.

To do that you'll need to go balanced out of and unbalanced in to your RMA.  It's crude but lacking a scope it could help narrow down the trouble spot.

I'm still digging away here on my problem. I ended up building the signal probe as I thought it would be useful.

So far the probing has me thinking that the issue is in the input stage. I have 1khz sine wave feeding in which sounds ok until I get to C7/R11 where it sounds to me like it is becoming slightly distorted.

I then probed the output stage components and it sounded to me like the distorted/oscillating signal was present at every point, therefore I figured that the problem is not in the output stage as I should have been able to detect a point where it goes from 'good' to 'bad' if it was being introduced in the output stage.

The problem is that listening to a sine wave with varying (subtle) differences plays tricks on your ears.

I have a few more observations/questions
- THD is at 0.2 when the unit is in full bypass. The problem is then worsened when the circuit is in (even with all bands bypassed), THD rises to nearly 0.7
- If the problem is present in bypass can that mean that I can at least exclude the areas in the circuit pertaining to each of the bands?  Can I concur that the problem has to be in the input or output stage?

Hopefully I am getting closer to narrowing down the problem... Thanks again for everyone's help

 

[biigniick]

try replacing U5...  swap with U6 maybe?  see if the problem migrates to output stage only.  that would indicate a bad IC, i would think,...

- nick

 

[frazzman]

try replacing U5...  swap with U6 maybe?  see if the problem migrates to output stage only.  that would indicate a bad IC, i would think,...

- nick

Thanks Nick, yep tried that...

I replaced the ICs already but they are all from the same "batch", I've got some "fresh" ICs coming in soon for the sake of being thorough

 

[ruairioflaherty]

0.2% distortion in bypass is awfully high, I need to look at the schematic again but from memory it's a full relay bypass.

What does your analyzer rig measure from output to input?  Within nothing in line.

I didn't mean for you to probe with tone and ears, use your probes to measure the distortion with your analyzer, again isolating each stage.

I would never buy ICs from ebay, too many fakes these days!  Hoping that maybe that is part of your issue.

 

[druu]

0.2% distortion in bypass is awfully high, I need to look at the schematic again but from memory it's a full relay bypass.

The unit uses relay to bypass but will only pass audio when powered on. So it's not true relay bypass by the schem.

 

[frazzman]

0.2% distortion in bypass is awfully high, I need to look at the schematic again but from memory it's a full relay bypass.

What does your analyzer rig measure from output to input?  Within nothing in line.

I didn't mean for you to probe with tone and ears, use your probes to measure the distortion with your analyzer, again isolating each stage.

I would never buy ICs from ebay, too many fakes these days!  Hoping that maybe that is part of your issue.

Hi there,

Yeah the THD is ridiculously high, even in bypass. With nothing inline it's almost 0.

I've used RMAA to bench mark many other builds and it's always looked ok. This is the first time I've incurred something so severe.

In a normal test passing some drums for example , the problem is obvious but I can still hear respective the boost and cuts, it actually sounds quite nice if you can get passed the weird sound in the background. It almost sounds like radio noise (but it's not...).

I will use the probe in conjunction with RMAA, I just thought that the problem is so evident under normal circumstances that I thought it would be just as evident under test circumstances - that said, listening to a sine wave for an hour does funny things to your brain !

I'm holding hope that it's dodgy opamps, I  am guilty of  buying a bulk amount of ne5532s on ebay. They always worked fine in the ssl stuff that Id built.

Thanks for your help!

EDIT:
- Here are the metrics from RMAA

1) BYPASS:

2) CIRCUIT IN - all bands bypassed

3) FF800 Interface loopback

 

[frazzman]

0.2% distortion in bypass is awfully high, I need to look at the schematic again but from memory it's a full relay bypass.

The unit uses relay to bypass but will only pass audio when powered on. So it's not true relay bypass by the schem.

Thanks man, you're right... My d-la2a is relay bypass too but passes audio with no power.

I'm just trying to work out if it's mainly the input and output stages that are in effect when in bypass, aside from the relay circuitry of course...

 

[biigniick]

The relay bypass does not bypass the input or output stages. In bypass signal passes through the input stage all the way to C7 and goes directly to C30 in output stage. Still lots of parts in the signal path even in bypass.

- nick

 

[frazzman]

The relay bypass does not bypass the input or output stages. In bypass signal passes through the input stage all the way to C7 and goes directly to C30 in output stage. Still lots of parts in the signal path even in bypass.

- nick

Thanks Nick!

There's absolutely no doubt in my mind that my problem is in the input stage.

Signal probing at C7, I can hear the distortion/oscillation. Just trying to work out what point it kicks in.

I tried some "known working" opamps but no luck!

Thanks for your help

 

[Gustav]

0.2% distortion in bypass is awfully high, I need to look at the schematic again but from memory it's a full relay bypass.

The unit uses relay to bypass but will only pass audio when powered on. So it's not true relay bypass by the schem.

Thanks man, you're right... My d-la2a is relay bypass too but passes audio with no power.

A little off topic.

I think of it as more correct to use relays as: Resting position = most natural path.

So when I do "hard" bypass, the unit will not pass audio with no power, since I see bypass as the intrusive state.  It still jumps the input to the output when I send voltage to the coil and make the switch jump. 

I just want to make sure I dont label anything incorrectly, so are you saying that the correct terminology would not be hard bypass for what I am doing?

Gustav

 

[druu]

Hard/True bypass means the in ties straight to the out when in bypass, completely skipping the circuit. Whether you have this in the relays 'resting' state is up to you but generally is the normal practise.

The BPEQ uses a 'buffered' bypass that maintains the in and out buffers and bypasses the main circuit but of course still needs power for the signal to 'skip' through when in bypass.

I'm currently waiting for some bypass PCB's to arrive to add a 'true' bypass to my unit as I'd rather not have my BPEQ turned on at all times to use another piece in my analog chain.

 

[petermontg]

Got some spare time to take another look at mine.
Power issue is solved no more 10r smoking and everything lights up, relays click etc etc 8)
Next step is some test.

 

[druu]

Got some spare time to take another look at mine.
Power issue is solved no more 10r smoking and everything lights up, relays click etc etc 8)
Next step is some test.

Nice. What was it? Swapped +/-18v wires from PSU?

 

[petermontg]

Got some spare time to take another look at mine.
Power issue is solved no more 10r smoking and everything lights up, relays click etc etc 8)
Next step is some test.

Nice. What was it? Swapped +/-18v wires from PSU?

I put it down to 2 bad ebay PSU in a row, failed regulators. I got a vari psu from Gus and works perfect now. I was chasing my tail there for a bit.

 

[petermontg]

A couple of things presented themselves in the right channel.

Mostly freq selection switch with only the last 90 degress of selection working the rest of the switch is boosting the entire spectrum. Cap problem?

right HPF drops volume when engaged.

Not major problems but does anybody have any hints.

Best
Peter

 

[Gustav]

A couple of things presented themselves in the right channel.

Mostly freq selection switch with only the last 90 degress of selection working the rest of the switch is boosting the entire spectrum. Cap problem?

right HPF drops volume when engaged.

Not major problems but does anybody have any hints.

Best
Peter

Would check the resistors on the switch at the point between where it works and it doesn't (check for a bad solder connection with your meter)

Would compare left/right channels for your HPF problem. See schematic for what is switches in on the HPF setting. Its a pretty simple signal path that way through.

Gustav