Audio circuit needs a second look.

[solo2racr]

Here's a little something I threw together that combines a couple of circuits from ESP (Elliott Sound Products) and puts them on veroboard (or stripboard if you like). The two projects from ESP are the P88 Preamp and P103 Phase Control along with the stereo signal combiner from Rane note 109 "Why not WYE?".

Would anyone care to take the time and give this a look for errors? If anyone should care to play with this layout, I can also upload the DIYLC file that I used to make up this layout. I believe it is good but being only my second veroboard layout, It would be nice for someone else to take a look. I'm not overly fond of letting out the "Smoke of Life" from components.

THANKS ALL!!!

 

[Harald Kapp]

It would be a great help to show us the schematic as well so it can be compared to the veroboard layout.

 

[solo2racr]

Just click on the links in the OP

 

[Harald Kapp]

That's not helpful, sorrry. How did you combine these circuits onto the one you want to prototype on the veroboard?
What does the connection between Pre-In and MONO_OUT mean? Same question for SUB PHASE-IN and PRE-OUT?
How is the circuit meant to be connected to the outside?
Last not least: What's the circuit supposed to do? Pre-Amp and low-pass filter for a subwoofer? Anything else?

 

[solo2racr]

I'll draw out the whole schematic. The"pre-in" etc (the small back text on the sides of the board) are notes for where one circuit ends and the next begins. They are located at each end of a jumper. What the circuit does is combine a stereo signal to a summed mono signal, through a pre-amp and on to a sweepable signal phase controller. "SUB-OUT" goes to the subwoofer plate amp. The low pass filter is already in the plate amp. The signal chain would be.... stereo source - signal summing - preamp - phase control - low pass filter - amp - subwoofer.

It will take me a couple hours to get the schematic drawn.

 

[solo2racr]

OK...I got it drawn out. Kinda have to relearn LTSpice again and even then, I couldn't find a model for a switch nor a pot, so I made do (with a little help from Photoshop). VR1 controls the signal phase and VR2 controls the pre-amp gain. SW1 switches between NORM and INVERTED signal phase. In the Pre-Amp section, the original P88 from ESP has 2, 2 channel opamps for stereo use. The first one was for the right and left first gain stage and the second for the right and left second gain stage. Since this is, at that point, a mono signal, I simply used just one 2 channel opamp, one side for each gain stage and eliminated the balance control in between. The "stereo to mono" section is straight from Rane and the Phase Control section is straight from P103 on the ESP page (links for both are on the OP). The pre-amp section (P88 from ESP) is the one I changed some for mono use.

I am also kinda wondering if it would be better to swap IC1 for a OPA2134, as also used in the preamp (IC2)

The purpose behind all this is so I can get a stronger, adjustable signal to the subwoofer amp as well as a better integration, phase wise, with the main speakers. I have a major response hole due to phasing centering around 80hz.

 

[solo2racr]

Is the schematic not helping?

 

[Harald Kapp]

The schematic doesn't seem to have any obvious faults. Give it a try...

 

[solo2racr]

Thanks. I knew I could take each published circuit and daisy chain each together. I was more interested in someone giving the veroboard layout a look for errors.

 

[Harald Kapp]

Sorry, I don't have the time for that.
At a first glance the veroboard doesn't look bad. Give it a try, not much harm can be done if something's not o.k.

 

[solo2racr]

I'm pretty sure it's right. I just figured another pair of eyes to give it a quick look for obvious flaws would be good.

 

[Harald Kapp]

No obvious flaws. Just one note: GND needs to go to the power supply, too (you've shown only wires to +.15V).

 

[(*steve*)]

You may find that cutting between holes in the veroboard is tricky. It's a lot easier to cut on a hole (you can just use a drill bit for that).

Also, your connections are quite close in places. I think it might pay to spread things out a little, but it's up to you.

 

[OLIVE2222]

R15 and R18 are paralleled, only one resistance will be OK, R17 is probably not needed. Also having wires under ICs will not be very easy, a second reason to spread things out a suggested by Steve.

 

[solo2racr]

I didn't really show much of the PSU. Only the +/-15vdc. 0vdc to GND was a given. FWIW.....The PSU will be a 25VA toroidal with LM317 and LM337 regs. Cleaner than 7815 and 7915.

Cutting strips has never been a problem for me. I use an engraving cutter on a Dremel. I also use a magnifying visor so I can see what I am doing. I made the layout tight to cut down on possible noise and to fit a section of veroboard I have.

I don't believe R15 and R18 are paralleled. R15 is in between pin2 on IC2 and GND. R18 traces back through C5 and R17 and then pin1 on IC2, with the other end of R18 going to GND.

You maybe right about R17. I just drew it straight from the ESP schematics (as well as laid it out on the veroboard from the ESP schematics). The wires under IC1 and IC2 are actually going on the strip side (underside) of the board. Insulated wire from pin4 to pin4 and from pin8 to pin8. Though, I may enough room under IC1 and IC2 for a bare jumper wire, but I'm not overly fond of this idea.

 

[OLIVE2222]

Sorry mistyped I mean R1 and R18 are paralleled
Olivier

 

[solo2racr]

You're right. Like I said, I just drew, and laid out on veroboard, straight from the ESP schematics. Any recommended changes?

 

[OLIVE2222]

Just try any of both values

 

[solo2racr]

Yea. I don't see a problem playing with the value of R18. Even omitted, I don't believe it would let the "Smoke of Life" out.

 

[(*steve*)]

I also noted the paralleled resistors. There are another two pairs if you look carefully. I don't think they'll cause an immediate problem, and if they do, one can simply be removed.

If you're can cut the tracks the way you say, then that's fine. Keeping things compact is great. If you need to rearrange the circuit later it can be a bad thing, but the only potential changes I see are the removal of some resistors.

You only have a single pair of power supply decoupling capacitors. Again, probably not a huge concern. If you really need more, you can place them on the back of the boars across the actual pins (they'd be most effective that way anyway).