Cavendish

[TonyW]

I got it working!
There are still a couple of issues
low 60hz hum
little more  Headroom would be nice, I don't know if by removing the 15k's and adding a jumper wire across  the 5532 is the correct way to proceed with this, no one seems to give me a direct answer on this, all they say is to remove them.
The sound-well it's got a little thicker sound then before.
Hope this post helps someone that purchases a Cavendish board.

 

[scott2000]

Great! I'm still at a loss as to how it works but it's irrelevant to me. I'm guessing it's single ended /unbalanced or something??? Just confusing because, from my limited knowledge, it almost looks like your omitting the negative polarity from the output circuit by leaving that stuff vacant.....would be nice to know for sure......

anyway, The manual says to take the ground from the Cavendish board to a spot on the GSSL close to the opamps..... Hard to tell where yours is going from the pic...... maybe hum from this???

Thanks for the updates! Glad it's working

 

[TonyW]

Just an update, after using this on my drum bus for a little while I determined  this dish thing belongs in the trash can . Total crap I spent a lot of money buying parts for this project also. Stay away from it.
Removed it from the GSSL and sounds much better. You also get no real  help from the people who sell it.

 

[TubeMonkey]

that's quite opposite of my experience.  Sounds great and really adds a lot of meat imo.

 

[TubeMonkey]

I don't have time for the next few days but can probably help you out: dont give up just yet

 

[Potato Cakes]

Remove the jumper wire across the 15k on the main PCB board. Then give it a go...


Thanks!

Paul

 

[TonyW]

Hi Paul

Have you installed this Cavendish in a GSSL?  I since removed it from the GSSL, and it's in a box came close to trashing it, but didn't yet.
Thanks for your advice , I tried jumpering the 15k,removing it, and re-installing it.
The hum is very present when you set the make-up gain up to where it should be level wise.
I have gone thru this whole circuit board even made a schematic.

Thanks for responding

Tony

 

[Potato Cakes]

Hi, Tony,

I do actually have one installed and am currently using it in a session. I did a write up on it in the GSSL Add On thread regarding this and a couple of other mods I did to this circuit (https://groupdiy.com/index.php?topic=65232.0). The 15k resistors on the output are feedback resistors that are being replaced on the Cavendish board with the resistor and trimmer to allow you to match output levels, so the ones on the main board are to be left empty. I would also recommend doing all of your connections between the boards via the IC connections except for ground. Go over to the Add On thread and see if any of that info helps. I can assure you this board works great. Also, you should know the guys at Expat have made many invaluable intectual and product contributions to this forum for the benefit of many.

Thanks!

Paul

 

[TonyW]

Thanks, Paul
I will try again when I get some time. did you see my post about the unity gain resistors?https://groupdiy.com/index.php?topic=71466.0

 

[Potato Cakes]

I did not.

If you look at the schematic, the 27k resistors are between the VCA out and output op amp. You can swap that to 15k or put a trimmer in there to fine adjust the level and find out what that resistance is. But you shouldn't have to crank your output pot all the way to get a good level if you have 27k in there currently. This tells me that something else must be going on. Swap the resistors first and see if this gets you where you want to be.

Thanks!

Paul

 

[Rob Flinn]

Just been reading this thread.  Regarding your 60Hz hum.  Looking at the first pic you posted of your unit you do seem to have the API output transformers remarkably close to your power transformer.    Most people would get them as far away as possible .....

 

[TonyW]

Thanks again Paul

The 27k's are actually at the input of the VCA, I did change the resistors to 15k and It made a difference
No longer need to crank the make-up gain.

Thanks Rob for chiming in, I will try the Cavendish one more time and move it as far away from the PS transformer.

 

[Rob Flinn]

Thanks Rob for chiming in, I will try the Cavendish one more time and move it as far away from the PS transformer.

If it still hums try rotating the mains transformer or the cavendish board.    I had a hum issue with a 4 channel Neve mic amp I made once.  I tried all sorts of earthing mods.  Tore out all my nice neat wiring that took ages.  In the end it was the mains transformer...............

 

[Potato Cakes]

Thanks again Paul

The 27k's are actually at the input of the VCA, I did change the resistors to 15k and It made a difference
No longer need to crank the make-up gain.

Thanks Rob for chiming in, I will try the Cavendish one more time and move it as far away from the PS transformer.

One step fin the right direction. Excellent.

Yes, input to VCA is what I really meant. I was trying to recall the schematic from memory and got that part backwards.

Thanks!

Paul

 

[TonyW]

I re-installed the Cavendish, moved the board away from the P.S. transformer, as per Rob's advice
Left the 15k's in, tried to remove them, but got no output signal . Seems to be working fairly well with them in.
I have a good signal since I replaced the 27k's with 15k's
No hum!! thanks's Rob.
I attached some pictures , notice I did't use all the interface wires, you only need IN(+) IN (-) and out for each 8 pin op amp socket.
It's best just to take the (-)&(+) 15v from the GSSL board and jumper wires on the Cavendish.
I hope this helps someone if they purchase one of these. Maybe the people who designed this can improve on the interface connections in the future.

 

[Potato Cakes]

Nice work getting it up and running! Also, the reason you were not getting any input signal with the 15k resistor removed by the NE5532 sockets on the main board is that omitted connecting Pins 1,2, and 3 from the main board to the Cavendish. This is fine as you found a workaround and are getting signal through your unit, but in case you are wondering why that is the reason.

Thanks!

Paul

 

[TonyW]

I don't know about that,  it looks like all the other pins on the cavendish except the ones for DC power and input/outputs are not connected to anything?

 

[Potato Cakes]

If you look on the GSSL schematic, the 15k that is by the NE5532 sockets is the feedback resistor for the first half of that output op amp. If you use all the socket connections to go back and forth with the Cavendish, you won't need the 15k as the In A+/- and out A as shown on the GSSL schematic are accounted for on the Cavendish which would then feed the B connections of the main board output 5532 which then feeds the Cavendish output DOA then to the transformer. By not using the A connections and not having that 15k resistor then signal is not getting from the VCAs to the B connections of the output NE5532 which in turn would not give you output to the Cavendish, which is why you needed that resistor in your configuration to make output happen. And it's totally fine the way you did it as long as you're getting proper output signal and no unwanted distortion. This is just a friendly explanation of what was transpiring.

Thanks!

Paul

 

[TonyW]

Thanks for the friendly explanation!
If I had the time I would draw the schematic out showing the interconnection for my own satisfaction , but your probably right.

 

[Potato Cakes]

No worries.

If I had to do it again I would use your approach to wiring. I think it would be simpler and cleaner.

Thanks!

Paul