Ok wow. Removed op amps 3,4,5 and signal is now good at pin 1 of A2. On the other channel I left op amps 3,4,5 in and still bad on that channel so I am assuming it is something in that section of the circuit but most likely not the chips themselves.
The output coming out of the preamp also looks good on the channel that I have removed the op amps from.
And yes to -15 at pin 4 of a2 as measured on the actual pin of the op amp body.
The output coming out of the preamp also looks good on the channel that I have removed the op amps from.
And yes to -15 at pin 4 of a2 as measured on the actual pin of the op amp body.
Well--I think the winner is...I'm an idiot. 2.2 ohm resistor at r21. Not 2.2k. Have no idea how I ended up there. Most likely this is the issue. Now I have to dig around and see if I have the resistors I was supposed to use in the first place. Will keep you updated. Thanks again to for everyone's patient help!
It could also be a pin that is folded underneat the body of the chip instead of being inserted into the socket. Happens now and then.
Remove the opamp from the socket, inspect the pins, if OK re-insert into socket, and/or re-align the poin. Check again.
Jan
Unlikely that's the issue. But it would be smart to re-check all resistor values. R20 could cause it if too low.
If you don't have that resistor, remove opamps A3, A4 and A5 from their socket. That should fix it if it is the cause.
Jan
If you are keen to try it then any equal values resistors in the 1k to 100k range should get it up and running, If there are any more 2k2's anywhere it is worth checking those are OK and correct fitments as well.
Just for info for those not used to swapping chips around... If you are not used to removing chips from sockets then the trick is to lever each end up a millimetre or so at a time with a thin driver. Try and do it one go and most likely you will end up with a chip firmly stuck in the end of your finger as it lets go suddenly... been there and done that many times, you learn the hard way.
Just a quick update--swapped in the correct resistor values. Works beautifully! Only a few minutes of listening so far connected with my f6 and fantastic!
Many many thanks to Mooly, Jan and others.
Looking forward to a laser cutting workshop tomorrow night so that I can start making my own case fronts--totally botched my order to modushop at least on the front. But the learning continues...
Many many thanks to Mooly, Jan and others.
Looking forward to a laser cutting workshop tomorrow night so that I can start making my own case fronts--totally botched my order to modushop at least on the front. But the learning continues...
I like this design and looks like a nice upgrade to the preamp. Do you have design files and software available? I would like to add something like this to my preamp. Looks great!Inspired by the discussion here about an IR controllable version of this preamp, I have started again to think of possible solutions. I have had many ideas which I often discussed with @Carl_Huff (thank you, Carl, for your time - I wouldn't have come this far without your help). Most of the ideas were quickly discarded, and some made it to a design/routing phase. Finally, I implemented a concept which allowed me to re-use the preamp PCB and the +-15V supply PCB:
- I designed a PCB to hold MCP41HV51 digipots which fits exactly on the original preamp PCB as a replacement of the mechanical pots. Luckily, I had one of these PCBs already at hand from an earlier try
- The IO PCB needed a few modifications:
- separate grounds for audio/relays
- low side relay switching with an ULN2003
- updated 12V supply
- for my convenience: selectable relay supply (onboard/external) and selectable output delay control (onboard/external)
- As microcontroller I am finally using an Adafruit Grand Central M4 Express which can be programmed using the Arduino IDE and many of the Arduino libraries can be used, too. Originally, I had used an Arduino Mega 2560 which caused a lot of headache to me as it turned out to be the source of hizz in my setup.
- I added a small RGB OLED (small enough to fit into a 1U case) and a rotary encoder + switch.
- The digital stuff is powered by a small 5V SMPS.
Some impressions:
Front:
View attachment 1085814
Digipots:
View attachment 1085815
Modified IO board:
View attachment 1085816
Everything combined:
View attachment 1085817
Example splash screen
View attachment 1085818
So far, I haven't done measurements yet but the preamp sounds good to me (=without audible noise/distortions) which is my primary goal. Nevertheless, there are things left to be done which I will follow up step by step:
I have a readily designed zero crossing detection circuit and all the parts for it at hand. But after listening tests, I am no longer planning to implement measures against zipper noise as there just isn't any that I could hear.
- Implement the IR control which I had honestly forgotten when designing the front panel
- Implement using the big standby switch
- Cable cleanup
- Implement NVM storage of settings
- ...
Any hints/suggestions/questions are always welcome!