In the pile of "To do" projects. Been on the shelf for several years, but not built yet.
Followed this thread from the beginning, and waiting until all the "improvements" have been presented, before I
even think of getting started 🤣
Hello. What capacitors are best to use at the M77 preamplifier output when connected to a class D amplifier with an input impedance of 10 kohm?
Hello! I finished the kit with the clone case. I’m lucky I didn’t get any hum. However, I do get some white noise that increases as I increase the volume and I have a lot of channel imbalance. I have tried changing the position of the tubes and changing them for some RCA NOS 12AU7s that I happened to have as they are supposed to have less gain, but no luck. They even pick RF which didn’t happen with the 12AY7s. Any suggestion? Thanks in advance
For all the matched components, potted inductive devices in fabricated copper pots and silver crap I put into one of the two I bought, my socks need to levitate off of my feet while my shoes are still on when I connect this thing into my mono block ACA’s.
Attachments
I just finished soldering the mj3000 and the zener diode. However the trimpot does not have any kind of stop and hence I don’t know how to set it to maximum resistance. Could you help me with that? Thanks in advance
Here some ideas:
Check the output noise when selecting a shorted input. Do you still hear something? It is quite common to hear white noise when the phono input is selected but nothing is connected.
Channel imbalance is odd, does it happen on all inputs or just the phono?
Do you have an oscilloscope, and can you use it to test if the output shows RF oscillations?
that would be helpful to further determine what is happening. In the 3-4 builds I was involved in, no oscillation happened and the two channels worked identical. We did however run into cross-coupling from unused inputs (the traces on the PCB run very close and in parallel over a long distance), but there is a fix documented in this thread.
Thank you for your help. Thats what I was doing but I can’t get to the maximum specified resistance. Guess its a cheap trimpot
If I remember correctly, it is 500Ohm, you could just put a fixed resistor of the same value....
The channel imbalance and noise happen in line in 1-2 and cd. The noise increases with the volume. I haven’t used the phono yet. Thats why I just finished changing the transistor and soldering the diode as suggested in the forum. I also changed the volume pot and i’m now waiting for a set of matched capacitors as the ones that came with the board are garbage and have signs of beating.
Despite the modest appearance and PCB, this line stage will react positively to good capacitors, both coupling as well as RIAA, IMHO.
Do you still have channel imbalance when turning up the volume to full? Just to make sure its not your volume pot....
Do you still have channel imbalance when turning up the volume to full? Just to make sure its not your volume pot....
Thats why I changed the volume pot. I bought an assembled pcb as I planned to upgrade it slowly. It is also one of my first tube preamps so I didn’t want to go too big. The quality of some of the components is questionable, that includes the volume pots, capacitors and condensers. Unfortunately the capacitors are taking forever to arrive and I already disassembled the ones included so I will have to wait until I can test it