A quick question from a novice, to try and work out whether a constant, quite low level hiss audible from one (left channel) only, level of which is unaffected by volume adjustment on the preamp, is more likely to be a tube (pre uses a pair of E88CC /6922 in the output stage) or something else? I've tried a couple of different power amps, and also tried the pre via its RCA phono and its balanced XLR outputs, and the hiss remains on the left channel in each set up, ruling out everything else, I think. Hiss isn't particularly loud, only audible with no music playing and when standing quite close to the speaker, just wondering whether a tube swap could fix it or if it sounds like something else? Pre is a ProJect Audio one where the tubes are bonded to the board horizontally, so a quick pull and switch around isn't as straight forward as some.
Although unlikely, switch the speakers around. Its possible one has a lower HF output (for whatever reason). At least eliminate that possibility first. I suppose it could be a valve in the preamp, passive components like resistors tend to be more randomly 'crackly' noisy when they fail. If it does prove to be the preamp then a circuit would help to determine where in the signal path the volume pot is and what any output buffer looks like.
Thanks, swapping speakers around on the outputs was one thing I hadn't tried, I'll give that a try tonight. I searched around and couldn't find schematics for it (or most other ProJect gear) so no luck there. Lots of surface mount stuff inside which is definitely beyond my abilities but the hiss is low level enough to be liveable with as it is, if necessary.
The most likely culprit is a noisy tube, which is unfortunate if the tubes are soldered to the board.
Last edited:
Hmmm, looks that way. Any valve after the volume pot has to be the next thing to try.
I always ask this 😉 Is this a recent acquisition with unknown history or have you had it a long time and it has failed in service?
Do also the pre, wires disconnected, connect only one, and the phono same to isolate from where the hiss is coming.
You swapped everything ahead of the speakers and the hiss remained on the L channel, then swapped the speakers and the hiss followed the speaker. How does that rule out the speaker?
Both speakers can hiss so its not a speaker fault.
I read this as relating to the electronics and swapping power amps to different models.
After swapping channels.
Thanks for all the replies.
Just to clarify, the test on the swap of speaker outputs was done after I had reverted back to the original left to left and right to right connection between pre and power amps. And when testing the pre with different power amps and via either the RCA outputs or the XLR outputs(but with the speaker outputs connected as normal rather than reversed), yes, the hiss remained on the left speaker in each case.
One other thing I thought to check when I remembered last night that the ProJect - being a combined DAC/Pre amp - can also be operated as a fixed output line level component into a line input of a pre or integrated amp. So I dug out a different pre amp and tried the ProJect via its fixed level output and the hiss in the left speaker was gone. I have been trying to establish whether the ProJect uses the E88CC in circuit at all times or only when operating via the variable output but it is not clear from anything I have found, the literature only says "the audio circuitry is using E88CC tubes for ultimate fidelity and components, that guarantee extremely low noise and distortion levels". At a guess I would say that means the tubes are in circuit at all times, which would rule out them as the cause, I think, given the lack of left channel hiss when on fixed output.
I will try it as a pre later on with no sources connected, just the connection between pre and power, and see what I get then.
PS - the tubes aren't soldered to the boards, at least i don't think they are from what I can see using a torch to see in the case. The tubes sockets are fitted at right angles and soldered to the circuit board, so that the tubes when inserted to the socket lay flat and are then bonded to the PCB with what appears to be silicone. So not impossible to remove, jst not a straight forward pull and switch. It is a new to me pre which is actually under warranty, and could also be easily returned if I wanted to, though it would be a shame to do so just for a bad tube, if that is all it is. I am not intending to void any warranty I have by opening the pre amp up and digging around inside, I just want to try and establish a likely cause of the issue before getting back in touch with the retailer to see how best to proceed.
Just to clarify, the test on the swap of speaker outputs was done after I had reverted back to the original left to left and right to right connection between pre and power amps. And when testing the pre with different power amps and via either the RCA outputs or the XLR outputs(but with the speaker outputs connected as normal rather than reversed), yes, the hiss remained on the left speaker in each case.
One other thing I thought to check when I remembered last night that the ProJect - being a combined DAC/Pre amp - can also be operated as a fixed output line level component into a line input of a pre or integrated amp. So I dug out a different pre amp and tried the ProJect via its fixed level output and the hiss in the left speaker was gone. I have been trying to establish whether the ProJect uses the E88CC in circuit at all times or only when operating via the variable output but it is not clear from anything I have found, the literature only says "the audio circuitry is using E88CC tubes for ultimate fidelity and components, that guarantee extremely low noise and distortion levels". At a guess I would say that means the tubes are in circuit at all times, which would rule out them as the cause, I think, given the lack of left channel hiss when on fixed output.
I will try it as a pre later on with no sources connected, just the connection between pre and power, and see what I get then.
PS - the tubes aren't soldered to the boards, at least i don't think they are from what I can see using a torch to see in the case. The tubes sockets are fitted at right angles and soldered to the circuit board, so that the tubes when inserted to the socket lay flat and are then bonded to the PCB with what appears to be silicone. So not impossible to remove, jst not a straight forward pull and switch. It is a new to me pre which is actually under warranty, and could also be easily returned if I wanted to, though it would be a shame to do so just for a bad tube, if that is all it is. I am not intending to void any warranty I have by opening the pre amp up and digging around inside, I just want to try and establish a likely cause of the issue before getting back in touch with the retailer to see how best to proceed.
I’m pretty sure Project Audio uses tube sockets. Get a warranty check on the tubes (if tubes are warranted).
I misunderstood what the OP meant by "bonded to the board." If changing the tubes would void the warranty, then I would return it. You shouldn't have to put up with any noise.
Large volume retailer who didn't have a direct contact available to really discuss this, only automated systems in place to enable a return for refund, which has been done. A shame, as other than the hiss it was a nice sounding thing with lots of functionality that suited my system. A positive from this is that I think I have fully tested every other component in my set up and am now confident they all work 100% 🙂
Thanks to all for taking the time to reply and for the help and advice.
Thanks to all for taking the time to reply and for the help and advice.