Ron Worley wrote:You could try a noise gate, that might make it a go, along with turning down and / or a 12AT7.....
Ron
A noise gate would be cool, except the noise is coming through while playing too. I'm not just playing at screech levels. I recorded a sample clip that highlights hiss coming through while playing. Unfortunately, my garageband program will only output mp4 files. Also, it's actually difficult to record the hiss that's going on in the room. For recording volume levels for guitar amps are not that forgiving. That is, I cannot turn up the baseline level of the guitar track loud enough to represent the amount of hiss that's in the room without distorting the recorded guitar track. another drat!!!!
Whatever, I'm building an airbrake this week. Maybe that will help. If not, I'm going back to my Two Rock....it's dead quiet while putting out drop dead gorgeous tone!
Just tried, again, a JJ gold pin ECC81 in V1. NICE. I forgot about that tube. It dropped the hiss enough to where I actually don't hear it when playing at softer levels. Cool. This is a reasonable compromise, for I definitely don't need all that gain.
Now if I could find a 12AX7 that would be as quiet as the ECC81 (12AT7), I'd be a happy camper!
High gain amp circuits by nature bring with them tube hiss. The two comments in this thread that will lead you to less hiss are:
1. Reduce the gain in the preamp stages
2. Try lots of different preamp tubes.
The best thing one can do to reduce any resistor hiss is use larger wattage rated resistors in the signal chain. I think the reward there is small though.
Try paralleling another 2k7 resistor piggy back with the one on the V1a cathode and see what that does to the hiss.
jjman wrote:The 1st tube also contributes significantly to the hiss level in this setup. I taped the hiss level from about 10 different 12ax7s during my crusade. Then eyeballed the volume levels of each and listened to each on it's own track on Sonar (Cakewalk.) Unfortunately the quietest 2 were a little microphonic. They were Chinese Ruby 7025STRs.
Among any brand you can find tubes, which are fairly low in hiss. But the ECC83's w/ the lowest hiss floor I've ever had (and still have) were Telefunken ECC83 w/ ribbed plates.
As for the plate resistor of the 1-st stage you can try a Metal Oxide type instead of a MF, they're still a tad quieter.
Further keep in mind, that any grid stopper in front of the 1-st stage is enhancing hiss, the quietest solution here is NO grid stopper. But check for RF issues and always use a high quality guitar cord.
Actually it wasn't easy to record the clip. My recording computer is setup upstairs. I ran a mic cable over my balcony and into the living room where the amp sits. You'd laugh watching me click record, then run down the stairs to my guitar play a few chords. Then run back up stairs to see if I got the input volume correct. There were quite a few trips up and down my stair case.
Actually it wasn't easy to record the clip. My recording computer is setup upstairs. I ran a mic cable over my balcony and into the living room where the amp sits. You'd laugh watching me click record, then run down the stairs to my guitar play a few chords. Then run back up stairs to see if I got the input volume correct. There were quite a few trips up and down my stair case.
a regiment of exercise always seems to come from the most unexpected activities. Now we know that recording can be considered a workout.
I built my liverpool and working on my rocket but my express was build by Nik at Ceriatone. He said make sure to shield the chassis and cab. I did it has been very noisy. I changed out the preamp tubes to various types that helped a little. Nik then said to put a 15K to 22K resistor from the input to pin 7 V1 with the shielded wire. I tried this and it did not work.
Mark
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The stuff that Barry noted on valve selection is certainly what will help you.. but I don't remember seeing gut shots of your build- Lead dress is sooo important. If you look very closely at the preamp input stages, Ken made sure that the wires were at 90 degrees to each other and with the heaters in particular, they made elegant loops up over the input wires at 90 as well...
I presume that you have the regular grounded coax wire into V1b, making sure that the ground braid come off the input jack side of the connection. Some have tried with success using this same method to the input to V2a...just a thought. The pot grounding scheme is important, did you use the copper buss wire setup?
Sorry if I'm going off ignorance of your build, just don't remember gut shots. Also, if you're running it without the cover plate, it will be WAY more noisy.....
Actually it wasn't easy to record the clip. My recording computer is setup upstairs. I ran a mic cable over my balcony and into the living room where the amp sits. You'd laugh watching me click record, then run down the stairs to my guitar play a few chords. Then run back up stairs to see if I got the input volume correct. There were quite a few trips up and down my stair case.
That's kind of how the Eurythmics recorded their downstairs neighbor's piano on their early recordings.
+3 for knocking down the gain. You aren't using it, you don't need it, and all it is doing is contributing noise.
Have you considered turning it into an EL34 Rocket?
You don't even need to replace the entire board - just move a few turrets around.
(RJ and I are actually looking at just how few parts have to be moved 'round to make the swap. Keep the mid control. And, if you don't mind the fixed bias, leave it too.)
Gotta run now. I hear the Wreck Police coming down the hall!
Zippy wrote:+3 for knocking down the gain. You aren't using it, you don't need it, and all it is doing is contributing noise.
Have you considered turning it into an EL34 Rocket?
You don't even need to replace the entire board - just move a few turrets around.
(RJ and I are actually looking at just how few parts have to be moved 'round to make the swap. Keep the mid control. And, if you don't mind the fixed bias, leave it too.)
Gotta run now. I hear the Wreck Police coming down the hall!
Nah, that's a cool idea. In fact I've started pricing out the parts in the BOM to build a Rocket. I've been talking to RJ about his chassis design and such.
I recorded a sample clip that highlights hiss coming through while playing. Unfortunately, my garageband program will only output mp4 files. Also, it's actually difficult to record the hiss that's going on in the room. For recording volume levels for guitar amps are not that forgiving. That is, I cannot turn up the baseline level of the guitar track loud enough to represent the amount of hiss that's in the room without distorting the recorded guitar track. another drat!!!! 
