Noise levels in Dumble amps?

[heisthl]

re: hum - it's amazing how modern 12AX7 production tubes can vary on Hum levels, we routinely have to hand select tubes for V1 & V2 to get minimum hum.

[Mark]

I still haven't gotten down to working through this issue. I had one of those experiences on the weekend which made me wonder. I normally get a lot of single coil hum in front of the laptop. I went away up the coast and I couldn't get over how quiet the guitar and laptop was. This makes me think the problem may be from the earthing in our house.

What can be done to minimise hassles with bad household wiring?

[amplifiednation]

Computer screens are big him inducers, same thing with florescent lighting. I just can't get into single coils unless they are noiseless. Oh and those energy efficient lights are even worse, also dimmers induce him.

Did you check all the grounds in your power supply?. Did you use a different scheme at all then HAD?

Henry is right you may have a bad tube.

There are so many variables that come into play. I think an isolation transformer could help you if its your house wiring, but I would continue to experiment before commuting to a purchase. I was having a similar problem last yeat-i thought the grounding in my house was bad, you could probably go find my thread. It turned out to be a wiring error in the amp

[martin manning]

Look for things like dimmers and flourescents nearby, and try other locations in your house. How's the shielding in your guitar? Does the control cavity have foil llining or conductive shielding paint, and is the pickguard shielded on the back?

[Mark]

Thanks for the reply Taylor, I have experienced the dimmer noise (we have two of them), but I've noticed one power outlet is noiser than the other one.

I'll have to find time to look at the amp again, work has been hectic!

I use to have Kinman's in my Strat, they were the quietest pickups I've ever used. I had the traditionals and the Woodstocks are what would have worked in the guitar.

Thank for the reply Martin. I will have to be careful about what power outlet I use and be mindful of earth loops. When I first tried the Dumbleator with the amp it was very quiet.

[aflynt]

I have an old house that that quite noisy power. I've found that using an Ebtech Hum X helps a great deal.

As far as single coils go, I love the sound of them and haven't ever gotten on with any of the noiseless options. What works amazingly well for me is the Ilitch Silent Single Coil backplate. It kills most of the hum but doesn't alter the sound of the pickups a bit.

As far hum from the amp goes, I recently went through that with my #102 build and wound up finding one particular 12AX7 that was much quieter than the rest.

-Aaron

[briane]

My amps are dead quite when dimed and all on- no input - that should be your standard.

I find almost all problems (aside from bad power and bad guitar location - and amp build issues) are due to the guitars - most have shoddy parts in them unless they have been rebuilt. I've rebuilt the electronics in far too many guitars to count - almost everyone has it done once they hear the difference.

Humbuckers, cts pots, and mallory/wima/PIO caps are required for a quite guitar - at a minimum. If you like the single-coils like myself then on to the bag o special tricks.

Lots of good advice from everyone else too. - especially about the variability of tubes, and where you place the amp - personally I build a faraday cage into my cabs - and that also really helps a lot (ie 2 sheilds, 1 faraday in cab, 2nd in chassy). Thats just a foil coating thats grounded.

-b

[sonicmojo]

I still haven't gotten down to working through this issue. I had one of those experiences on the weekend which made me wonder. I normally get a lot of single coil hum in front of the laptop. I went away up the coast and I couldn't get over how quiet the guitar and laptop was. This makes me think the problem may be from the earthing in our house.

What can be done to minimise hassles with bad household wiring?

I just had the same experience. After a four month absence from amps and building, I just got everything moved from my old house in Tampa to my new house in Honolulu. Older house here but new wiring and I totally noticed that all my amps are MUCH QUIETER and consistent at different times of the day than before. Hawaii isn't known for great, stable electricity but I must have had a major issue in Tampa, either in my house or before. We always had power going out in storms there and sflickering and uch. I suspected both areas as potential problems but never really investigated. Sounds like you may want to try to troubleshoot it.

[Mark]

I had an opportunity to listen to the amp yesterday, there does appear to be too much hiss in the amp.

Step 1 is check out the photo's of the build.

[IMG768]http://i149.photobucket.com/albums/s69/ ... CN4911.jpg[/img]

[IMG768]http://i149.photobucket.com/albums/s69/ ... CN4912.jpg[/img]

[IMG768]http://i149.photobucket.com/albums/s69/ ... CN4913.jpg[/img]

[IMG768]http://i149.photobucket.com/albums/s69/ ... CN4914.jpg[/img]

[IMG768]http://i149.photobucket.com/albums/s69/ ... CN4915.jpg[/img]


[IMG768]http://i149.photobucket.com/albums/s69/ ... CN4916.jpg[/img]

[IMG768]http://i149.photobucket.com/albums/s69/ ... CN4917.jpg[/img]

[IMG768]http://i149.photobucket.com/albums/s69/ ... CN4918.jpg[/img]

All critique welcome.

[Mark]

This time I tested it without the Dl/lator, just the D'Lite and the speaker cab with 2 X Celestion 65 watt speakers. The amps sound great, but the hiss in the overdrive when nothing plugged in is a bit much, I don't notice the hiss when i play though. I will make measurements and post pix.

[bluesfendermanblues]

I have two suggestions

a) The input jack doesnt appear to be isolated from ground.

Looks like the buss bar is grounded at the input jack and further that the input is connected to the chassis ground point behind the jack.

This creates a small ground loop, that can cause noise, but more likely hum than hiss. So maybe not the reason for hiss. However, try an isolated input jack to see if that helps.

b) If hiss only appears in OD mode, like 'da Geezer' I would suspect the V2 tube. Try another tube to see if that helps.

My #102 clone is not noisy in OD mode and the PAB or Mid boost does not add any noise at all (and why should they? - its just a passive circuit mods).

[10thTx]

My D-inspired amps have some hum. However, the amp hum is LESS than the hum of either of my guitars volume pot set at "8". With the guitar volume pot at below 7 or at 10, the amps are very quiet.

With the "clean" channel engaged, I think it would be possible to walk into a room (& if not paying attention) not realize the amp is on.

I do get some additional noise with the midboost engaged. I think with the midboost engaged, one would notice the amp is on when walking into a room.

This is with the amp played at volumes that I would play at home or with a band and the amp mic'd. IF I dialed everything on the amp to "10", the amp would be waaayyy noisey, IMO.

However, when I listen to the U-toob clips of many of the Dumble amps, I'd say my floor noise is comparable or less. I would also say the noise level is less than the Princeton Reverb I owned or the Blues Deluxe that my son owned.

The amps are the Tweed BluezMeister (17w sort of a cathode biased D) and the D'Mars OD Special (23w which is sort of a Marshall clean with a Dumblish OD using a 5879 & CF in the second OD gain stage).

With respect, 10thtx

[Structo]

Nice looking build Mark.

I think too that if you have a lot of hiss in OD then more than likely it is the V2 tube.

Try a few different tubes there to see if there is a difference.

[Mark]

Thanks for the replies and thanks for the compliment Tom.

I did take some voltage readings with the CRO and the signal generator. I do want to check the readings again as I found my four year ago had got amongst the test equipment.

What I've seen today would lead me to think the noise present on the plate of V1 (tone controls on ten) is 5.4mV. If I put 30mV peak to peak into the grid I get roughly 1.2V peak to peak on the plate.

The clean tones aren't an issue but I have to know where the problem starts.

[Gaz]

Mark, I agree with the comments about tubes, but what is the input grid stopper you're using? 22-27K? The input grid stopper is actually the biggest contributor to hiss, and it makes sense if you think about its locus in the circuit. Try reducing it down to 10K all the way to 0. I think you will be surprised by how much it reduces hiss in a high gain amp like a Dumble.