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Hi,
My plexi has got alot of hum at the moment.
Quiet as a mouse on standby and it makes no difference pulling the tubes out.
It only happens when a guitar is plugged in.
I've been using it with a vvr but when i went to crank it up it had alot of hum and i don't
remember it being there before.
With volume on full when i turn the gain up there is a hum present and I don't know where the hum is coming from.
I get it in both channels worse with boost on.
I've redone every ground point, shortened all ac lines resoldered all jack sockets and gone over the shielded cable, but nothing has helped it.
I've replaced all the tubes apart from the rectifier tube.
I'm on 240vac mains just so you know.
Also i lose 20 vdc with the vvr i'm not sure it matters, is that why my voltages seem on the low side
b+ is 340 in and 318 out of the vvr.

Here are my voltages.They were measured with 1 probe on ct and the other one going
to all the pins.
v1 pin1 147
pin3 1
pin6 147
pin8 1

v2 pin1 168
pin3 1.5
pin6 247
pin8 168

v3 pin1 186
pin2 57 but it switches off when i touch it
pin3 75
pin6 184
pin7 55 but switches off when i touch it
pin8 86

v4 pin3 11
pin7 332
pin9 314

v5 pin3 11
pin7 332
pin9 314

v6 pin1 290ac
pin3 340dc
pin7 290ac
This is bugging the hell out of me.
If you do make suggestions could you make it as simple as possible as this is my first build,
Thanks.

That's a sign that the problem lies in your guitar, the input jack or even the guitar cable.

_________________
Great tones come in small glass jars!

So when you have NO guitar plugged in and the amp ON (not on standby) does it hum? If so, I agree with Zaphod and there is a ground problem with our guitaar or cable. Did ou try another guitar or cable?

Can you post a pic of the input jacks?

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

It still hums when the cable is plugged in with or without a guitar.
One thing though, when you hold the strings on the guitar it is alot quieter and acceptable i think, but how much hum is normal as i don't know.
I still think there is some sort of ground problem somewhere or could something be faulty.
I've included some pictures.
I was trying to keep it tidy but welcome some more building advice for the
next one.

You can try this. Remove the grounds from the normal channel pots & all the input jacks and run them all separately to the preamp ground post.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

You're not standing near a flouresent light fixture or a light dimmer or something like that?
Stew

No it's not near any flourescent lights.
I'll try doing the grounds differently on friday.
Why don't i need to run a seperate ground for the tmb volume pot, as this is grounded on the bus bar and the hum is in both channels.
Still trying to understand this problem.
Also does the vvr affect the amp in some way.

You can do that too. It wont hurt, butthe nput jacks can be very sensitive.



Try disconnecting the VVR and bypass it. See if the problem goes away. It can cause noise on the power supply.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Hi,
I decided to leave it alone for the moment after hearing this you tube clip of jtm45 kit.
http://www.youtube.com/watch?v=s7SrBYqcNeU
at 1min36 into it he turns it up and mine sounds like that when the volume is on full
and gain maybe 4 or 5, can someone tell me if that is normal it's also louder when i take
my hands off the strings.

That's normal with my SIIIv6
With the amp turned up and the volumes up on the guitar you will get some "white noise" through the amp, what I call the noise floor.
When you start playing the volume (of the guitar through the amp) should be much louder than the white noise and it (white noise) should not be decernable while playing the guitar.

When you have the guitar plugged in and you are not touching the strings YOU are an ungrounded antennae and are causing the increased noise Try setting the plugged in guitar on the couch and move away from it, the noise will go down, a lot.
When you touch the strings, the noise goes down because you are getting grounded through the guitar string ground.

You can try different preamp tubes, some are noticably quieter than others and will lower the noise floor, another source MAY be CC resistors in the pre-amp circuit.

Hope this helps