USB and microphone mixer using a valve.

[ckpr2]

Just finished a USB and mic mixer using a 12AU7 valve.
The valve seems to sweeten up and clarify the sound quite a bit.
So not all distortion is bad.
17998

[Nakatomi]

Great stuff, but what happens if it develops a fault & you get 300V DC on your USB? :O Genuine question. I'm curious.

[ckpr2]

Great stuff, but what happens if it develops a fault & you get 300V DC on your USB? :O Genuine question. I'm curious.

Its only 300 volts at 2mA so shouldn't do much damage.

There is a high voltage capacitor in series with the microphone input so it should never go live.

But other faults aren't impossible. If it is dropped who knows what strange problems could occur.

On the other hand most of what we use has mains on it somewhere.

[Nakatomi]

Its only 300 volts at 2mA so shouldn't do much damage.

There is a high voltage capacitor in series with the microphone input so it should never go live.

But other faults aren't impossible. If it is dropped who knows what strange problems could occur.

On the other hand most of what we use has mains on it somewhere.

Yeah I guess everything we use has the potential to deliver nasty voltages to signal paths or whatever in extreme conditions. or in the case of fake CE marked gear, not so extreme conditions.

I've seen inside some cheap laptop & phone chargers.. oh man they've just not heard of creepage & clearance distances.

[ckpr2]

Yeah I guess everything we use has the potential to deliver nasty voltages to signal paths or whatever in extreme conditions. or in the case of fake CE marked gear, not so extreme conditions.

I've seen inside some cheap laptop & phone chargers.. oh man they've just not heard of creepage & clearance distances.

I remember the first valve pre amp I made in about 1980 as a young lad.
I powered it up and it didn't work so I started testing it and touched the power supply capacitor and got a huge shock.
My tutor said I needed to discharge the power supply capacitor before working on it.
So next time I discharged the capacitor, touched the circuit and got a huge shock again.
I had forgotten to turn it off ! Doh...

[Nakatomi]

I remember the first valve pre amp I made in about 1980 as a young lad.
I powered it up and it didn't work so I started testing it and touched the power supply capacitor and got a huge shock.
My tutor said I needed to discharge the power supply capacitor before working on it.
So next time I discharged the capacitor, touched the circuit and got a huge shock again.
I had forgotten to turn it off ! Doh...

Ouch. I work on high voltage & high current stuff in my day job a lot of the time & have to be very careful or it won't just be a jolt I get.

[DJ Jules]

Great stuff, but what happens if it develops a fault & you get 300V DC on your USB? :O Genuine question. I'm curious.

I wonder how they deal with that on commercial valve amps? Isolating transformers on inputs?

[Nakatomi]

I wonder how they deal with that on commercial valve amps? Isolating transformers on inputs?

More than likely yes. Better than mere DC blocking caps for sure.

[ckpr2]

More than likely yes. Better than mere DC blocking caps for sure.

Guitar valve amplifiers were famous in the 1960's - 70's for killing people.
A fault could occur where the guitar ground line became live.

Valve amps were also famous for picking up radio like taxi firms.
I heard a story about one group wanting paying a local cab firm to stop using their radio during the gig.
They refused due to it would meaning losing too much money.
During the gig radio broadcasts could be heard.

[CRAZY K]

Guitar valve amplifiers were famous in the 1960's - 70's for killing people.
A fault could occur where the guitar ground line became live.

Valve amps were also famous for picking up radio like taxi firms.
I heard a story about one group wanting paying a local cab firm to stop using their radio during the gig.
They refused due to it would meaning losing too much money.
During the gig radio broadcasts could be heard.

This is unbelievable but true--I clearly remember playing in a Band in the 60s at the City Hospital Social Club, St.Albans when the PA picked up "outside conversations"

Yes we had a valve PA amp.

Confused---yes we were.

What the :Censored:is that ???????????? ;););)

[ckpr2]

Here is my stereo version of the same mixer.
It has a USB DAC stereo input.
The mic/line/guitar input is converted to stereo.
There are two valves in this version to get the extra channel.
18077