Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: acheld on September 15, 2022, 02:40:52 pm

Title: Signal strength for testing
Post by: acheld on September 15, 2022, 02:40:52 pm

I want to follow the signal through a preamp section with my 'scope, mostly to see for myself what happens to the signal after each triode. 

The question is:  what should be the signal strength I send?   I tried to measure the output of one of my guitars, but I'm questioning the results.

Using a Fluke 117 in AC V Max/Min function, six string strum is at about 80mV;  the A string comes in at about 30mV.  This is from a stock Ibanez single humbucker measured at the amp's input jack. Seems low to me, but . . .

What signal strength are you 'scoping with?   

Title: Re: Signal strength for testing
Post by: sluckey on September 15, 2022, 06:37:29 pm

1KHz, 100mV, sine wave is easy to remember.

Title: Re: Signal strength for testing
Post by: shooter on September 16, 2022, 02:40:57 am

^^^
I've found 800hz is more pleasing to my ears.
once i've run the test signal and recorded the stages, I typically leave the scope connected to the speaker, then slowly bring up the test signal til the scope display just starts to distort.
measure n note the signal amplitude as "max clean input"
that is the value I use for da math

Title: Re: Signal strength for testing
Post by: acheld on September 16, 2022, 10:15:17 am

Many thanks!

Title: Re: Signal strength for testing
Post by: pdf64 on September 16, 2022, 10:49:27 am

FYI my Les Paul, which has vintage PAF type rather than hot pickups (Burstbuckers I think), puts out 2Vpk on initial pick attack.
If an input stage is underbiased, it’ll cause noticeable clipping there.

Title: Re: Signal strength for testing
Post by: acheld on September 18, 2022, 09:53:59 am

Quote

2Vpk on initial pick attack.

Whoa.  I think that would clip on any of my amps!