adding an AC level (~1V 3KHz Sinus) on a DC level (30 to 100 V) line

Possibilities are:

1) A transistor common emitter amplifier 2) resistor network 3) transformer 4) RC circuit 5) summing amplifier

D from BC

--
Assuming you mean "add" as in "algebraic summation":,
view in Courier:


.DC>---[L]--+----->DC+AC
.           |
.          [C]
.           |
.AC>--------+

"jsmith" schreef in bericht news: snipped-for-privacy@y80g2000hsf.googlegroups.com...

What impedances are you talking about? Or you'd better tell something about the application. Crucial for a usefull advice.

petrus bitbyter

berichtnews: snipped-for-privacy@y80g2000hsf.googlegroups.com...

impedance is about 1 MegaOhm piezo driver

Transformer couple the signal to the DC voltage. AKA "Modulation transformer".

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

The most easy approach will be to use audio transformers having a split line side. Put a non-polarized cap (1 or 2 mFd.) across the line-split leads of the transformers (usually called the A and B leads). Put the dc voltage on the A and B leads at one end of the line. Put the 3 kHz signal on the primary of the transformer. At the other end of the line receive the dc on the A and B leads, and the 3 kHz signal ar the transformer secondary.

Don

berichtnews: snipped-for-privacy@y80g2000hsf.googlegroups.com...

It may be a megohm at DC, but I'll bet a dollar it is lower at 3kHz. What is the capacitance of the piezo device?

berichtnews: snipped-for-privacy@y80g2000hsf.googlegroups.com...

I should measure capacitance of output long cabel and piezo, but it will be less than 1uF

"jsmith"

** Better not apply 100 volts DC direct to a piezo driver - it will blow it up.

....... Phil

it is a piezo valve and its work range is up to 100V

On a sunny day (19 Apr 2007 11:17:19 -0700) it happened jsmith wrote in :

Small transformer secondary in series.

On its primary for example a 807 tube amp or a trans-sister.

Ah, a piezo valve ranging 30-100Vdc and a "impedance" of about 1M. That's an important piece of information. But, all piezo elements I'm aware of have a capacitance too. That capacitance needs to be charged/discharged when switching on/off *and* it is much lower an impedance then 1M for a 3kHz sine. The line will have some impedance (mostly capacitive) too, highly depending on the type and length of the wiring used. On the other side of the line you will have a 30-100Vdc power source which also has an impedance. Depending on the type it might even be a shortcut for the 3kHz sine. (Some

47uF smoothing capacitor for instance). That 3kHz sine source will also have some (output) impedance I guess. So I still can't give an appropriate answer to your question.

petrus bitbyter

It had better be. If the total capacitance were 1 uF, the impedance at 3 kHz would be 53 ohms. It will make a lot of difference to the driver if the total capacitance is 100 pF or 1000 pF.