Search found 73 matches

by Hans
Mon Jun 27, 2016 12:09 pm
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 499
Views: 772354

Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

To measure the Offset current accurately, you only have to measure between TP1 and TP2 with 1) the input shorted and 2) with the input open, i.e. only having the 2x 499 between the inputs. Subtract the two voltages, divide by 158000 (=50dB*499)and you have the Offset current in nano-amps. Thus 15.8m...
by Hans
Mon Jun 27, 2016 8:59 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 499
Views: 772354

Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

I did some additional measurements with 56 dB gain and with the hum field nulled. Rsource is 3R3 Rgain 1R 2X ZTX851 and NJM2068. The OPA1612 performs identically to the NJM2068DD. Ein of -143 dBu. Voltage noise density 3.67 nV/√Hz Env = 8.3 Ohms https://proaudiodesignforum.com/images/jpg/Flat_Movin...
by Hans
Sun Jun 26, 2016 7:15 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 499
Views: 772354

Re: A Low Noise Balanced In Moving Coil Preamp Using the ZTX

All effort has been successfully invested in getting a very low noise input noise, but what about DC current flowing into the cart. With 5 to 10mA collector current per ZTX851, Ibias and for that reason Ios must be in the many multi micro amps. Isn´t that much too high and therefore over the top for...