Search found 72 matches

by Hans
Mon Sep 17, 2018 5:20 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Wayne,

In my Sim I used a noise free voltage reference for amps A and B. And also no servo was included.
I will complete my model to be exactly what you have proposed, the outcome possibly giving you some extra support.

Hans
by Hans
Sat Sep 15, 2018 9:56 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Wayne, A few things do not seem to match quite well between your Measurements against a full Simulation. 1) With 2 Ohm between both emitters, 316 Ohm feedback resistors and the two That1240 circuits, theoretical gain should be 56 dB. However your measurement shows 54 dB, 2 dB less of which 0,65 dB (...
by Hans
Tue Feb 28, 2017 11:45 am
Forum: Pro Audio Design
Topic: THAT2252 RMS Detector Replacement Using A THAT300 Array
Replies: 37
Views: 28836

Re: THAT2252 RMS Detector Replacement Using A THAT300 Array

Has anyone ever looked at this VU meter topology.
It uses a complete different way to achieve a log conversion.

http://www.naun.org/main/NAUN/mcs/17-130.pdf

Hans
by Hans
Mon Jul 18, 2016 3:25 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

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

While I'd be inclined to roll my own discrete buffer between the op amp output and 99 ohm feedback network but for an off the shelf solution consider a LME49600 buffer capable of 250ma (I've never used one but similar parts have been around for a long time). I don't keep current with the modern ube...
by Hans
Sun Jul 17, 2016 1:45 pm
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

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

I find it difficult to worry about a -3dB point of 1Mhz JR Neither do I. What I do worry about is the feedback resistor of 99,5 Ohm, that no OPA can drive. On the other hand, to achieve 30dB overload op to 20kHz, Gain cannot be more than 100. To solve this, the 2 Ohm resistor could be increased, or...
by Hans
Sat Jul 16, 2016 6:03 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

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

Here are the freq. responses with the ZTX851 and the BF862 both with the same gain of 40dB.
By only changing the 330p cap to 110p, responses are identical.

Hans
Freq.jpg
Freq.jpg (258.15 KiB) Viewed 11303 times
by Hans
Fri Jul 15, 2016 5:43 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

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

Just to be practical 8x BF862 is still lower Ciss than 1x IF3601. The 862 appears to be a HF device. JR There are two 220pF capacitors at the input of the circuit diagram, these components should be left in case of using the IF3602. And indeed the BF862 has in this specific application a gain-bandw...
by Hans
Thu Jul 14, 2016 8:51 am
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

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

I found it hard, having this LTSpice simulation model, to resist not replacing the Bipolars by Fets at the input. The BF 862 was used for that purpose, with 0.8nV/rtHz at 1kHz at Vgs = 0 Volt I inserted not only a single pair, but also a quadruple pair. One pair plus a 2 Ohm resistor in between will...
by Hans
Mon Jul 11, 2016 3:01 pm
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

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

Less noise than a 2 ohm resistor is impressive. Do real world results match that? JR It matches perfectly well. On page 3 of this thread, Wayne has published 2 graphs. Looking at the second graph, a total noise of -143.5dBu is measured, with a 3.3 Ohm resistor at the input, simulating the Cart. In ...
by Hans
Mon Jul 11, 2016 12:30 pm
Forum: Pro Audio Design
Topic: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851
Replies: 483
Views: 174395

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

JR. wrote:Real devices have noise current and 1/F noise.
JR
After some searching I could find a complete spice model of the ZTX851
Here it is including the ZTX851.
Noise is even lower as with the simulated Rbb of 2 Ohm, 44nV Flat and 34nV A-Weighted.

Hans
Wayne Circuit.jpg
Wayne Circuit.jpg (212.96 KiB) Viewed 8536 times