sbelyo Posted October 3, 2016 Report Posted October 3, 2016 Is there a balanced to unbalanced (single ended) board that is recommended? Twisted Pear has two options but they use op amps, and then there's the Broskie Cathode Follower, and Unbalancer Two. Those two use tubes. What else is out there?
Bespav Posted October 3, 2016 Report Posted October 3, 2016 Amb alpha24Or you can use simple THS4131+LM6171 if your source can work with something like 2-10 kOhm load.
kevin gilmore Posted October 3, 2016 Report Posted October 3, 2016 my balanced/unbalanced/cast to balanced/unbalanced. but its a pile of transistors, single resistor gain control, and would need a buffer for low impedance loads.
Skooby Posted October 4, 2016 Report Posted October 4, 2016 I've used Jensen transfo for XLR-2-SE. Not sure it's the best/cheapest method. May be a step-down transfo's better than 1:1
sbelyo Posted October 4, 2016 Author Report Posted October 4, 2016 21 hours ago, kevin gilmore said: my balanced/unbalanced/cast to balanced/unbalanced. but its a pile of transistors, single resistor gain control, and would need a buffer for low impedance loads. Is that the board that you posted with mention of using it in a modular preamp of sorts?
sbelyo Posted October 4, 2016 Author Report Posted October 4, 2016 Is it this one ? http://gilmore.chem.northwestern.edu/boards/balancedoutputcast2.zip
RudeWolf Posted October 18, 2016 Report Posted October 18, 2016 There's also THAT - http://www.neurochrome.com/product/that-receiver/ The board's a bit pricy, but should be easy to implement. 1
Craig Sawyers Posted October 18, 2016 Report Posted October 18, 2016 (edited) The most significant issue with the THAT 1200 series of receivers is noise, -107dBu. It is dominated by the rather large values of noise-generating resistors inside (7k typical). With a good discrete design, or clever use of opamps you can get to -120dBu, which challenges measurement (<1uV in a 20kHz bandwidth). Edited October 18, 2016 by Craig Sawyers 1
RudeWolf Posted October 18, 2016 Report Posted October 18, 2016 Interesting, just checked the datasheet and the noise figure checks out. I wonder how the guy got his -140dB noise measurements. He's an EE at TI and should know better than that.
Craig Sawyers Posted October 18, 2016 Report Posted October 18, 2016 He doesn't say what the measurement bandwidth was. Which really makes it a very loose specification. The only hint is the very sharp mains harmonics in the noise plot, which are way sub-Hz in width. To get to -158dBV (-155.8dBu) from -107dBu on a 20kHz B/W you would need a measurement bandwidth of 0.25Hz, Shockingly badly specified. 1
sbelyo Posted October 24, 2016 Author Report Posted October 24, 2016 I found this post... Did these designs go any further?
sbelyo Posted January 12, 2017 Author Report Posted January 12, 2017 On 10/3/2016 at 9:03 PM, Skooby said: I've used Jensen transfo for XLR-2-SE. Not sure it's the best/cheapest method. May be a step-down transfo's better than 1:1 I think this might be the best solution... anyone else do this compared to an opamp based solution?
sbelyo Posted January 12, 2017 Author Report Posted January 12, 2017 Here's the schematic on the jensen website http://www.jensen-transformers.com/wp-content/uploads/2014/08/as089.pdf It will go starting with a dual mono BIII to a passive 1 in 3 out xlr switch box (the transformers will be one of the three positions) to a 1 in 3 out RCA switch box. D you guys see any issues with that?
sbelyo Posted January 12, 2017 Author Report Posted January 12, 2017 For my tube amps I would need the dampening circuit according to jensen. For best response it says to keep my cable run under 2 feet. I might make a box separate for each tube amp. That would keep the cable run under two feet.
Craig Sawyers Posted January 13, 2017 Report Posted January 13, 2017 Any audio signal level transformer has a resonant peak at some frequency, hopefully outside the audio bandwidth, caused by leakage inductance resonating with distributed winding capacitance. The RC network on the output is chosen to damp that resonant peak. But if you put a cable after it, which has some capacitance, it screws with the damping. The catchall of using less than two feet of cable comes from that consideration. 1
sbelyo Posted January 13, 2017 Author Report Posted January 13, 2017 I understand... That was an excellent explanation, thank you
kevin gilmore Posted January 17, 2017 Report Posted January 17, 2017 this is coming soon http://gilmore.chem.northwestern.edu/diffinput2.pdf a lot less parts than the other version, almost the same thd 2
congo5 Posted January 19, 2017 Report Posted January 19, 2017 (edited) The diffinput works, files posted , and tested. Edited January 19, 2017 by congo5 4
MLA Posted January 20, 2017 Report Posted January 20, 2017 Board files were posted yesterday and you have a working prototype today? Most impressive !!!
kevin gilmore Posted January 20, 2017 Report Posted January 20, 2017 boards at the speed of light. updated version of the board with input resistors just posted. by adjusting a few resistors you can get up to 6db (12db balanced) gain
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