Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Equipment & Tools From test equipment to hand tools

QuantAsylum QA400 and QA401
QuantAsylum QA400 and QA401
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 19th December 2016, 03:40 AM   #2271
davada is offline davada  Canada
R.I.P.
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
That schematic is straight out of the app notes for depletion mosfets.
__________________
David.
  Reply With Quote
Old 19th December 2016, 03:43 AM   #2272
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
QuantAsylum QA400 and QA401
Tell LTSpice that. . . I'm sure it would work. Not sure if there would be any nonlinearities. However a quick breadboard would answer all. The Mosfets would get 400V out of the circuit which would be very attractive.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 19th December 2016, 03:46 AM   #2273
davada is offline davada  Canada
R.I.P.
 
Join Date: Jul 2004
Location: Fort St John, BC Canada
Quote:
Originally Posted by 1audio View Post
Very interesting trick. I just tried a simulation using LSK389 (closest in my database to a J110, which is what I would use). Attached is a simulation I just tried. With a 100K source I get about -96 dB for HD3 which is not bad. That would be the effect of the cap modulation in the reversed biased diodes.

I'll look into breadboarding it and trying it in something, but not for a while. I'm really busy until CES is over. Maybe someone else is interested?

I tried simulating with depletion mode Mosfets and LTSpice crashed hard.
It ran for me using depletion mosfets but it was ugly.

Lamps don't distort until the frequency gets low. Like 10Hz.
__________________
David.
  Reply With Quote
Old 19th December 2016, 04:03 AM   #2274
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
QuantAsylum QA400 and QA401
Even at 10 Hz with microamps through the filament its not going to affect the distortion. The Jfets looked promising. it would be a simple breadboard. Just no time for now.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 19th December 2016, 01:58 PM   #2275
Bob Cordell is offline Bob Cordell  United States
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by BlacK_Chicken View Post
With "transdiode" you refer to a BE-shorted BJT?

I like the Idea of the series-Connection :-)
I think a transdiode is a transistor with the input signal connected to the emitter, the base connected to a reference voltage (often ground), and the collector connected in such a way that its current, which appears essentially as the signal current when the signal is sufficiently negative (for NPN), is used in some way, often as part of a limiting circuit. As such, it is not the same as a diode-connected BJT where the diode function is implemented with the CB junction. The transdiode is often found in a logarithmic amplifier, where it implements the feedback path around an op amp in the inverting configuration.

When just using a BJT with BE shorted to form a diode, it is important to recognize that the reverse breakdown of the diode formed is often only on the order of perhaps 4V; so it acts as a Zener diode. BTW, reverse BE conduction (breakdown) in a BJT will usually degrade the transistor over time, resulting in a reduction of its beta. Of course, in some applications this may not matter.

I have not tried it, but a JFET with drain-source shorted together can also be used as a diode, and it will typically have a significantly higher reverse breakdown. The capacitance of the gate-channel junction formed may, however, have significant capacitance, especially for large-area low-noise JFETs like the LSK389. The LSK489 has substantially less capacitance.

Another reasonable approach is the 1N4149, which has lower capacitance than the 1N4148.

Cheers,
Bob
  Reply With Quote
Old 19th December 2016, 05:18 PM   #2276
1audio is offline 1audio  United States
diyAudio Member
 
Join Date: Mar 2004
Location: SF Bay Area
QuantAsylum QA400 and QA401
All very interesting stuff to explore. For me mid January but maybe someone else can give it a try sooner.
__________________
Demian Martin
Product Design Services
  Reply With Quote
Old 30th December 2016, 05:34 PM   #2277
BlacK_Chicken is offline BlacK_Chicken  Germany
diyAudio Member
 
Join Date: Nov 2005
Hello again, the attenuator-project is still ongoing but currently I am quite busy exploring all the features of the QA401. Just now I did a test of the stepped-frequency response plugin. Somehow the phase-information seems to be lost.

Actually, looking at the phase-display in the upper right corner of the qa401-application-window during the sweep, the displayed figures seem to be correct BUT the exported .csv is definitely wrong. See plot below. Has anyone ever tried and got the same results?

The Visual-Studio stuff is still installing (since 3hrs now )... anyways, I attempt to write my own script to overcome this issue.
Attached Images
File Type: png 20161230_01_hpf.csv.png (54.7 KB, 318 views)
  Reply With Quote
Old 30th December 2016, 06:06 PM   #2278
jan.didden is offline jan.didden  Europe
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Westende Resort, BE coast
Quote:
Originally Posted by BlacK_Chicken View Post
Hello again, the attenuator-project is still ongoing but currently I am quite busy exploring all the features of the QA401. Just now I did a test of the stepped-frequency response plugin. Somehow the phase-information seems to be lost.

Actually, looking at the phase-display in the upper right corner of the qa401-application-window during the sweep, the displayed figures seem to be correct BUT the exported .csv is definitely wrong. See plot below. Has anyone ever tried and got the same results?

The Visual-Studio stuff is still installing (since 3hrs now )... anyways, I attempt to write my own script to overcome this issue.
The magnitude response seems spot on.
Maybe the phase is in radians rather than degrees? Then it would also seem to be OK.

Jan
  Reply With Quote
Old 30th December 2016, 07:01 PM   #2279
BlacK_Chicken is offline BlacK_Chicken  Germany
diyAudio Member
 
Join Date: Nov 2005
Hello Jan, thanks for the input. I did a second measurement to confirm this behaviour and plotted results with rad->deg transformation. Looks like expected and the 45deg crossing point is around 184Hz, these results look promising but I am still a little bit suspicious.

I guess the huge spread above 10kHz is due to general inaccuracy around 0deg?
Attached Images
File Type: png 20161230_02_hpf.csv.png (58.3 KB, 301 views)

Last edited by BlacK_Chicken; 30th December 2016 at 07:04 PM.
  Reply With Quote
Old 30th December 2016, 10:06 PM   #2280
BlacK_Chicken is offline BlacK_Chicken  Germany
diyAudio Member
 
Join Date: Nov 2005
Jan you were absolutely right - spot on

Here is an overlay of two measurements. One is done via QA401 with 0dBV an 10points per octave between 20Hz and 48kHz. The second was captured with the very same circuit, wiring etc. Despite the fact that a PicoScope (15bit resolution) was used with 25points per decade between 10Hz and 100kHz, level was 1V.
Attached Images
File Type: png 20161230_qa_hpf_10k_100n.csv.png (73.2 KB, 284 views)
  Reply With Quote

Reply


QuantAsylum QA400 and QA401Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
QuantAsylum 401 & 405 B&W_arthur Equipment & Tools 5 22nd March 2016 04:27 PM
QA190 and QA400 Gains sgtnoah Equipment & Tools 4 17th July 2015 03:46 AM
Question on QA400 Alan0354 Equipment & Tools 7 10th July 2015 06:34 PM
FS QuantAsylum QA400 audio analyser jan.didden Swap Meet 3 29th September 2014 05:10 PM
New Quantasylum QA190 Differential Input Probe stellavox Equipment & Tools 3 20th March 2014 06:06 PM


New To Site? Need Help?

All times are GMT. The time now is 03:05 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki