Search found 24 matches

by sheldon
Thu Feb 07, 2008 6:43 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Thanks for looking at this one Dave. Yes, as far as I can tell probing these little SMD things, it does have a cap output. My buffer (OPA2134) is DC coupled. You are right that loading the IT secondary modulates the response in the low frequency region. Looks like something a little over 100k gives ...
by sheldon
Mon Jan 21, 2008 11:51 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

In making the previous measurements, I used a little single channel battery powered OPA2134 preamp, that is adjustable for up to 3x gain. I made the preamp because the sound card puts out a max of 1VRMS and I wanted to be able to push some of my amps harder. What I found interesting is that without ...
by sheldon
Mon Jan 21, 2008 11:40 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

More measurement fun and games

Back on the FET amp, I was curious about the frequency response, since the OPT is a trifilar SE to PP, so it steps down 2:1. I do get a rising response starting about 5K, so that makes some sense. I assume that this is a function of the OPT, but could the input transformer contribut too? The DCR of ...
by sheldon
Mon Jan 21, 2008 6:23 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

I cleaned up my test system. Here's THD at just under 1W output. It looks like this until about 3W, then the higher level harmonics start to increase. Interesting is that when I tried a cascode DN2540 current source on the 6SN7, the distortion increased slightly. This was true for both at 1W and 3W....
by sheldon
Wed Jan 16, 2008 12:15 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

I did a little more testing. With the scope and signal generator (and DMM), I don't see significantly more bump as I scan from 1k up to 20kHz, or down to 100, at maximum power. I put a pot on the input to the sound card, so I could bump up the amp output as much as possible without clipping in the s...
by sheldon
Tue Jan 15, 2008 3:31 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

from the top: bifilar THD parafeed THD bifilar frequency plot parafeed freq Green trace is soundcard control. Plots are a bit noisier than I see with the amp all buttoned up. Edit: I apologize for not scaling these to expand the frequency resolution. Note, that if you look close, there is a bit of r...
by sheldon
Tue Jan 15, 2008 3:15 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Have you done a frequency sweep of the bifilar version at full output? I'm just curious if we kept the copper losses low enough to avoid the level shift as you transfer from magnetic to capacitive coupling. Also, earlier you said the parafeed was -3dB @ 50K ad the bifilar -3dB @ 35K but above you m...
by sheldon
Tue Jan 15, 2008 1:54 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Ok, here's the latest configuration for listening tests. I changed the load resistor on the FET follower to a CCS, otherwise only the transformer and output configuration change. One curious issue is that I get oscillations if the input is left with only a 300k resistor to ground. Didn't do that be...
by sheldon
Tue Jan 15, 2008 1:52 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

So far, I'm liking the bifilar plate transformer version. A little better bandwidth on the top end, essentially no distortion above 4th order (the parafeed version has a trace of 5th - down over 100dB), fewer parts. Can't say I really hear a dramatic difference in sound, but I haven't done back and ...
by sheldon
Tue Jan 01, 2008 5:59 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

front
by sheldon
Tue Jan 01, 2008 5:54 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

A little additional testing shows the frequency upper limit is determined by the OPT - the 3dB point is around 50kHz with parafeed, about 35k as a transformer. Some difference between channels, which appears mostly to be differences in the two OPT's. I need a new sound card to play around and look a...
by sheldon
Mon Dec 24, 2007 7:25 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Ok, here's the latest configuration for listening tests. I changed the load resistor on the FET follower to a CCS, otherwise only the transformer and output configuration change. One curious issue is that I get oscillations if the input is left with only a 300k resistor to ground. Didn't do that bef...
by sheldon
Sun Dec 23, 2007 1:46 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

OK, I had already assumed so and did some quick testing with the scope. Both ways look just fine. None of the upper frequency distortion seen with the other choke. Bandwidth is good. Both methods start to show distortion at full power (about 4.5W) around 100 Hz. That may reflect the limits of the OP...
by sheldon
Sat Dec 22, 2007 10:49 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

try # 1 is done... the L vs. I plots are below. The inductance is a bit lower than i had hoped, how much current are you running? Driven as an IT with a 4K source and a 12K load we are -1dB at 70K and -3dB at 137K with a few slight 0.2dB wiggles between 20K and 70K. I'd expect the plate choke behav...
by sheldon
Sat Dec 01, 2007 5:18 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

the final Schematic is interesting. I could do something like the attached, which would be straightforward. Maybe the center tap is not necessary and one could substitute a virtual CT to make the transformer easier? Hmm. Playing with a toroid got me thinking about this one. I guess that with the hi...
by sheldon
Fri Nov 30, 2007 8:52 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Hi Dave,

I'm running just under 30mA. But, I favor a separate amp for the low end anyway.

Sheldon
by sheldon
Sat Nov 24, 2007 12:53 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

the final Schematic is interesting. So while you are winding those chokes how bout pondering this one. As it is now, I have a LL1674 as the input transformer. It's configured with the primaries in parallel, so it steps up 1:4 as a phase splitter. I can drive this directly with a low impedance (75R)...
by sheldon
Wed Nov 14, 2007 3:15 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Oh, I forgot to add that the trifilar tranny was gapped with a 0.075mm (0.003") shim. I wasn't too concerned about low frequency performance and wanted to account for any imbalance.

Sheldon
by sheldon
Tue Nov 13, 2007 7:20 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Ok, let's take a shot at the Choke/IT for the 5W amp to start with, and I'll ponder the 1/2 watter a bit. Regarding the FET follower amp, yes by my calculations I'm operating the outputs in class A. I'm not sure the impedance of the OPT, but here's the description: It's trifilar wound with 0.8mm wir...
by sheldon
Wed Nov 07, 2007 4:26 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Dave, I consider myself reasonably intelligent, but in these matters mostly ignorant. Dangerous combination for all concerned, but I think I'm starting to get it. Just to make sure we're talking about the same things here: The choke/IT is for the 5W A2 amp. It finally sank in that you weren't talkin...
by sheldon
Wed Nov 07, 2007 5:41 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

by moving to IT's i was referring to wiring the bifilars aseither plate chokes or IT's and listening both ways. If you think the bifilar choke would work, I'd give it a shot. What size core would you use? Using as an IT is interesting, but would require a much beefier input stage no? indeed a 1/2 w...
by sheldon
Fri Nov 02, 2007 3:23 pm
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Thanks Dave, I'm open to any and all approaches - regular SE, parafeed, exotica like bifilar chokes. When you mention moving to IT, do you mean for this amp, as a replacement for the fet follower? While you are pondering solutions to the choke issue, here's another transformer to think about, though...
by sheldon
Fri Nov 02, 2007 5:25 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

Thanks for the reply. Yes, I did that. No change. I tried a completely different OT too. I got basically the same outcome. I wrote the following to someone else I was corresponding with: "Reversing the choke leads didn't change much. It may have changed the amplitude a little but the basic shap...
by sheldon
Sun Oct 28, 2007 1:06 am
Forum: Inductors
Topic: 801 parafeed choke
Replies: 33
Views: 53046

801 parafeed choke

I made a couple of resistor loaded 801 amps based on the design in Steve Bench's site. Needing more than the 400mW for an application, I converted one to a regular parafeed style amp, that can go into A2 for higher signal levels. The amp is shown attached. So far, so good. But when I measured the ou...