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

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Help troubleshooting my first SE OPT
Help troubleshooting my first SE OPT
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 8th February 2018, 06:30 PM   #11
Elerion is offline Elerion  Spain
diyAudio Member
 
Join Date: Sep 2017
6A3sUMMER , thanks for you very detailed reply.

After some more study, I got some nice results.
Just to share them with you, here they are.

Primary inductance (measured under working amplifier, and dc current):
13.08 H
Core saturation frequency (at triode full output power):
20.2 Hz
Core saturation frequency (at -6dB full output power):
14.5 Hz

The low cut-off frequency due to inductive loading of the primary, is 34 Hz.

So the air gap is perfect!
If I increase it, primary inductance would fall, and with it, the low cut-off frequency would raise above 40 Hz, much before saturation effects come into play. Don't want that.

More primary turns would be needed to use a bigger gap, and get better bass response overall.
Or decrease primary impedance, which I can't (it is already low, near 2k5).
As I filled most of my winding window, this is my best right now.
So, I'm quite happy with this, my first SE OPT

Last edited by Elerion; 8th February 2018 at 06:33 PM.
  Reply With Quote
Old 8th May 2018, 01:00 PM   #12
Elerion is offline Elerion  Spain
diyAudio Member
 
Join Date: Sep 2017
Default Listening to my first SE OPT. Lacks bass and power.

I just finished a SE amplifier which uses my first handmade SE OPT on one channel, and another profesional OPT on the other.
My OPT seems great in basic tests using generator/scope, and it didn't saturate, even at 30 Hz, full power. Voltage ratios (anode, and UL tap), as expected.

Now, it doesn't sound really bad, but comparing it to the other pro OPT, there's a definite loss in bass and volume, and a bit "trashy" sound (though no distortion, and relatively clear voices).

I tried both ultralinear and triode modes.

I'm planning to dissasemble the enclosure to add some more gap, and re-test (I already did this in the scope test, and the gap seemed to be just fine, but this time I'd a listening test instead).

Appart from this, is there anything I could? Any advice?
Thanks!
  Reply With Quote
Old 8th May 2018, 03:13 PM   #13
popilin is offline popilin  Argentina
diyAudio Member
 
popilin's Avatar
 
Join Date: Oct 2010
Location: Traslasierra
Bass reproduction depends mainly on primary inductance

Lp = [4 π μ(eff) S Np²] / (9 l x 10⁸)

If you increase the gap

μ(eff) ≈ l μ / [l + l(gap) μ]

μ(eff) will decrease, and Lp will decrease too, making bass reproduction worse.

How did you calculate the number of primary turns?

The thread has changed!!!

Conclusions may change too.

How did you alculate the air gap? It seems too low now.
__________________
I do not suffer from insanity, I enjoy every minute of it. - Edgar Allan Poe
He has the most who is most content with the least. - Diogenes of Sinope

Last edited by popilin; 8th May 2018 at 03:32 PM.
  Reply With Quote
Old 8th May 2018, 03:14 PM   #14
GoatGuy is online now GoatGuy  United States
diyAudio Member
 
GoatGuy's Avatar
 
Join Date: Dec 2012
Location: SF Bay Area
deleted...
I didn't read the entire post.

Poplin is providing the right technical answer(s).
__________________
John Curl's Golden Rule…: 100 kHz bandwidth, 3 μs risetime, 100 W mean output, 100 V/μs slew rate, 2 Ω dynamic load, 20 amp min current source/sink

Last edited by GoatGuy; 8th May 2018 at 03:16 PM.
  Reply With Quote
Old 8th May 2018, 03:22 PM   #15
jazbo8 is offline jazbo8
diyAudio Moderator
 
jazbo8's Avatar
 
Join Date: Jan 2011
Location: In Transient
Help troubleshooting my first SE OPT
@Elerion - please do not start multiple threads on the same topic, which is against the Forum Rules.
  Reply With Quote
Old 8th May 2018, 07:17 PM   #16
popilin is offline popilin  Argentina
diyAudio Member
 
popilin's Avatar
 
Join Date: Oct 2010
Location: Traslasierra
Quote:
Originally Posted by Elerion View Post
More primary turns would be needed to use a bigger gap, and get better bass response overall.
This is my guess too.

Hints (cgs units are used, except [U]=Volts [i]=Amperes)

i) With your lamination choice, determine Bac(max) and Bdc(max), in order to not saturates the core.

ii) Calculate the number of primary turns

Np = (Uac x 10⁸) / [√2 π fo S Bac(max)]

iii) Calculate the effective permeability, μeff, from here

Bdc(max) = [4 π μeff Np i(DC)] / (9 l)

iv) Calculate the air gap from here

lgap = l (μ - μeff) / (μ μeff)

As it is evaluated twice, for the real air gap (plastic sheet) you must divide it by 2.

v) Calculate primary inductance from here

Lp = (4 π μeff S Np²) / (9 l x 10⁸)
__________________
I do not suffer from insanity, I enjoy every minute of it. - Edgar Allan Poe
He has the most who is most content with the least. - Diogenes of Sinope

Last edited by popilin; 8th May 2018 at 07:30 PM.
  Reply With Quote
Old 10th May 2018, 03:18 AM   #17
kokoriantz is offline kokoriantz  Lebanon
diyAudio Member
 
Join Date: Dec 2015
Location: south east asia
Apply tetrode mode ,open feedback loop, load 2.7k resistor across the primary, secondary unloaded, apply 1khz input until the primary starts clip. Now, with 20hz input adjust the air-gap for maximum excursion despite distortion on the primary . Load now the secondary instead, and measure with the same input level, the power bandwidth of your amp.
  Reply With Quote
Old 10th May 2018, 07:04 AM   #18
Elerion is offline Elerion  Spain
diyAudio Member
 
Join Date: Sep 2017
Quote:
Originally Posted by jazbo8 View Post
@Elerion - please do not start multiple threads on the same topic, which is against the Forum Rules.
Sorry. Will not happend again.

popilin, I agree with you, in that higher primary inductance helps bass reproduction, BUT a bigger gap does not mean less bass power.
A small gap leads to core saturation at low frequencies.
There's an optimun spot in the middle.
Anyway, I appreciate your detailed answer very much.

I already did tests like kokoriantz is suggesting, and the results were near perfect.

So, yesterday I did this: swap the anode taps of the two OPT, so they drive the opposite channel. And, guess what: now, my OPT sounds great, and the pro OPT sounds bad.
So it must be something with the circuit in one of the channels, even though they are the same, and share the same chassis. I checked and re-checked everything, but I might have missed something.

I swapped power tubes, and preamp tubes, problem persists.

The only strange thing I measured before connecting the amp to speakers, is that the the "bad" channel's preamp tube is a bit higher in idle anode voltage (190 vs 170 V), and that changing the GNFB trimmer seems to make almost no change in the output sine wave.
Both output tubes share the same fixed bias voltage. There's a single trimmer to tune it. Both tubes are nearly matched, and idle current is very close.

Today I'll remove GNFB and re check the circuit again.
Caps are correct values, and polarization.

Any guess?
  Reply With Quote
Old 10th May 2018, 11:09 AM   #19
Molenaar is offline Molenaar
diyAudio Member
 
Join Date: Aug 2016
Could this be a bad solder connection in the feedback loop?
  Reply With Quote
Old 11th May 2018, 05:20 AM   #20
popilin is offline popilin  Argentina
diyAudio Member
 
popilin's Avatar
 
Join Date: Oct 2010
Location: Traslasierra
Quote:
Originally Posted by Elerion View Post
popilin, I agree with you, in that higher primary inductance helps bass reproduction, BUT a bigger gap does not mean less bass power.
A small gap leads to core saturation at low frequencies.
There's an optimun spot in the middle.
I did not say that, what I sayd is

Quote:
Originally Posted by popilin View Post
Bass reproduction depends mainly on primary inductance
You have a misunderstanding about the air gap

i) The air gap is mandatory in SE OPTs because it limits DC magnetic field and hence core saturation.

ii) The air gap is related to effective magnetic permeability and hence primary inductance.

iii) The air gap increases the linearity of transformer because (wel design is supposed) effective magnetic permeability is quite constant over the magnetic hysteresis loop.

A small gap DOES NOT leads to core saturation at low frequencies, and a big gap DOES NOT mean nor less bass power neither more bass power.

Transformer equations are consistent, and a correct calculation yields the correct air gap. If in the middle of calculation you do some guesstimates, obviously you must fine tune the air gap experimentally, DO NOT blame the equations.

If your lamination is not good enough, or your core choice is wrong, or your calculations are wrong, the transformer will pay the consequences, but DO NOT blame the air gap.

In the middle of my first reply, the thread was merged with a previous one, YOUR FAULT, and that affected conclusions.

Equations on post#16 where derived from Maxwell's equations and they were checked many times and used with total success, so use them with confidence.


You did not answer any of my requests, that is not a good attitude from someone asking for help, capisce?
__________________
I do not suffer from insanity, I enjoy every minute of it. - Edgar Allan Poe
He has the most who is most content with the least. - Diogenes of Sinope

Last edited by popilin; 11th May 2018 at 05:27 AM.
  Reply With Quote

Reply


Help troubleshooting my first SE OPTHide 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
GFA-535: Looking for troubleshooting help lancer7703 Solid State 4 3rd May 2013 05:57 PM
Help w/ Troubleshooting FM Tom7227 Everything Else 1 14th August 2008 08:13 PM
NAD 705 Troubleshooting jocko_nc Solid State 6 15th July 2006 08:23 PM
Troubleshooting. castlesteve Tubes / Valves 30 26th June 2006 02:02 AM
Help troubleshooting Zen V4 ophilip Pass Labs 18 11th February 2006 12:39 AM


New To Site? Need Help?

All times are GMT. The time now is 08:17 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki