Go Back   Home > Forums > >

Headphone Systems Everything to do with Headphones

Designing my headphone amp
Designing my headphone amp
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
Old 17th September 2021, 08:13 PM   #191
NickKUK is online now NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
Quote:
Originally Posted by hpasternack View Post
The formula for the instantaneous rate of change with respect to time of a voltage
v(t) = A * sin(wt)
is
v'(t) = A * w * cos(wt)
This is all you need to know. There is no guessing, no mystery.
The dV/dt figures on the capacitor data sheet are not relevant to the slew rate of the amplifier you might design using the capacitors.
Ok. That makes sense. Reading around the subject from this morning, I'm aware the slew rate in terms of an amp becomes the lowest component slew rate, be it due to opamp used, cap or particular filter with deliberate control over slew rate for stability. Coupling caps would be on the signal path hence are one part of the chain.
__________________
V1 - low gain tube HPA OTL, fully balanced cascode 12BH7A, 12BH7A CCS, 12BH7A drivers and ECC99-BJT hybrid circlotron. (build)
V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)
  Reply With Quote
Old 17th September 2021, 08:31 PM   #192
hpasternack is offline hpasternack
diyAudio Member
 
Join Date: Sep 2002
Location: New England
Quote:
Originally Posted by NickKUK View Post
Ok. That makes sense. Reading around the subject from this morning, I'm aware the slew rate in terms of an amp becomes the lowest component slew rate, be it due to opamp used, cap or particular filter with deliberate control over slew rate for stability. Coupling caps would be on the signal path hence are one part of the chain.
You go to engineering school, they teach you (hopefully) how to think systematically about this stuff. You can jump to the wrong conclusions and just confuse yourself if you go at it willy-nilly. Just saying.
  Reply With Quote
Old 18th September 2021, 06:15 AM   #193
NickKUK is online now NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
Quote:
Originally Posted by hpasternack View Post
You go to engineering school, they teach you (hopefully) how to think systematically about this stuff. You can jump to the wrong conclusions and just confuse yourself if you go at it willy-nilly. Just saying.
Hehe, my day job is digital and IT, with some oddities like quantum cryptography hence a passing familiarity/critique with complex number wave functions and sine waves. So the world of amp design and tubes is a welcome change and a chance to have fun, learn and make mistakes (especially when not following process or procedure). I don't see much difference between systems/software design and amp design. There's quite a few step-by-step guides and books on that I've found in reading.

The requirement for low Zout was always part of the requirements, only shifting requirements at the end of design in an attempt to drive bigger speakers in addition to headphones is why there's some gnashing of teeth.
__________________
V1 - low gain tube HPA OTL, fully balanced cascode 12BH7A, 12BH7A CCS, 12BH7A drivers and ECC99-BJT hybrid circlotron. (build)
V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)
  Reply With Quote
Old 19th September 2021, 02:56 PM   #194
NickKUK is online now NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
Screenshot 2021-09-19 at 15.48.56.png

I've simplified the backend to remove unneeded components:
* the mirror BJT in the tube line isn't required - they are all connected so a cap bank provides all the required current that's required.
* removed cap banks - leaving one for the combined tubes and one for the BJTs base isolation. The multiple banks were, in fact, in parallel.
* stripped out resistors used for quazi-biasing - these, in a 60 second sim end up causing the system to fight. Biasing has to be via a negative to the grid (just like the original circlotron).

I've tuned up the tube side by disconnecting the BJTs (I may make this a switch) - this is the output at full 4V peak input and a full 160mA peak-to-peak across 55ohm:
Screenshot 2021-09-19 at 15.45.14.png

That's enough not to worry about BJTs.. I'm just waiting for a sim to finish with the BJTs connected.. it balances nicely - the BJTs provide power and the tubes backoff their peak-to-peak voltage swings.

Screenshot 2021-09-19 at 16.00.04.png

Bottom combined through load current (green)
Middle combined tube peak-to-peak (blue)
Top a single BJT current combined bias and signal (pink)
__________________
V1 - low gain tube HPA OTL, fully balanced cascode 12BH7A, 12BH7A CCS, 12BH7A drivers and ECC99-BJT hybrid circlotron. (build)
V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)

Last edited by NickKUK; 19th September 2021 at 03:02 PM.
  Reply With Quote
Old 21st September 2021, 07:18 AM   #195
NickKUK is online now NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
Just leaving this simulating for today - pure tube direct connected version (no isolating caps). This is essentially an M60 in class A only operation.

Screenshot 2021-09-21 at 08.28.09.png

It's very well behaved on startup - load current with 1.5V peak input with the front end tuning the same as the capacitor version.

Screenshot 2021-09-21 at 08.17.40.png

In terms of safety sims I need to try:
* Tube open
* Tube short
* PS short
* PS open
* startup with the above
* shutdown with the above
Logically, through inspection the amp rebalances but I want to check.

EDIT: updated 240Vrms.
__________________
V1 - low gain tube HPA OTL, fully balanced cascode 12BH7A, 12BH7A CCS, 12BH7A drivers and ECC99-BJT hybrid circlotron. (build)
V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)

Last edited by NickKUK; 21st September 2021 at 07:29 AM.
  Reply With Quote
Old 23rd September 2021, 05:33 AM   #196
NickKUK is online now NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
I've also been looking into the hybrid backend power supplies - in theory it would make sense to run the 40V and 150V from the same 40V power supply using a voltage multiplier for the lower current higher voltage. However both supplies are floating in their respective circlotrons and normally a voltage multiplier needs a zero reference (usually ground). I could make a virtual ground but this would mean that one circlotron is balanced but the other is likely to be out of balance. I could use two isolated secondaries off a customer toroid - one for 40V higher current, the other being 150V lower current. This would save space and probably be the easiest option. Getting both channels on a single transformer would be good.

As it is the power transformers will probably be:
* Toroid 1 - Cascode supply - two secondaries for rails +320 -320
* Toroid 2 - Left Circlotron B1 - two secondaries for rails +150, +150
* Toroid 3 - Right Circlotron B1 - two secondaries for rails +150 +150
* Toroid 4 - Right Circlotron B1 & B2 - four secondaries for rails +40 +40 +40 +40
* Toroid 5 - Heater supplies - two secondaries for heaters B+
* Small 5Vdc - housekeeping and soft switching.

The two heater supplies are elevated and referenced to the 320V supplies. I've also assumed that the cathodes for the circlotron can be kept within 100V of the upper heater supply. I have considered making a power shut off should any of the voltages get too far out of balance. A circlotron can self balance but that is relative to the opposing half and not a static referenced heater!

Now initially I was thinking of a single 9H coke each supply but two 3H chokes work better. However this causes an issue with room. I could house the first choke above the chassis along with the power transformers and the second of each power supply below to reduce noise. Alternative is to use a 3H choke and a floating regulator.
What is nice about the chokes and a headphone amp is that the capacitors can be relatively small compared to RC.
__________________
V1 - low gain tube HPA OTL, fully balanced cascode 12BH7A, 12BH7A CCS, 12BH7A drivers and ECC99-BJT hybrid circlotron. (build)
V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)

Last edited by NickKUK; 23rd September 2021 at 05:40 AM.
  Reply With Quote
Old 25th September 2021, 04:55 PM   #197
NickKUK is online now NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
So I have a soft start.

Screenshot 2021-09-25 at 17.45.18.png

The aim of the soft start is to keep under 6A for the IEC filter (rated for 6A). There are two transformers (although I need to updated the sizes in terms of henries). Plus, currently, the heater transformers are missing.

Screenshot 2021-09-25 at 17.46.28.png

A Triac with an inductive load rather than reactive. I use a back of resistors to provide a start resistance, limiting to about 4.5A (2A rms). The MOC provides a optical isolation from the 5V soft start switch and also provides zero crossover triggering for the 10A capable triac. I still need to model the relay contact bounce.

I'm familiar with SMPS and the fact that a triac attached to a transformer becomes a SMPS switched inductor boost controller. I've put snubbing in to prevent large spikes. This also causes problem for optical isolators likes the MOC (https://www.st.com/content/ccc/resou...DM00451014.pdf)

This approach provides a tube like soft startup with all the power supplies and parts starting up at the same time but at a restricted rate.
__________________
V1 - low gain tube HPA OTL, fully balanced cascode 12BH7A, 12BH7A CCS, 12BH7A drivers and ECC99-BJT hybrid circlotron. (build)
V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)

Last edited by NickKUK; 25th September 2021 at 05:02 PM.
  Reply With Quote
Old 25th September 2021, 05:17 PM   #198
Mark Johnson is offline Mark Johnson  United States
diyAudio Donor
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Designing my headphone amp
I suggest you include jumper options to adjust the delay between switch-on and softstart bypass. Here's measured data on a solid state power amp (using a current probe), at two different settings of the delay. Personally, I like the long delay better. But this choice does heat up the inrush limiting series component a lot more, since it's conducting current and dissipating power for more time.

Click the image to open in full size.


Click the image to open in full size.
  Reply With Quote
Old 27th September 2021, 06:59 AM   #199
NickKUK is online now NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
The snubbing is important, not from an audio noise perspective as it's muted, but from a heater power voltage spike perspective.

The crossover point for the ZCD triac initial trigger is just far enough up the wave form to create about a 26mA spike which carries through that needs snubbing.
The ZCD then causes 230uA spikes on each successive waveform crossover.

Here is the ZCD triac (not the main triac) just operating by itself - although a sim using the official model for that ZCD triac, it hints at some of the noise expected and the additional snubbing required to remove the noise. Noise/spikes on this output current then cause issues for the main triac.

Snubbing an AC waveform is a PITA, you add capacitance to solve the spike, but you then cause a transition issue for the AC waveform.. So the method I'm looking at is a low pass filter configured to allow the AC rising waveform through but not the spike.

Screenshot 2021-09-27 at 07.57.32.png
__________________
V1 - low gain tube HPA OTL, fully balanced cascode 12BH7A, 12BH7A CCS, 12BH7A drivers and ECC99-BJT hybrid circlotron. (build)
V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)

Last edited by NickKUK; 27th September 2021 at 07:09 AM.
  Reply With Quote
Old 27th September 2021, 08:47 AM   #200
NickKUK is online now NickKUK  United Kingdom
diyAudio Member
 
Join Date: Dec 2019
Further more - having power transformers in parallel, as the system charges, the reaction changes, thus the waveform response to the switching changes.
__________________
V1 - low gain tube HPA OTL, fully balanced cascode 12BH7A, 12BH7A CCS, 12BH7A drivers and ECC99-BJT hybrid circlotron. (build)
V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)
  Reply to this post

Reply


Designing my headphone ampHide this!Advertise here!
Thread Tools

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
I'm designing a TPA6120 based headphone amp, is there anyone can give me some advice shadownee Headphone Systems 13 31st August 2012 04:50 AM
C&C request: designing a headphone amp Thalyn Chip Amps 0 14th April 2012 12:12 PM
Designing a super low distortion headphone amp. Rainwulf Chip Amps 41 1st April 2011 12:24 AM
designing horn for compression driver & tweeters jayam000 Multi-Way 0 15th April 2009 09:26 AM
Designing for guys who like designing Sch3mat1c Tubes / Valves 14 31st August 2003 11:46 AM


New To Site? Need Help?

All times are GMT. The time now is 10:35 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 13.64%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki