The all DHT SET Headphone Amp - Page 53 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

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

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 16th February 2013, 04:23 PM   #521
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by Pano View Post
Since this has turned into a search for the perfect transformer, I really don't have much to contribute. Guess I just get impatient will all the sims and talk, sorry. Too many threads turn into nothing more than talk. I want to solder stuff!
I don't think there is a lot to search for. Transformers with very low distortion for this application already exist and one doesn't need special cores. One just needs high quality transformers made with quality materials, including iron cores. If you have a look at transformers THD measurements inside the Gary Pimm site you will see that you don't need special cores even with very low signal (i.e. 0.01V primary voltage!). Above 100Hz the transformer THD is typically between -80dB and -120 dB! I don't think you will find a DHT that is able to match these numbers...
As mentioned before one has to be careful about the frequency range below 100Hz. Here primary inductance is a main factor to get low distortion. Namely the ratio XL/Req at the lowest frequency (30Hz is a good choice for SE) has to be as high as possible. A good compromise is a value between 6 and 8 for SE amps. XL =2*pi*f*L, Req is the equivalent resistance given by the source impedance in parallel to the load.
As I said I would choose a Lundahl or any other existing transformer that will perfectly match one application.

Problems arise when one wants "a full barrel and a drunk wife"!

Last edited by 45; 16th February 2013 at 04:32 PM.
  Reply With Quote
Old 16th February 2013, 04:28 PM   #522
diyAudio Member
 
Join Date: Aug 2009
Location: Sacramento
Solder this:

I have this one up and running; a 12AU7 Aikido driving a SET strapped
6BQ6 amplifier using $225 (pair) Electro-Print 3 watt 7K : 300 transformers and HD-600 headphones. Not DHT, however it rocks.

DT
  Reply With Quote
Old 16th February 2013, 04:33 PM   #523
diyAudio Member
 
merlin el mago's Avatar
 
Join Date: Sep 2009
Location: Catalonia - Europe
@45
YHPM

@DualTriode
Have you received my pm & email?
  Reply With Quote
Old 16th February 2013, 04:44 PM   #524
diyAudio Member
 
Join Date: Feb 2012
Location: Hyperspace
Quote:
Originally Posted by Pano View Post
Since this has turned into a search for the perfect transformer, I really don't have much to contribute. Guess I just get impatient will all the sims and talk, sorry. Too many threads turn into nothing more than talk. I want to solder stuff!
That's electronic engineering: 99% of time is pencil or display(s), 1% soldering. Also 90% of effort goes to bin, the other 10% creates the future.

Now back to business. The headphones of interest are in a rather tight Z range of 32~64Ω. The 300Ω (HD6x0) and (why in the world, but) 600Ω will get shunted to the nearest (64Ω) value. Any odd values, like 52Ω (HD380pro) will get a small series resistor to the same nearest value. The Z range of interest (32~64Ω) goes well with off-the-shelf LL1623. The 8Ω speaker gets the 3+3 secondaries paralleled, so total 6 out of 8 are used, same as headphones (6 for 32Ω and 38Ω, 7 for 52Ω, 8 for 64Ω). With all that, the primary Z stays in acceptable range (2500~3000Ω) with any load. The good thing in all this is automation: the commutation and shunting will be fully automatic, sensor-based. That is where my thoughts took me so far.

And a word about thinking out of the box. My personal project is wider than DHT headamp, but similar in the DHT part, and another part of it is a little illuminated button with a DHT triode sympol on it, which turns 'the magic' on. When it doesn't have to be on, or if I want zero THD+N, or for casual listening to save the DHT's life, or simply to fill the room with quiet background music, a simple and as close to perfect as possible PCM1794A-LME49990-LME49600 4W zero-capacitor-zero-inductor-signal-path headamp will extract precision sound from a tiny SD card with all my dear music on it. Perfection of form and perfection of essence in one (also perfectly constructed inside and out, Moth-style) device. There will also be some additional interesting parts in it. That's my music "box".

Last edited by Radium; 16th February 2013 at 04:51 PM.
  Reply With Quote
Old 17th February 2013, 02:41 AM   #525
BudP is offline BudP  United States
diyAudio Member
 
BudP's Avatar
 
Join Date: Feb 2007
Location: upper left crust, united snakes
Some sophisticated thinking going on here, even if Pano gets antsy.

Were I to build another headphone amp that actually used M series core in place of capacitors to couple the 6922 long tailed cascode circuit to headphones, the phones would be EnABL'd. This would allow me to hear what M core does best. And by the way, Phillips Jan 6922 are so much better sounding than their commercial ken, the 6DJ8, that it is silly to use anything else.

Since the core quits transformation in any effective sense above 400 Hz, every thing else is antenna event, subject to dielectric materials as a control agent. I choose this to avoid the problem Per faces with amorphous core and others face with nickle core. A lack of internal gradient information in tones and transients. You will notice that all of Lundahls amopphous core coils have primary and secondary windings separate on the core. They must do this to avoid huge peaks in FR, just beyond the audible range.

Nickle, which functions to 3.5 kHZ for 48% and 10 kHZ for 80%, is also facing this problem, though you can have some interleaving. Mostly you have to quadfillar wind all primaries and secondaries,s to obtain enough losses in capacitive structure, which is not a single grouped event by any means though always portrayed as such for simple power transformers. This sort of arrangement does have a clearly characteristic sonic quality. A sweetness and also a comparative lack of internal structures to notes and transients.

Please note, these are not necessarily draw backs, for either type of material and how they must be used. Just a personal choice based upon your taste, that simple distortion measurements will not provide you enough information to make choices about. To wit, Gary Pimm's very clear presentation of distortion analysis between Dave's transformers and mine. Below 250 Hz his measure 20 db lower in distortion than mine. Gary uses mine in his amplifiers.

The reason is that mine have a huge amount of internal structure information. This because they have a huge amount of coupling surface Vs winding depth. Means that while I have higher measured capacitance, more of it is doing work as opposed to just laying around absorbing small signal information. I can also build in a dielectric circuit to emphasize this coupling. Since M3 rise time is equivalent to 80% nickle, I don't loose any leading edge information either.

Just my personal choice to solve the question of how to build a transformer that responds to nonlinear events with aplomb, balance and elegance. My peers provide equally good solutions, though aimed at expressing characteristics that are audibly different in availability, but very difficult to find in the grass of a plot of any kind, though wavelet analysis may change that to a degree.

Thanks Bas! I had not looked for Pieter's name, spelled correctly, before and was exhibiting my typical murican blindness to other territory's. I hope Pieter will forgive me.

Bud
__________________
"You and I and every other thing are a dependent arising, empty of any inherent reality" Tsong Ko Pa
  Reply With Quote
Old 17th February 2013, 09:04 AM   #526
regal is offline regal  United States
diyAudio Member
 
Join Date: Jan 2004
Location: MD
Quote:
Originally Posted by Pano View Post
OK, not my cup of tea, so I'll leave you alone and get back to the 4P1L thread. I've already built, measured and listened to an all DHT-SE headphone amp. Not perfect, but at least real world stuff that tells me a lot.
We need an empiricist, once we nail down parafeed vs single feed we can get down to the nuts and bolts. I just don't want to repeat mistakes made with the OPT again (been "fooled twice now.)


Quote:
Originally Posted by Radium View Post
The Z range of interest (32~64Ω) goes well with off-the-shelf LL1623. The 8Ω speaker gets the 3+3 secondaries paralleled, so total 6 out of 8 are used, same as headphones (6 for 32Ω and 38Ω, 7 for 52Ω, 8 for 64Ω). With all that, the primary Z stays in acceptable range (2500~3000Ω) with any load.
But Lundahls own datasheets recommend against 6 primarys as having too much insertion loss and 8 isn't even shown as a config. Seems that we lose the benefits of a C-core design by not folloing the "known" configs? Also I'm finding that a 5k primary works well with all the output tubes of interest from the 4P1l to the 300B.


Quote:
Originally Posted by BudP View Post
Some sophisticated thinking going on here, even if Pano gets antsy.

Were I to build another headphone amp that actually used M series core in place of capacitors to couple the 6922 long tailed cascode circuit to headphones, the phones would be EnABL'd. This would allow me to hear what M core does best. And by the way, Phillips Jan 6922 are so much better sounding than their commercial ken, the 6DJ8, that it is silly to use anything else.
This is a much different headphone design. Where we are using a big powerful DHT to cruise along like a Mercede's SLR on I-70 intead of the Autobahn, gives better linearity and alows transformer coupling which I believe has a benefit over OTL and servoed SS.


Quote:
Originally Posted by BudP View Post

Nickle, which functions to 3.5 kHZ for 48% and 10 kHZ for 80%, is also facing this problem, though you can have some interleaving. Mostly you have to quadfillar wind all primaries and secondaries,s to obtain enough losses in capacitive structure, which is not a single grouped event by any means though always portrayed as such for simple power transformers. This sort of arrangement does have a clearly characteristic sonic quality. A sweetness and also a comparative lack of internal structures to notes and transients.
This is where the decision is difficult. With a parafeed nickle design we don't have to worry about the secondary. A 1W 40 ohm secondary would work for about any phone.

My experience with single feed M-core transformers has been the transformer designer takes a 45 tube output transformer design and just makes the 8 ohm secondary 4x as long. This doesn't work. I ended up with a pair of transformers that literally cut my design power in half due to the voltage loss on the secondary DCR and the difficult inductive load.

Is it possible to start from the ratio instead of the core/primary when designing an OPT for headphones? I mean we need an OPT with 11:1 ratio instead of 25:1, this should be an advantage instead of being a disadvantage?
Bud, any insight on this one would be appreciated.

The other thing we are struggling with is "balanced" drive (see attached). It may be easier to spec a 5k transformer to have two 8 ohm secondaries which I've been told would impedance match with a 32 ohm headphone. I haven't been able to get this to simulate with LTSpice, do you have any thoughts on this or know the math behind it?
Attached Images
File Type: png balanced headphone OPT.png (39.0 KB, 282 views)

Last edited by regal; 17th February 2013 at 09:13 AM.
  Reply With Quote
Old 17th February 2013, 01:18 PM   #527
diyAudio Member
 
Join Date: Feb 2012
Location: Hyperspace
A brief relief from transformer troubles:

Regal, what do you think about LCD2? Better, worse, same as HE-500? Looks much better made, costs a bit more, the same orthoplanar principle. Important difference is efficiency 91 dB/mW and Z=60Ω, which with LL1623 with all secondaries in series makes reflected Z=2693Ω -- right in the middle of 2500~3000Ω range.
  Reply With Quote
Old 17th February 2013, 03:02 PM   #528
45 is offline 45  Italy
diyAudio Member
 
45's Avatar
 
Join Date: Dec 2008
Location: UK
Quote:
Originally Posted by regal View Post
My experience with single feed M-core transformers has been the transformer designer takes a 45 tube output transformer design and just makes the 8 ohm secondary 4x as long. This doesn't work. I ended up with a pair of transformers that literally cut my design power in half due to the voltage loss on the secondary DCR and the difficult inductive load.
I don't think the secondary DCR is the problem because on one side it becomes 4 times higher but on the other side the turn ratio is 4 times lower. From the point of view of transformer efficiency at low frequency nothing changes. The problem lies in the combination you make with those secondaries because from the point of view of AC losses they are not the same! That's why the layout for secondaries connections has to be a precise one. You have to connect the terminations in a precise order. If you do an apparently identical combination the result will not be the same. This happens mainly because the interface capacitances between a secondaries and a primaries are the dominant stray capacitances and obviously depend on the surface they share which is not the same going from the start of the winding to end.
  Reply With Quote
Old 17th February 2013, 04:06 PM   #529
regal is offline regal  United States
diyAudio Member
 
Join Date: Jan 2004
Location: MD
Quote:
Originally Posted by Radium View Post
A brief relief from transformer troubles:

Regal, what do you think about LCD2? Better, worse, same as HE-500? Looks much better made, costs a bit more, the same orthoplanar principle. Important difference is efficiency 91 dB/mW and Z=60Ω, which with LL1623 with all secondaries in series makes reflected Z=2693Ω -- right in the middle of 2500~3000Ω range.
This is true but I am bit smitten with the Hifiman midrange sound its really nice. Would like a design that can handle both brands. A good design (tube/topology/transfo) that delivers 1W at 40 ohm secondary should have no problem with the Audez phones (no need for a special 60 ohm tap.) I am by no means "ruling" out the LL1623 just want to explore my options.


Quote:
Originally Posted by 45 View Post
I don't think the secondary DCR is the problem because on one side it becomes 4 times higher but on the other side the turn ratio is 4 times lower. From the point of view of transformer efficiency at low frequency nothing changes. The problem lies in the combination you make with those secondaries because from the point of view of AC losses they are not the same! That's why the layout for secondaries connections has to be a precise one. You have to connect the terminations in a precise order. If you do an apparently identical combination the result will not be the same. This happens mainly because the interface capacitances between a secondaries and a primaries are the dominant stray capacitances and obviously depend on the surface they share which is not the same going from the start of the winding to end.
It depends on who makes your transfo, my builder just quadrupled the secondary left the primary/core the same as for a 45 and I got a "nice" 10 ohm DCR secondary, the tota efficiency of the transfo gave about 50% less power than an "ideal" model, this is what I am "warning" folks about. Most transfo winders have a formula that is based on a 25:1 primary/core size and a headphone secondary is just considered a low quality "add-on." Rather than an opportunity to take advantage of the 11:1 ratio.

So hence my interest in the dual 8 ohm secondary "balanced out headphone drive" idea/rumor. Trafo builders have years of experience with 5k:8 transformers.
  Reply With Quote
Old 17th February 2013, 07:06 PM   #530
BudP is offline BudP  United States
diyAudio Member
 
BudP's Avatar
 
Join Date: Feb 2007
Location: upper left crust, united snakes
Regal,

As a thumbnail, secondaries can be doubled by multiplying them or dividing them by 4. So, 4 X 8 = 32, whereas 2X 16 does not equal 32. So a dual 8 ohm secondary will provide 32 ohms of load impedance reflection into the primary and into the plate. If you want to understand the formula, here it is in text, since I know from nothing about math notation from a keyboard in Windows.

5000 ohms primary load impedance. To find the turns ratio divide 5000 by the averaged impedance wanted and derive the square root of that. This is your turns ratio. For secondary turns in a SE OPT it is divided into the primary winding turns. For push pull it is both halves of the primary.

As for your concerns with your current transformer. Loses are not defined by the secondary alone. To get within a few % of the total power loss you must take the square root of the turns ratio and multiply the primary DCR by that, and, add it to the secondary DCR to approximate the infinitely reflected losses between the two. There is a core loss but it is insignificant enough to be ignored in a properly designed transformer.

In a general sense any SE OPT with more than 100 ohms primary DCR is going to have a high insertion loss. A 50% loss is pretty ridiculous, but 45 tubes require a fairly high inductance and with their desired current flow and the resultant gaps, you are stuck with either high DCR, a large (14 pounds 3.75" X 4.55" core perimeter) M core transformer, an amorphous core or a nickle C Core transformer, to generate the required inductance. Much better to accept a bit of flavoring and use a lower mu tube, like the 300B or 2A3.

Even with a lower mu tube you are better off with big than little, it just looks silly. What you will end up with is a SE DHT amplifier with an input transformer that you can switch from 1:1 to 4:1 or even 8:1 to get the gain down. If you can afford him Pieter's are the best in the world.

This does imply a possible push pull driver stage, with the inherent benefits of lower noise and distortion. A balanced out put that you could parallel for speakers or series for headphones begins to make a lot of sense.

I have found that DHT's actually require a good bit of current capability from their driver circuits. Paralleled driver tubes works. In my upcoming build I plan to use the very new lateral Fets, not Mosfets, on carbide substrate, in push pull config, with two stages to generate ~3 watts to drive a SE 300 B. The most linear load line for a 300 B is found at 4.545 kZ, by the way. A 2A3 will work the same from 3K to 7 kZ load line. The 45 is very particular and 10k is it's ideal. This implies a voltage and current, at zero signal level, that matches the load line. Once AC swing is applied, all load line / impedance matching is out the window anyway and the only important characteristic is how linear the voltage change is across the tube curve chart / real life.

Bud
__________________
"You and I and every other thing are a dependent arising, empty of any inherent reality" Tsong Ko Pa

Last edited by BudP; 17th February 2013 at 07:09 PM.
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
High end Ortho Amp on a basic Russian Tube DHT SET DIY design regal Headphone Systems 2 7th December 2012 12:46 PM
300b all-DHT SET andyjevans Tubes / Valves 16 24th August 2012 09:06 PM
Help on designing full DHT SET power amplifier milen007 Tubes / Valves 56 11th August 2011 10:38 PM
Class A, DHT driven, headphone amp iko Headphone Systems 100 26th March 2011 03:54 PM


New To Site? Need Help?

All times are GMT. The time now is 05:36 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2