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

12HL7-triode SE Headphone Amp - I finally built something!
12HL7-triode SE Headphone Amp - I finally built something!
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 5th July 2018, 10:25 PM   #21
Wavebourn is offline Wavebourn  United States
Designer & Technologist
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
12HL7-triode SE Headphone Amp - I finally built something!
You can use 6J4P instead of 6J7, to match 12CA5 size.
__________________
Nothing in the universe is perfect. The ideal things are the ones that are most optimal. Optimization criteria, what matters. When I hear "No Compromise Design", I want to take a sledgehammer and test how impact-proof it is.
  Reply With Quote
Old 6th July 2018, 12:57 AM   #22
rongon is offline rongon  United States
diyAudio Member
 
rongon's Avatar
 
Join Date: Jul 2009
Location: Across the river from Rip's big old tree...
12HL7-triode SE Headphone Amp - I finally built something!
^ ^ ^ ^ ^ Yeah, what he said! ^ ^ ^ ^ ^

And hey, if you want to stick to US-made tubes, 6J4P = 6AU6, which is a common little 7-pin pentode that looks good wired triode.

You could even wire it up with the plate and suppressor grid connected to ground, use the screen grid as the 'plate', use the control grid as normal. That would make a nice triode with mu of about 30 using up only about 5mA 'plate' current. Check this out:
6AU6 Triode Mode

6AU6A data sheet with triode curves:
http://www.mif.pg.gda.pl/homepages/f...93/6/6AU6A.pdf

--

Last edited by rongon; 6th July 2018 at 01:10 AM.
  Reply With Quote
Old 6th July 2018, 01:10 AM   #23
e_fortier is offline e_fortier  Canada
diyAudio Member
 
e_fortier's Avatar
 
Join Date: May 2001
Location: Eastern Canada
12HL7-triode SE Headphone Amp - I finally built something!
For a 7 pin pentode you could use the 6AQ5 triode strapped.
  Reply With Quote
Old 6th July 2018, 02:16 PM   #24
rongon is offline rongon  United States
diyAudio Member
 
rongon's Avatar
 
Join Date: Jul 2009
Location: Across the river from Rip's big old tree...
12HL7-triode SE Headphone Amp - I finally built something!
Experimenting...

cc: famousmockingbird --

Last night I installed some nice enamel-coated 100R 5W wirewound resistors across the OPT secondaries (from 50 ohm tap to Common). The idea is to smooth out the impedance wobbles of my Sennheiser HD650 cans, and to bring the HD650's 310 to 500 ohm impedance down closer to the nominal 50 ohm impedance of the OPT secondary.

The strangest thing happened. The resulting sound from the HD650 is improved quite a bit. It was really damned good. Now there's enough bass. While still a tad bright sounding, the tonal balance is quite good. Apparently the 100R across the secondary does help optimize the OPT for that load, and I enjoyed the sound very much.

But when I connected my other headphones, 50 ohm Fostex T50RP, I noticed they now sounded dark with overactive midbass (in the 100Hz region maybe) and rolled off highs. They didn't sound like this without that 100R resistor.

Any idea what's happening here?

I'm thinking of mounting a DPDT switch near the output jack so I can switch in/out those 100R resistors.

Adding the 100R resistors reduced the gain a bit, but the amp's gain is still adequate. With the Fostex cans, which aren't very sensitive, turning the amp up all the way results in a sound that's still subjectively clean-sounding, but would make me well and truly deaf if I listened that loud.

--
  Reply With Quote
Old 6th July 2018, 02:40 PM   #25
H713 is offline H713  United States
diyAudio Member
 
Join Date: Nov 2017
Location: Wisconsin
Well I would assume it's having the same effect on the Fostex headphones as it has on the HD650s, but the Fostex headphones are already at around the right impedance. If we do a simple parallel resistance calculation, you're at around 33.33 ohms.

The ideal solution would be to have an OPT with multiple taps on the secondary, so maybe 50, 300 and 600 ohm taps. Something along those lines.
  Reply With Quote
Old 6th July 2018, 03:22 PM   #26
rongon is offline rongon  United States
diyAudio Member
 
rongon's Avatar
 
Join Date: Jul 2009
Location: Across the river from Rip's big old tree...
12HL7-triode SE Headphone Amp - I finally built something!
Quote:
Originally Posted by H713 View Post
The ideal solution would be to have an OPT with multiple taps on the secondary, so maybe 50, 300 and 600 ohm taps. Something along those lines.
Of course. I could just spend money and have transformers custom wound, even. But what fun is that? I'm hoping this will be a learning experience...
  Reply With Quote
Old 6th July 2018, 03:37 PM   #27
H713 is offline H713  United States
diyAudio Member
 
Join Date: Nov 2017
Location: Wisconsin
Right. And it would be a lot more expensive, and a bigger hassle. I'm currently looking at having a pair of 50W transformers custom wound... I talked to Electra-Print, but I'm not sure I want to blow $400 in transformers. I talked to Edcor, but I don't want to wait two months. I contacted MagneQuest and Heyboer, and have yet to get a response. Though to Heyboer's credit, I left a message on a national holiday... they might not be back from vacation yet. Though I did email them about two weeks ago and still haven't gotten a response. I sure hope they aren't closing shop.

And Transcendar isn't taking orders

And I'm told that James isn't making transformers anymore, plus that would be shipping from Taiwan.

So if you can use something off-the-shelf, that's always preferable. I'm seriously considering just buying something from Hammond and being done with it.

So to make a very long story short, just stick with your $15 Edcors if you like the sound
  Reply With Quote
Old 6th July 2018, 04:55 PM   #28
famousmockingbird is offline famousmockingbird  United States
diyAudio Member
 
Join Date: Dec 2010
Location: Nottingham, NH
Quote:
Originally Posted by rongon View Post
Experimenting...

cc: famousmockingbird --

Last night I installed some nice enamel-coated 100R 5W wirewound resistors across the OPT secondaries (from 50 ohm tap to Common). The idea is to smooth out the impedance wobbles of my Sennheiser HD650 cans, and to bring the HD650's 310 to 500 ohm impedance down closer to the nominal 50 ohm impedance of the OPT secondary.

The strangest thing happened. The resulting sound from the HD650 is improved quite a bit. It was really damned good. Now there's enough bass. While still a tad bright sounding, the tonal balance is quite good. Apparently the 100R across the secondary does help optimize the OPT for that load, and I enjoyed the sound very much.

But when I connected my other headphones, 50 ohm Fostex T50RP, I noticed they now sounded dark with overactive midbass (in the 100Hz region maybe) and rolled off highs. They didn't sound like this without that 100R resistor.

Any idea what's happening here?

I'm thinking of mounting a DPDT switch near the output jack so I can switch in/out those 100R resistors.

Adding the 100R resistors reduced the gain a bit, but the amp's gain is still adequate. With the Fostex cans, which aren't very sensitive, turning the amp up all the way results in a sound that's still subjectively clean-sounding, but would make me well and truly deaf if I listened that loud.

--

https://www.innerfidelity.com/images/FostexT50RPMk3.pdf


I am guessing they are just dark headphones. Look at the db vs frequency, it's highest is 100Hz and the midband is -10db down. Frequency looks flat out to 10k so I don't know if there is some sort of compensation built in?

The 12HL7 has an impedance of 1.3k, so the reflected back impedance of a 33 ohm load would be ~5k which is adequate for loading a triode. Maybe the distortion has changed or something where the sound at low frequencies is now more distorted? The 100 ohm resistor value is a tradeoff, ideally with the 50 ohm headphones you don't want it there so maybe make it switched? That way there with the 50 ohm headphones you can take the resistor out of circuit but with the 300 ohm headphones switch it back in to smooth things out.
  Reply With Quote
Old 6th July 2018, 05:58 PM   #29
rongon is offline rongon  United States
diyAudio Member
 
rongon's Avatar
 
Join Date: Jul 2009
Location: Across the river from Rip's big old tree...
12HL7-triode SE Headphone Amp - I finally built something!
That all makes a lot of sense. The T50RP are 'dark' sounding headphones, but usually in a 'good' way (as in 'mellow sounding' as opposed to 'muffled'). Did you notice that its impedance curve is ruler-flat at about 52 ohms?

I think I will put in that switch. I have some suitable mini-toggles on hand. It could be that the 100R across the secondary is making these 50 ohm headphones unhappy, but might do nice things for some 32 ohm headphones that sound too harsh/zippy. A tone control of sorts. Definitely worth trying.

Thanks for your input on this.
  Reply With Quote
Old 6th July 2018, 07:06 PM   #30
Wavebourn is offline Wavebourn  United States
Designer & Technologist
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
12HL7-triode SE Headphone Amp - I finally built something!
Wait; matching impedance did you think that 1W would be a bit too much for ordinary headphones?
__________________
Nothing in the universe is perfect. The ideal things are the ones that are most optimal. Optimization criteria, what matters. When I hear "No Compromise Design", I want to take a sledgehammer and test how impact-proof it is.
  Reply With Quote

Reply


12HL7-triode SE Headphone Amp - I finally built something!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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Finally built my 6SL7, 2A3/6A3 amp mig-ru Tubes / Valves 39 19th September 2011 08:21 PM
EZDAC two-box DAC built, finally! baldrick Digital Source 0 22nd January 2011 01:20 PM
Finally built a subminiature guitar amp... now I need help! Hendrixon Instruments and Amps 8 20th March 2007 12:16 AM
Finally built something :) wintermute Multi-Way 9 14th February 2004 12:25 PM
finally built a gainclone nobody special Chip Amps 5 27th January 2004 08:32 AM


New To Site? Need Help?

All times are GMT. The time now is 10:05 AM.


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