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

Headphone Systems Everything to do with Headphones

ESP HPA
ESP HPA
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 7th August 2017, 05:19 PM   #21
prasi is offline prasi  India
diyAudio Member
 
prasi's Avatar
 
Join Date: Jan 2014
Location: Near Western Ghats
ESP HPA
Quote:
Originally Posted by Bonsai View Post
No problem Prasi - please go ahead.
thank you very much Bonsai!
__________________
My revamped site https://sites.google.com/site/analogdesign1234/
  Reply With Quote
Old 14th October 2017, 02:28 PM   #22
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
ESP HPA
Hi Prasi,

I built up one channel of the ESP HPA on veroboard with an LME49740 (will use two chan of a quad). It oscillated badly at first. I had to add a 680pF input low pass film cap filter to block RF in, I added output Thiele 100nF film and 4.7R (which also blocks RF feeding in from headphone cable), and added 33pF silver mica across 22k feedback resistor. Probably had a lot to do with P2P layout as Elliot warned about if doing in veroboard. It's stable now and plays music. I am not sure what the bias is supposed to be but quiescent is very low at 2mA. When it was oscillating (400kHz and 8v p-p), and bias measured 150mA.

I built it according to this circuit (I using nice Silmic II 100uF for C2, and 1uF 63v Wima MKS on C1):
ESP HPA


Now stable, no input, output measures 0.0mVac on Fluke 101 and 115. But if I turn volume up on my preamp (Focusrite 2i2 DAC), the Fluke 115 (true rms) will show increasing noise - hiss amplified from DAC. But even at 0.0mV it is not dead quiet on headphones. On scope, I can still see about 4mV of high frequency hash. Not really audible when music playing, but not dead quiet like my SE Class A discrete headphone amps that I am used to building. I wonder if this is opamp noise? This LME49740 had very good noise specs though.

Anyhow, listening to it in pseudo stereo and sounds decent. Just puzzled by the low quiescent bias current - is that normal? If I want to turn this to Class A with 120mA bias current all the time, is it as simple as changing 10R emitter resistors to smaller value (maybe 2.2R?).

Actually I want to use this not as a headphone amp but a powerful instrumentation amp where I need to have low distortion signal to drive a sensor. Having a simple push-pull pair of BD139/140's seemed to be a good way to give an opamp some muscle.

You will recognize that I am using the shunt regulator (nice PSU) from your Juma BJT HPA project.

Here is a photo showing amp with just left channel wired up (components are in place on right but no wires connected yet).
ESP HPA-esp-hpa-build-01-jpg

Here is quick FFT driving 700mV into the on-board 4.7R/100nF (Thiele) load. Not bad, but has some elevated 5th harmonic. Dominant 2nd is nice to have rather than 3rd.
ESP HPA-esp-hpa-fft-png

I think bass authority could be improved if we change those emitter resistors to smaller value. But in general, probablyI agree with your choice to add input filtering,and output Thiele. It would be good idea to include a feedback compensation capacitor pad in parallel across R4 for a 5mm pitch silver mica (circa 33pF) But looks like a worthwhile PCB layout and certainly I would use it if you finished the layout. Thanks for doing this - the circuit actually sounds surprisingly good for how simple it is.

I should mention that one benefit of using an opamp on the input gain stage (with some negative feedback) is that the DC offset is automatically servo controlled to zero. This is DC coupled output and I measure 0.0mV DC offset and it is always so.

Thanks,
X
Attached Images
File Type: jpg ESP-HPA-build-01.jpg (440.3 KB, 1101 views)
File Type: png ESP-HPA-FFT.png (156.3 KB, 662 views)
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio

Last edited by xrk971; 14th October 2017 at 02:57 PM.
  Reply With Quote
Old 14th October 2017, 02:59 PM   #23
prasi is offline prasi  India
diyAudio Member
 
prasi's Avatar
 
Join Date: Jan 2014
Location: Near Western Ghats
ESP HPA
Hi X,
Nicely built and thanks for sharing.
Yes, ESP warns about capacitive coupling and oscillation possibility due to wide bandwidth.
I wonder why the 5th harmonic is so dominant as it is a very conventional design.
Yes I recognize the Nazar shunt regulator (It gave me plenty of problems due to wrong resistor and fake IC).

Do share your stereo experience.

Yes, Syr posted here that 120ohm inline resistor helped with bass authority. You could try the same.

regards
Prasi
__________________
My revamped site https://sites.google.com/site/analogdesign1234/

Last edited by prasi; 14th October 2017 at 03:01 PM.
  Reply With Quote
Old 14th October 2017, 03:09 PM   #24
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
ESP HPA
Quote:
Originally Posted by prasi View Post
Hi X,
Nicely built and thanks for sharing.
Yes, ESP warns about capacitive coupling and oscillation possibility due to wide bandwidth.
I wonder why the 5th harmonic is so dominant as it is a very conventional design.
Yes I recognize the Nazar shunt regulator (It gave me plenty of problems due to wrong resistor and fake IC).

Do share your stereo experience.

Yes, Syr posted here that 120ohm inline resistor helped with bass authority. You could try the same.

regards
Prasi
I forgot what the woes were with the Nazar - it works fine now, but I do recall it took a change somewhere to get the full adjutment capability. It is very stable now though. Funny thing is I am using some nice audio grade Toshiba BJT's for the shunts - just because that was all I had on had at the time.
"Audiphool grade shunt reg"

I should mention that I put the ESP HPA on a scope and cranked the output up to see what max drive into high impedance load was and it was impressive at 28v p-p before clipping. That will do nicely for my need for 24v p-p as instrument power amp with room left over.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 14th October 2017, 05:37 PM   #25
prasi is offline prasi  India
diyAudio Member
 
prasi's Avatar
 
Join Date: Jan 2014
Location: Near Western Ghats
ESP HPA
Quote:
Originally Posted by xrk971 View Post
"Audiphool grade shunt reg"

Quote:
Originally Posted by xrk971 View Post
I should mention that I put the ESP HPA on a scope and cranked the output up to see what max drive into high impedance load was and it was impressive at 28v p-p before clipping. That will do nicely for my need for 24v p-p as instrument power amp with room left over.
Thats really nice. i wonder if it can be used as a small power amp for sensitive speakers as suggested by esp.
__________________
My revamped site https://sites.google.com/site/analogdesign1234/
  Reply With Quote
Old 17th October 2017, 05:39 PM   #26
prasi is offline prasi  India
diyAudio Member
 
prasi's Avatar
 
Join Date: Jan 2014
Location: Near Western Ghats
ESP HPA
Quote:
Originally Posted by thimios View Post
Prasi,it seems that you have to draw another pcb!
Thimios,
as promised.
Just a rough layout to see if single sided is possible..I know you only need diy friendly PCB's.

So here it is, I will refine it a bit further and post pdfs.
It unfortunate that we dont have Bonsai here on diya anymore to guide us.

regards
Prasi
Attached Images
File Type: png bonsai-ha-sch.png (16.3 KB, 332 views)
File Type: png bonsai-ha-lay.png (61.4 KB, 299 views)
__________________
My revamped site https://sites.google.com/site/analogdesign1234/

Last edited by prasi; 17th October 2017 at 05:56 PM.
  Reply With Quote
Old 17th October 2017, 07:22 PM   #27
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
ESP HPA
That Class A buffer from Bonsai (too bad he is no longer on DIYA) looks really nice too. Very useful moderate power instrumentation amp.

I should point out that using an Apex FX8, sans lateral MOSFET output stage and replacing all transistors with higher voltage variants like 2N5551/5401 and KSC3503/KSA1381, one can also make a nice Class A buffer with higher voltage output (I have run at +/-50V) and it is quite low in distortion too. It can swing 80v p-p no problem.
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio

Last edited by xrk971; 17th October 2017 at 07:25 PM.
  Reply With Quote
Old 18th October 2017, 02:00 AM   #28
bimo is offline bimo  Indonesia
diyAudio Member
 
bimo's Avatar
 
Join Date: Sep 2010
Location: Depok, West of Java
Quote:
Originally Posted by jaycee View Post
I've built this design on stripboard and it works quite well - however depending on the source and the headphones you are using, you will definitely want to reduce the gain!!
I agree.
Change gain about 5x is good compromise for many headphone impedance, I think.
__________________
#Perkutut#Emprit#GagakHitam#Elang#Pelatuk#Colibri# Blameless100#Blameless150#Blameless1200#AX14Mod#FX 8Mod#AX11Mod#LM1875InvertingWithBuffer#LM3886Inter tingWithBufferAndDCServo#more...
  Reply With Quote
Old 18th October 2017, 06:46 AM   #29
xrk971 is offline xrk971  United States
Got Foam?
diyAudio Member
 
xrk971's Avatar
 
Join Date: Oct 2012
Location: Metro DC area
ESP HPA
Hi Prasi,
I have another one for you that is similar to the title circuit but is Class A and uses a very low distortion THAT differential input driver. It's a clever way to control the bias too. I think Kirkwood is a designer from THAT Corp? If you have time, pllease consider making another layout.
Thanks,
X

ESP HPA-img_6310-jpg
Attached Images
File Type: jpg IMG_6310.JPG (258.4 KB, 1306 views)
__________________
XRKaudio https://www.etsy.com/shop/XRKAudio
  Reply With Quote
Old 18th October 2017, 08:54 AM   #30
thimios is offline thimios  Greece
diyAudio Member
 
Join Date: Aug 2009
Location: Agrinion
Quote:
Originally Posted by prasi View Post
Thimios,
as promised.
Just a rough layout to see if single sided is possible..I know you only need diy friendly PCB's.

So here it is, I will refine it a bit further and post pdfs.
It unfortunate that we dont have Bonsai here on diya anymore to guide us.

regards
Prasi
Quote:
Originally Posted by xrk971 View Post
That Class A buffer from Bonsai (too bad he is no longer on DIYA) looks really nice too. Very useful moderate power instrumentation amp.

I should point out that using an Apex FX8, sans lateral MOSFET output stage and replacing all transistors with higher voltage variants like 2N5551/5401 and KSC3503/KSA1381, one can also make a nice Class A buffer with higher voltage output (I have run at +/-50V) and it is quite low in distortion too. It can swing 80v p-p no problem.
Thanks prasi!
What you mean saying that Bonsai isn't in DIYA anymore?
  Reply With Quote

Reply


ESP HPAHide 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


New To Site? Need Help?

All times are GMT. The time now is 01:42 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki