Dual Class-A Line and Headphone Output Board Documents

Construction information for DIY projects, including the MS Mid Side Matrix, Elliptic Equalizer, Mastering Console, Phono Transfer System, Insert Switcher and the Dual Class-A Amplifier. You can post your baby pictures here.
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mediatechnology
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Re: Dual Class-A Line and Headphone Output Board Documents

Post by mediatechnology » Fri Jul 06, 2012 3:35 pm

I lashed-up a Dual Class-A headphone build with RCA inputs for use on the bench.

Image
Dual Class-A Output Headphone Amp Build

This one had been tested as a line output and already had 47R build-out resistors which I chose to keep.
The Sony MDR-7506 are rated at 63? and most of my earlier tests were either 0R or 33R build-outs.
I think I preferred the low end with 47R build-out resistors more than 0R.

This particular version uses the THAT1646 and THAT1240 so it's unity gain.
There's more than enough drive available with -10 inputs with plenty of control range.

Since this particular HPA is going to be on the bench I used an inexpensive pot.
https://ka-electronics.com

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Re: Dual Class-A Line and Headphone Output Board Documents

Post by mediatechnology » Sun Jul 08, 2012 9:00 am

Those inexpensive pots are usually fine until you try to use the first couple of degrees of rotation...
Yeah it was in the junk box, cirrca 1989 from Radio Shack and Alps. Fortunately with the gain structure I'm usually working the middle to upper third.
It tracks well there.
I have two Alps Black Beauties that I may break down and use.
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gar381
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Re: Dual Class-A Line and Headphone Output Board Documents

Post by gar381 » Wed Feb 06, 2013 8:48 pm

Hi guys

Has anyone had any luck sourcing the CTS 7-342-1PP-BA heat sinks ?
I can't find any in stock anywhere at the moment. Any help pointing
me in the right direction would be much appreciated.

Gary

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mediatechnology
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Re: Dual Class-A Line and Headphone Output Board Documents

Post by mediatechnology » Thu Feb 07, 2013 6:28 am

Gary - Those got disco'd a couple of months ago by Digi-Key.

My reccomendation is a simple aluminum bar made from extrusion that couples all three output devices (or all six) together.

Single TO-series smaller heatsinks can also be used on each BD1XX as long as there is a bar or something to couple them thermally.

Home Depot sells aluminum bar stock that's ideal for it. Another builder recently used a chunk of an unused rack panel.
https://ka-electronics.com

Meme World https://www.memeworld.com/
Project Veritas: Google "Machine Learning Fairness" Whistleblower Goes Public, says: "burden lifted off of my soul." https://www.youtube.com/watch?v=g1VeElB ... e=youtu.be
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rondr
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Re: Dual Class-A Line and Headphone Output Board Documents

Post by rondr » Fri Feb 08, 2013 2:42 pm

gar381 wrote:Hi guys

Has anyone had any luck sourcing the CTS 7-342-1PP-BA heat sinks ?
I can't find any in stock anywhere at the moment. Any help pointing
me in the right direction would be much appreciated.

Gary
My first post and thanks Wayne for signing me up. I hope to learn a lot here. I'm still in the experimental stage and just trying different things with this project. I had the same problem trying to find the heat sinks. Somewhere in a previous post there was talk of just a rackmount blank being cut out so I tried that. I made it 1.25"x4.5" and it is about 1/8" thick. After I powered up the amp and give it some time to stabilize the temp at the BD1XXs was slightly over 110 deg. at 70mA. I run the current up close to 85mA and the temp ran right at 130 deg. Went to Radio Shack and purchased (4) of catalog number 276-1368 aluminum heat sinks. These are tapped with 4-40 threads so that made it easy to attach them to the back of the 1/8" thick aluminum blank. Again allowing time for the temperature to stabilize it then was right at 115 deg. Ambient room temp. at the time was 74 deg. Please excuse pic quality but it shows how its put together. Hope this helps.

Thanks,
Ron
Attachments
HPA RS 4 Heat sink 280 mV.JPG
HPA RS 4 Heat sink 280 mV.JPG (121.83 KiB) Viewed 16903 times
HPA heat sink RS top.JPG
HPA heat sink RS top.JPG (128.89 KiB) Viewed 16903 times
HPA heat sink RS board.JPG
HPA heat sink RS board.JPG (146.64 KiB) Viewed 16903 times

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mediatechnology
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Re: Dual Class-A Line and Headphone Output Board Documents

Post by mediatechnology » Sat Feb 09, 2013 7:39 am

Ron - Thanks for joining us here and your post.

The temps your seeing are very close to what I see with the discontinued CTS heatsink.
I love the imagery of the thermometer on it and the finished heatsink looks very cool.
Even the 130F number (55 deg C) is pretty conservative.

FWIW When I built the circuit up with DRV134s the first time and was comparing the offsets (low), idle current and heatsink temp it performed exactly like the THAT1646 thermally and DC-wise.
What became obvious is that the whole gizmo - in addition the being a headphone amp - is a heat regulator, not a current regulator.
As the ambient temperature rises the bias circuit drops the idle current. There is a desired negative temperature coefficient.
I ran this experiment last winter with the central heat cycling and could see the bias current raise and lower with the ambient. But the heatsink temperature was virtually constant.
It makes sense when you think about the feedback being thermal.
But the point is that if you see Iq shift slightly with ambient temperature that means everything's working according to plan.
https://ka-electronics.com

Meme World https://www.memeworld.com/
Project Veritas: Google "Machine Learning Fairness" Whistleblower Goes Public, says: "burden lifted off of my soul." https://www.youtube.com/watch?v=g1VeElB ... e=youtu.be
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gar381
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Re: Dual Class-A Line and Headphone Output Board Documents

Post by gar381 » Tue Feb 12, 2013 2:17 pm

mediatechnology wrote:Gary - Those got disco'd a couple of months ago by Digi-Key.

My reccomendation is a simple aluminum bar made from extrusion that couples all three output devices (or all six) together.

Single TO-series smaller heatsinks can also be used on each BD1XX as long as there is a bar or something to couple them thermally.

Home Depot sells aluminum bar stock that's ideal for it. Another builder recently used a chunk of an unused rack panel.
Thanks Wayne

I got some 1.25 wide 1/8" stock sitting on the shelf. I'll give it a shot. :D
Ron's Idea also looks interesting.
Gary

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Re: Dual Class-A Line and Headphone Output Board Documents

Post by mediatechnology » Wed May 29, 2013 2:52 pm

Mouser seems to be stocking the CTS 73422PPBA heatsink again (Mouser Part #: 774-73422PPBA)

http://www.mouser.com/Search/ProductDet ... -73422PPBA
https://ka-electronics.com

Meme World https://www.memeworld.com/
Project Veritas: Google "Machine Learning Fairness" Whistleblower Goes Public, says: "burden lifted off of my soul." https://www.youtube.com/watch?v=g1VeElB ... e=youtu.be
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tmuikku
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Re: Dual Class-A Line and Headphone Output Board Documents

Post by tmuikku » Fri Sep 20, 2013 2:54 am

Hi!

I'm finally putting these together. Its been over a year since I purchased some PCBs :) I've got some questions:
I have purchased 18VAC mains transformer for the project. Running the PSU with +-15V DC for four head amps will get the regulators run very hot... I could run the PSU with +-18V to save some heat Watts but I cannot wrap my head around if it affects the initial trimmer R35, R46 positions anyway, no? Whats the worst that can happen? I'll just try out. It would be nice to know how to determine how you endup the line in build document "Adjust R35 and R36 for ~400 mV at pin 4 of IC1 and IC2. Check TP1 and TP3 for ~0V."? I can't wait to get the fírst one working :)

Thanks!

tmuikku
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Re: Dual Class-A Line and Headphone Output Board Documents

Post by tmuikku » Fri Sep 20, 2013 4:15 am

Alright got the first one working :) I adjusted as per build document with +-15V supply and then changed it to +-18V. The pin4 on IC1 and IC2 was now measuring around 410mV. Between TP:s I got ~200mV and adjusted that to around 250mV for first test. Sounds good! :shock:

But, got problem with pot. I think I've got cheap Alpha or something dual 10k log pots. If I turn it completely down I hear a little bit of the sound and very distorted (maybe viper loosing contact at the extreme position). Also, about 70% of the rotation doesn't affect volume at all! So the volume goes up the first 20% or so, then nothin and at the very end a little bump in the volume. I've got drv134 at the output and THAT1240 at input. I'll try buffer stage between pot and drv234.
Last edited by tmuikku on Fri Sep 20, 2013 5:56 am, edited 1 time in total.

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