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Old 6th July 2017, 03:51 PM   #891
twocents is offline twocents  South Africa
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Hi X,

I see there is a serious debate about balanced vs single ended connection for headamps. Now, I know nothing about the technicalities involved - but just a stupid question: with your current balanced setup using two PCA's - is that not similar to running two monoblocks? Or will two single ended PCA's not give a similar improvement?
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Old 6th July 2017, 04:41 PM   #892
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by diyRookie View Post
Hi X,

I see there is a serious debate about balanced vs single ended connection for headamps. Now, I know nothing about the technicalities involved - but just a stupid question: with your current balanced setup using two PCA's - is that not similar to running two monoblocks? Or will two single ended PCA's not give a similar improvement?
I do not know why there is debate. If you have an amp that has limited voltage swing (like a portable amp with two 9v or a car battery with 12v of lead acid), using balanced drive will essentially double your output drive capability. Perhaps the debate is, if you have a Class AB amp and are not limited by your rail voltage, simply increase your rails to get the same swing.

Using two separate monoblock amps but without balanced drive will only buy you extra stereo channel separation (currently -72dB to -85dB in same box depending on whether source follower or CFP topology).

Here is a measurement of the output from the pocket amp in single ended drive vs balanced drive into 270ohm load. For balanced drive each amp already has a 270ohm internal load resistor plus an external 270ohm floating load resistor connected to just the output from each side's cap coupled output. So I think the resistance (or impedance) may be 270 parallel (270x2) or 180ohm equivalent.

The voltage swing is almost doubled - while keeping the amp in a lower distortion operating range vs pushing 10v with a single amp (which is above clipping). Balanced drive is also referred to in car audio amps as bridge tied load (BTL) amps in order to realize more voltage swing.

Single ended drive into 270ohms:
Click the image to open in full size.

Balanced drive into 180ohms but same input:
Click the image to open in full size.

So based on the above, don't you think balanced drive for a voltage limited SE Class A amp makes a difference?
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Last edited by xrk971; 6th July 2017 at 04:44 PM.
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Old 6th July 2017, 04:55 PM   #893
twocents is offline twocents  South Africa
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Proof of the pudding is in the eating. You heard a significant improvement right? That beats technical measurements in my books.

But I think you need a new thread for this new beast being born.
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Old 6th July 2017, 05:14 PM   #894
xrk971 is offline xrk971  United States
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The output voltage swing doubled so the gain increased and the max SPL before clipping increased substantially. All this translates to better dynamics by allows higher dynamic range to be played at higher volumes. It's is quite noticeable and apparent - night and day difference.

I am working up a new design with a MOSFET CCS and BJT CFP output stage with balanced drive capability. Bias will probably be in 125mA range and still SE Class A.
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Last edited by xrk971; 6th July 2017 at 05:24 PM.
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Old 8th July 2017, 02:59 AM   #895
yourownbuzz is offline yourownbuzz  Australia
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Nice setup! I felt a bit of pain seeing those headphones just willy nilly in a box though =/

Quote:
Originally Posted by stellarelephant View Post
Finally got my new work space up and running in the shop. Even built myself a vent hood entirely out of junk I had laying around!

My second board is making music! I upgraded pretty much every component this time around:

-All resistors are Vishay MELF
-Higher bias via R4 value of 51R
-Bit higher dummy load via RL value of 1K
-Power rail caps are 25V 1500uF Panasonic FR
-Power bypasses are original value, but TDK C0G
-Input caps are my DIY stacked and leaded 2x 63V .68uF WIMA SMD-PPS
-Still auditioning output cap options

The sound is awesome, though so far I have only tested it with my cheap AKG K-55 cans, just to be safe about possible DC leakage with all the caps pressure fit. Even so, dynamics and detail are just superb.

I spent some time last night auditioning my DIY PPS input caps vs. the stock polyesters, and quickly heard a difference (hopefully not my subjective bias ). The polyesters have a creamy sound with a lot of bloom and soft treble. The PPS opens up the sound significantly with better precision, speed, and especially more air--exactly what I was hoping for! I soldered them in without hesitation. Anyone interested can see how I assembled these caps in post #664. They require some sanding of the inner side of the input jack to slide in, at least with the caps shrink-wrapped like I did.

I need to place an order for more output caps to experiment with, but right now I am loving the sound of this amp with the trusty 25V 470uF Nichicon KA standing alone on output duty.

This amp is measuring 7.5VDC by the way.
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Old 8th July 2017, 12:57 PM   #896
yourownbuzz is offline yourownbuzz  Australia
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so, cap rolling, totally forgotten about it, cuz the 64mA bias and 2000uF KZ is too enthralling. might try tweaking the bias on my original 2200uF KA amp to see if that gives the same results. it does chew through batteries like crazy though
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Old 9th July 2017, 02:28 AM   #897
xrk971 is offline xrk971  United States
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Does a 2000uF KZ cap fit in a tin?

I have been using 1000uF oscon + 470uF KA + 10uF Silmic II which is pretty much an all around great combo. A 1uF Wima in place of 10uF Silmic works welll also.
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Last edited by xrk971; 9th July 2017 at 02:31 AM.
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Old 9th July 2017, 03:57 AM   #898
yourownbuzz is offline yourownbuzz  Australia
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most definitely not lol, its 2x 1000uF KZ per channel = 4x 1000uF KZs. It's that "game of thrones" cap setup I posted a while back. It might fit into those larger tins I got, but since this was intended for testing I haven't bothered to put it into a tin.
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Old 9th July 2017, 04:27 AM   #899
stellarelephant is offline stellarelephant  United States
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Quote:
Originally Posted by yourownbuzz View Post
so, cap rolling, totally forgotten about it, cuz the 64mA bias and 2000uF KZ is too enthralling. might try tweaking the bias on my original 2200uF KA amp to see if that gives the same results. it does chew through batteries like crazy though
I definitely would like to hear that! Good desktop choice, no doubt. I'm about to order some of the different Nichicons that will fit in the tin, from the FG, FW and KW audio grades. I am also going to try X's recommended combo, as well as the big 470uF Silmic that Funch used. Not sure If I'll be able to fit two 12.5" wide caps side by side though, and still have room for batteries.
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Old 9th July 2017, 05:14 AM   #900
yourownbuzz is offline yourownbuzz  Australia
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Quote:
Originally Posted by stellarelephant View Post
I definitely would like to hear that! Good desktop choice, no doubt. I'm about to order some of the different Nichicons that will fit in the tin, from the FG, FW and KW audio grades. I am also going to try X's recommended combo, as well as the big 470uF Silmic that Funch used. Not sure If I'll be able to fit two 12.5" wide caps side by side though, and still have room for batteries.
You could just change it into a desktop amp haha use the entire tin for caps and have a power jack, and as a portable setup could have another tin of just batteries, which you could plug in longer runtimes too

Well I still have 2200 or 3300 FGs to try, and 1000uF Silmics are backordered till Aug 3 =(

I do have the smaller values of FG/KZ/Silmics though (~47uF - 470uF) got them thinking to use as bypassess if I found another large value cap which sounded good lol
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