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Cavalli EHHA Embedded Hybrid Headphone Amp - Page 117

post #1741 of 1817

Soooooo.... anyhow my ehha is in pieces.  But my 4 channel space heater is up and running, waiting on the other 2 channels for the ehha, no idea when those will come.  I am considering adapting the ehha for speaker use, but I probably won't as I would have to get creative with my heatsinking.  I got my little 9v toroidals in but my little lm317 regulator may be ill equipped for the job.  I'll give it a shot though when my new case comes in early next week.  I suppose I could try it as is now since the tube filament current should be constant anyhow (just doubled soon).  I have it screwed to the back panel of the current box that now houses a b22 but it's like a giant aluminum heatsink anyhow...  Will see how hot it gets :P.  I have parts coming in for an lt1084 regulator that will be slightly bigger than my lm317 regulator but better equipped to handle a constant 1.32a I think...  Hopefully I can find a good way to mount it inside the amp case.  Shouldn't be too hard... the b22s are really squished into the case and that seems to run far hotter than my ehha ever did.  I am seriously considering practically cutting out almost all of the top panel and attaching a metal screen of some sort there...


That said I haven't really done any work on the psu case besides filing out the hole for the iec plug a bit.  I could get a bigger case to accommodate off board heat sinks and use the case I was gonna use for the ehha to house multiple S22s and go ahead with the speaker amp :O.  Ahhh decisions :(

post #1742 of 1817

Question regarding a input selector switch.


I'm planning to use a goldpoint selector switch for my balanced EHHA.  I'm going to have (3) pairs of XLR inputs to choose from.  Do I need to be switching the ground (pin-1), or can I simply tie the grounds for each channel together and wire as shown here?  Not sure if this will create any ground loop issues.  I'm hoping to get by with a single (4) Pole - (3) throw selector.  If I have to run the input grounds through the selector switch, then I am stuck spending more money a multi-deck selector.

Edited by Horio - 1/5/11 at 1:43pm
post #1743 of 1817

Separate, switch the ground, don't tie together, IMO.

post #1744 of 1817

Yea, the more I think about it, it makes more sense to switch the input grounds.

Originally Posted by holland View Post

Separate, switch the ground, don't tie together, IMO.


post #1745 of 1817

Another one lives.  I need to vacuum the interior and put the cover on, but here's an inside shot right now, as I am tweaking the bias.  I was going to do a 3-channel, but when I started calculating the interior space, that plan fell apart.  2-channel it is.EHHA 1.JPG

post #1746 of 1817

Sweet!!..nice one Holland..what's the input selector and attenuator board you are using there?


What tubes are you using and is it aBJT or MOSFET?




ANd of course..first impressions ??!! :D

post #1747 of 1817
Originally Posted by sachu View Post

Sweet!!..nice one Holland..what's the input selector and attenuator board you are using there?


What tubes are you using and is it aBJT or MOSFET?




ANd of course..first impressions ??!! :D


Thank Sachu.  It's from diyclub.biz, the dual mono selector and relay attenuator.  99 steps.  I got their case as well, it has a nifty remote, so I can sit back and control the volume.  I'm running a gain of ~4.3x.


MOSFET of course, you BJT junkie ;)  I am using the default 6GM8 from GJA, MOSFETs at 160mA, but might dial it back a bit.  Preliminary temps have the FET case temperature of ~60C.  I have some 6N27P coming from Russia, but it's been a month so I'm wondering if it got lost.


First impressions.  Using my Buffalo DAC (ES9008), it's very nice.  Impactful, good separation, good soundstage, and good tone.  It's definitely up there with a B22.  The upper frequencies seem spot on, not harsh.  It's going well with my HD650 so far.  I've only heard a few tracks, but will need a much longer listen for other sonic traits.

post #1748 of 1817
Very Nice build Holland! I really like the concept of the 99 step attenuator. What kind of a pot do you use to control it?

Where is your diode bridge-based ground loop isolator? I am interested in seeing that implementation.
post #1749 of 1817

Thanks jdkJake.  It's pushbuttons with a remote control.




You can see part of the ground loop breaker here.  The 10W wirewound power resistor is hidden under the ribbon cable.  In the first picture, next to the perfboard, you can see the diode bridge.  In the second picture in the link, you can see the cap, but the diode bridge disappears in the background color.  The power resistor is under the ribbon cable.


I used a terminal strip, then connected the diode bridge to the lug that connects to the chassis and another pin.  The AC side goes to chassis earth.  The DC side, goes to DC ground.  I use a ground bus from that, the long 10 gauge bare copper wire.  The cap goes between those 2 points, the start of the ground bus and the earth connection, as does the power resistor.  This setup has never failed me.  Points of contact for chassis earth has been sanded with a dremel to get to the bare metal, then I put dielectric grease on top to avoid corrosion.  The earth connection to the chassis is on the 6.3V transformer, oversized so I get ~7.3V AC under full load.


The heater board is a homebrew, basically a standard LT1085 reference implementation, but I used a low voltage drop diode bridge for space.  It's fine for heaters, but would use different rectifiers if not for heaters.


Edit: Damn this thing is big.  It dwarfs my other builds, particularly being a single chassis build and full rack component size.  I'm pulling out my other Cavalli amps to compare, but I don't recall the SOHA II sounding as clean.

post #1750 of 1817

Holland congrats mate that’s an awesome build, I’m looking forward to further impressions against your SOHA II.

post #1751 of 1817

Thanks John, will do.  I haven't listened to the SOHA II in a while.  I meant to, but I'm going to give it a few weeks for the EHHA I to settle and more time for my ears and mind to adjust.

post #1752 of 1817

So I started my initial checks on my balanced EHHA.  I have a 33.2kOhm resistors installed at R22 & R23 (negative feedback) and 2kOhm resistors at R13 for a gain of 6x (12x balanced).  My o22 is putting out about 29V +/-.  Trim-pot R21 is turned fully counter-clockwise, and R6 is at the mid-point (counted turns).  With the 6GM8's in I am getting the following readings on my first two boards:


Resistor:  Board 1/Board 2 (Target Voltage)


R4:  1.29V/1.31V (1.5V)


R10 & R14: 1.31V/1.29V and 1.26V/1.28V (1.5V)


R15 & R17:  0.50V/0.55V and 0.57V/0.60V (0.85V)


R16 & R18:  0.65V/0.65V and 0.59V/0.59V (0.6V)


R26 & R29:  0.58V/0.58V and 0.58V/0.58V (0.6V)



So the voltages seem a little low across  R3/R4 and R10/R14.  They are even more off (low) for R15 and R16.  The others seem to be reasonably close.  You guys have any thoughts?

post #1753 of 1817

Adjusting the R6 trimpot should balance the voltage across R3/R4.

post #1754 of 1817

So I tried rolling in some other different tubes (Amperex 6GM8) I had, and the voltage came up but only a little bit.  R3 is exceptionally low, so I am wondering if the problem is related to this value:


Resistor:  Board 1/Board 2 (Target Voltage)


R3:  1.16V/1.19V  (1.5V)


R10 & R14: 1.36V/1.36V and 1.30V/1.30V  (1.5V)


R15 & R17:  0.57V/0.60V and 0.61V/0.63V  (0.85V)


R16, R18, R26, R29:  All between 0.58V and 0.65V

post #1755 of 1817

I double checked all the parts and made sure they were in the right spots.  So the only thing I didn't do was install C2 and C3 yet.  Could this have something to do with the low voltage readings (especially at R3)?  I'm a little stumped at the moment.

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