and now for something completely different part 3

[spritzer]

The EHT has been refurbished plus some other fixes here and there but I know that 48 year old panels aren't working correctly.  A refurbed unit will not sound the same as it will be working correctly. 

[gepardcv]

Trying to understand the inputs and outputs: does each channel need two uberamp boards?

[kevin gilmore]

if you want a fully balanced amp, then you need 2 amp boards per channel plus one input board

plus 2 goldenreference boards one set for 40v and the other set for 30v

plus a very large transformer, a pair of 25 amp diode bridges and some really honking large power caps and mass quantities of heatsinks.

if you ever saw the original levinson monoblock class A amps, those were 18 watts (really about 30) This is 100.

you can also build the unbalanced version which is still pretty silly and less parts. And still stable into 1 ohm.

 

[gepardcv]

Thanks, Kevin. This is kinda sick and tempting at the same time.

I'm not good at estimating heatsink size for the power dissipation requirements, but could the balanced version be built in one large (4U or 5U) chassis, assuming heatsinks with 50-75mm fins (I'm sure Fischer sells something useable), or would it require monoblocks?

[kevin gilmore]

I think it's closer to a 6U as a stereo balanced

the board is 4.35 inches high and 11.55 wide

the transistors take up a bit of extra space past the board

so say 10 inches X 15 inch heatsinks

[Marc Edwards]

Very excited for this project.

Sounding off [For the love of Quad]! Busted a diaphragm recently. Going to have to repair mine. : / 
Should note the other (working) segmented driver electrodes in mine are misaligned veritcally by ~2.7 or 3mm.... Perfectly
explains why this one sound lesser than the other.. 

Photos' are old, notice the lack of an amp.
Recently have been using an Aaragon 8008ST. 

Can't wait to hear about what Kerry's thinking on. 

[luvdunhill]

So, I don't think I would have ever said this, but this is probably overkill. What part are you using for the .47 resistors?

[kevin gilmore]

overkill?

ME?

NO, never.

the resistors i picked are actually 1.5 inches long, the layout is 1.8 inches. So you can use the concrete resistors.

i don't like the sound of protection circuits. So this amp is capable of about 30 amps into .1 ohm.

Its just so much simpler this way.

[spritzer]

Also...electrostatics.   

[wink]

Overkill is only disdained for those who thrive on mediocrity.

 

One man's feast is another man's survival rations.

[Marc Edwards]

Has an appropriate transformer, or toroid consensus begun to materialize. Prefer the status quo, or off the shelf if around. Looking to queue the iron. 

[Mirko]

On 2016-01-20 at 3:00 PM, kevin gilmore said:

the opamp blows up at +/-40V would have to check the other parts, but +/-30V should absolutely work

speaking of power...

unbalanced/balanced/cast to balanced input block for all sorts of things, but mainly the uberamp, just need to find a way to get it into the box will probably involve splitting off the driver section.  Uses GR power supply +/-30V for the front end and another GR power supply +/-40V to run the regulated output voltages to the output amp.  If i add zeners to the servo amp, can easily go to +/-50V  and as shown, its 100 watts of pure class A, and something north of 225 watts A/B

front end NO feedback of any kind, .0025% thd at 20khz, 2nd harmonic.   3rd harmonic not measurable. output amps are current feedback.

i think i have created a monster 

What size of capcitor would be suitable, 47000uF or more?

~1000VA transformer ok?

Also where can I find the pdf or gerber for this?

[congo5]

Question regarding the Uber amp..

to make Stereo Balanced Amp you would need 2 input boards, 4 driver and output boards.

one GRLV @ 30v for the input spliters and a 30v-0-30v 50va transformer

4) GRLV for the driver/output boards and  4) 40v-0-40v 600va transformers

Is this right?

[kevin gilmore]

2 input boards, 4 driver boards, 4 output boards

one grlv @ 30v or 2 if you really want to do dual mono

one grlv @ 40v or 2 if you really want to do dual mono

one or 2 bigass transformers, stack of unregulated caps and 25 amp diode bridges mounted to the bottom.

current version looks a bit different. for the driver board, can stuff parts either top or bottom (other than opamp)

and all the holes line up to stack all 3 boards on top of each other.

Edited February 23, 2016 by kevin gilmore

[ang728]

HI All,apolgize for my english first

I'm planning to build a CFA3, but when reading gerber layout , 

http://i.imgur.com/T2QaX1X.jpg

I see silkscreen prints 

"
GAIN=10K SS,1.5K ZF 
Input=5K SS,100 ZF
"

and also noticed SS,ZF marked on silkscreen.I assumed ZF is for Zero Feedback and SS for Super Symmetry but not so sure whay they actually mean.so asking what are they mean and how to adjust them if needed to.

Another question is about bias.it seems to be measured by 1Ohm and adjusted by 5K pot,but how much bias is appropriate?

Thanks

Edited February 26, 2016 by ang728

[kevin gilmore]

I would go with the new input board above, and then 2 x cfa2 output boards per channel.

[ang728]

54 minutes ago, kevin gilmore said:

I would go with the new input board above, and then 2 x cfa2 output boards per channel.

OK Thanks ,I will consider it  

but how much should the bias be?I read 150mV across 1Ohm somewhere,is that right ?

[kevin gilmore]

depends on how much heatsink you have.

150mv is a good starting point

[MLA]

if coming from a balanced source, is there an advantage to running it through the input board, rather than straight to a CFA2 quartet for balanced out?

[kevin gilmore]

that is a good question.  i'm not really sure of the answer, why not build both and let us know if it sounds any different.

however using the input board gives much more common mode rejection. At least 10db, probably closer to 15

 

[MLA]

Does sound like an interesting challenge to spot the difference! 10-15 dB should make a difference though.

I'll get an input board from Sorens groupbuy and see what comes out of it...

[kevin gilmore]

well it only really makes a difference if you have a dac with significant amounts of dc offset. otherwise who cares.

[MLA]

True, and my dac is actually quite well behaved, so no real reason

However, I was going to expand my CFA2 to balanced anyway. A friend is building a Dynahi and I'm interested in comparing those two, and putting the input board in front will help test  some single ended sources others have recommended.

[congo5]

One channel of the Uber amp running on a + - 20v bench supply into 10R load

[Laowei]

Impressive as all hell.