Yes on the sound quality I think it is a very fine amplifier.  Clean, fast, detailed, neutral etc.  I noticed that it was very stable in respect to temperature.  (The breadboard did use the full final heatsinks).  It would come up to temp and then the offset/ balance would not change much for hours.  I did not engage the servo.  I tried a version with and without the cascode current sources but didn't carry out detailed listening comparisons.  I also ran 10mA to 20mA and was perfectly happy with the 20mA performance.

I've run my Carbon with and without the opto servo. Without the servo, the Carbon is very stable and quickly settles as everyone is saying. With that said, the opto servo does work very well and is effective almost as soon as the amp is powered on. 

I would like to have two more pairs of the individual GR LV boards and can also see them being useful in a few other projects.  These are the small single boards 3.75" x 2.4"  (95 x 61mm).

I will be buying some (from England) and if you want to get on a mini buy please let me know.  I am away next week so will place an order in early June. The price would be starting at $16 each and come down a bit if the order quantity goes up.  (plus postage and pp fee).

Please pm me if interested.

Edit - to explain.  I am based in England so that is where I am placing orders and shipping from. (and yes my first language is English!)

Same arrangement and supplier as for the KGST GB I did.

 

UPDATE; 7 June:  I'm ready to order.  The price is $24 for a pair of latest GR LV boards. Postage and paypal fee to add.

pm me if you want any.

UPDATE; 7 June:  I'm ready to order.  The price is around  $20 for a pair of latest GR LV boards. Postage and paypal fee to add.

YES $20 per pair now.  pm me if you want any.

 

 

 

 

 

 

 

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Edited June 7, 201610 yr by headinclouds

On 5/21/2016 at 7:44 PM, johnwmclean said:

Thanks guys!

As to the sound,

I’ve had a fairly good listen now, I can confidently say It’s a good improvement in performance from the KGSSHV’s and BHSE I have on hand. I’ve always maintained the BHSE and KGSSHV were a similar calibre, with different signatures depending on your taste and music genre.

Interestingly I find myself in the same scenario with the Carbon and the T2, I don’t prefer one over the other, both have slight contrasting differences. To be crude and simplistic, the Carbon has transparency and the T2 sweetness and tone, but both amps do everything exceptionally well.

The Carbon is unquestionably the most stable amp in my arsenal, do we need servos on the next board runs?

John,

What tube are you running on both the BHSE and T2?  Superb builds John!

Thanks Purk, 
Winged C’s in the BHSE, Winged C's in the T2.
I really need to invest in some decent glass, shame on me, I’m sure there’d be an improvement by a significant magnitude, so please take my comments bearing this in mind.

To clarify the T2 is not my build, I have on loan from "wink".

Edited June 13, 201610 yr by johnwmclean

Hi all, I'm in the process of building the Carbon (I believe the amp boards are v6) and in need of a pointer.  "Servo 1" and servo 2" jumpers should be connected?  Thanks.

 

 

Test and trim the board first without jumpers.
To activate the servos jumper one or the other, not both at the same time, you decide which servo to use.

Edited June 14, 201610 yr by johnwmclean

Thanks!

Kevin has posted somewhere about the 2 different servos on this board. One of them needs +20V offset on start-up. 

Edited June 14, 201610 yr by johnwmclean

I have a problem with the PSU. Started without load and grounds connected to safety earth.

Trafo: 360volt AC x2  and PSU ready for 400 volt DC

LV: OK;  +15,1 volt and -15,4 volt.

Bias: OK; 579 volt at the test point.

HV: both sides +119 volt and -119 volt.

I don´t see something wrong or blown.

Any idea?  What can be wrong?

 

Are the reference chips 10v ?

looks like they may be 5v

1 hour ago, kevin gilmore said:

Are the reference chips 10v ?

looks like they may be 5v

they do look to be 5v versions

I agree it looks like 5V refs ...but how should that result in 120V output?

Probably because the 5V doesn’t like shunt mode. From LT1021 datasheet: Three voltages are available: 5V, 7V and 10V. The 7V and 10V units can be used as shunt regulators (two-terminal zeners) with the same precision characteristics as the three-terminal connection.

Thanks for your help guys. Yes it's 5 volt. I don't know why use this and I don't remember reading anything about. I ordered this on digikey.

In any case, it's my fault and is quite easy to solve.

So the correct is the 10 volt versión?

Yes, 10 volt is correct.

Edited June 16, 201610 yr by JoaMat

Thanks!!!

Finally made good progress with my build. PSU works, +403V and -406V on the rails (I guess I didn't match the resistors closely enough to get it perfect), and 560V bias (and climbing slightly as the 5% tolerance zeners warm up), all of which I believe should be fine. The 4 LEDs on the amp boards all light up.

What is the procedure for adjusting the Carbon output current? Does it need a test tone playing? I put multimeter probes on the current adjust test points, but my DMM shows ~0.30mA, which quickly drops to ~0.06mA. Turning the trimpots doesn't do anything.

I do not have the Stax jacks or pot connected yet.

Test in volts not milliamps. 1V is the setting for 20mA.

Thanks, John! So it's the current across the 50ohm resistor?

33 minutes ago, gepardcv said:

Thanks, John! So it's the current across the 50ohm resistor?

Yes, you should see 2 test points next to each of the two 50 ohm resistors on each channel.

I have music! Pretty obvious this is something special. It was pretty easy to adjust, and the circuit seems fairly stable so far.

Still, something strange is going on: when I turn the amp off, all offsets jump to >250V, and then slowly down to 0. It's looks like the HV rails short to the output. I don't think this happens with my KGST and KGSSHV builds. Is this expected, or did I fuck something up while wiring the amp?

I think this is normal.

 

Thanks, Kevin. In light of this, any concerns with keeping headphones plugged in while turning the amp off?

as long as the voltage goes up on turnoff, no issue.