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Old 22nd March 2007, 10:34 PM   #1511
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Quote:
Originally posted by AndrewT
Hi,
45Vac to 50Vac will put a LOT of extra stress on the output devices.
It may become just an 8ohm amp with that level of PSU voltage.

Jens' five pair PCB would be more suitable for these higher voltages.

Understood. I'd use three or more pairs of TO3s, and probably a fan.

Jens was planning on running at 70V.

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Old 23rd March 2007, 07:48 AM   #1512
AndrewT is offline AndrewT  Scotland
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Hi,
Quote:
use three or more pairs of To3s
3pair is not going to cut it on 45Vac unless you seriously undersize the PSU to protect the output stage on continous output.
I ran 3pair of 230W devices through Bensen's spreadsheet.
comparing 40Vac to 45Vac, the 8ohm capability on reactive load fell from an easy (well inside DC SOAR) 60degree phase angle to just 40degrees.
into 4ohm it fell from 46degrees to 23degrees.
I would consider it marginal on 4 to 8ohm speakers if driven hard.
I did not look to checking 50Vac.

If you do want serious power you will also need to check the drivers against the output gain (hFE) at worst current and phase angle.

Jens,
the bias falls from Vre=25mV to Vre=15mV when I let the sink get hot during testing. Still within the range suggested in other threads for optimum ClassAB bias.
The reduced bias allows the sink temp to recover more quickly after working hard and I suppose that is an advantage.

I tried a variety of caps on the output (700mVac) ranging from 100nF to 2.2uF//8r0. Still sending the squarewave test signal through the input filter.

There was very slight squaring of the corner into 100nF//8r0 but the bigger caps caused considerable oversheet (upto 30% at worst) lasting about 2 damped cycles before disappearing. At 1kHz the overshoot had disappeared into the dead flat calm within about 10% of the flat top. At 10kHz it lasted about 50% of the square wave top. I have not measured the ringing frequency but guessing from the ripple wavelength it could be around 100kHz.
Should I inject the test signal after the input filter?
Where should I scope the output signal? before or after the Thiele network?
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Old 25th March 2007, 01:44 PM   #1513
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Quote:
Originally posted by AndrewT
Hi, 3pair is not going to cut it on 45Vac unless you seriously undersize the PSU to protect the output stage on continous output.
I ran 3pair of 230W devices through Bensen's spreadsheet.
comparing 40Vac to 45Vac, the 8ohm capability on reactive load fell from an easy (well inside DC SOAR) 60degree phase angle to just 40degrees.
into 4ohm it fell from 46degrees to 23degrees.
I would consider it marginal on 4 to 8ohm speakers if driven hard.
I did not look to checking 50Vac.
Thanks for the note of caution, always good to keep the magic blue smoke inside the TO3s.

Where can I get the spreadsheet you used?

Jens, did you ever try your 5 pair amp with 70V rails?
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Old 25th March 2007, 02:11 PM   #1514
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Quote:
Originally posted by bremen nacht
Jens, did you ever try your 5 pair amp with 70V rails?
Yes I did, and have not see any problems with it.

I have an other amp (non Leach) it runs at +-68V DC with 2 x 300VA transformers pr. channel and lots of capacitors on the rails. It has run in a 6 Ohm system since 1996 and it has seen some abuse at times.

The output devises are Thoshiba 2SC3281/2SA1302A, they have never failed. The heatsink is not huge by any measure compared to what is often displayed on these pages...

\Jens
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Old 28th April 2007, 01:27 PM   #1515
AndrewT is offline AndrewT  Scotland
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Default Jens' 3pair PCBs - plugable INPUT options.

Hi,
anyone out there that still has to assemble the PCBs?

The three input holes at the edge of the PCB can be filled with 0.1inch PCB pins. Signal ground, AC input, DC input.

Attach the input cable on the back of the pins, screen to signal ground, core to AC input pin.

Attach a 0.1inch shorting plug from screen pin to AC input pin for testing (Rs=0r0).
Move the shorting plug to engage one end for normal AC input.
Move the shorting plug to DC input + AC input to bypass the DC blocking cap.

This allows all combinations of input using the plugable 0.1inch pins. Very convenient.
I wish I had spotted this before I did my first pair of PCBs, now done to PCB 3 and gone back and added pins to PCB 1 & 2 (with difficulty).

From post1512
Quote:
Should I inject the test signal after the input filter?
Where should I scope the output signal? before or after the Thiele network?
Any clues forthcoming?
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Old 28th April 2007, 07:03 PM   #1516
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Default Re: Jens' 3pair PCBs - plugable INPUT options.

Quote:
Originally posted by AndrewT
From post1512
Any clues forthcoming?
Try and check the frequency of the ringing, it might be the output inductor and the paralle C of the load you are looking at.

If you short out the output inductor the ringing may well go away.

\Jens
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Old 29th April 2007, 08:48 AM   #1517
AndrewT is offline AndrewT  Scotland
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Hi Jens,
yes, the Thiele network, as far as I know, always shows this inductor/load interaction.
But, if I am examining amp output do I scope before or after the Thiele components?
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Old 29th April 2007, 08:58 AM   #1518
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Andrew,

IMO You should exclude the output inductor and RC filter from this type of measurement, so you will have to get rid of them if you want to see the true step response of the amp...

The only problem is that the filter will be present when the amp is in use so I'm not really sure what the best way is to measure the step response.

What info do you want to get from the measurement? slewrate? stability?

\Jens
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Old 29th April 2007, 09:40 AM   #1519
AndrewT is offline AndrewT  Scotland
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Hi Jens,
stability, with and without a source connected.

BTW, have you experienced a surge in the front end at switch on?
I am using 820uF caps and F200mA fuses and I lost a second one and don't know why.
Oh, how I wish I could find the European plug-ins for the fuse location. When I ordered mine the fuses arrived but the plug-in mounting had been de-stocked.

But, on both occasions the output offset stayed below 150mV, when one front end supply rail was down.
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Old 28th May 2009, 08:06 AM   #1520
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Default Lot's of boards aren't delivered

According to the wiki lot's of boards aren't delivered? Is that true or isn't the wiki updated? Is this group buy closed? It should be considering the time when it was started.
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