The ultimate DIY? A Stax SRM-T2!

[cetoole]

Of course it goes into heat, but where? There is no shunt element, so what is dissipating the extra current that the load isnt using, especially during no load scenarios?

Maybe odd idea, but for dual tracking, how about instead using a differential i/o opamp for the error amplifier, running on something like +/-15v instead of +30v like the current error amp? One would, of course, need to invert the negative supply parts.

[deepak]

Any estimates for the power consumption?

[sawyers]

Of course it goes into heat, but where? There is no shunt element, so what is dissipating the extra current that the load isnt using, especially during no load scenarios?

The current flow is via the series pass transistor, through the amp, and then back. So if the amp is not connected, no current can flow. These actually aren't formally being used as constant current sources as such - they are essentially current limiters with a limit current set by the cathode-gate resistor. In the words of the datasheet:

Applications

Highly stable voltage sources

Current surge limiters

Transient voltage protection

Instantaneously reacting resetable
fuses

Soft start-up circuits

This is totally different to a shunt current regulator, which dissipates maximum power when the current drawn is zero. The principle there is that the current regulator power dissipation plus the amp power dissipation is a constant. They do have significant benefits as compared to a series regulator, apart from (as Kevin says) the frying eggs syndrome. Most shunt current regulators will thermally die if a dummy load is not connected unless they have huge heatsinking.

Craig

[spritzer]

This is not about saving a few dollars.

We should have that engraved on the amp...

Any estimates for the power consumption?

200W+

[Inu]

Hi all

I've also gone through the amplifier BOM, and found a couple of minor inconsistencies as compared with the actual board.

1. 300k, 2 needed (not 6)
2. 390k, 8 needed (not 12)

Oh - and there are two R44's, one in the 700V battery (390k) and one and one between the supressor grid of the left hand 6CA7 and anode (220 ohms).

Basically I cross checked the boards (took a photo so I could cross parts out as I checked them), cross referenced it to the schematic parts numbers, then listed out the parts numbers in sequence to ensure I had a sequential list with nothing duplicated or obviously missing. So I *think* it is consistent. It definitely, *definitely* needs cross checking with similar things others on the forum are doing.

I've also broken the BOM into separate sheet for passives, semiconductors and hardware (I haven't checked the hardware) and provided a column for schematic parts cross reference.

BOM is here http://www.tech-enterprise.com/tekst...ts3cgsedit.xls

Craig

Craig,
Thank you for the update.
Neutrik Female XLR connectors: 568-NC3FAH-2 > 568-NC3FD-H (or H-B or H-BAG).
I will keep my NC3FAH-2s for other project…

[cetoole]

The current flow is via the series pass transistor, through the amp, and then back. So if the amp is not connected, no current can flow. These actually aren't formally being used as constant current sources as such - they are essentially current limiters with a limit current set by the cathode-gate resistor. In the words of the datasheet:

Applications
Highly stable voltage sources
Current surge limiters
Transient voltage protection
Instantaneously reacting resetable
fuses
Soft start-up circuits

This is totally different to a shunt current regulator, which dissipates maximum power when the current drawn is zero. The principle there is that the current regulator power dissipation plus the amp power dissipation is a constant. They do have significant benefits as compared to a series regulator, apart from (as Kevin says) the frying eggs syndrome. Most shunt current regulators will thermally die if a dummy load is not connected unless they have huge heatsinking.

Craig

OK, so it is just a protection device, with no significant benefits to ripple rejection. Thanks, that answers that.

[kevin gilmore]

No, you are WRONG... shorting out the current sources and there is 6db more noise.
I just measured it. But no reason for me to argue.
Dynamic impedance of the current source reduces the noise.

NOTE!!!!!
D20 is labeled wrong on the power supply board. Needs to be flipped.
Schematic is correct. Power supply and time delay circuit now fully
tested.

picture of D20 correctly installed soon.

[kevin gilmore]

OK, here you go

http://gilmore.chem.northwestern.edu/t2powerfix.jpg
http://gilmore.chem.northwestern.edu/t2power.jpg

cetoole...
a naar veizt men nit kayn halbe arbet

[sawyers]

NOTE!!!!!
D20 is labeled wrong on the power supply board. Needs to be flipped.
Schematic is correct. Power supply and time delay circuit now fully
tested.

Wow, well spotted. That would've given an interestingly high -12V line!

While thinking of lurking silk screen gremlins, the amp circuit board has R56/57 as 10k on one channel, but 100k on the other. I guess that 10k is the correct value?

Craig

[kevin gilmore]

While thinking of lurking silk screen gremlins, the amp circuit board has R56/57 as 10k on one channel, but 100k on the other. I guess that 10k is the correct value?
Craig

Correct value 10k. Mentioned a few pages back.

And when i tested the low voltage supply and found the -12 was -19 i knew instantly what was wrong.

So far, 2 silk screen errors. Total. Plus the holes on the 3381's a bit tiny.
Plus one zener hole a bit tiny.

Pretty fucking good for a project of this magnitude.
I challenge anyone to do a project of this scope and get it 99.99999999% right the first time.

[kevin gilmore]

all 3 transformers mounted.

http://gilmore.chem.northwestern.edu/t2power2.jpg

need slightly longer 1/4-20 nylon bolts

Its starting to get heavy...

[n_maher]

Kevin,

If those are SumR transformers double check the secondaries by hand. On the last trafo he made for me (for the BHse) he mis-marked the center tap on one of the secondaries, which thankfully didn't cook anything.

[Beefy]

That's obscene, Kevin. Certainly puts my meager efforts in their place

[sawyers]

So far, 2 silk screen errors. Total. Plus the holes on the 3381's a bit tiny.
Plus one zener hole a bit tiny.

Pretty fucking good for a project of this magnitude.
I challenge anyone to do a project of this scope and get it 99.99999999% right the first time.

Absol-bloody-lutely! Stunningly great piece of work Kevin. I've never done PCB design anything like this large or complex, and I've always had a greater mistake density.

Didn't mean to come across as a knit-picker

[kevin gilmore]

Kevin,

If those are SumR transformers double check the secondaries by hand. On the last trafo he made for me (for the BHse) he mis-marked the center tap on one of the secondaries, which thankfully didn't cook anything.

I always test the AC out of all transformers first.
And unloaded power draw checking for shorted turns.

In fact i also check every semiconductor (especially the led's) and
measure the resistors. Saves a lot of time later.

[spritzer]

Checking every component is well worth it (especially the leds since they are a pain to remove later on). Thanks for the warning Nate, the CT on my KGSS transformer was in the wrong spot or I just misunderstood the SumR specsheet.

[nattonrice]

I'm glad that I'm not the only sod who checks every resistor

[n_maher]

Checking every component is well worth it (especially the leds since they are a pain to remove later on). Thanks for the warning Nate, the CT on my KGSS transformer was in the wrong spot or I just misunderstood the SumR specsheet.

That's exactly what happened on mine, the CT was marked wrong. Thankfully it was a low-voltage mistake but I'm not happy to hear it's happened more than once.

[kevin gilmore]

The 534-1847 are the wrong size, I will have to measure again...

Should be 534-3487... So .5 instead of .625 (actual is .55 which is .5 with a .05 spacer)

I ordered .375 anyway ??

[kevin gilmore]

http://gilmore.chem.northwestern.edu/t2chassis29.jpg

Soooo close...
1 more resistor value on backorder
wire stax jacks

Will finish wiring the power supply tomorrow.

Few more screws, nuts and bolts...