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Informative questions before starting β24 build

beta24

Re: Informative questions before starting β24 build

Postby amb » September 7th, 2017, 1:00 pm

Yes to all three questions. If the D-G-S markings match the pins of the JFETs then you have it right. Note that the Toshiba datasheet pin-out diagram is bottom-view.

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Re: Informative questions before starting β24 build

Postby FishHead » September 18th, 2017, 10:38 am

I am thinking about this build and what it will cost to complete (besides time). I will be using USD. New parts of recommended grade. Class A/B.
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Re: Informative questions before starting β24 build

Postby amb » September 18th, 2017, 12:28 pm

FishHead wrote:I am thinking about this build and what it will cost to complete (besides time). I will be using USD. New parts of recommended grade. Class A/B.

The cost could vary a lot depending on your choice of power supply configuration, power transformer(s), casing/heatsinks and any customization (milling, engraving, etc.). Where you get the parts also influence the cost.

Do you have the β24 documentation PDF file? If not, send me your email address and I'll provide a copy, and then you could mull over the parts list and do some pricing research on your own.
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Re: Informative questions before starting β24 build

Postby FishHead » September 18th, 2017, 1:23 pm

A rough ballpark was what I was looking for. I would hate to run out of cash 5/8 the way through.

PM sent. Thanks in advance.
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Re: Informative questions before starting β24 build

Postby Pieterh » October 22nd, 2017, 10:35 pm

to be sure about the mounting of the mosfets to the dissipante heat sinks: I just apply the heatsink thermal compound (567-120-SA) to both sides of the bergquist isolation pads before mounting the mosfets, right? I don't need to treat the black anodized heatsinks before mounting the mosfets (sandpaper/polish)? (There are some people who do that)

The cadock resistors can be mounted directly to the heat sinks with some thermal compound (567-120-SA) in between ?

Status update: I am progressing slowly but steady.....E24 and B22 boards are ready, excluding testing. B24 boards are almost ready, only mosfets need to be installed. Dissipante chassis with predrilled holes in the heat sinks (m3 thread) arrived, transformer from toroidy arrived, waiting for some nuts and bolts and connectors. Front panel design is ongoing.....the options are unlimited, learned some FreeCAD drawing.

I made 3D FreeCAD drawings for the heatsink holes (m3, thread) with the same measures as Ti's reference built, can I upload these files in freecad and DXF formats here so people can use it for customization at modushop?
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Re: Informative questions before starting β24 build

Postby amb » October 22nd, 2017, 10:45 pm

You don't need to use thermal compound with the specified Berguist pads.
The Caddock resistors mount on the heatsink with thermal compound.
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Re: Informative questions before starting β24 build

Postby Pieterh » November 22nd, 2017, 3:12 am

All boards are completed, power supply is assembled, testing has started.

Can i check with you the LED current limiting resistors of the Sigma 22 and their mounting. Both sigma 22's boards are working fine with nearly 36v output, except that I smelled something and I found that all the LED current limiting resistors get quite hot (hence the little smell). I use LED (mouser nr. 941-C4SMFBJFCR24Q4T2, Vf= 3.4V, Led current = 20mA, they are quite bright) between 2 resistors ( 594-5073NW1K600J, 1.6kOhm, 1 Watt). I used 36 V (one side) for the voltage supply in the calculator. I think these resistors are right, and probably the fact they get hot is normal, and maybe I need to mount the resistors elevated from the board?
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Re: Informative questions before starting β24 build

Postby amb » November 22nd, 2017, 4:51 am

You should use 10KΩ for R16 and R17 on the σ22. The LED is rated for a maximum of 20mA, but you should not operate it at that current, or you may risk premature failure of the LED. Usually 2-4mA is enough current to make the LED glow brightly. Same goes for the LEDs on the β24 boards.
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Re: Informative questions before starting β24 build

Postby Pieterh » November 22nd, 2017, 5:54 am

Thanks!
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Re: Informative questions before starting β24 build

Postby Pieterh » January 14th, 2018, 4:13 am

I understood from other questions and answers that Matching BC550C and BC560C is not required but matching might make the initial set up more easy. Can I check with you these three thoughts that I have?
1) it is best to choose transistors (BC560C and BC550C) that have equal hFE in the left (+) and right (-) side of the B24 scheme?
2) In a optimal situation, it is best to choose the BC560C and BC550C with hFE's to be as close as possible? So BC560C with hFE=550 is better than 500, and BC550C with hFE=615 is better than 700.
3) It does not matter for the gain/sound quality whether the BC560C and BC550C hFE values on one B24 board differ from the other B24 board (other channel) due to the cascode design (and initial set up with VR1 to VR4)?

And one question about the CRD's: I found in a previous B24 board (the one that didn't set up well) that especially CRD 1 and CRD 5 were having relatively low forward voltages of 1.7V and 1.8V. The other 'good board' I have, has those CRD's with forward voltages that were 1.9V and 2.0V. Is it in your opinion important to match those six CRD's?
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