AMB Laboratories DIY Audio Forums

[goliraja]

Greetings, Everyone!

Over the past few weeks I was able to put together β24 amp, custom enclosure pending.

Got few issues during the setup/alignment process for both the channels/boards.

1st issue was very similar to Nishant's post https://www.amb.org/forum/nishants-beta24-alpha10-integrated-amp-build-log-t2193.html which was resolved (for both boards) by shortening the GND wires.

2nd issue (board 1) was cold solder joint - had to reflow.

For Board 1:
Was unable to setup with input as 4V(R7). Was getting very similar results as to Pieterh https://www.amb.org/forum/initial-set-up-issue-beta24-board-t3689.html. By increasing the value to 4.5V, the setup completed successfully.

Issue:
Q11, Q12, Q15, Q16 become too hot as compared to Board 2.

For Board 2:
No issues during setup. Was able to configure with input as 4V(R7).

Issues:
None

Components stats:

IDSS (in mA)

jfet	Board-01	Board-02

Q1	9.36		8.97
Q2	9.35		9.17
Q3	9.59		8.61
Q4	9.58		8.62

Q41	9.64		7.08
Q42	9.61		7.04
Q43	9.48		7.56
Q44	9.48		7.46

BJT hFE

Board-01:

550C	 		          560C

Q5,Q7			Q6,Q8
499, 498 		       450, 451

Q10,Q12			Q9,Q11
500, 502		       441, 440

Q14,Q16			Q13,Q15
509, 509		       437, 438

Board-02:

550C			          560C

Q5,Q7			Q6,Q8
506, 510		       470, 475

Q10,Q12			Q9,Q11
512, 513		       425, 424

Q14,Q16			Q13,Q15
 516, 515		       478, 482

I've seen Ti's response in another thread on the reason why the BJTs (Q11, Q12, Q15, Q16) are getting too hot.

Question: Is it safe to operate in this mode or do I need to make any changes to Board 1?

Appreciate everyone sharing their experience as well as Ti's contribution.

Pictures coming soon ...


Thanks!

[amb]

Do you have an IR thermometer? Take some temperature readings of those transistors and post them here. We can determine whether they’re too hot.

[goliraja]

Not sure how accurate the thermometer is, but here are the readings from both boards.

For Board-01:

Q11-Q16 ~ 114 - 117°F

For comparison, captured D7-D10 temp from Board-01 as well:

D07-D10 ~ 116 - 120 °F

For Board-02:

Q11-Q16 ~ 100 - 106°F
D07-D10 ~ 116 - 120 °F


Thanks!

[amb]

Those are hot but safe temperatures.

If you want, you can add TO-92 clip-on heatsinks on the transistors, such as Aavid 575200B00000G, available from Mouser and Digi-Key.

[goliraja]

Thanks, Ti. I'll add clip-on heatsinks.

[cobretti]

Did you touch D7-D10? How hot they get...........

[amb]

He said 116-120°F (about 47-49°C).

[cobretti]

D7-D10 run about 90 deg C in my amp. Certainly not at 50. 50 deg C for transistors or diodes is nothing.

[amb]

The DO-41 diode package has much higher power dissipation and operating temperature ratings than the TO-92 transistors.

[goliraja]

Started putting things together in an enclosure. It's not completed yet.

Powered on both channels and connected to small 2-way speakers. Listened to few different sources for an hour.
It's different! You have to listen to believe the quality - it's a true reference-class amp!
Thanks for the amazing design, Ti.

Here is a glimpse of the system:

amb_001.jpg

There is no noise/hum when switched to balanced mode. Get faint noise in unbalanced mode (if I get too close - ear next to the speaker), else won't notice.
So far have only floating star ground. Have not added the ground loop breaker yet.

Custom enclosure is built using IKEA's cart (BEKVÄM): https://www.ikea.com/us/en/catalog/products/30240348/.
Other major parts include:

• 2 channel β24
• Power switch driver with temp sensor
• Dual Sigma 22 PSU
• Plitron x'former - for unregulated supply
• SumR x'former - for regulated supply
• 8"x10" heat sink from heatsink usa (amp pcbs): https://www.heatsinkusa.com/8-000-wide-extruded-aluminum-heatsink/
• Neutrik 19" rack panel for I/O (input, output & selector s/w): https://www.neutrik.com/en/product/nzp1ru-8
• Middle Atlantic UFA-8 Device Mounting Rackshelf (1 RU, Single, 8" Depth): https://www.bhphotovideo.com/c/product/868093-REG/Middle_Atlantic_UFA_8_UFA_Shelf_1_Space.html
• Gator Cases Rackworks Perforated Rack Panel (2U & 3U) (for ventilation): https://www.bhphotovideo.com/c/product/1132802-REG/gator_cases_grw_pnlprf3_rackworks_1_2mm_steel_slotted.html
• Acrylic plastic (outer cover): Tap plastics https://www.tapplastics.com/
• Other hardware: local stores - OSH & HSC (unfortunately both stores closed)

Will upload other images.

Thanks!