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β24 Pieterh's build

beta24

β24 Pieterh's build

Postby Pieterh » February 15th, 2018, 9:15 am

Dear all, After my threads with 'Informative questions before starting B24 build' (informative-questions-before-starting-beta24-build-t3575.html) and an 'Initial set up issue' with one board (initial-set-up-issue-beta24-board-t3689.html), ending in a total catastrophy for one B24 board (RIP....), I'd like to share with you the finalisation of my B24 build in the coming weeks/months. Months you say? Well, I still have 8 months to go, in order to finish the Beta24 power amp before the 'two year' deadline I 'gave' myself. That long, some of you may think? Well,......those with families, other sports hobbies or busy jobs may have found themselves in a similar situation where finding enough (consecutive) hours in a weekend is really difficult, so one has to take it a bit easy.

So why did I start anyway with the B24? Well, looking at the attached picture the DIY virus probably infected me in back in 1990/1991 with a school project where we made a lab PSU with a frequency generator. I enjoyed electronic classes much, but still my career went in a different direction. Then at a certain point in time I got interested in listening music through good hifi equipment (like my father, the story of the tree and the apple...) and thought why not looking for options to build gear myself and create a nice hobby? So, that is how I ended up at the site of Ti whose unique approach to support and service gave me confidence that even I could finish this big amp. Started October 2016, I am currently quite confident that I will meet my 'deadline' in October 2018.

So, at which stage am I currently? I got the E24, PSU, S22's and B24 boards all ready. Design and panels have been send to front Panel Express in Berlin. Probably ready this or next week. Hereafter, I will post pictures of parts of my build and finally .... the complete B24. But please, give me some time for new posts, duty is calling......

lab PSU School Project.jpg

Workplace.jpg
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Last edited by Pieterh on April 6th, 2018, 12:43 pm, edited 1 time in total.

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Re: β24 Pieterh's build

Postby Pieterh » February 16th, 2018, 10:37 am

Starting something new is the most difficult stage of a project some people say. The B24 project let you start with the smallest part of all, the 1.2pf SMD capacitor (0805 package). The first time I had no fluxpen at my disposal. I managed this first time, but the second time it went much better and easier....because I bought a flux pen and I watched the Curious Inventor dot com video on SMD soldering with simple tools on youtube [ http://www.youtube.com/watch?v=3NN7UGWYmBY ]. I can really recommend this! I even ordered a 'smd soldering training kit' on one of these asian websites. Different small packages for training. Fun!
0805.jpg

SMD training KIT.jpg
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Re: β24 Pieterh's build

Postby Pieterh » February 16th, 2018, 10:40 am

Then the matched JFETS, have to be mounted in a slight different position than the silk screen. Here are my photo's of those.
JFET positioning 1.jpg

JFET Q1 Q3 Q41 Q43.jpg

JFET Q2 Q4 Q42 Q44.jpg
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Re: β24 Pieterh's build

Postby Pieterh » February 17th, 2018, 2:23 am

Except for the SMD's and the JFETS, populating the B24 is mostly rather straight forward. Still there are some parts that one can give special attention in terms of matching. Although, the BC550C and BC560 transitors do not need matching in principle, matching can still favor a smooth initial set up of the B24 board is what I understood. This is what Ti said about it:

amb wrote:1. Look at the schematic and you'll see the four quadrants. For every BJT in one quadrant, there will be a counterpart in the other quadrants. If you want to match hfe's, then match them left side to right side, as well as upper to lower. Exact hfe numbers don't matter, just make them as close as possible to each other.
All this matching business (and trimpot tweaking) on the β24 is strickly to establish a well-behaved DC quiescent baseline. It has no impact on the performance of the amp, except output bias settings, due to the cascode topology of every stage.


As I encountered some initial set up issues with one board before, I ordered 200 pieces of BC550 and BC560 as there are really cheap. Then I used a DMM with HFE measurement possibility and a transistor tester (some cheap fun kit from an asian site, see pic) to match transistors.
Measurement gear.jpg
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Re: β24 Pieterh's build

Postby Pieterh » February 17th, 2018, 2:36 am

As I stay close the reference build of Ti, I also use the Dissipante chassis (U4 300mm deep) from Modushop Italy. Using the heatsinks of this chassis implies that you need to bend the mosfets as the heatsinks are not that high. Here are some photo's to illustrate what has to be done.
Mosfet bending 1.jpg

Mosfet bending 2.jpg
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Re: β24 Pieterh's build

Postby zhanqian » February 17th, 2018, 5:36 am

Hi Pieterh,
Nice work.
I am ready to continue my Beta24 project right after the Chinese Spring Festival holiday, can't wait to start. :D

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Re: β24 Pieterh's build

Postby obee » February 17th, 2018, 8:29 am

Hi Pieterh,
Very nice! You have a good workshop to work with. I only have a desktop of about 90cm x 60cm with monitor, keyboard and mouse. Each time I need to work with beta24. I need to take away my PC monitor, keyboard and mouse.

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Re: β24 Pieterh's build

Postby bk_856er » February 17th, 2018, 1:45 pm

I also have a b24 build underway and was actually planning to solder the transistors today. I like the idea of (optional!) BJT matching to maybe make setup a bit easier. Was 100/ea of BC550 and BC560 sufficient to get reasonable matches? From what you wrote, I believe the total between the two types was 200 pieces? Nice price break at 100.

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Re: β24 Pieterh's build

Postby obee » February 17th, 2018, 10:57 pm

I ordered 100 pieces of bc550 and 560(total 200) for both beta22 and 24. They are enough for matching as not all need good match.
Anyway, it’s really cheap so it’s not a bad idea to order more. I have burnt some in my beta22 so having spare always a good thing to do.
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Re: β24 Pieterh's build

Postby Pieterh » February 17th, 2018, 11:20 pm

Thank you for your responses and contributions here! It is nice to share our hobby, right?

bk_856er wrote:I also have a b24 build underway and was actually planning to solder the transistors today. I like the idea of (optional!) BJT matching to maybe make setup a bit easier. Was 100/ea of BC550 and BC560 sufficient to get reasonable matches? From what you wrote, I believe the total between the two types was 200 pieces? Nice price break at 100.BK

Within this 'optional perfectionism' 200 is more perfect than 100, but 100 will do just right I assume :-). I remember the first time I ordered those BC550/560's, I ordered those in almost exact numbers following the BOM, I had only 4 extra pieces or so. the second time I realized they are only around 5-6 euro's per 100, so I didn't want to come short....this way I could select all BC550C within HFE 620-635 and BC560C within 520-535, and choose same values for transistors in the same position in the scheme.
Last edited by Pieterh on February 17th, 2018, 11:30 pm, edited 1 time in total.
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