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β22

beta22

β22

Postby KASaudio » June 27th, 2018, 5:23 am

Hi, everybody. I want to build an amplifier for the B22 headphones. I do not have much experience in this business, so something turned out. I have audio-technica Ath-AD2000X headphones, so I think this amplifier will fit them. At the moment I have a GRADO RA1 amplifier, Audinst HUD-MX2, Lehmann Audio Linear, but I think I really like this one. Interested in one question on the selection of a BJT, what evidence in the selection should be considered more correct 4.2 or 5, 2 mA. Just when building the Board on the selection of BJT, I did not pay enough attention and noticed that with full heating (about 20 minutes of work), the initial settings began to change and I could not bring them to a normal position (constantly floating quiescent current and output DC offset). When checking BJT (BC550. BC560) I noticed that they are very different from each other (from 0.1 to 1.5 mA) and decided to pick them up, what is the main criterion in the selection? The main thing that they were all the same in mA, or is there some other more important indicator? Thanks in advance for the clarification.
Last edited by KASaudio on July 30th, 2018, 1:42 am, edited 1 time in total.
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Re: β22

Postby KASaudio » July 28th, 2018, 4:08 am

Hi, everybody. Set up the first Board first worked fine, as the warm-up began to float settings, I think the problem is in the quality of the elements, it is in BC 550C and BC 560C because they did not check for compliance. Extracted all BJT checked for compliance all indications are different from 0.2 to 1.4 mA. I have a question, and what indications need to be considered correct? What is better when the BJT shows 4.2 mA or 5.2 mA? Or in all this the main thing that all BJT had the same testimony. I ask for clarification in this matter.
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Re: β22

Postby KASaudio » July 28th, 2018, 4:18 am

Hi, everybody. Set up the first Board first worked fine, as the warm-up began to float settings, I think the problem is in the quality of the elements, it is in BC 550C and BC 560C because they did not check for compliance. Extracted all BJT checked for compliance all indications are different from 0.2 to 1.4 mA. I have a question, and what indications need to be considered correct? What is better when the BJT shows 4.2 mA or 5.2 mA? Or in all this the main thing that all BJT had the same testimony. I ask for clarification in this matter. There is another question which need to put a resistor on the active land is 475 Ohm (R1)? Since the addition is written not to install 475 Ohms (R1).
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Re: β22

Postby KASaudio » July 29th, 2018, 11:06 am

KASaudio wrote:Hi, everybody. I want to build an amplifier for the B22 headphones. I do not have much experience in this business, so something turned out. I have audio-technica Ath-AD2000X headphones, so I think this amplifier will fit them. At the moment I have a GRADO RA1 amplifier, Audinst HUD-MX2, Lehmann Audio Linear, but I think I really like this one.
Need help in determining the BJT, what parameters you need to pay attention to in the selection, how much better is 4.2 or 5.2 mA, which force coefficient is more correct or need all the readings to be the same?
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Re: β22

Postby amb » August 5th, 2018, 3:13 pm

Check the hfe of the bipolar transistors. See the “Device matching” section of the β22 website.
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Re: β22

Postby KASaudio » August 5th, 2018, 5:22 pm

amb wrote:Check the hfe of the bipolar transistors. See the “Device matching” section of the β22 website.

Thanks Ti. With BJT I figured out, it is clear that you need to pick up with the same readings. I can not understand what to do with the 475 Ohm resistor (R1), what should I put instead of it, or still do not put anything?
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Re: β22

Postby KASaudio » August 5th, 2018, 5:25 pm

amb wrote:Check the hfe of the bipolar transistors. See the “Device matching” section of the β22 website.

Ti, forgot to mention that I mean the 475 Ohm resistor for the PCB under active ground.
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Re: β22

Postby amb » August 5th, 2018, 10:02 pm

R1 is 475Ω in all configurations (or you could simply not install it on the ground channel). R2 is 1MΩ for the left/right channels, but use 1KΩ on the ground channel.
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Re: β22

Postby KASaudio » August 7th, 2018, 3:34 pm

amb wrote:R1 is 475Ω in all configurations (or you could simply not install it on the ground channel ) . R2 is 1MΩ for the left/right channels, but use 1KΩ on the ground channel.

Thanks Ti.
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Re: β22

Postby KASaudio » August 11th, 2018, 2:30 am

amb wrote:R1 is 475Ω in all configurations (or you could simply not install it on the ground channel). R2 is 1MΩ for the left/right channels, but use 1KΩ on the ground channel.

Hi Ti. I wanted to clarify, I was able to better align the input JFET (since I had the extra 2SK370BL and LSJ74B) I hope this will only improve the quality of the amplifier. And here is another question: is it enough to select BC550 and BC560 for each Board to be the same, or do you need to have THE same on all 3 boards? The resistors in the circuit try to use only precision with a tolerance of 0.1 %, but some install and 0.5 % (RN55D DALE)
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