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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: Attn Woodman posted by mikee55 on February 4, 2004 at 14:09:40:
Hi Mike,Beta matching is gain matching. There is a transistor spec called hfe which is essentially the gain of the transistor.
I have done this only on amplifiers, but I have discovered that many xsistor amps use the same devices throughout the input path (guess this is a cost saving measure). What I do is remove these xsistors and plug them into a transistor tester, write down the number and keep the tested devices with the number. The pairs with the highest and closest matching numbers are reserved for the input pairs and the rest are used to get the best left and right channel symmetry depending on where they go in the circuit. It really helps to have a schematic to do this.
Alternatly, since TO-92 packages are cheap, you can get several handfuls of new xsistors and find perfect matches with the highest gain. Ideally, testing the hfe at the operating temperature should be even better as the input pairs would be more likely to thermal track better (remember Q-point shifts with temperature change).
Yes, beta matching can also be done with output devices (BJT's not MOSFETS), but they are rather expensive and I don't think the advantages are as audible as setting up the input pair. Matching is more important for MOSFETS (Vgs), but you have to build a circuit to match them.
The point of this is to get the lowest noise, widest bandwidth and the truest signal from the input before it is amplified further. I think Harvey Rosenberg said if you can't get the first stage to sound good, then the rest of the amp won't sound good.
Hope this made sense I'm a bit off today...
-JamesW-
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Follow Ups
- Re: Attn Woodman - woodman 10:04:51 02/05/04 (1)
- Re: Attn Woodman - mikee55 15:06:50 02/05/04 (0)
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