I did build a dim bulb tester and I will use that.
I was wondering if for a first startup (checking assembly, bias, etc) if it made any sense to use my LM317/LM337 power supply. Set to something like +/-10 to +/-15V. (A minimal voltage to check for gross faults with the speed of a semiconductor/LM317 for current limiting.)
Does that make any sense? Does anyone do that? Or should I just pick my lowest voltage transformer and go with the dim bulb tester?
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You could use the variable supply, but I generally use the DBT with a 40w/60w bulb and if everything goes well try with a 150w bulb as final test. A 150w bulb on small amplifier may only reduce DC voltage 2-3 volts, unless there’s a problem.
Then I test for DC on speakers and play some music at low volumes. If it all checks out, I take the DBT out of circuit and re-check and set final bias and enjoy.
Then I test for DC on speakers and play some music at low volumes. If it all checks out, I take the DBT out of circuit and re-check and set final bias and enjoy.
Most of my diy amplifiers tested using this method.
I use two bench power supplies, one for the positive rail and the other for the negative.
Smoke free!
Well I took a hybrid approach with both the Dim Bulb Tester and the LM317/LM337.
Of the two AliExpress FH9 one biased up with a reasonable bias current at +/-18V while the second flashed the bulb and measured 230 mV (about 0.5V). [At only +/-18V.] So I quickly brought the bias down. These have 0.25 Ohm emitter resistors so I set 75 mV across the two (0.5 Ohms) or 150 mA.
I am glad I did not power up with +/-45V initially because I think the one that flashed the dim bulb with the cranked bias would have been in trouble.
With both at 150 mA they sound nice. In particular I thought the bass was very good. I am not sure how exactly to describe it but perhaps I could say that the bass was very "flowing" and "musical". Is that the experience of others with the FH9?
If others buy these from AliExpress beware that the bias might not be set right (one of mine was good, the other very high) and that the soldering is messy and should be carefully checked. Perhaps turn down the bias pot before first power up just in case. I used a 60W bulb.
Can I ask what is the optimum supply voltage for 4 Ohms for this design? I do not want to use excessively high supply voltage resulting in excessive output transistor heating with 4 Ohms.
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APEXAUDIO MM38?
Hello, APEXAUDIO. Tell me MM38 working scheme. He began to make a test assembly, spread the board, assembled. And the scheme does not want to work. Power supply + -24V. Is there already a ready-made board for assembly? Here's my option that I'm testing. What can be a rake?
Hello, APEXAUDIO. Tell me MM38 working scheme. He began to make a test assembly, spread the board, assembled. And the scheme does not want to work. Power supply + -24V. Is there already a ready-made board for assembly? Here's my option that I'm testing. What can be a rake?
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Mister Miele, please tell me with which letter index it is better to use the Y, GR or BL transistors.
Thanks.
Add reverse RIAA on input.
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