C101 and C201 I just measured ?
Right Channel
After cap = 04.0mv slowly dropping lower over time
Before Cap = 7.3v
Left Channel
After cap = 24mv slowly dropping over time
before cap = 12 or 13v but is slowly changing over time too
I guess if i left it on some time it would become stable but it doesn't look to good!
Right Channel
After cap = 04.0mv slowly dropping lower over time
Before Cap = 7.3v
Left Channel
After cap = 24mv slowly dropping over time
before cap = 12 or 13v but is slowly changing over time too
I guess if i left it on some time it would become stable but it doesn't look to good!
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The BA-3 front end has gain, so it's actually much more appropriate to drive a F5T than the B1.
You would need to adjust the gain down for best results, but that's a ratio of 2 resistors. Easy. (I don't remember which off the top of my head...)
The B1 has no gain. (actually just a teensy bit negative, but it's essentially neutral) For most power amps, which need about 1-2 volts to full output, most modern sources (Computer, iPod, CD player, etc...) have enough oomph to drive the amp all by itself -- the B1 adds attenuation and impedance adjustment. Nice!
The F5 amps need about 4V to full output. So your sources (and through the B1) will not have enough swing to get the F5 all the way up... a little bit of gain would be necessary to do get full power.
The F5 amps need about 4V to full output. So your sources (and through the B1) will not have enough swing to get the F5 all the way up... a little bit of gain would be necessary to do get full power.
The B1 has a very wide voltage range from about 12V minimum to somewhere in the region of 36V at the top end. The optimum voltage has been discussed many times, I run mine at 18V, but it will work fine between the voltages above.
Already mentioned above, the DC voltage before the output caps should be about Vcc/2 with well matched FETs.
BUT, you should always arrange for the pre-amp (B1) to be ON before it is connected to the power amp input.
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... Walter
There is another solution - if you don't want to have an active preamp to get the signal to full output, make the amplifier more sensitive so your 1.5V can drive the amp to full output.
It's very simple - make the feedback resistors (R7, R8, R9, R10) 220ohm. This will increase the amps gain at the expense of a little feedback and you can now clip it with a CD player or computer.
yeah, but that's a mini F5 in front of my big F5
Too many components....there must be a simpler circuit, like B1, to give that 3 times voltage gain?
Rixsta the PCB is listed under 'preamplifiers'.
Thanks
Im with you on that, thinking along those lines simple circuit.
Post 53 of this thread juma has a great simple pre that I have been using for some time. I have it at one input of my dcb1 to help my iPad out.
http://www.diyaudio.com/forums/pass-labs/125893-preamp-ideas-f5-6.html
http://www.diyaudio.com/forums/pass-labs/125893-preamp-ideas-f5-6.html
So Im thinking that the B1 I got was from china, possibly dodgy fake transistors causing the problems. SO before i give up on B1 am going to order some 2SK170 from germany, no wonder the sound didn't sound good before!
Will check the resistors before ordering the new Fets.
Regarding this suggestion on increasing the amp's gain, by doubling the values for the feedback resistors.
I assume the only penalties are an increase in harmonic distortion (which is aleady quite low) and an increase in output impedance. Has any one actually done this and measured it. Or is there a calculation that will give me a ballpark estimate.
Thanks