Hi Leif, I'd love to see a picture of the PSU you've build, sounds very intresting. What caps/values did you use?
of course.
Lets start with the case home made. It is really huge.....
I'm a big fan of DIY chassis projects - assuming one has the tools needed. Yours appears clean and efficient - nice classic style. I might suggest some twisting and routing separation (mostly aesthetics) of the wires coming off the PS, but if you don't have any hum/distortion that's not an issue. Thanks for the pics.
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I've been reading about this amplifier for awhile and have been collecting components and knowledge on and off over the past couple of years haha. I'm an electronic novice and I plan on starting my build before the year end. I have some questions and could use a sanity check to see if I'm doing the right calculations and making the right assumptions.
I'm fairly certain I'm going to need an active preamplifier. I came to the conclusion from some of the specs posted about the amplifier, namely 25 watts output at 8ohms and 15dB of gain.
Using ohms law V² / 8 = 25 I see it will take roughly 14.14 volts for max output.
To find the input voltage required to get 14.14 volts with 15dB of gain I used the following formula:
15dB = 20 log (14.14 vout/x vin)
And see that I would need roughly 2.5 volts to drive this amp at full power. Is this correct? I am fairly certain my phonostage cannot get close to 2.5V and thus would need an active preamplifier. If this is the case, do you have any suggestions on which preamp I should build?
My second question is how do I know when this amplifier is clipping? Or more importantly, know before it's actually happening? I know tweeters can be easily damaged by it.
I have tried to answer these questions before posting, but no luck, so I apologize for asking such basic questions. Thanks!
I'm fairly certain I'm going to need an active preamplifier. I came to the conclusion from some of the specs posted about the amplifier, namely 25 watts output at 8ohms and 15dB of gain.
Using ohms law V² / 8 = 25 I see it will take roughly 14.14 volts for max output.
To find the input voltage required to get 14.14 volts with 15dB of gain I used the following formula:
15dB = 20 log (14.14 vout/x vin)
And see that I would need roughly 2.5 volts to drive this amp at full power. Is this correct? I am fairly certain my phonostage cannot get close to 2.5V and thus would need an active preamplifier. If this is the case, do you have any suggestions on which preamp I should build?
My second question is how do I know when this amplifier is clipping? Or more importantly, know before it's actually happening? I know tweeters can be easily damaged by it.
I have tried to answer these questions before posting, but no luck, so I apologize for asking such basic questions. Thanks!
You are right and it is posted many times in the various F5 Threads.
Your pre-amp could have switchable gains of +6dB and +12dB. That will cover all Sources with maximum outputs of 600mVac to 2500mVac
And would be nearly adequate with sources down to 300mVac. Just can't reach clipping but possibly loud enough.
The rise in "not nice" sound as volume pot is turned up, is the operators best guide to avoid audible clipping and pushing drivers too hard.
It sets in surprisingly early.
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You are correct, you told us years ago! I didn't intend to clutter up the forum.
Even though the math and theory is beginner level, I am somewhat pleased I was able to calculate the correct answer by myself instead of just being told. I appreciate your patience in helping me.
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with +0dB of closed loop gain, there will be an extra 16dB of feedback.
That will probably require major work in determining new/additional stability compensation components.
hello
have built a pair of F5Turbo monoblocks
after months of struggle they´re up and running with choke input psu
bias is 350mA across 1R
32vdc from psu and offset is cruising around +/- 3-4 mv
sink temp is below 50C
yesterday I thought I´d try to replace R2=47K input resistor with a grid choke and the funniest thing happens....the offset goes bananas above 1v and continues so during the warmup period
but the swings rapidly narrows in and finally settles when approaching target bias
will try again tonight, but does anyone have a clue what happens?
the grid choke is 8000H and 1,8mA
not sure about dcr, but probably very low
all input is of interest...
best
Leif
have built a pair of F5Turbo monoblocks
after months of struggle they´re up and running with choke input psu
bias is 350mA across 1R
32vdc from psu and offset is cruising around +/- 3-4 mv
sink temp is below 50C
yesterday I thought I´d try to replace R2=47K input resistor with a grid choke and the funniest thing happens....the offset goes bananas above 1v and continues so during the warmup period
but the swings rapidly narrows in and finally settles when approaching target bias
will try again tonight, but does anyone have a clue what happens?
the grid choke is 8000H and 1,8mA
not sure about dcr, but probably very low
all input is of interest...
best
Leif
I found it but want to make an unbalanced one.Euvl does not guarantee to work it
I want to run 4 ohm speakers with higher class a power.This is why i want to have an amp with lower voltage and higher bias.Normal f5 amp does not give high class a power to 4 ohms as much as it gives to 8 ohms
I want to run 4 ohm speakers with higher class a power.This is why i want to have an amp with lower voltage and higher bias.Normal f5 amp does not give high class a power to 4 ohms as much as it gives to 8 ohms