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Progress so far

Posted 6th January 2012 at 12:02 PM by rjm (RJM Audio Blog)
Updated 7th January 2012 at 02:00 AM by rjm

The first stage is getting the power supply installed and running. That's the little board by the transformer, which just has the diodes, main filter capacitors, and isolation resistors on the voltage rails. The case top lid is transparent plexiglass, so the internals are lit by three white LEDs to show off, and light the control labels, which are printed on the top lid rather than the front and back sides of the case.

You'll notice I have followed the instructions and removed the plastic covers on the electrolytic capacitors.

For the record I do think they sound better that way, I just normally can't be bothered as, for example, my phonoclone 3 boards have 28 of them and I consider the exposed metal surfaces a bit of a safety issue as well.
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47 Labs 0247 unboxing, part deux

Posted 5th January 2012 at 10:29 AM by rjm (RJM Audio Blog)

My kit was missing the amplifier circuit boards! So many other neat stuff distracted me from this vital fact!

So far I've wired the AC power line components, transformer, and the power supply board. It's slow progress, mainly for wanting to be sure of getting it right the first time. It's dense and fiddly, desoldering stuff in there to fix a ****-up would not be pleasant work at all.
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Posted 3rd January 2012 at 04:44 PM by rjm (RJM Audio Blog)

If we accept that conventional wisdom that the audio bandwidth extends from 20 Hz to 20 kHz, a good rule of thumb for the f(-3 dB) high and low cutoff points of the frequency response of each audio circuit element is 5x the bandwidth, or 4 Hz to 100 kHz. In practice most designs tend to shift that range a little to the higher frequencies, so perhaps 5 Hz - 200 kHz, or 4 - 250 kHz.

Personally I "tune" my circuits to 4 Hz. That is, the time constants are adjusted to about 4 ms. Capacitance is usually cheap enough to go even longer, but the influence on sonics is typically net negative.

The high frequency side is more interesting, since many circuit elements naturally run into the megahertz range, the the question is do you actively try to prevent that, and if so, where and how?

The biggest issue is bypassing: a small value electrolytic (100 uF) is probably fine up to 100 kHz or so, but quite useless at 2 Mhz. The textbook solution is...
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How much power is enough for an amp?

Posted 2nd January 2012 at 02:09 AM by alexcp (My DIY projects)

Bruno Putzeys posted:
About power ratings, well... Normal "critical listening" levels hover around a long-term average of 85db SPL at the listening position. If we're assuming uncorrelated signals (rather inaccurate assumption but it'll do for the purpose) that is 82dB SPL for each speaker alone. Crudely calculating back from a 2m listening distance to the 1m standard measuring distance that's 88dBSPL, one speaker, one meter. It's not unusual for speakers to have an efficiency of 88dB/1w/1m so 1W is roughly the required amplifier power.

The current crop of unlistenable hypersquashed pop music has a peak to average range of around 4dB. So all it takes to reproduce pop at a reasonable level without clipping is a 4dBW (2.5W) rated amp.
Before the loudness war got into swing (say until the early 90's) peak-to-average ranges up to 14dB could be found in mainstream music. To play Sultans of Swing at the same average level requires an amp rated at 14dBW
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Posted in Speakers
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Improved current source

Posted 2nd January 2012 at 12:18 AM by klewis
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Solid state relay

Posted 30th December 2011 at 10:55 PM by klewis
Updated 3rd January 2012 at 02:43 PM by klewis


Pavel's Scheme
Also see post #340, increase R1 to 100k and C3&4 to 47uf
recommendation for mosfets: #314
In general, you are seeking for a MOSFET with very high Vdsmax, very low Rdson and very high Idmax. Regarding Vdsmax, it must be higher than the sum of positive and negative supply rail voltage, and the output should be provided by clamping diodes connected to supply rails, reverse polarized. My tips are

Type Vdsmax Rdson Idmax
IRFB1227 200V 0.0197ohm 130A
IRFP90N20D 200V 0.023ohm 94A
IRF3710ZG 100V 0.018ohm 59A (too low Vdsmax to me)
IRFS59N10D 100V 0.025ohm 59A (too low Vdsmax to me)
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Mk3: How to do this...???

Posted 30th December 2011 at 08:45 PM by cberger
Updated 30th December 2011 at 08:47 PM by cberger

hmmm...the plan calls for 5 degree angles for some cuts. How to do those? Just sand it away?
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Posted in Mk3
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it's xmas time

Posted 30th December 2011 at 08:30 PM by cberger
Updated 30th December 2011 at 08:48 PM by cberger

So I finally decided to build my first set of speakers: The Frugel-Horn mk3.
  1. Fairly high WAF
  2. Looks good (see point 1)
  3. Can be built with "cheap" components
  4. Reasonably challenging wood work
  5. full range driver = no crossover needed
Most of the stuff I ordered so far I ordered based on recommendations / suggestions from the people here like Planet10 Dave, ChrisB and others.

Some stuff that I ordered on Monday arrived already :-)
2 CHR-70 Drivers
CSS UltraTouch insulation

Just now I ordered some terminals, a circle jig (jasper #400), and Acousta stuff
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Posted in Mk3
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Pass B1 buffer

Posted 25th December 2011 at 11:53 PM by klewis
Updated 26th December 2011 at 02:47 PM by klewis

Post #166 board layout
omron G6H2 12v relays
Motorized alps pot m=250467804650
Post #1062 for relays
Post 1031 cap tweak
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Tapped Horn

Posted 22nd December 2011 at 02:34 PM by DougL

Found this Discussion and resources:
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