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Old

Deeper into variant one

Posted 12th January 2012 at 10:47 AM by Wolfsin (SE-BRGD a bridged mono 'wire')
Updated 12th January 2012 at 10:54 AM by Wolfsin

Will be fleshed out with image of reversed wiring for inverted channel
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Old

Mutants

Posted 11th January 2012 at 10:16 PM by Wolfsin (SE-BRGD a bridged mono 'wire')
Updated 12th January 2012 at 10:13 PM by Wolfsin (rename second variant)

When asked where frankenwires were to be filed, qusp replied

Quote:
Originally Posted by qusp View Post
file it under mutants...

...and their amplifiers
There are two variants of what I originally called the SE-BRGD frankenwire. Both start as rework boards. One gets a pair of LME49860 to replace the LME49990 using the simple surgery below. The + and - inputs to the second 49860 are reversed and resistors adjusted so the gain is equal on both sides. The effect of that reversal is to invert the signal on the second leg so it becomes a mono amp, whose differential outputs are ready to bridge one can.

The second variant, more correctly referred to as the BAL-BALM, requires no rework surgery (so could just as well not even be a rework pcb), just the addition of a tiny adapter to mount an opa1632 and leave off the 49990s. Power connection is not as clean as the first variant. It is effectively half a BAL-BAL, perfect for the audiophile with only one ear.

...
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Old

The Brush Development Co. BL-905. What is it?

Posted 9th January 2012 at 10:41 AM by tonekwest

I have what looks to be an amplifier of some sort and was wondering if any of the forum members may be familiar with what I actually have. So far, my search results have come up with nothing.
It is from the Brush Development Company. Type BL-905. Will try to post list of tubes in the unit tonight.
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Old

one small step...

Posted 8th January 2012 at 12:58 AM by cberger

... for mankind, but one giant step for me

After sucking big time in Halo, In felt like I needed some positive experience today, so I hooked up my CHR-70s to my trusted, semi-retired NAD.
Took about 1h, involving looking for my cutter to cut some old CAT5 and strip the wires, do the actual cutting and stripping, hooking up the receiver, connecting the cables and turning on the whole assembly.
And *drum roll* FM94.9 played Motorhead's "Ace Of Spades" Can it get any better???
First listening impression: sounded a bit like AM radio, but given the way the drivers are hooked up I'm not really surprised...

in other news: parts express delivered some fluff and my terminals
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Old

SouthSemi modified F2J Clone

Posted 7th January 2012 at 09:13 AM by Tea-Bag
Updated 21st November 2010 at 12:46 PM by Tea-Bag

This last weekend I replaced the IRFP240 in my F2 Clone with the R100 SouthSemi Power-JFET.

tubes-guy used psychic powers to control my mind and force me to do it.

The bias dropped off the bat. I re-biased and gave it an A-B listen to the standard channel. Seemed to be a bit 'cleaner' sounding the the default channel.

Nelson has recommended the following changes to the circuit, which I hope to implement soon. I will be re-wiring these on Peter Daniels boards.
The Peter Daniel boards are still available I believe.
http://www.diyaudio.com/forums/group...group-buy.html

Papa sayz...

The F2's that I have updated with the JFETs need the
following changes:

R6 = 47k (changed to 8.2K of FW Site)

C1 = 10 uF

Z1 removed

The potentiometer must be re-adjusted for minimum
distortion at 4.5 watts (symmetric clipping) and readjusted
...
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Old

Progress so far

Posted 6th January 2012 at 12:02 PM by rjm
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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Old

47 Labs 0247 unboxing, part deux

Posted 5th January 2012 at 10:29 AM by rjm

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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Old

Five-times-bandwidth

Posted 3rd January 2012 at 04:44 PM by rjm

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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Old

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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Old

Improved current source

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

http://www.diyaudio.com/forums/solid...urce-sink.html
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