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whit3rd <whit3rd@gmail.com>: Dec 30 01:37PM -0800 On Monday, December 29, 2014 4:32:20 PM UTC-8, Phil Allison wrote: > **Hi,   > what specs does an audio generator need to make it ideal for servicing guitar amps?   In the 'convenience' category, consider an iPod with a few recorded test tracks.   > 1. Ability to adjust the output level to well below 1mV and smoothly up to several volts.   Probably that means you need calibration of the output, too? A ten-turn pot and a trueRMS meter would be helpful.   > 2. Circuitry not linked to the AC safety ground to avoid hum loops.   Battery powered, then; the iPod and an old HP204C (Wien bridge) generator would fit. Or, anything with a good signal-level transformer. > 3. Have a fixed level output to connect to the external trigger input on a scope - so the trace remains in synch despite noise, hum and harmonics.   Any generator, with an external attenuator, will do that.   > 3{a}. Square wave output for checking tone circuits and amplifier stability.   Or, maybe a white-noise output? Mainly, (3) and (3a) will require an arbitrary waveform generator, nowadays; other sine/square combos are mainly inaccurate.   > 4. Frequency from 10Hz to 100kHz, preferably in four overlapping ranges. Arb or HP204 will qualify.   > 5. Amplitude remains steady when frequency setting or range is changed. Arb should do that. > 6. THD not more than 0.1% with low order harmonics.   After warmup, the HP204 will do that. Or, an expensive arb. Or, a good CD player.   I can't think of any single item that does all these (but simple, easily available equipment can do any of 'em).

Phil Allison <pallison49@gmail.com>: Dec 30 02:15PM -0800 whit3rd wrote:   > > **Hi,   > > what specs does an audio generator need to make it ideal for servicing guitar amps?   > In the 'convenience' category, consider an iPod with a few recorded test tracks.   ** Several times worse than useless.       > > 1. Ability to adjust the output level to well below 1mV and smoothly up to several volts.   > Probably that means you need calibration of the output, too?   ** Nope. Markings on a dial are plenty accurate.   > > 2. Circuitry not linked to the AC safety ground to avoid hum loops.   > Battery powered, then;   ** Nope. A plug-pak supply woul be fine.         > > 3{a}. Square wave output for checking tone circuits and amplifier stability.   > Or, maybe a white-noise output?     ** Worse than your other mad ideas.   > Arb should do that.   > > 6. THD not more than 0.1% with low order harmonics.   > After warmup, the HP204 will do that.   ** You may have one of them, but they are not plentiful worldwide.     > I can't think of any single item that does all these   ** I had to build my own ideal bench generator.   Combination of a 2Hz to 200kHz low THD oscillator, squarer circuit, 1000:1 stepped attenuator, fine frequency adjust, fixed level transformer isolated output for scope synch, another fixed output for the frequency counter.   Amplitude stabilisation is selectable between a glass bead thermistor or a diode limiter - the latter resulting in zero bounce but 0.2% THD.   Frequency adjustment uses a log wound, double gang 15kohms WW pot - for stability and low noise.   THD of the oscillator is 0.002% and with the aid of a -100dB notch filter I can test nearly anything.       .... Phil     ... Phil

RobertMacy <robert.a.macy@gmail.com>: Dec 30 07:03PM -0700 On Mon, 29 Dec 2014 17:32:16 -0700, Phil Allison <pallison49@gmail.com> wrote:     > 5. Amplitude remains steady when frequency setting or range is changed. > 6. THD not more than 0.1% with low order harmonics.   > ..snip..   You can do all this with some very inexpensive stuff. To cover the whole range from 10Hz to 100kHz [well more like 10Hz to 89kHz, or any specific smaller range you want] with a little C/C++ coding and the ASIO interface to directly work with a 24 bit soundcard, like Creative Labs EMU1212 [old and cheap], you can make a generator to pretty much accomplish everything you want.   You can drive the generator with variable amplitude, with a set of simultaneous tones that will show you passband, phase, and distortion. Use a scope, or the soundcard's inputs to get a lot of information. From memory the drive is low noise, better than 16 bits with amplitude fairly well calibrated. The output is like a pure tone accurately/repeatably set to selectable amplitude.   For passband, I suggest driving with an independent set of tones, not square wave, but tones that just cover the complete range. Monitor the amp's drive with one input, monitor the amp's output with the other, do FFT's on both channels preserving the phases. Then comparing the FFT's will provide a great deal of information regarding not just passband and phase shift, but also the amount of distortion AND noise in the amp. Plus, you can even measure the spectral noise across the band, spot excessive [well, relatively excessive] noise peaks, like AC mains related.   I have my own set up and software for this, but more readily available with a simple to use GUI try Bob Masta's SW and use your own soundcard already in your system. The SW is small and non-obtrusive to a system. I think there's a free trial time for the full blown and if purchased you keep with rights to ALL future downloads. If you opt out after trial you get to keep some features anyway, like the generator capability, a very useful generator. Also this version has LCR Meter capability.   DAQARTA v7.60 Data AcQuisition And Real-Time Analysis <http://www.daqarta.com> Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusiq generator Science with your sound card!

Phil Allison <pallison49@gmail.com>: Dec 30 08:27PM -0800 Robert Macy wrote:     > > 6. THD not more than 0.1% with low order harmonics.   > > ..snip..   > You can do all this with some very inexpensive stuff.     ** Which does NOT qualify in any way, shape or form as a BENCH AUDIO GENERATOR suitable for day in day out, knock down drag out bench repair work on smelly, dirty, rusty old guitar amps.   Bet a software wanker like YOU has never even seen the insides of one.       ... Phil

RobertMacy <robert.a.macy@gmail.com>: Dec 31 08:42AM -0700 On Tue, 30 Dec 2014 21:27:17 -0700, Phil Allison <pallison49@gmail.com> wrote:   > GENERATOR suitable for day in day out, knock down drag out bench repair > work on smelly, dirty, rusty old guitar amps.   > Bet a software wanker like YOU has never even seen the insides of one.   not a software guru, just had to learn once for a project.   I have two guitar amps. One is a Fender, and yes they are robust construcion [they're in storage and I can't remember model numbers]   My main contribution is pure analog design of a unique mag pickup. Turns a 'cheap' $1100 guitar into sounding like a $10k acoustic guitar. Absolutely the first time I've ever heard great sounding E-A string harmonics. Maybe been around too many cheap guitars, but usually I HATE when those two strings are strummed. Always sounds a bit sour, but NOT with my pickup.

Leif Neland <leif@neland.dk>: Dec 31 03:22PM +0100 John-Del kom med denne ide: >> curtains?   > Check ebay; you can find LEDS in any size, color, and power you want. Very > cheap, but they'll take a couple of weeks to get from China.   If they are mostly used for christmas decorations, there is plenty of time :-)   Leif   -- Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske beslutning at undlade det.

Cydrome Leader <presence@MUNGEpanix.com>: Dec 31 04:12AM > tidiness to the workshop.   > Has anyone else been through this process and felt better for it at the end, > or am I just going to regret doing it for years to come ... ?   I run out of space and toss stuff, but never think "I'm so glad I threw that away" years later. With no doubt many publications have not and will not be scanned, or if they are many are just unusable due to poor quality.   Good quality manuals are fun too read too. I think I still have the plain manual for a Franklin apple ][ clone that had a well presented and full schematic- it was standard docs that shipped with the machine. Apple never bothered with this.

mike <ham789@netzero.net>: Dec 30 10:32PM -0800 On 12/30/2014 8:12 PM, Cydrome Leader wrote: > manual for a Franklin apple ][ clone that had a well presented and full > schematic- it was standard docs that shipped with the machine. Apple never > bothered with this.   One problem is that some manuals were never converted to PDF and are simply not available anywhere. I wanted to program a GAL20V8. There was no information available anywhere. Fortunately, I saved the original databook.   In 2010, I replaced my carpets with wood flooring. I had to remove everything from the rooms. When I put it back, I sorted/compacted/organized the stuff. It's 2015 and the family room still looks like a hoarders fantasy with piles of stuff that I'm gonna throw out...I promise... Yes, I live alone ;-)   After marathon trips to the thrift store and/or the dump, it usually takes me about a week to realize that the thing I really, really need today was in the last purge. The opposite side of that coin is that if I hadn't purged it, I probably wouldn't be able to find it anyway.   I have most of what I need on one Anthro Cart in front of my easy chair. But I still have to move something to make a space to put down a coffee cup. If I threw away everything I haven't touched in a decade, the place would be barren.

mike <ham789@netzero.net>: Dec 30 10:45AM -0800 On 12/30/2014 6:45 AM, Sam Seagate wrote: > mA.   > I have a current resistor set for each four LED candle since each one > drew a different current amount with the same resistor. All set for 10 mA.   The reason for that was mentioned earlier. 12V is not enough voltage to reliably run 4 in series. Two sets of two in series with two resistors will be far more stable over temperature and with variations in led characteristics. The cost is twice the energy consumption.   You might find that 3 in series at 15mA gives you more light and only 50% energy penalty. It's always something... > I'd like to place the polyswitch at the power supply output before it > branches off to either the two or four candle arrangement.   > Any tips here would be helpful.   On the surface, it seems silly to replace incandescents with LED, then use an incandescent as a current limit. BUT Incandescent lamps make excellent positive-temperature-coefficient resistors. You just use a 12V lamp. Pick the lamp current so that, when you short the output, the lamp doesn't overload the power supply. Can get them at any auto store and they last forever in this mode.   The polyswitch has a hockey-stick resistance curve and is clearly a superior device for this application. But you might already have a bulb in a drawer somewhere. I just measured a 1458 lamp. It drops 0.44V at 40mA so you'll need slightly smaller series resistors...or just not worry about it. Probably won't work well with 4 LEDs in series. Higher current incandescent will have lower voltage drop at 40mA   You will still want to use two sets of two series LEDs/candle. There will be some interaction between candles if you plug/unplug one.   And you get a "short indicator" for free.     Life is a tradeoff...or two...

Sam Seagate <saseag44419@yahoo.com>: Dec 30 07:48PM -0500 On 12/30/2014 01:45 PM, mike wrote: >> 10 mA.   > The reason for that was mentioned earlier. 12V is not enough voltage to > reliably run 4 in series.   I wasn't clear on your reason. So far, so good. The 12 V input divides down to 3V per bulb in series with each holding at the 10 mA level.   > resistors. You just use a 12V lamp. Pick the lamp current so that, > when you short the output, the lamp doesn't overload the power supply. > Can get them at any auto store and they last forever in this mode.   I like the lamp idea and actually forgot about it. I used to use such a set up with a high voltage circuit. Been so long ago that I forgot about it. I'll have to see how much total current the circuits use and then try out a bulb. I don't see any reason I couldn't place the bulb at the power supply point before it branches off to the 2-4 candles. Would certainly be a lot easier than trying to wire one up per candle. Thanks for the idea here!   > worry about it. Probably won't work well with 4 LEDs in series. > Higher current incandescent will have lower voltage drop at 40mA   > You will still want to use two sets of two series LEDs/candle.   So you're saying I would have been better off with two sets of two LED's in series per bulb. A series-parallel combination, but that would have required more resistors to set the current correctly per set.

mike <ham789@netzero.net>: Dec 30 10:03PM -0800 On 12/30/2014 4:48 PM, Sam Seagate wrote:   > So you're saying I would have been better off with two sets of two LED's > in series per bulb. A series-parallel combination, but that would have > required more resistors to set the current correctly per set.   I'm saying that if you start with 12.0 volts and drop .44V across the bulb and need 3V per LED...you don't have it. The purpose of the resistor is to normalize the current given variances among the LEDs. With 4 in series, the resistor gets so small that it doesn't normalize very well.   Sure, the candles may light, but you'll get a different intensity per candle and the resistance of the bulb will create interaction between the candles.   I'm suggesting that if you put two LEDs in series with a resistor. put two of those series combinations in parallel in each candle put the candles in parallel put one bulb at the power source You'll be at the sweet spot of low cost, long life, fault tolerant, happy wife and just works.   In reality, you can probably tweak it to work with 4 in series.   What I'm trying to teach you, and people reading this next year, is the importance of system design where the performance is largely independent of the parameter variations of the devices. And single point failures will not set anything on fire. And if you built a thousand of them, they'd all perform the same. And if you substituted a red LED, it'd still work the same. And if you put it outside in below freezing temperatures, it'd still work the same. And if your power supply was 11V or 13V, it'd still work the same. And the margins are so wide that you'd never have to test any of that. It will just work. The obvious tradeoff is that it takes twice the energy to run it.   We haven't discussed your wall wart. If it's electronically regulated, it's likely current limited to a level that protects itself and won't supply enough current to set your house on fire. If so, forget the bulb/polyswitch and let the wart take care of the current limit.   If you wanna discuss more "clever" designs, we can do that. If you want a bullet-proof design that anybody could build using random LEDs without any test equipment or exotic devices, this is my recommendation.   Are we having fun yet?

sam@repairfaq.org (Samuel M. Goldwasser): Dec 30 05:48PM -0500 > diameter. It also talks about a "new high-frequency rating" for > rectangular pulses, but that seems to have more to do with current > and pulse shape, than voltage.   Yes, I beleive that's the one I found. I suppose it's possible this unit that part and they simply labeled a much better part "N" to satisfy a specific order.   Thanks for checking!   -- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html   Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

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