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Old 26th June 2012, 04:17 AM   #321
RNMarsh is offline RNMarsh  United States
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I found an eBAY low distortion sine wave signal source on pcb, loaded/built for $39. The fixed 1 KHz signal only has .00005% thd. That works for me. Ordered 2 of them. Look under electronics test equipment.
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Old 26th June 2012, 04:21 AM   #322
RNMarsh is offline RNMarsh  United States
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Be sure the series L of the supply to the circuit are as low as possible. Short, low L/Z distribution is best. One way is to make a wide, closely spaced traces for low L, high C pcb path. For DIY'ers this also helps prevent ringing and possible oscillations in wideband circuits. At low freqs small series L may not matter. However, at low freqs the DIY'er needs to keep signal and power returns from one another.

The more advanced forum members might want to look into the books by Don White (ICT) on EMI control et al as many of the digital products, if sold, would have to pass UL EMI/RFI or other countries requirements and it starts at the pcb to contain. Not for this Headphone amp subject but think if you do such work, it just becomes habit when designing pcb for anyting else - audio, even..... just becomes habit.

Back on your heads !

Last edited by RNMarsh; 26th June 2012 at 04:43 AM.
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Old 26th June 2012, 05:09 AM   #323
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by rjm View Post
Pure awesomeness.

Though I thought "moating" (so its a verb, who knew?) was pretty common in DAC/ADC layout design. In analog, also: RNMarsh's example above does, and, heck, my boards too!
??? if you cut a ground plane up into areas, you increase the inductance (Z) of that ground plane. This is often seen when there is one ground plane on the same level as the signal traces. Better to have ground plane on seperate pcb level or opposite side from singal traces. Not the same thing here with seperate ground planes.

Last edited by RNMarsh; 26th June 2012 at 05:13 AM.
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Old 27th June 2012, 05:36 PM   #324
RNMarsh is offline RNMarsh  United States
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Originally Posted by jcx View Post
only 1-2 slides mention <100 kHz - which I think is the 1st order of concern for audio electronics layout, wiring - "down there" plane partitioning, slots, moats do work - if you want to control the current paths you have to do it with conductor geometry, explicit pwr return routing - can't rely on proximity effect, image currents in planes - Resistance matters

the laminated bus rails do look like good possibilities at PA levels but I've not used them yet - DIY with Kapton and Cu roof flashing or sheet/bus bar stock?

(I have professionally designed Industrial Instrumentation for >2 decades - including strain gage instrumentaiton with Ethernet, USB 2, 100 MHz processors, DSP within inches of Av 4000 amplifiers, 16-20 bit ADC)




I worked up this simple sim for the xfmr CT current - some have scoffed, use faulty reasoning about circuit symmetry to claim the CT is "clean"

load on PS rails simulated with Isources - Class A bias conditions

busy plot but shows how a load frequency differing from line multiple can give large CT currents as each polarity supply cap is unevenly discharged/recharged

look at the Red R-ct trace spikes, C1,2 currents

but these nonlinear pulse contaminated currents sum to the mostly linear load current
the R2 current is equal to the (inverse) load current - is as linear as your load's impedance - can be very good for headphones
No complainst here about what you have said..... remember though - a circuit capable of 1MHz and beyond can become unstable with uncontrolled stray L/c in the layout.

[My background is in RF/microwave precision measurments (secondary standards lab), Power systems and their grounds from 230Kv to 13.8KV to 480 v/3000A buss and their grounds and for pulsed power experiments of 10 megaWatt levels. Grounding of complex systems with computer facility system grounds, control system grounds, ac/dc/pulsed power grounds all together in large experimental facilities. Instrumentation for underground nuclear 'events' back in the day. Ground planes for experimental plasma excellerator using Maxwell cap banks discharging 100Kv into gas/plasma/ emi/rfi/emp etc etc etc. I understand the grounding issues from power to microwaves and how they interact in a system. --- just in case anyone is interested. ]
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Old 27th June 2012, 06:05 PM   #325
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Interested? Ohhh yeah. I'm actually re-working a little headphone chip amp based on what I've learned here. I've eliminated some 'wrongs' thanks to the tips on here and reading up on some stuff rjm has on his site. Drinking it down!
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Old 27th June 2012, 06:41 PM   #326
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Quote:
Originally Posted by RNMarsh View Post
Maxwell cap banks discharging 100Kv into gas/plasma/ emi/rfi/emp etc etc etc.
So that's how a flux capacitor works, didn't know that.
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Old 27th June 2012, 09:46 PM   #327
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Quote:
Originally Posted by RNMarsh View Post
No complainst here about what you have said..... remember though - a circuit capable of 1MHz and beyond can become unstable with uncontrolled stray L/c in the layout.

[My background is in RF/microwave precision measurments (secondary standards lab), Power systems and their grounds from 230Kv to 13.8KV to 480 v/3000A buss and their grounds and for pulsed power experiments of 10 megaWatt levels. Grounding of complex systems with computer facility system grounds, control system grounds, ac/dc/pulsed power grounds all together in large experimental facilities. Instrumentation for underground nuclear 'events' back in the day. Ground planes for experimental plasma excellerator using Maxwell cap banks discharging 100Kv into gas/plasma/ emi/rfi/emp etc etc etc. I understand the grounding issues from power to microwaves and how they interact in a system. --- just in case anyone is interested. ]
Ah, thanks for that background! I'll remember and now know where to ask my questions!

I have played with 60Kv into laser capacitor banks in my career. But what specifically is a Maxwell capacitor bank? Google comes up with a brand name, and I presume that is not it.

There actually is such a thing as a flux capacitor! But it uses magnetic flux and behaves as a capacitor not an inductor! The phase angle is what you would expect from a capacitor because of the way the field is loaded!
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Old 27th June 2012, 11:24 PM   #328
RNMarsh is offline RNMarsh  United States
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Originally Posted by simon7000 View Post
Ah, thanks for that background! I'll remember and now know where to ask my questions!

I have played with 60Kv into laser capacitor banks in my career. But what specifically is a Maxwell capacitor bank? Google comes up with a brand name, and I presume that is not it.
Maxwell Technolgy out of san diego have the nitch on HV discharge caps... yes, were also used in flash lamps for pumping lasers to higher energy levels.
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Old 29th June 2012, 06:23 PM   #329
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Anything objectionable about this:

Click the image to open in full size.
No. Thats fine. can also put a bypass cap across the 10 ohms so the ground is low at Hf and only affective at 'hum' frequencies.
Also can try using shunt caps, as shown on pcb, withOUT lowest esr for damping, if needed.
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Old 3rd July 2012, 06:10 PM   #330
sonidos is offline sonidos  United States
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Default resistor wattage

@jackinnj

What wattages did you use on the BJTs? 1 W enough? Looks like you put some Dales on your proto.
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