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Old 14th January 2012, 08:45 PM   #481
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by kenpeter View Post
Yeah, but put your style of sensing between an OTA and rails,
and feed back to Iabc. I think you might have a circlophone?
Yeah, until now I had not realized it, but stated that way, it seems obvious.
Quote:
An actual circlophone, though with chip limited dissipation.
Maybe enough for a headphone or something?
Could be combined with a Kuroda-like scheme, to increase the power

Quote:
It would be helpful if an OTA fully brought out the two currents
as differential drives, rather than collide them inside the chip.
Maybe some existing OTA already has a differential current
output configuration suitable to drive something external?
If such a chip exists, I am unaware of it, but searching...
Maybe this is doable with a conventional OTA as a CFP?
By abusing the currents to either rail as-if they were drives...
There are a number of flavors of current conveyors, perhaps one variety would be suitable

Quote:
You are using class B, current sensing, and the threshold of
a logic based rule to nudge the bias up to ideal AB + CCS.
I am using enriched class A, current sensing, and threshold
of a curved sum rule to nudge the bias down to AB + CCS
(very non-ideal AB+CCS rule, but also very low part count).
Same exact things, except completely different.

Once you breach the OTA chip no-no, might as well bust
out with LM3Whatever output devices. I know you gone
there before too, so no playing innocent...
Hours of endless fun in perspective....
Quote:
other notes:
The current seen by R8, R11, R24 is low because of the paralleled heavy duty schottky diode.
Good point Daniel: the Circlophone is designed to use only 0.25W resistors.
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Old 14th January 2012, 11:27 PM   #482
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Default Yet another PCB revision

I slightly modified wakibaki's PCB for my next build. I attached drivers on pcb (requires isolator if using heatsink bar), just remained 6 pads for output transistors. I saved up two wire jumpers

I populated silkscreen respecting original schematic and added some useful comments.

For those who interest for build one of the PCBs shared in this topic (including this one), posts #56 , #182 , #25 contain useful guide.

Hope you 'enjoy the silence' of Circlophone.
Attached Images
File Type: jpg drawing.jpg (154.0 KB, 593 views)
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File Type: pdf drawing2.pdf (121.3 KB, 155 views)

Last edited by terranigma; 14th January 2012 at 11:35 PM.
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Old 15th January 2012, 06:09 AM   #483
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Quote:
Originally Posted by kenpeter View Post
Once you breach the OTA chip no-no, might as well bust out with LM3Whatever output devices. I know you gone there before too, so no playing innocent...
Why don't we try something more useful instead?

A tidy compact discrete parallel no-ballast power fet output device daughtercard seems useful, like a discrete alternative to. . .
TDA7293V/TDA7294S with the input shorted set to unity gain output buffer, uses slave mode modular parallel listed in the datasheet. The chip is neither tidy nor significantly powerful, but it can parallel without ballast. Can you do it discrete instead?

I also think it is interesting to possibly improve the efficiency a bit so as to reduce the popularity of fan cooling.

I think it would be interesting to see a Small Signal preamp or Headphone sized Circlophone, perhaps with a Jfet input.
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Old 15th January 2012, 08:58 AM   #484
heinz is offline heinz  Germany
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I am very sorry, but there is a mistake in PCB posted in 395. Please do not build it that way. (Error: pin of C12 has a short to the jumper wired).
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Old 15th January 2012, 11:59 AM   #485
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Quote:
Originally Posted by Elvee View Post
Good point Daniel: the Circlophone is designed to use only 0.25W resistors.
I'm working on a bit of derating at this time and wonder if I've braced up the 25w design to correctly support 180w. Well, there's somewhat a question if it is left switched on for. . . 30 years.

Does it remain true in all conditions, such as 0.25w resistors (and diodes too) never exceeding 42% of their nonstop current capacity and never exceeding their surge capacity, despite my 86v unregulated supply? Or the easier version of the same question: For which resistors is there any excuse to use 1/2w capacity?

How much amperes is seen at D4 when the amplifier is doing 180 watts?

What is a non-zero value for C11 if output devices are TIP35C if I just wanted to know parameters even if it is tiny picofareds? Does having C11 make "reduced risk" of output device explosion?

Which of the tiny capacitors is it important to upgrade and not use ceramic disc?

Can flyback diodes be used for output device protection?

Is there a capmulti accessory could be made with leftover driver compliments (BD139, 2SD669, 2SC2238, 2SC5171, 2sc2073) and leftover output compliments (MJ2955, MJL21193, MJW21195, TIP36C) that aren't used in Circlophone?

P.S.
Progress report:
Accidentally purchased enough parts for five Circlophones, and can now evict the LM3886 infestation from my favorite old stereo receiver.
Still awaiting BC556B or BC560 and any of 2SC1845, 2SC2240, 2N5551 despite duplicate orders, although plenty of other interesting parts arrived.
From Bigun's modular schematic, figured out how to do the rightmost third on a tiny vertical daughtercard easily held by the to220 shottky's.
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Old 15th January 2012, 12:33 PM   #486
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Quote:
Originally Posted by terranigma View Post
I slightly modified wakibaki's PCB for my next build. I attached drivers on pcb (requires isolator if using heatsink bar), just remained 6 pads for output transistors. I saved up two wire jumpers

I populated silkscreen respecting original schematic and added some useful comments.

For those who interest for build one of the PCBs shared in this topic (including this one), posts #56 , #182 , #25 contain useful guide.

Hope you 'enjoy the silence' of Circlophone.
I like it. You going to build it?
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Old 15th January 2012, 01:12 PM   #487
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Quote:
Originally Posted by odysseybmx414 View Post
I like it. You going to build it?
Of course, at least two channels. I wonder if I match that silence again. It was very abnormal and I think there is something about this pcb's layout. Surrounded ground? 45 degree intersections and paths? I don't know.

Last edited by terranigma; 15th January 2012 at 01:20 PM.
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Old 15th January 2012, 03:26 PM   #488
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by danielwritesbac View Post
I'm working on a bit of derating at this time and wonder if I've braced up the 25w design to correctly support 180w. Well, there's somewhat a question if it is left switched on for. . . 30 years.
180W on a single pair of transistors is a really tall order ....

Quote:
Does it remain true in all conditions, such as 0.25w resistors (and diodes too) never exceeding 42% of their nonstop current capacity and never exceeding their surge capacity, despite my 86v unregulated supply? Or the easier version of the same question: For which resistors is there any excuse to use 1/2w capacity?
The resistors dissipating the highest power in the whole circuit are R8, R11 and R24.
Normally, their dissipation should remain well below 150mW, unless the schottkys you use are really lousy (or are non-schottky).
R17 can be larger than strictly required by power considerations, it will be beneficial.

Quote:
How much amperes is seen at D4 when the amplifier is doing 180 watts?
Approx. 3.2A average

Quote:
What is a non-zero value for C11 if output devices are TIP35C if I just wanted to know parameters even if it is tiny picofareds? Does having C11 make "reduced risk" of output device explosion?
C11 is required if the OP devices have a Ft in excess of 20MHz.
Some picofarad will have no effect at all.
With or without, there isn't more or less risk of device explosion.
In general, it can affect the cleanliness of the transitions, and at the extreme, it can avoid oscillations, but of the marginal variety, not susceptible to damage tweeters or the amp itself

Quote:
Which of the tiny capacitors is it important to upgrade and not use ceramic disc?
Ceramic disc are advisable everywhere. Very low grades like Z5U should be avoided for C6
Quote:
Can flyback diodes be used for output device protection?
You mean antiparallel diodes on Q8 and Q10?
Any diode, even a 1N4004 would be OK, you can use "flyback diodes", whatever that is.

Quote:
Is there a capmulti accessory could be made with leftover driver compliments (BD139, 2SD669, 2SC2238, 2SC5171, 2sc2073) and leftover output compliments (MJ2955, MJL21193, MJW21195, TIP36C) that aren't used in Circlophone?
You mean a capacitance multiplier?
I am not too enthusiastic about that: the rails have to be decoupled by good physical capacitors of at least 47µ, and I do not know how the combination of an emitter follower directly connected to a low esr cap would behave.
One could have unpleasant surprises with the resulting impedance.

Quote:
I wonder if I match that silence again. It was very abnormal and I think there is something about this pcb's layout.
I am beginning to wonder if a side effect of the quadrature servo couldn't be an indirect reduction of the differential noise level.
The quietness is really out of the ordinary, and I think it deserves some investigation.
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Old 15th January 2012, 06:23 PM   #489
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Quote:
Originally Posted by Elvee View Post
C11 is required if the OP devices have a Ft in excess of 20MHz.
Some picofarad will have no effect at all.
With or without, there isn't more or less risk of device explosion.
My last builds are using Sanyo 2SD1047's (15mhz) and they aren't contain C11. This setup is in usage at least for 4 weeks without any problem. I tested C11 with this setup and I felt slight change in sound signature. Then, I decided to not to use C11 with this setup. This impression is totally related with my setup and may vary with some others.

My first build was blowed up due to insufficent cooling and my speakers has survived after failure of output transistors. So Elvee, in case of a failure at power transistors committed by any reason, is there a risk for throwing rail voltages to the speakers? Yes, Circlophone is such an amp like many others and may contain common risks along with them. Your opinion about applicable dc-protection methods for Circlophone may involve us.

Thanks.
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Old 15th January 2012, 07:13 PM   #490
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
My first build was blowed up due to insufficent cooling and my speakers has survived after failure of output transistors. So Elvee, in case of a failure at power transistors committed by any reason, is there a risk for throwing rail voltages to the speakers?
You have been very lucky to get away with your speakers intact.
The circlophone is like any other class B amp, when one output device fails, one of the rails becomes connected to the speaker. Perfect symmetry doesn't extend to failure modes, except when you have a lot of luck.
That's why I think Daniel is playing with the devil trying to extract 180W out of two miserable transistors.
Quote:
Yes, Circlophone is such an amp like many others and may contain common risks along with them. Your opinion about applicable dc-protection methods for Circlophone may involve us.
I think protection measures are sensible, good speakers are something precious and need to be protected.
A simple fuse is enough, since there is no power on or off thump, but the fuse should be inside the feedback loop: that will make it totally transparent from an audio point of view, but it will protect your speakers the same.
That's simple, cheap, effective, and very reliable: exactly want you want here.
A sophisticated protection that refuses to connect your speakers because of some minor malfunction is very frustrating, and it is worse when it misses the coach for the one and only occasion it is really needed.
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