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Old 20th April 2012, 09:53 AM   #31
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Hi Terranigma,
I'm not sure if I understand what you mean by dead silence "issues". My Circlophone is dead silent at full volume with my ear up against my speaker cones. I don't consider that an issue Other builds of other amps have had dead silence issues, usually just after grossly exceeding the output transistors SOAR
Ido not plan on mounting the drivers on the main heatsink so cannot comment on RF interference.
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Old 20th April 2012, 10:19 AM   #32
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Quote:
Originally Posted by TonedeafDIY View Post
Hi Terranigma,
I'm not sure if I understand what you mean by dead silence "issues". My Circlophone is dead silent at full volume with my ear up against my speaker cones. I don't consider that an issue Other builds of other amps have had dead silence issues, usually just after grossly exceeding the output transistors SOAR
Ido not plan on mounting the drivers on the main heatsink so cannot comment on RF interference.
If you were familiar enough with main Circlophone thread, you may aware that I'm struggling with some RF Interference issue due to my location's heavy ambient RF noise. This very specific case for me. I recently noticed that if I connect driver heatsinks with a wire, RF issue remains in acceptable levels but not going to dead. I think my driver heatsinks working as antenna and I have to do something for proper grounding.
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Old 20th April 2012, 10:26 AM   #33
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I have seen your problems in the main thread, I see what you were asking now. I am only a builder of amps, my electronic knowledge is very limited and as such I cannot help you in any meaningful way. I wish I could.
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Old 22nd April 2012, 03:09 PM   #34
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Quote:
Originally Posted by terranigma View Post
If you were familiar enough with main Circlophone thread, you may aware that I'm struggling with some RF Interference issue due to my location's heavy ambient RF noise. This very specific case for me. I recently noticed that if I connect driver heatsinks with a wire, RF issue remains in acceptable levels but not going to dead. I think my driver heatsinks working as antenna and I have to do something for proper grounding.
Chassis
Have you identified the bandwidth of the powerful radio signal? If so, then you could Avoid making any metal parts (heatsinks, cables) a multiple/division of that size signal. Try for "wrong size antenna" instead?

.

Power supply
Secondaries and diodes: Maybe the signal is coming over the power line, so try putting lossy little polyester dip cap (looks like green or red bubble) parallel to each diode of your bridge rectifier. About 10nF should do, but this size is mostly related to transformer size (range is 1nF to 15nF). If using efficient caps like polypro or ceramic, you'd need to make RC's (zobels) per each diode. If dulled sound, then use next size smaller caps. On success, "snubbed rectifier" will remove 1v to 1.5v of noise that you didn't need anyway, and you can measure that ~1v less on the rails.
This applies to standard diodes and convenient 1-piece bridge rectifiers. For fast/shottky diodes, a working method is somewhat different, but you can certainly put RC's across the transformer secondaries to limit the transformer passband to lower pitches.

Primaries: Next, try putting an MOV and an RC (or high voltage rated polyester dip cap/specialty AC cap) parallel with the transformer primary (mains)--you can recycle those mains rated pieces from the input of a retired computer power supply. The hookup is same as the input protection of the PC power supply. The point is to limit the passband at the transformer primaries down to allow lower pitches but hinder higher pitches.

Now both ends your power supply are somewhat RF resistant.

.

Amp Input
After that, you can also locate an RF filter at either side of your input cap (big uF cap pin must touch small pF cap pin if forming a blocker). A blocker looks like a voltage divider structure except that you've used caps instead of resistors for it. This blocker is also known as a CapDiv because of its appearance. The location for the added input filter is the spot where I put the thump blocker since it is also slightly capacitive. You can put a picofareds cap at that spot.

Heavy shield XLR cable is also workable for radio production (rf pollution) environment.

And then lastly, look at the schematic. See that 1M? It is a "token" load. This is power amp schematic, not integrated amp schematic. You'd probably want to shunt more than 1M worth of current if radio environment use. Instead of 1M, I'd probably start with 100k and then explore from there.
That spot is another good place for an RF filter. Those work better if RC instead of just a cap, so just make "tone control" that is higher than the audio band. Probably good is an RC//R--A super high pitched tone control parallel with a stronger input load. In this case there is dramatically increased load for all pitches higher than the audio band. This section is easy--play some classical and do it by ear. Just choose a cap small enough that it doesn't reduce your treble at all.

A last resort is a picofareds cap set from in+ to in- (same place as those 470R) to short out RF frequencies. Unfortunately that sort of filter also reduces the speed of the amp. It is probably okay to do that if you're not also maxing out your gain setting. Reducing the resolution also reduces the capacity for gain. This filter can work for high frequency radio like Megahertz FM radio as you are free to trim off anything faster than the amp. The prospect is abrupt and noticeable, so the cap size is easily found--just choose a small enough value that doesn't interfere with the main task of audio replay.

I hope these help.

Last edited by danielwritesbac; 22nd April 2012 at 03:14 PM.
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Old 22nd April 2012, 07:22 PM   #35
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Thank you Daniel, for your very kind support. If you taste quieteness of Circlophone first, there is no way to satisfy yourself with solutions those helping for "atteneuate" the problem. If you had destroy completely something evil once, you can't even bear the idea of living with a small portion of it again. I perceive that the problem is lying somewhere simple, somewhere front of my eyes..

If you take a look at photo of my very first Circlophone, you can see that driver transistors (2SA1930) have attached to the main heatsink using a piece of FR4 pcb board. After my last experiment with driver heatsinks, I felt that I'm on right direction. I want to play with them just before your helpful suggestions.

Thanks.

Click the image to open in full size.

Last edited by terranigma; 22nd April 2012 at 07:52 PM.
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Old 22nd April 2012, 10:04 PM   #36
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Quote:
Originally Posted by terranigma View Post
If you take a look at photo of my very first Circlophone. . .
Something about that is unable to amplify RF.
Putting the drivers back onto the main heatsink, seems like a worthy experiment. Adding shields over the drivers and outputs shouldn't be a problem, but I'd go for a more secure mounting, like screws for the drivers this time, and good thermal pads to add electrical insulation for the Harris.

I keyed an FM transmitter (with the filters shut off for a raunchy output) right at a Circlophone, to no effect whatsoever, and then I keyed a 9 meter AM ("breaker breaker for a radio check?") and got absolutely nothin' out of the Circlophone, but there was a confounded truck driver about 6 miles away. Probably every T-amp in range (such as the neighbors--sorry guys) went bonkers but Circlophone stayed silent.

Last edited by danielwritesbac; 22nd April 2012 at 10:13 PM.
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Old 23rd April 2012, 03:38 AM   #37
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You know what else would shield those drivers? I just now thought of it--a big washer for each.
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Old 30th April 2012, 12:02 AM   #38
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Maintenance post:
This post has replacement graphics displayed at post 1. Previously some graphics were at an off-site server; however, attaching graphics to a post makes a more durable presentation.
Attached Images
File Type: gif circlophone-original.gif (23.4 KB, 591 views)
File Type: gif circlophone-sections.gif (27.2 KB, 499 views)
File Type: gif circlophone-mouser.gif (22.6 KB, 517 views)
File Type: gif circlo-size-chart.gif (14.9 KB, 502 views)
File Type: jpg hitachi.jpg (68.4 KB, 351 views)
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Old 5th May 2012, 09:02 AM   #39
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I'm documenting C11, just in case someone wants to use output devices faster than the preferred devices listed in post 1. Extra speed is unnecessary for outputs; however, a reason to do it is if you happen to have some conveniently sitting around.

Just now I was told the common name for Q12, Q13 is "Negative Current Sensor" and that bit of documentation has been added at post 1, since it might assist discussion. This area of the Circlophone is sensitive, so one wants to use good quality authentic devices there.

Some people had trouble viewing the post 1 schematic on a tablet or netbook screen, so I put the schematic size at 1024x600 so one can use full screen display on a netbook and it will display clearly.

Here's the replacement with these three minor touch-ups.
Attached Images
File Type: gif circlophone-sections.gif (28.9 KB, 556 views)
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Old 5th May 2012, 10:27 AM   #40
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Default Sonic Signature

The transistor with the most effect on sonic signature is the outputs.

Elvee provided a list with a quality score for outputs and then I edited the listing at post 1 to only good varieties.
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