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Old 19th May 2012, 09:42 PM   #951
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Thank you Elvee for reissuing CFP version. Are you planning to share an official version of CFP further? Are you planning to analysis a real circuit?
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Old 20th May 2012, 08:48 AM   #952
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
Thank you Elvee for reissuing CFP version. Are you planning to share an official version of CFP further? Are you planning to analysis a real circuit?
Yes, it is in the pipeline. I'll make tests and optimization on a physical circuit.

In the mean time, existing CFP boards can already be upgraded, since the mods boil down to mere changes in component values.
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Old 21st May 2012, 10:32 AM   #953
Elvee is offline Elvee  Belgium
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I have investigated the effect of schottky diodes in the power rails.

Apart from the DC drop, the effect seems quite minor, see picture.

It somewhat raises the impedance of the supplies, leading to an increased modulation by the audio signal, but the effect is too small to have a negative impact on the performances of the Circlophone.

What could be the benefits?
As I said earlier, in multi-channel systems it could marginally increase the channel separation.

Other than that, it could also act as a signal-driven, dynamic low pass filter: at low currents, the diode's dynamic resistance is higher, lowering the cut off frequency.
It could contribute to reduce the no-signal hum for amplifiers having a poor PSRR, without wasting the power of an equivalent purely passive RC filter.
With the Circlophone, the effect will be much less apparent, because of the relatively high quiescent current
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Old 21st May 2012, 06:38 PM   #954
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Thank you Elvee, for allaying some of our anxieties.

But, what do you feel about the 'mods' that have been done in the interests of fidelity? That is, making the PSU a neutral and effective thing that would let the amp do its job, and facilitate that capably. My plan is to employ the same scheme --surge-limited 'heavy' capbank with snubbered diodes and R-C suppressors serve as the primary PSU, with a cable feeding the L-R channel Circlophones in a single enclosure, isolated by the two sets of Schottkys and bypassed by a single small (220 -- 470 uF) electrolytic at each supply node. Additionally I would want to cut the input ground trace and wire it directly to the 'star ground'. The input socket and the RF kill filter/low-pass will also have a direct lead to the star ground. The PCB main hi-current ground trace will have another connection to the star ground. This sort of wiring had given me the best possible results with medium power discrete amps in the past. This could be 'overkill' for the 'super-silent' Circlophone, though. Still your opinion counts... for many of us as the last word!

I gotta ask a foolish question. When a BAT54/85 cannot be had for D7, is it in any way possible to substitute it with a 1N5819, which is a 1 Amp rectifier?
And what about the 1N5822, a 3Amp rectifier, as stand-in for D4/5 ?
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Old 21st May 2012, 10:59 PM   #955
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When a BAT54/85 cannot be had for D7, is it in any way possible to substitute it with a 1N5819, which is a 1 Amp rectifier?
And what about the 1N5822, a 3Amp rectifier, as stand-in for D4/5 ?
I've updated the builder's thread further to answer these questions and provide even more shopping links to click on. Conveniently, there's no need for wrong parts.

"Rectifier schottky" at D7 will put disinformation into the sensor, eventually resulting in blown output devices. So, to avoid that problem, must use BAT type "signal schottky" There is a significant difference.

The spec for D4, D5 is "lowest forward voltage drop" and if you look at a 3A schottky's datasheet graphs they'll answer the question on how little current it takes to begin more extreme voltage drop that you don't want. Probably a 3A schottky will actually work for D4, D5 but "slack off" on the transients, cutting available power at possibly inappropriate moments, such as providing clipping instead of bass. Problem versus success depends on how much power output. For example: With the 25vdc+25vdc operating voltage shown in post 1 and with 8 ohm speakers (about 35 watts), then, in that case, using a 3A schottky for D4, D5 is okay.

Here is a link to datasheet for the 3A schottky shown in the post 1 (original) schematic). The forward voltage drop versus current graph provides the needed information.
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Last edited by danielwritesbac; 21st May 2012 at 11:10 PM.
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Old 25th May 2012, 03:33 AM   #956
abetir is offline abetir  Philippines
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Sir Daniel/Elvee,

I've been thinking of powering this amp at -/+50vdc, do I need to replace BAT85(D7) and MBR745 (D4/5) for a higher power rating?

Regards!
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Old 25th May 2012, 08:08 AM   #957
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Originally Posted by abeteer View Post
Sir Daniel/Elvee,
I've been thinking of powering this amp at -/+50vdc, do I need to replace BAT85(D7) and MBR745 (D4/5) for a higher power rating?
Regards!
Elvee told me that the reverse voltage spec isn't used since there's no reverse voltage employed at those locations. At D4/5, the 35v and 45v diodes are fine.

At D7, you could use BAT86 if you wanted a stronger part, but BAT85 will also do fine.

P.S.
There's no 50+50vdc listed on the constructors chart in the build thread. That voltage is possible but it could be abusive to the output devices. Perhaps you could employ a Fairchild Stealth diode bridge rectifier along with a CRC or CRCDC type power supply and drop a bit of voltage in trade for better filtering? The "slack" of a bit of current drop will help preserve the output devices. Hopefully you've got 8 ohm or 16 ohm speakers?
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Old 25th May 2012, 08:33 AM   #958
abetir is offline abetir  Philippines
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It so happen that what I had for a power transformer was -/+36vac...
I will be using 2SC5200s for the output and an 8 ohms speaker. I will try Elvee's CFP design while waiting for Piersma's final lay-out...
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Old 25th May 2012, 09:06 AM   #959
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Originally Posted by abeteer View Post
It so happen that what I had for a power transformer was -/+36vac...
I will be using 2SC5200s for the output and an 8 ohms speaker
I think you are going to surpass Daniel's goal.. except that you have 8 ohm speakers. 2sc5200 is a fast (30Mhz) device and it hink that it ain't to be a good start for a Circlophone. In Philippines, you could find a plenty variety of good transistors out there.
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Old 25th May 2012, 02:32 PM   #960
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Originally Posted by terranigma View Post
I think you are going to surpass Daniel's goal.. except that you have 8 ohm speakers. 2sc5200 is a fast (30Mhz) device and it hink that it ain't to be a good start for a Circlophone. In Philippines, you could find a plenty variety of good transistors out there.
It would surely take a trick power supply to save those output devices. They're rated for a 100w amp, not a 150w amp. Perhaps 4 of these trick diodes for a bridge rectifier (center tap config) and a CRCRC type power supply for yet more current dumping. Let's see, 7v drop plus about 2v more drop from the transformer. . . about 100w amplifier. That and some luck and some fuses would probably do. However, peak power might could be delivered to 150w (until the power caps run out), and if that took longer than the peak rating, then the output devices may not survive. So, we're definitely talking about a fuse party and maybe even a current dumper cable like a retail amplifier. That's how Kenwood does their Sanken's--the current dumper cable allows the high advertised figures while the long thin cable between rectifier and transformer migatates the difference between the transformer voltage and the output device SOAR.

-or-
Probably MJ15003 could do the job up at 150w. Those metal can devices have 250w dissipation rating. MJ21196 has a 3a to 1 second SOAR test and MJ15003 has a 5a to 1 second SOAR test. One plastic transistor, the MJW18020 has similar specs and should be able for the 150w. This power output also needs some relatively sturdy drivers.
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Last edited by danielwritesbac; 25th May 2012 at 02:48 PM.
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