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Old 31st March 2013, 08:26 AM   #1161
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
So, what this mean? Is Cbe a critical value for bias servo here? Do we consider that BD140 ones obviously out of spec?
Cbe is indicative, not critical: during normal operation with bias applied, it should be swamped by the diffusion capacitance.
It could begin to cause troubles only if it is way excessive.
By contrast, Ccb is always important
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Old 31st March 2013, 06:12 PM   #1162
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In this case, a 25% difference is just that. You decide whether 25% is a big difference or not. I would worry if it was around 100% (doubled) or so.

645pF for a C5171 would indicate a counterfeit! Compare the values you find to the SPICE model values, which are specified at 0V bias.

Last edited by keantoken; 31st March 2013 at 06:14 PM.
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Old 3rd April 2013, 05:23 PM   #1163
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Quote:
Originally Posted by terranigma View Post
I consider that I finished my PCB layout of N-Darlington output version of vanilla Circlophone. I built two channels and they are running for a while. Purity, dynamics, punchy bass.. I think this version is no less than original output scheme. Even with those ST TIP142's. . . .I used BD140's as servo transistors because mine were good quality ones from Philips and Harris. I measured their cb capacitance at 0V and Harris ones were always lower (35pf vs 52pf).
Terranigma, I need some help with the documentation for it.
Unobtainium parts reliance issues: So, not a random BD140, but rather a little "super driver" sort with fine specs. Neither the Harris nor the Philips are widely available. I wonder what we can find for substitute at Mouser, Digikey, etc. . . Perhaps Fairchild has something for us? We need to list something with higher availability, for the documentation.
Click the image to open in full size.
Other than the unobtanium vas, this version looks fantastic because it is the easiest and most compact way to build a Circlophone.
Given the 30+30vdc (60v) operating voltage and unregulated power (surges happen) we might need to list something other than BC556B (maxed at 60V) in the sensor area.
So, basically, we need an updated photo that lists alternate transistors for vas and sensor, in order to assure expected operation on all builds.
P.S.
Have you tried replacing the zener with transistor, per Elvee's post#1151 above?
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Last edited by danielwritesbac; 3rd April 2013 at 05:40 PM.
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Old 3rd April 2013, 10:33 PM   #1164
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Quote:
Originally Posted by danielwritesbac View Post
Terranigma, I need some help with the documentation for it.
Unobtainium parts reliance issues: So, not a random BD140, but rather a little "super driver" sort with fine specs. Neither the Harris nor the Philips are widely available. I wonder what we can find for substitute at Mouser, Digikey, etc. . . Perhaps Fairchild has something for us? We need to list something with higher availability, for the documentation.
I also tested 2SA1220 (Nec), 2N5401, 2N2905A in place of BD's during tracing overshoot behavior. Actually I couldn't manage any difference between their behavior with oscilloscope. I showed BD140 part on layout because I consider that builder is aware of NOT to choose a random BD device. If I could find a 2sa1360 (2.5pf Cob) from a local store maybe it is going to be shown in the layout. It would be a good candidate for higher supply voltage usage. It is very easy to adapt mounting holes for 8-10pf capacitors between c-b legs of servo transistors in current layout. Maybe these self compensation caps aren't going to be necessary. I can't be sure until test it on real circuit.


Quote:
Other than the unobtanium vas, this version looks fantastic because it is the easiest and most compact way to build a Circlophone.
Given the 30+30vdc (60v) operating voltage and unregulated power (surges happen) we might need to list something other than BC556B (maxed at 60V) in the sensor area.
KSA922, 2SA970, 2N5401 (and their couples) are suitable for sensors in higher supply voltage usage and they are easily attainable. Transistor leg arrangement must have considered in this case.

Quote:
So, basically, we need an updated photo that lists alternate transistors for vas and sensor, in order to assure expected operation on all builds.
No problem.

Quote:
P.S.
Have you tried replacing the zener with transistor, per Elvee's post#1151 above?
I consider it must be applied as shown in Elvee's jfet buffered schematic at post #637 (but using a PNP device?) If so, it is possible to alter zeners with a single transistor without altering layout. Not an artistic way but it is doable at least.
Attached Images
File Type: jpg zener-to-bjt.jpg (26.5 KB, 273 views)

Last edited by terranigma; 3rd April 2013 at 10:42 PM.
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Old 4th April 2013, 07:59 AM   #1165
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Quote:
Originally Posted by terranigma View Post
I consider it must be applied as shown in Elvee's jfet buffered schematic at post #637 (but using a PNP device?) If so, it is possible to alter zeners with a single transistor without altering layout. Not an artistic way but it is doable at least.
I just realized that layout must have altered due to compensation network placement according to schematic.
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Old 4th April 2013, 10:16 AM   #1166
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Here is the altered layout in case of using an extra transistor in place of zeners.
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File Type: jpg Circlo-NDarlington-PCB-Layout2.jpg (135.2 KB, 253 views)

Last edited by terranigma; 4th April 2013 at 10:40 AM.
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Old 6th April 2013, 04:20 AM   #1167
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Ah, not good sounding to use the speaker output as the reference point; however. . .
Quote:
Originally Posted by Elvee View Post
If you want to mimic more closely the effect of zener with a transistor, you can tie its base to the ground instead of the output.
I assume that should sound very similar to using the zeners, except with the convenient automation of a transistor instead of buying voltage specific zeners.
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Last edited by danielwritesbac; 6th April 2013 at 04:22 AM.
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Old 6th April 2013, 10:36 AM   #1168
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Elvee, it seems, your private message limit reached.

In case of inverting whole layout of my darlington setup but not to come down a pnp transistor as output, then I need a pnp-npn mixed darlington pair. If I understand correctly, your suggestion is complementary darlingtons like TIP121/27 , BDX53/54. Do you mean Sziklai pair? Is there something like Sziklai pair in one package?

http://www.onsemi.cn/pub_link/Collateral/MJH11017-D.PDF

Last edited by terranigma; 6th April 2013 at 10:57 AM.
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Old 6th April 2013, 11:42 AM   #1169
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Ok I understand... If using complementary type of darlingtons (not sziklai in one package) there should be nothing to worry too much. I'm a bit confused with definition of "complementary".
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Old 6th April 2013, 03:11 PM   #1170
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
Ok I understand... If using complementary type of darlingtons (not sziklai in one package) there should be nothing to worry too much. I'm a bit confused with definition of "complementary".
I gave examples of complementary darlingtons to show that there is little difference (in print) between the P and the N.
Of course, in an amplifier you only use one variety, P or N, not a mix.
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