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DLH Amplifier: The trilogy with PLH and JLH amps
DLH Amplifier: The trilogy with PLH and JLH amps
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Old 8th March 2018, 05:26 PM   #451
diegomj1973 is offline diegomj1973  Argentina
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DLH Amplifier: The trilogy with PLH and JLH amps
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Old 8th March 2018, 06:57 PM   #452
marconi118 is offline marconi118  Germany
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My input cap is NP mkp 1.5uF
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Old 8th March 2018, 11:57 PM   #453
diegomj1973 is offline diegomj1973  Argentina
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The value of the input signal coupling capacitor is correct (it would give very roughly a lower cutoff frequency of 0.125 Hz, or something around).

There are delays in the stabilization of final parameters, without applied signal, which will depend on the time constants involved in the circuit. Basically, in your circuit there will be two relatively important time constants: the conformed by the input network (approximately around 6.37 seconds, neglecting certain terms in its calculation) and another constant of around 23.5 seconds (again, approaching rudely).

To set idle parameters, remember to disconnect signal source and short-circuit the AC signal input to the DLHSB. Wait for the times mentioned between each readjustment, until reaching the final parameters.
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Old 9th March 2018, 06:55 AM   #454
marconi118 is offline marconi118  Germany
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But I find strange that the offset pot has to be 850k to achieve 1/2 Vcc at output
You put a 500k pot
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Old 10th March 2018, 12:13 AM   #455
diegomj1973 is offline diegomj1973  Argentina
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It would not be strange that you have to finally modify the nominal value of the trimpot for DC offset, in the very basic configuration for the polarization of the base of the BC560C, since it is a configuration that depends a lot on the parameters of that same transistor.

The design was based on a transistor model with hFE of 330 (the one that was available in my library when designing it). You claim to have hFE of 550. It is for this reason that the relationship between the values ​​of trimpots tends to be similar to the relationship between hFEs.

Although very basic, this configuration behaves better against offset shifts due to temperature, than a potentiometric divider of lesser value that polarizes the base of the BC560C.

If the DC shifts with the temperature are excessive with this basic configuration, you can implement the compensation with two transistors that has been tested by XRK971.
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File Type: jpg DLHSB DC Offset.jpg (313.6 KB, 446 views)

Last edited by diegomj1973; 10th March 2018 at 12:21 AM.
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Old 15th March 2018, 09:01 PM   #456
marconi118 is offline marconi118  Germany
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Still using the simplified version with single psu rail and output cap.
Modified as follow:
Feedback network of 150r + 150r to ground without decoupling cap. 300k resistor at base of input trans to set the output at 1/2Vcc.
Will this affect performance? What would be the gain? 2X?
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Old 18th March 2018, 05:04 AM   #457
diegomj1973 is offline diegomj1973  Argentina
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The performance should be excellent.

The gain in voltage is X2 or 6dB.

How does it work as you have built it?
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Old 19th March 2018, 08:15 PM   #458
marconi118 is offline marconi118  Germany
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Compared to the super buffer Sound is more bright top end maybe a bit more aggressive.

Is the feedback network without cap bad? DC Current flows al the time In the 2 150ohm resistors they become a bit hot. Current in transistors is 10mA (10v across the 1k pot)
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Old 20th March 2018, 12:54 AM   #459
diegomj1973 is offline diegomj1973  Argentina
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If you have built a low gain DLH amplifier, but with a simple polarity power supply, you should add a capacitor in series to one of the two 150 ohm resistors of the feedback network (ie, in series with the resistor that connects with 0V). Otherwise, one of the resistors could dissipate up to about 431 mW in the absence of signal, for which both should preferably be at least 2 W.

It could work without that capacitor, only it will have a little more drift with the temperature and some more Johnson noise in the absence of signal (which could imply a very small decrease in the resolution of very low signal levels).

Remember that if you add a capacitor there, it should be of important value so as not to limit the response at low frequency.

Did you like the sound quality you get from DLH and DLHSB?

Have you played with the SE / PP setting?

Best regards

Last edited by diegomj1973; 20th March 2018 at 01:00 AM.
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Old 20th March 2018, 02:19 AM   #460
diegomj1973 is offline diegomj1973  Argentina
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Quote:
Originally Posted by marconi118 View Post
Compared to the super buffer Sound is more bright top end maybe a bit more aggressive.
Try placing a capacitor between 47pF to 68pF, in parallel to the 150 ohm resistor (which is connected between the node to the output and the base pin of the BC550C.) That should remove the "aggressiveness" at high frequency .

Without that capacitor, a certain nonalignment in the high frequency response could occur.

As a reference, it would have to be connected in a similar way to the 82 pF capacitor in the schematic cited in post 1.

Last edited by diegomj1973; 20th March 2018 at 02:38 AM.
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