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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 15th March 2018, 09:01 PM   #451
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   #452
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   #453
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   #454
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   #455
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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Old 20th March 2018, 11:16 AM   #456
marconi118 is offline marconi118  Germany
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ok I will add a 47pf cap in parallel to the 150r that comes from the output.

I didn't used any electrolytic cap to decouple the 150r to ground.
is this ok?


I know that in this way dc current flows in the feedback resistors and noise is increased... but i didn't noticed any noise on the speakers
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Old 20th March 2018, 11:34 AM   #457
diegomj1973 is offline diegomj1973  Argentina
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About the electrolytic capacitor, there are no problems if you do not want to use it. Just consider what I said about the power dissipations in both 150 ohm resistors. They should be able to dissipate each one at least 2 W.

About the increase in Johnson's noise, it will surely occur at still imperceptible levels, even with very sensitive speakers. You have already verified this.
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Old 20th March 2018, 11:38 AM   #458
xrk971 is online now xrk971  United States
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DLH Amplifier: The trilogy with PLH and JLH amps
Good to see activity in his thread. I may have missed it but do you have photos of your working amp Marconi? Good to see others making the DLH - a fine sounding amp.
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Old 20th March 2018, 12:17 PM   #459
marconi118 is offline marconi118  Germany
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I will post some picts later... don't be shocked it is p2p directly on the pins of the mosfets on the heatsinks
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Old 22nd March 2018, 08:52 AM   #460
kokoriantz is offline kokoriantz  Lebanon
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This is an other way of providing +/-15v output excursion.
I tested the irfp150 , at 250ma the simulated shows one A/V but measures in real world 0.45 .
Worst , the input capacitor datasheet values1.9n ,the simulator measures 3.9n. And still the model is provided by Tina ti .

Diegomj1973 , PRR mentioned about Christopher Rush created this circuit in 1964 . Have you found it . I looked in many on line technical libraries us archives ,the name is unknown to the profession. If such has existed in bipolar transistors, the output swing would be limited to +/-0.7v only instead of +/-4v with mosfet ,unless a remedy is applied , that PRR forgot to give notice .
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