especialista
Junior Member
Offline
Posts: 50
Thank You
-Given: 84
-Receive: 161
|
|
« on: December 29, 2018, 05:19:06 17:19 » |
|
This is a simple amplifier for those ol' fashioned way PCB audio pickers, did by me in the past. RV1 - Adjusts input signal RV2 - Ajusts clipping between Q1 and Q2 (First post, sorry if I did any mistake!)
|
|
« Last Edit: January 01, 2019, 04:31:45 16:31 by especialista »
|
Logged
|
|
|
|
PM3295
Senior Member
Offline
Posts: 312
Thank You
-Given: 358
-Receive: 155
|
|
« Reply #1 on: December 31, 2018, 02:43:30 14:43 » |
|
If you use global feedback instead of local feedback, you should be able to get rid of the large electrolytics, improve LF response and reduce the THD% figure by a factor of about 20.
|
|
« Last Edit: December 31, 2018, 03:23:59 15:23 by PM3295 »
|
Logged
|
|
|
|
metal
Global Moderator
Hero Member
Offline
Posts: 2420
Thank You
-Given: 862
-Receive: 678
Top Topic Starter
|
|
« Reply #2 on: December 31, 2018, 05:41:31 17:41 » |
|
what's the output power? Can we increase it and keep the profile as above?
|
|
|
Logged
|
|
|
|
especialista
Junior Member
Offline
Posts: 50
Thank You
-Given: 84
-Receive: 161
|
|
« Reply #3 on: December 31, 2018, 08:59:23 20:59 » |
|
what's the output power? Can we increase it and keep the profile as above?
Never measured, but I'd tell something around 3/4[W] at maximum. It was not designed for "rock'n'roll". Just to amplify small signals to a small acoustic box.
|
|
|
Logged
|
|
|
|
PM3295
Senior Member
Offline
Posts: 312
Thank You
-Given: 358
-Receive: 155
|
|
« Reply #4 on: January 07, 2019, 06:14:14 18:14 » |
|
With a few more simple modifications, it should perform very well. Together with the higher supply voltages, it could produce about 20 W into a 4 ohm speaker load at a low THD near 0.004%. As shown all harmonics of the 1 kHz input tone is down almost 90 dB. Bear in mind that the original design without global feedback may have produced over 3% THD at full power. For good thermal stability, the diode should be mounted close to the heat-sink.
Make sure you set P1(multi-turn) for an idling current between 10-20 mA flowing in the main output transistors once the amplifier has warmed up.
Posted on: January 01, 2019, 12:33:38 12:33 - Automerged
Distortion and noise can be further cleaned up by using a better low noise opamp like the LT1028. It shows nearly a 4 times reduction in the THD going from the LF351 to a LT1028.
|
|
|
Logged
|
|
|
|
Faros
Senior Member
Offline
Posts: 254
Thank You
-Given: 141
-Receive: 178
|
|
« Reply #5 on: January 10, 2019, 10:13:05 10:13 » |
|
@PM3295
which software is used for those analyses ?
|
|
|
Logged
|
|
|
|
dennis78
Active Member
Offline
Posts: 122
Thank You
-Given: 272
-Receive: 154
|
|
« Reply #6 on: January 10, 2019, 01:41:53 13:41 » |
|
I think this is TinaTI software
|
|
|
Logged
|
|
|
|
PM3295
Senior Member
Offline
Posts: 312
Thank You
-Given: 358
-Receive: 155
|
|
« Reply #7 on: January 10, 2019, 08:47:34 20:47 » |
|
I think this is TinaTI software
That is correct, although some of the features are only available on the full registered industrial version.
|
|
|
Logged
|
|
|
|
mr_byte31
Hero Member
Offline
Posts: 600
Thank You
-Given: 75
-Receive: 144
|
|
« Reply #8 on: January 16, 2019, 09:17:17 09:17 » |
|
I think it is better to avoid using opamp ( specially LM741) , they have bad frequency response. I used one before and it made the sound quality very bad.
Posted on: January 16, 2019, 04:14:42 04:14 - Automerged
I also remember that you need to add a small resistance (5 Ohm) on the common of Q3 and Q4 to avoid mismatch ! at least that what I remember since long time ago.
|
|
|
Logged
|
Do not trifle with the Moderators , as you are small, and crunchy, and taste good with ketchup.
|
|
|
especialista
Junior Member
Offline
Posts: 50
Thank You
-Given: 84
-Receive: 161
|
|
« Reply #9 on: January 16, 2019, 08:52:44 20:52 » |
|
I think it is better to avoid using opamp ( specially LM741) , they have bad frequency response.
You're absolutely right. That's why I've choosed High Speed JFET LF351 for this amplifier. You should try one of these: They are amazing for pre-amp.
|
|
|
Logged
|
|
|
|
PICker
Active Member
Offline
Posts: 162
Thank You
-Given: 207
-Receive: 110
|
|
« Reply #10 on: January 17, 2019, 07:12:06 07:12 » |
|
I agree, the JFET input OPA does the difference. There are new designs for reducing distortion and noise and increasing precision like the TI OPA3234 SoundPlus.
|
|
|
Logged
|
|
|
|
metal
Global Moderator
Hero Member
Offline
Posts: 2420
Thank You
-Given: 862
-Receive: 678
Top Topic Starter
|
|
« Reply #11 on: January 18, 2019, 02:22:43 02:22 » |
|
I agree, those OPAs sound much better than 741 and NE5532..
|
|
|
Logged
|
|
|
|
|