OPA134 controlled headphone amplifier.
The output is a diamond buffer working in Class A.
Transformer can be 2x9VAC.
Or a 2x12VAC with regulated supply.
The input potentiometer is 10kOhm.
The output is a diamond buffer working in Class A.
Transformer can be 2x9VAC.
Or a 2x12VAC with regulated supply.
The input potentiometer is 10kOhm.
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Built and tested/measured? BTW the input filter (bravo!) is at the wrong side of the potentiometer and is therefore a variable filter. Should be before the potentiometer.
I have tested the impact of the potentiometer on the filter.
With 10k potentiometer there is only a small variation on the bandwidth.
This is because of the large value 3k3 resistor.
With 10k potentiometer there is only a small variation on the bandwidth.
This is because of the large value 3k3 resistor.
I did a big transistor test a few days ago: 2N types were consistently unsuitable in terms of sound: gray, colourless, cloudy, unclear, lifeless. broken.
My experience regarding BD139/140: some batches that have a special sonic character. But they are generally unfluid, lifeless, slowed down, have a gray haze.
)-;
My experience regarding BD139/140: some batches that have a special sonic character. But they are generally unfluid, lifeless, slowed down, have a gray haze.
)-;
I'll have a look at my notes this afternoon.
The problem here is that they are tendentious statements. My experience is that the same parts from different batches sometimes sound considerably different. But I think I can find 2 or 3 pairs that I can recommend to test. Maybe one of them will click in. I could make a long list of parts that have never been suitable for audio;-)-;
Aside, we now have thousands of transistors and other parts on the market. A maximum of 10% are suitable for audio: they have basic cleanliness and a special character. And max. every 30 is outstanding in its qualities that make it universal. It would probably be enough to develop 5 different ones of each size for the audio sector. Then there would be an intentional choice in terms of character: it would be possible to choose at all - if standards are maintained in production.
The problem here is that they are tendentious statements. My experience is that the same parts from different batches sometimes sound considerably different. But I think I can find 2 or 3 pairs that I can recommend to test. Maybe one of them will click in. I could make a long list of parts that have never been suitable for audio;-)-;
Aside, we now have thousands of transistors and other parts on the market. A maximum of 10% are suitable for audio: they have basic cleanliness and a special character. And max. every 30 is outstanding in its qualities that make it universal. It would probably be enough to develop 5 different ones of each size for the audio sector. Then there would be an intentional choice in terms of character: it would be possible to choose at all - if standards are maintained in production.
By the way: when it comes to sound, I would prefer single ended. For the reasons mentioned above: the audible difference between equal parts. And even parts of the same batch are audibly different: test per psu: connect two double mono psua together to get one. For my sake per switch or plug-in system. And just listen and listen. and at some point turn off the music, take your time, pour the next tea or coffee or wine or beer or whisky or what ever, then switch, and turn the music back on;-) Just relaxed listening to music;-)
TTA004/C004 are good swaps for BD139/140.
MJE340/350 also good.
BD139/140 are competent and generally easy to come by from legit sources. I usually use the ST Micro version as the pre-output drivers.
This amp might be a good candidate to build with transistor sockets and play around with different outputs until you are happy with the sound.
MJE340/350 also good.
BD139/140 are competent and generally easy to come by from legit sources. I usually use the ST Micro version as the pre-output drivers.
This amp might be a good candidate to build with transistor sockets and play around with different outputs until you are happy with the sound.
I have not yet heard these MJEs.
Regarding TO-92:
No 2N, no MPSA.
The SC types did sound consistently musical. I just listened to three 2SC2240s, three different batches and ages: clear differences, but all in the same class. I have just listened to, to control: older 2SC1815, new 2SC1845, 2SC2383, to control. All consistently listenable.
I want to recommend the BC 546 - BC560 because they are cheap: just buy and listen to everything available from one seller. They are not the worst, and occasionally there are very good ones: for example, I had a lucky strike a year ago: a BC549 that sounded almost mystical.
And I once had a lucky MPSA44.
The PNP complementaries will sound different! As far as PNP is concerned, I'm only sure about two three transistor pairs: they sounded in the corner of the complementary.
I will be able to tell you next week how much the non-deviation can be. On a BD441 - BD442: to test PNP types, I will convert my follower from a NPN to a PNP. All components remain the same, except for these transistors. Unless the direction of the current makes decisive changes to the sound...-)
I generally recommend these: BD441, BD442. There are two or three that are more detailed, but the musical flow, the coherence is enormous. I also have a few batches: an older BD441 has a kssssss-permeation in the soundstage - reminds me of PP amplifiers;-)
One more tip - just heard again in practice: always use the smallest possible transistors. In the case of this HPA, I would use TO-92 or TO92L instead of the TO-126 outputs. They are consistently clearer, more contoured, smoother, more authentic. Upper midclass TO-92L (SC2383) much better than upper class TO-126 (BD441, my BD437).
Regarding TO-92:
No 2N, no MPSA.
The SC types did sound consistently musical. I just listened to three 2SC2240s, three different batches and ages: clear differences, but all in the same class. I have just listened to, to control: older 2SC1815, new 2SC1845, 2SC2383, to control. All consistently listenable.
I want to recommend the BC 546 - BC560 because they are cheap: just buy and listen to everything available from one seller. They are not the worst, and occasionally there are very good ones: for example, I had a lucky strike a year ago: a BC549 that sounded almost mystical.
And I once had a lucky MPSA44.
The PNP complementaries will sound different! As far as PNP is concerned, I'm only sure about two three transistor pairs: they sounded in the corner of the complementary.
I will be able to tell you next week how much the non-deviation can be. On a BD441 - BD442: to test PNP types, I will convert my follower from a NPN to a PNP. All components remain the same, except for these transistors. Unless the direction of the current makes decisive changes to the sound...-)
I generally recommend these: BD441, BD442. There are two or three that are more detailed, but the musical flow, the coherence is enormous. I also have a few batches: an older BD441 has a kssssss-permeation in the soundstage - reminds me of PP amplifiers;-)
One more tip - just heard again in practice: always use the smallest possible transistors. In the case of this HPA, I would use TO-92 or TO92L instead of the TO-126 outputs. They are consistently clearer, more contoured, smoother, more authentic. Upper midclass TO-92L (SC2383) much better than upper class TO-126 (BD441, my BD437).
also thinking you might need small value resistors in series with bases of Q1 & Q2 for the built & tested version ...
Another chance is also: since each half-wave of this amplifier has an NPN and a PNP, I would use identical pairs: so in each half-wave both characters add up: each half-wave has an identical character. However, color and flow is lost, it will sound grayer and duller and flatter and less musical, just by adding the components compared to just a single stage. My tip: 2 pp stages are maximum.
Maybe, Reichelt Germany does send to Sverige:
https://www.reichelt.com/se/en/shop/product/npn_to-126_transistor_80_v_4_a_36_w-5196?search=bd441
https://www.reichelt.com/se/en/shop/product/npn_to-126_transistor_80_v_4_a_36_w-5196?search=bd441
This is a new version.
I added base resistors and use identical pairs.
Distortion is still low and I have 102 mA in the output.
I added base resistors and use identical pairs.
Distortion is still low and I have 102 mA in the output.