I will try some of these PEGs here. Maybe they are all very good audio capacitors. But not for another two weeks;-)
https://www.mouser.de/c/passive-com...electrolytic-capacitors-axial-leaded/?m=KEMET
I got myself a PA-940. Super condition. I listened to it yesterday and compared it with the 1-stage follower in my NAD. And also did two, three mods quickly. I'll open a PA-940 thread today or tomorrow.
If people would knew: this PA-940 also sounds great. It's just a 2-stage SE preamp and a 2-stage complementary transes push-pull power follower. Almost identical to the NAD, but with many fewer faults, and much more "power". You practically can't buy anything as cool as this in the analog transistor pp "HiFi", "High-End" sector.
However, the transformer is fat! I have 3 meters distance, but after 20 minutes of listening to music I'm exhausted. I will probably remove the transformer and place it 6 meters away;-) This is a general recommendation - to ALL: keep the transformers far away, set up toroidal transformers and point the "hole" towards the listening position (lowest EMF). Many "square" ones have their lowest EMF at the top or bottom, so a steel plate is angled and the transformer is screwed to it tilted. This is occupational safety and health protection! Please also pay attention to your neighbors and children and cats and dogs and budgies and fish and dust mites;-) This is NOT taught in standard electrical training courses - just as little as audio or method development and criticism and others;-)
One reason why many of the people writing here are irritable, driven, restless and quick-tempered, sleapless, with palpitations and headaches: they are sitting in the EMF of their measuring devices and their many and often fat supposedly High End devices)-;
BUT: after a few weeks I connected my little 2 watt SE again. First of all: the difference is huge, like galaxy and sun system. These push-pull concepts sound tired, flat, gray, overcast, powerless. The bass is also practically non-existent, neither in terms of resolution, contour nor power. But my 2 watts SE can't reach disco levels;-) Complementary parts PP concepts sound (in comparision) distorted, dirty and lifeless even at a single watt)-;
Nevertheless, my advice is to work step by step on one or two already planned and built push-pull concepts in order to develop, to discover, to get know the basics for good sound, for audio.
Some caps above are ordered.
If people would knew: this PA-940 also sounds great. It's just a 2-stage SE preamp and a 2-stage complementary transes push-pull power follower. Almost identical to the NAD, but with many fewer faults, and much more "power". You practically can't buy anything as cool as this in the analog transistor pp "HiFi", "High-End" sector.
However, the transformer is fat! I have 3 meters distance, but after 20 minutes of listening to music I'm exhausted. I will probably remove the transformer and place it 6 meters away;-) This is a general recommendation - to ALL: keep the transformers far away, set up toroidal transformers and point the "hole" towards the listening position (lowest EMF). Many "square" ones have their lowest EMF at the top or bottom, so a steel plate is angled and the transformer is screwed to it tilted. This is occupational safety and health protection! Please also pay attention to your neighbors and children and cats and dogs and budgies and fish and dust mites;-) This is NOT taught in standard electrical training courses - just as little as audio or method development and criticism and others;-)
One reason why many of the people writing here are irritable, driven, restless and quick-tempered, sleapless, with palpitations and headaches: they are sitting in the EMF of their measuring devices and their many and often fat supposedly High End devices)-;
BUT: after a few weeks I connected my little 2 watt SE again. First of all: the difference is huge, like galaxy and sun system. These push-pull concepts sound tired, flat, gray, overcast, powerless. The bass is also practically non-existent, neither in terms of resolution, contour nor power. But my 2 watts SE can't reach disco levels;-) Complementary parts PP concepts sound (in comparision) distorted, dirty and lifeless even at a single watt)-;
Nevertheless, my advice is to work step by step on one or two already planned and built push-pull concepts in order to develop, to discover, to get know the basics for good sound, for audio.
Some caps above are ordered.
Oh my god, I have missed this so much. These amplifiers are such unbelievable pleasure machines! But at least now I am on the positive side of the balance sheets. So we're back in business.
Finally some time off work, time to study all of this goodness, but I've been enjoying music so much 🫠 I couldn't bring myself to do anything with the amp lest the music would have to stop. I know I will, I want to hear more, but it's so good already, I just want it to keep playing.
Finally some time off work, time to study all of this goodness, but I've been enjoying music so much 🫠 I couldn't bring myself to do anything with the amp lest the music would have to stop. I know I will, I want to hear more, but it's so good already, I just want it to keep playing.
PA-940 thread starts:
https://www.diyaudio.com/community/...y-stage-audio-jb-systems.416921/#post-7775600
https://www.diyaudio.com/community/...y-stage-audio-jb-systems.416921/#post-7775600
C 411, C 412 removed. There does seem to be a bit of a greater clarity and less mushiness. I can hear the voice more clearly and understand better.
R 407, R 408 removed. I'm trying to hear a difference, but I don't think I'm hearing anything. Something sounds different, but I think it's still the same improvement I'm witnessing from C 411 and C 412 that makes it sound different from what I've gotten used to.
One thing new is that when the potentiometer is not turned all the way up there is a lot of noise, but I cannot tell which change caused this. And the general noise floor seems to have raised.
Also the amp no longer plays upon disconnecting the power. I'm afraid it might be getting direct current to the speakers, oh and the bias is way off. 3.15V is the best that I can get it turning the dial all the way to one side. With resistor back in place the bias is 0.015 V also turned all the way to one side. For now these resistors are put back into place.
#11
#11
#13
#15
#48
#35
#43
I replaced the main power transes (Q415 Q417) on one side, but I get intermittent connectivity between the middle leg and the heatsink. Deburring wasn't needed as mine was clean. I'm using a thermal paste with silver so I thought that might have been the issue, but I tested it and it's not conductive to electricity. Mica disks seem to fit exactly.. I will try to remount them (❍ᴥ❍ʋ)
R 407, R 408 removed. I'm trying to hear a difference, but I don't think I'm hearing anything. Something sounds different, but I think it's still the same improvement I'm witnessing from C 411 and C 412 that makes it sound different from what I've gotten used to.
One thing new is that when the potentiometer is not turned all the way up there is a lot of noise, but I cannot tell which change caused this. And the general noise floor seems to have raised.
Also the amp no longer plays upon disconnecting the power. I'm afraid it might be getting direct current to the speakers, oh and the bias is way off. 3.15V is the best that I can get it turning the dial all the way to one side. With resistor back in place the bias is 0.015 V also turned all the way to one side. For now these resistors are put back into place.
#11
I removed F504 4A fuse and f505 1A fuse. I think the difference is rather subtle if it's there, but the bass seems to be a little bit tighter and clearer. Other than that I'm not sure I'm even hearing a difference. Did I remove the correct fuses? Are these the lower power rated transformer windings?
#11
Just so that I don't make a mistake, these are the C 503 and... which capacitors that I shall remove?
#13
#14
I seem to be unable to locate Q 401 and Q 402 neither in the manual nor on the actual board. And pardon the ignorance, but how does one connect this trimmer exactly? What kind of trimmer should I be looking to purchase? When we talk about ground are we talking to the same negative lead from the speakers or is there another place I should be looking for ground. 120kOhm I reckon is achieved by adjusting the aforementioned trimmer.
#15
You recommend replacing the original coupling capacitors with Panasonic KA-A. Which caps are to be replaced? And should all the original values be maintained or is that open to experimentation?
#48
Well I hope you don't listen to laptop soundcard ALL of the time. As for bridging the potentiometer, do I understand correctly that I am to remove the wires I solder to C 302 and C 301 and solder them directly to the RCA rca sockets? The other ends soldered to R 401 and R 402 should remain in the same place? I'm sorry if these are stupid questions, I'm still pretty ignorant as to where is what on the circuit board.
#35
So, should I do some modification here as well with the C 433, 435 and 434, 436?
#43
Are R 421, R 423 and R 422, R 424 supposed to be replaced by 1 kOhm each or R 421 and R 423 replaced by one 1 kOhm, if so which one should be the one to house the resistor and which one should be left empty?
I replaced the main power transes (Q415 Q417) on one side, but I get intermittent connectivity between the middle leg and the heatsink. Deburring wasn't needed as mine was clean. I'm using a thermal paste with silver so I thought that might have been the issue, but I tested it and it's not conductive to electricity. Mica disks seem to fit exactly.. I will try to remount them (❍ᴥ❍ʋ)
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F 503, F 504, both 4 A, are the power amp fuses (original 1 1/2 power amp stage;-). Remove one of these.
I hadn't even tried F 505 and F 506. THese are the "pre amps" (active psus) and the green LED.
The nice thing about these fuses is that you can simply put them in and take them out so that you can quickly and easily compare them repeatedly.
Q 401 and Q 402 are the very first input transistors. This is difficult to recognize on the circuit diagram. These should be closest to the newly laid input cable.
Trimmer: I mostly use these things. They can be set very precisely and sound even better than most fixed resistors.
Yea: ground = negative load from the speakers too. To be on the safe side, simply connect a Ohm meter to speaker minus or cinch minus or power supply ground.
120 kOhm will be the set value between base (of Q 401 and Q 402) and ground. I will probably use a lower trimmer later, perhaps 500 k Ohm. The value between base and ground should then be less than 50 kOhm. Let's see.
Attachments
C 401, C 402, both input.
C 429, C 430, both bias-network bypass - these about 50 V types.
The capacitance values are based on the resistance values. Here we want to have a lower cut-off frequency of < 20 Hz.
As a rule, coupling capacitors cannot be too large. Some are used as a high-pass filter (record player bass, for example). Here the value is chosen on purpose.
Many people use smaller values because they want to use "high-quality audiophile capacitors", because small electrolytic capacitors are usually said to sound worse. If you compare components, you will find equally good or better sounding electrolytic capacitors that enable a higher capacitance and therefore a lower frequency limit.
Yes, correct.
(Exacter: The other ends to C 401, C 402 - if you want to remove R 401, R 402)
Leave all the others in for now.
With a half wave symmetrically constructed follower, there should be no more oscillation problems. I think I will run both the power follower without feedback and also take the last driver, follower of the preamp out of feedback. I'll see if I can limit the feedback to the Volt amplifiers (Q 401 + Q 405, Q 402 + Q 406) only. It may well be that then there are no, or only minor (or other;-?) oscillation problems;-)
Later.
C 405, C 406 are removed. So remove both Rs: R 421, R 423 and R 422, R 424 and set a new 1 kOhm resistor each over the entire route, right across. Regardless of the courses and holes in the circuit board.
I enlarged the hole here by deburring the contact point. I also chose new washers with a smaller hole. Then I moved the transistor back and forth a little until it fitted. Some kind of miracle is going on here;-)
I don't use thermal paste meanwhile. This is usually not necessary. It also makes the work cleaner and faster.