Curious, Would you measure a lower noise floor with these?
https://www.antekinc.com/ca-300-steel-cover/
https://www.antekinc.com/ca-300-steel-cover/
Generally I’d recommended NPO/COG for the job, but those will work fine. Keep the leads short and put the caps right at the input connector signal ground to chassis.
Thank you for the guide, Mr. Bonsai. It answers many questions I've had about wiring and laying out an amp, and changes how I will compose my work-in-progress amp.
I would very much like to learn the rationale for the design decisions. Could you please briefly remark on these points, perhaps just give pointers / keywords for further research?
1. Why twisting the power cables? This includes mains power, PSU outputs, speaker wires. Those are relatively low Z, high voltage circuits - is there any possibility for them to pick up noise that will actually be audible or at least measurable, and that would be reduced by winding?
As far as I understand (which is, admittedly, not too far) , the most noise-sensitive wire is the input, low voltage and high Z, but you gave no instruction to twist that one.
2. What if there is a single transformer instead of two? This is what makes the amp dual mono, right? So if it's a single transformer, does it simplify the wiring? Does it reduce the performance? I have more or less read the whole thread, and you said that regular stereo amps can be as good, if not better, than dual mono?
3. What's with the T part on the bulk caps? What would change if this part is reduced to a single point for all wires?
4. What about SMPS instead of toroids? Two pairs of SMPS (L/R x plus/minus) vs. a single pair with two amps fed in parallel?
5. What about homes without earth connection (no 3rd pin in the outlet)? Is it only a safety issue, or noise rejection issue as well? Based on the use of ground lifters I assume the former, but maybe I missed something.
6. The biggest amp question I have: plastic case vs. conducting case (steel, aluminium)? I would feel much safer using an insulating case, and no risk of accidentally grounding something you should not. But what about noise rejection? A metal case is a Faraday cage, right? Or wrong?
I would very much like to learn the rationale for the design decisions. Could you please briefly remark on these points, perhaps just give pointers / keywords for further research?
1. Why twisting the power cables? This includes mains power, PSU outputs, speaker wires. Those are relatively low Z, high voltage circuits - is there any possibility for them to pick up noise that will actually be audible or at least measurable, and that would be reduced by winding?
As far as I understand (which is, admittedly, not too far) , the most noise-sensitive wire is the input, low voltage and high Z, but you gave no instruction to twist that one.
2. What if there is a single transformer instead of two? This is what makes the amp dual mono, right? So if it's a single transformer, does it simplify the wiring? Does it reduce the performance? I have more or less read the whole thread, and you said that regular stereo amps can be as good, if not better, than dual mono?
3. What's with the T part on the bulk caps? What would change if this part is reduced to a single point for all wires?
4. What about SMPS instead of toroids? Two pairs of SMPS (L/R x plus/minus) vs. a single pair with two amps fed in parallel?
5. What about homes without earth connection (no 3rd pin in the outlet)? Is it only a safety issue, or noise rejection issue as well? Based on the use of ground lifters I assume the former, but maybe I missed something.
6. The biggest amp question I have: plastic case vs. conducting case (steel, aluminium)? I would feel much safer using an insulating case, and no risk of accidentally grounding something you should not. But what about noise rejection? A metal case is a Faraday cage, right? Or wrong?
As a first-time builder, this thread is a great resource - thanks Andrew @Bonsai.
Hopefully it's still alive, as I have a great example of how-not-to-do-it for you, and would welcome some specific guidance.
I have 2x working TDA7293 mono amps, thanks to the excellent work of Dibya, Jhofland, X and many others over on the Xmas amp thread.
I chose a dual mono config in order to try and maximise the sound stage / imaging potential of my finished power amp, without the added complexity of a twin mono block form factor.
I was offered some excellent Canterbury Windings 230 / 20-0-20 200VA audio grade transformers, which fit the bill, and drove the choice of chassis, which is 3U x 19" - plenty of room to work in. Heat sinks are ex-Dell workstation. PSUs are commercial off-the-shelf.
The photo shows my current layout - a first attempt, guided by intuition and experimentation more than engineering.
Hopefully it's safe - safety bond is present and correct. Exposed metal parts are covered; heat sinks and trafo interwinding screens are connected to 'dirty' star ground (brass buss bar for now) which is, in turn, connected to chassis bond.
The 'clean' PSU 0V ref and amp board grounds are connected to the 'dirty' ground via a ground loop breaker circuit incorporated into the amp board (upper right standoff hole). Signal ground at the speaker output from the amps are connected directly to each respective PSU 0V. Signal grounds at the input are not connected to each other.
The good news is that in this config, each channel, when connected to a single RCA input, is quiet - dead silent, with ear close to speaker.
In other news, there's a hum when both RCA inputs are connected, suggest a cross-channel ground loop.
That's about as far as I've got so far. The obvious first next step was to connect the input signal grounds - this didn't cure it.
I'd welcome some general advice, particularly around safety if I've made some obvious howlers, but thought I'd update this thread with photos and descriptions of my progress and invite suggestions from the community on what to prioritise and how to proceed.
It feels like I'm very close to getting this amp 'good enough' to really enjoy. The sound so far has been terrific.
Regards, Haden
Hopefully it's still alive, as I have a great example of how-not-to-do-it for you, and would welcome some specific guidance.
I have 2x working TDA7293 mono amps, thanks to the excellent work of Dibya, Jhofland, X and many others over on the Xmas amp thread.
I chose a dual mono config in order to try and maximise the sound stage / imaging potential of my finished power amp, without the added complexity of a twin mono block form factor.
I was offered some excellent Canterbury Windings 230 / 20-0-20 200VA audio grade transformers, which fit the bill, and drove the choice of chassis, which is 3U x 19" - plenty of room to work in. Heat sinks are ex-Dell workstation. PSUs are commercial off-the-shelf.
The photo shows my current layout - a first attempt, guided by intuition and experimentation more than engineering.
Hopefully it's safe - safety bond is present and correct. Exposed metal parts are covered; heat sinks and trafo interwinding screens are connected to 'dirty' star ground (brass buss bar for now) which is, in turn, connected to chassis bond.
The 'clean' PSU 0V ref and amp board grounds are connected to the 'dirty' ground via a ground loop breaker circuit incorporated into the amp board (upper right standoff hole). Signal ground at the speaker output from the amps are connected directly to each respective PSU 0V. Signal grounds at the input are not connected to each other.
The good news is that in this config, each channel, when connected to a single RCA input, is quiet - dead silent, with ear close to speaker.
In other news, there's a hum when both RCA inputs are connected, suggest a cross-channel ground loop.
That's about as far as I've got so far. The obvious first next step was to connect the input signal grounds - this didn't cure it.
I'd welcome some general advice, particularly around safety if I've made some obvious howlers, but thought I'd update this thread with photos and descriptions of my progress and invite suggestions from the community on what to prioritise and how to proceed.
It feels like I'm very close to getting this amp 'good enough' to really enjoy. The sound so far has been terrific.
Regards, Haden
Hello Alexium, apologies for the very late reply - I'm not following this thread so I missed your questions.
1. Twisting cables. The radiated electromagnetic field (EMR) is i.a.o. determined by the area of the radiating source on the generator side and the loop area on the receiving side as well. By twisting the generating cables (so for example the mains wires to the transformer) you are minimising the generator loop area, so you therefore minimize the radiated noise. The same logic applies to the receiving loop. If you twist the input wires, the loop is minimized so you reduce noise pickup. Builders most often use screened cable for the input wiring - this works because the loop area is minimized due to the cable construction - twisting works just as well. You must always twist the inputs wiring or use screened cable for best noise performance.
2. There has been a lot of discussion about dual mono design, mono blocs, dual transformers etc. The engineering says if the amplifier PSRR is good - which most amplifiers are - then dual mono construction to improve channel separation or cross channel interference through the PSU is not really needed. Douglas Self also discusses this point in one of his books. However, dual mono construction if that is what you want to do, is fine, but you have to take precautions to ensure you don't create any cross channel ground loops - the best way to achieve this is to make sure there is one and only one connection between the channels.
3. The 'T' is simply a way of making sure to manage the power grounds so that you do not create common impedance coupling. The most important thing is that there is only 1 connection between the '-' which is where you take off to connect all the amplifier grounds. On a typical amp you will have 10-15A peak charging currents running across the '-' part of the 'T' and if you simply make your ground connections to this part, you will create hum issues. A star ground works just as well, but the rule of course must be that the junction of the two filter capacitors must come into the star from the '-' part of the 'T' so that the charging current pulses are kept out of the amplifier PSU 0V and signal grounds.
4. I have not tried using SMPS on any of my audio work, but either approach you ask about will work successfully. The same grounding rules as used with a transformer apply but in addition, take care for any potential HF noise coupling.
5. You only need a earth connection for safety - you do not need it to reduce mains noise. You can see this from double insulated consumer equipment (CD players, TV etc) that does not have an earth connection and yet is completely quiet. For double insulated products that do not have an earth connection, HF noise filtering is usually accomplished mains LC filters, clamp on ferrites and special transformer winding techniques in the case of SMPS. These techniques (and especially with SMPS) work very well and there are nowadays few cases where these products generate excessive noise.
6. You can build a quiet amplifier without a metal housing. At LF, the metal housing if made of aluminium, offers virtually no attenuation from externally generated mains noise EMR . If the housing is made of mild steel, it will offer some protection from external radiated LF noise. The issue comes with HF i.e. RFI. Here, a metal housing does offer protection from RFI ingress, provided you follow the guidelines for interconnect cables and make sure that at HF the housing(s) and cables form a single enclosure (see the ground loop slides for an explanation of this). If you are building an amp in a metal housing, you should make sure it has a safety ground (earth) connection. Although I show how to use a ground lifter, I prefer not to and none of my builds since 2013 have used them although I provide that facility on some PCB's.
Note, there is one special case with an aluminium (or mild steel) chassis and mains noise and that is if the transformer inside the aluminium chassis is radiating noise, it will generally be quieter in a fully enclosed chassis. This is because the radiated field will couple to the metalwork and cause circulating currents to flow in the metalwork. Without the metal enclosure, the radiated field just couples to the amplifier wiring, generating noise. This is why if you measure an amplifier's noise floor with the chassis lid off, its usually a bit noisier than when you have it screwed in place.
🙂
I have to add to bonsai's excellent answer that I see several errors in your build (which is normal considering it's the first one).
THE basic rule is to always do a "BLANK" test on a breadboard before the final clean assembly, then when everything is ok, the rest is common sense, such as allowing the heatsinks to "breathe" to have a current of convention which will assure the dissipation.
I also see that you have not two but three supply transformers and that can be a problem, moreover your supply transformers are not "closed" or "short circuited" via a bell or upper and lower spacers which can be important with toroidal transformers.
it's probably not going to make you happy (but that's how you learn) but (for me) the only way to eliminate your BUZZ is to take everything apart and try it out in your box or on a board. bread .
That's just my opinion, do what you want. 😉
THE basic rule is to always do a "BLANK" test on a breadboard before the final clean assembly, then when everything is ok, the rest is common sense, such as allowing the heatsinks to "breathe" to have a current of convention which will assure the dissipation.
I also see that you have not two but three supply transformers and that can be a problem, moreover your supply transformers are not "closed" or "short circuited" via a bell or upper and lower spacers which can be important with toroidal transformers.
it's probably not going to make you happy (but that's how you learn) but (for me) the only way to eliminate your BUZZ is to take everything apart and try it out in your box or on a board. bread .
That's just my opinion, do what you want. 😉
Well, diagnosis is underway. I'm working my way through @Bonsai 's helpful presentations on wiring up amps and preventing hum and noise problems, to help further my understanding.
A question, though, at this stage - I have identified a cross-channel ground loop, but there is phase cancellation too. When I plug both channels in, the bass diminishes (compared to one channel only playing) and there's a 'rushing' out-of-speakers effect, suggesting to me that the channels are out of phase.
Is it likely this is a symptom of the same issue, or might I have something else going on? I've checked and double-checked input and output polarity.
A question, though, at this stage - I have identified a cross-channel ground loop, but there is phase cancellation too. When I plug both channels in, the bass diminishes (compared to one channel only playing) and there's a 'rushing' out-of-speakers effect, suggesting to me that the channels are out of phase.
Is it likely this is a symptom of the same issue, or might I have something else going on? I've checked and double-checked input and output polarity.
Does the bass diminish listening to the speakers, or is the bass diminishing because to measured the output voltage of the amp at low frequencies, say with a scope?
Have you got you speakers phased correctly? If the + and - terminals are swapped on one of the channels you will get this problem.
Any help on how to dual mono preamp grounding? I imagine if its done the same way as your amp the ground loop is inevitable because the bonded input of the preamp and the amp forms a big loop.
I've checked the internal input and speaker output wiring, but will triple-check later as this seems a likely cause.
I mean that the sound appears to be coming from in between the speakers. I know that imaging in this way can be a desirable design goal, but it just sounds wrong - the bass is not present compared to playing from only one input.
The amp is on my bench in the garage, with a floating, battery operated source / pre-amp.
This evening I will bring it in and connect to my main source, pre-amp and speakers, which will allow us to eliminate whether there is an issue at source.
I mean that the sound appears to be coming from in between the speakers. I know that imaging in this way can be a desirable design goal, but it just sounds wrong - the bass is not present compared to playing from only one input.
The amp is on my bench in the garage, with a floating, battery operated source / pre-amp.
This evening I will bring it in and connect to my main source, pre-amp and speakers, which will allow us to eliminate whether there is an issue at source.
I would never put on my HPs, connect it to the power amp output and move around things inside a power amplifier - what if you get a "blip" or "blob" for some reason - you eras will bleed. Beware!
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Dual mono wiring questions.
Hello Gents,...I'm working on the Wolverine amp with the follwing specs:
2 500VA transformers (one per channel) with 4 fullwave rectifiers. Each transformer has 2 seperate secondaries (no centre tap) of 42 VAC > approx 57.5 DC
I'm awaiting the PSU boards so meanwhile I'm looking for some wiring position advise. I've read a lot about it but are still a bit unsure on the do's and don'ts as this is my very first diy amp.🙂
willem
Target setup
Hello Gents,...I'm working on the Wolverine amp with the follwing specs:
2 500VA transformers (one per channel) with 4 fullwave rectifiers. Each transformer has 2 seperate secondaries (no centre tap) of 42 VAC > approx 57.5 DC
I'm awaiting the PSU boards so meanwhile I'm looking for some wiring position advise. I've read a lot about it but are still a bit unsure on the do's and don'ts as this is my very first diy amp.🙂
- I've stacked the transformers with one of them upside down. Is that good or not in terms of cancelling out eachothers emf / noise?
- The 4 mains wires (white ones). I was thinking of putting them below the chassis plate. Is that good practice or doen't it matter?
- Filter cap capacity. I was thinking about 4 caps per channel with 10.000 uF / 80V caps. Is that suffienct
willem
Target setup