Jean-Paul, hi
Yes but, I'm not quite there yet as this is the best I can achieve, this is with the chassis earthed and the signal GND, linked with a 0.01 TDK ceramic from the RCA in to the chassis as recommended, no direct link. Taking the in unit in and out of the chassis has confirmed the chassis is no longer a major issue (Yes more graphs, but for me useful)
These measurements have helped me to see and understand why I find the BPSP500 silent and the BK1000 still too noisy for me. I simply don't want to sit down and listen to any noise from the seating position as I have 14 mono amps on and yes I hear a small amount of transformer hum, but it's small (naim 135's do have a tendency to have a little mechanical noise). I will also try increasing the high frequency cut off and also remeasure with the measurement advice from Andrew, I'm also looking again at how to do a marginally better job with the relocation of the GND paths and reducing impedance and loop area as suggested by Bill.
I will get there and appreciate all the help the 500 amp is the same basic power amp circuit, I have three pre-amps to experiment with today as well, given the 500 has a pre amp in place as part of the unit. and the 5 of them I have are silent I haven't given up or finished yet.
This is the area (red) I am hoping to reduce further as my 18" is pretty inefficient beyond 1KHz, I have no audible noise at 50Hz and as suggested this would appear to be the measurement related - at least in part, so I'm not really looking at the 50Hz bump
Yes but, I'm not quite there yet as this is the best I can achieve, this is with the chassis earthed and the signal GND, linked with a 0.01 TDK ceramic from the RCA in to the chassis as recommended, no direct link. Taking the in unit in and out of the chassis has confirmed the chassis is no longer a major issue (Yes more graphs, but for me useful)
These measurements have helped me to see and understand why I find the BPSP500 silent and the BK1000 still too noisy for me. I simply don't want to sit down and listen to any noise from the seating position as I have 14 mono amps on and yes I hear a small amount of transformer hum, but it's small (naim 135's do have a tendency to have a little mechanical noise). I will also try increasing the high frequency cut off and also remeasure with the measurement advice from Andrew, I'm also looking again at how to do a marginally better job with the relocation of the GND paths and reducing impedance and loop area as suggested by Bill.
I will get there and appreciate all the help the 500 amp is the same basic power amp circuit, I have three pre-amps to experiment with today as well, given the 500 has a pre amp in place as part of the unit. and the 5 of them I have are silent I haven't given up or finished yet.
This is the area (red) I am hoping to reduce further as my 18" is pretty inefficient beyond 1KHz, I have no audible noise at 50Hz and as suggested this would appear to be the measurement related - at least in part, so I'm not really looking at the 50Hz bump
Also interesting that 9 of these don't have any 'hiss' or noise other than minor transformer mechanical noise. I can see the distinct lack of the 'T' !
But low impedance GND connections all individually back to the caps 0v
But low impedance GND connections all individually back to the caps 0v
Yes I do think I can work with signal GND not linked to the chassis and only the safety earth (a UK thing)
If the chassis is made from anodized aluminium, you will need to scrape through it - that’s why it’s best to check with a meter.
The signal ground and the safety earth are there for different purposes. You don’t need a safety earth for low noise.
Excessive hiss and an obscure chassis safety earthing problem points to an oscillating amplifier as previously mentioned by Bonsai . I accept the amplifier should not be oscillating but the symptoms suggest it is . To help dismiss this idea change C5 and C6 to 47pF , they appear to be Miller compensation capacitors .
Agree - HF oscillation can really wreak havoc. The HF gets into everything and is modulated by any mag fields around (transformer, wiring etc) and then gets demodulated by the diode junctions in the semi devices, appearing as buzz and hum. And any unexpected hiss or 'shh' sound is often also an indicator of this as well.
I have hunted around and will need to order some small caps, I have some polystyrene 22pf, 220pf but nothing that close to 47pf. I did also try grounding the DAC GND to the power supply and other areas just to see but no significant difference with the A>D. It is a super cheap Behringer UCA202 but alas no real difference I guess the DAC is just cheap, as no 'hum' at 50Hz I can ignore that.
As I intened to use a pre amp between the DSP and the power amp, like all the other sub amps, I tried a few options a simple 5532 base unit and a cheap sub with filter panel. No real difference other than adding a bit of noise and not better on the noise front, just worse (no surprise I guess.
Is it worth desoldering the ceramic disc caps to see if they are in spec and close to 27pf as I cant measure them accurately on the board, C5 and C6
As I intened to use a pre amp between the DSP and the power amp, like all the other sub amps, I tried a few options a simple 5532 base unit and a cheap sub with filter panel. No real difference other than adding a bit of noise and not better on the noise front, just worse (no surprise I guess.
Is it worth desoldering the ceramic disc caps to see if they are in spec and close to 27pf as I cant measure them accurately on the board, C5 and C6
Off topic (won't hurt I think 🙂) but that R3 value makes it not the most easy load to the source. It also makes that a larger value input cap is needed.
I noticed the blue sleeve Philips caps, ROE caps and tantalum caps yes THAT tantalum caps. These are very old and sometimes notorious. If you cut yourself by having 14 of such aging devices with notorious parts you have work to do.
I noticed the blue sleeve Philips caps, ROE caps and tantalum caps yes THAT tantalum caps. These are very old and sometimes notorious. If you cut yourself by having 14 of such aging devices with notorious parts you have work to do.
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Tks, I'm super cool with the naim 135 monoblocks they get serviced every 10-12 years with all new tants and electrolytics. They sound great and they are keepers for the bed channels, but much less happy with the new to me BK MF1000's !
Looks like the R3 4k7 seems to be part off the bandpass for the high frequency ?
Perhaps increasing the 1K too reduce the 100uf input cap. I did measure the input cap and it is in spec (100uf)
https://uk.farnell.com/passive-filt...wRsZJl_TiqSn6uQ8zinsV8WM4dNIBP2Z-5yWCtzdOdY4w
Looks like the R3 4k7 seems to be part off the bandpass for the high frequency ?
Perhaps increasing the 1K too reduce the 100uf input cap. I did measure the input cap and it is in spec (100uf)
https://uk.farnell.com/passive-filt...wRsZJl_TiqSn6uQ8zinsV8WM4dNIBP2Z-5yWCtzdOdY4w
No it is the 4k7 not the 1k. More or less exactly as I wrote, just like that the caps in post 122 are simply very old. The 1 kOhm is for the RC filter with C2 being an unknown value so we can not calculate the filter. Should be around 100 kHz. Anyway I don't know what the source is but with 14 amplifiers I guess some are used in parallel with regards to inputs!? Then an irregular low input impedance of the power amplifiers in parallel may have consequences.
It would be good to know the value of R9.
Yeah great and excellent and always something to do as stuff gets multiplied by 7 😉 Please do not replace the tantalums for the exact same drop type versions of the same brand/type/age. Today's tantalums by the still existing A brands are good, older stuff created the devastating reputation of tantalum caps. I notice the habit in brand oriented circles to replace old stuff for exactly the same old stuff but now unused. This is insecurity and a good thing to those that stock old parts. Certainly modern tantalum(manganese)/niobium polymer caps are much improved in many aspects.
It would be good to know the value of R9.
Yeah great and excellent and always something to do as stuff gets multiplied by 7 😉 Please do not replace the tantalums for the exact same drop type versions of the same brand/type/age. Today's tantalums by the still existing A brands are good, older stuff created the devastating reputation of tantalum caps. I notice the habit in brand oriented circles to replace old stuff for exactly the same old stuff but now unused. This is insecurity and a good thing to those that stock old parts. Certainly modern tantalum(manganese)/niobium polymer caps are much improved in many aspects.
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the diagram of post 129 has no rail decoupling - if they are missing from the board, install some.
Jean-Paul,hi
The R9 is indeed 390R, I replaced this as it was a 270R. This did help a little with noise levels the C2 band cap was two 900pF in series which measured 450 pF, I have used the BPSP spec as a start as without the inline filter this sub amp have a frequency range of 3Hz- 1KHz. At the monent I have a 22nf in so think its around 1.5Khz, easy to swap out
Ctrix, hi
Be easier to just add the circuit to the thread. As this is no longer in production and this is about solving a problem, I don't think BK will mind
I am familiar with local power rail decoupling for Opamps and the like but no experienced with power amps could you say where you might add perhaps a 100nf Ceramic or similar ?
Be easier to just add the circuit to the thread. As this is no longer in production and this is about solving a problem, I don't think BK will mind
I am familiar with local power rail decoupling for Opamps and the like but no experienced with power amps could you say where you might add perhaps a 100nf Ceramic or similar ?
The problem of changing too many things when just one issue needs to be solved. Despite the nice graphs and measurements I can not get my head around the way of solving matters. Must be that I am a tech or something like that. Introducing new variables will not solve matters.
Hypothesis: IF this device is known to be silent AND/OR if you have ones that are fully identical and silent then it is not the design itself that must be changed. Then you should not change anything anymore but merely look for the cause.
So:
Idea 1: did it occur to you to pull the fan and see if that makes a difference?
Idea 2: that 7815 might be oscillating. It has a pretty dumb voltage dropping pre regulator with a 1k2 resistor/24V Zener diode but no decoupling input cap.
Idea 3: what is the input voltage of that 7815 in reality?
Idea 4: are the main filter caps or even all electrolytic caps still the original ones? Samwha electrolytic caps were notorious in the past and these seem to be from the past.
Hypothesis: IF this device is known to be silent AND/OR if you have ones that are fully identical and silent then it is not the design itself that must be changed. Then you should not change anything anymore but merely look for the cause.
So:
Idea 1: did it occur to you to pull the fan and see if that makes a difference?
Idea 2: that 7815 might be oscillating. It has a pretty dumb voltage dropping pre regulator with a 1k2 resistor/24V Zener diode but no decoupling input cap.
Idea 3: what is the input voltage of that 7815 in reality?
Idea 4: are the main filter caps or even all electrolytic caps still the original ones? Samwha electrolytic caps were notorious in the past and these seem to be from the past.
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I honestly don't know if there is a single problem or a number of problems/issues. I also don't know if the design would benefit from changes, or some parts have aged etc. I do know that the noise is unacceptable to me and although it seems that making some of the GND alterations to the board have improved the performance of one of the boards it's still too loud to be of use in my system (its's not loud in that you would not notice it juts walking in the room, but sit in the listening position and you can hear it, which is not the case with all of the other amps
The both units are similar with the noise and I think but am not 100% sure, that the reason one is a little quieter issue to the revision of the GND on that unit
It is possible that in a more PA situation the noise is more than acceptable. The reason I am keen to pursue is the BPSP 500's have a very similar power amp design and are silent in the same position, approx same gain etc.
It is not known to be loud or noisy, but that is a very subjective thing as we know, so I am guessing as to any views of quietness and acceptability.
The both units are similar with the noise and I think but am not 100% sure, that the reason one is a little quieter issue to the revision of the GND on that unit
It is possible that in a more PA situation the noise is more than acceptable. The reason I am keen to pursue is the BPSP 500's have a very similar power amp design and are silent in the same position, approx same gain etc.
It is not known to be loud or noisy, but that is a very subjective thing as we know, so I am guessing as to any views of quietness and acceptability.
No you introduced/plan to introduce modifications which may not have to do with the hum issue. OK so these are known to be silent and this is not that subjective as 99% of customers hate hum. Simple. No serious manufacturer sells stuff that hums. Hum in audio is the engine rattling in a brand new car when the seller starts it and then wants to hand over the keys. Practically everybody refuses that new car.
So let's focus on the unusual hum without graphs but just a few simple tests. Could you reply on the ideas? I better had called them questions.
I just hope it are not completely dried out Samwha filter caps after 139 posts 😀
So let's focus on the unusual hum without graphs but just a few simple tests. Could you reply on the ideas? I better had called them questions.
I just hope it are not completely dried out Samwha filter caps after 139 posts 😀
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Humm - With the input RCA having a 0.01uf Ceramic to the case and the case earthed the majority of hum and 'GND' loop like noise is significantly reduced, also putting a pre amp in series with the DSP is better than the DSP direct in this respect. This still a minor issue as it seems somewhat inconsistent as putting other subwoofers (not bed channel amps) can increase this noise, audibly and measurably (if that's a word). I hope with more experimentation with GND, loop area and other changes I can get this to be low enough to be ignored - possibly
'Noise' the equivalent of 'hiss' - This increases with gain (no surprise) also seems that the basic pre amps have pots that do act like an arial and touching the metal gain wheel adds noise. Overall this is too high, I don't want to sit and hear the sub making a small but audible 'hiss'. I do a wonder if part of the silence of the BK 500's is the fact that I have a manual low frequency cut off and they are set at about 160Hz even though I do all digitally I preferred the results with keeping some manual roll off with the amp filters
I was hoping that trying a cheap filtered sub pre amp (Fleabay - £8) I could test this and I think this will help, but thus cheap unit is not helping with noise overall.
I did pull off the 27pf tiny discs even though one was in between heat sinks looking very much like it was fitted before adding the surrounding heat sinks. They both measure well 26-27pF
A fair challenge on the Samwha's my ESR meter has gone back for repair but the capacitance is similar to the ones fitted on my <5 year old BPSP500's. I will recheck ESR when my meter comes back. The caps are available at £10 each, so that's starting to add up with 8 of them
PS at 6.00 I will be having a drink as I am very dry 😏
'Noise' the equivalent of 'hiss' - This increases with gain (no surprise) also seems that the basic pre amps have pots that do act like an arial and touching the metal gain wheel adds noise. Overall this is too high, I don't want to sit and hear the sub making a small but audible 'hiss'. I do a wonder if part of the silence of the BK 500's is the fact that I have a manual low frequency cut off and they are set at about 160Hz even though I do all digitally I preferred the results with keeping some manual roll off with the amp filters
I was hoping that trying a cheap filtered sub pre amp (Fleabay - £8) I could test this and I think this will help, but thus cheap unit is not helping with noise overall.
I did pull off the 27pf tiny discs even though one was in between heat sinks looking very much like it was fitted before adding the surrounding heat sinks. They both measure well 26-27pF
A fair challenge on the Samwha's my ESR meter has gone back for repair but the capacitance is similar to the ones fitted on my <5 year old BPSP500's. I will recheck ESR when my meter comes back. The caps are available at £10 each, so that's starting to add up with 8 of them
PS at 6.00 I will be having a drink as I am very dry 😏