I'll try to intall a wire short across each R17 when I get a little time, probably in a day or two now. Let's see how that works out but if there's still a problem my inclination is to just get some replacement boards as the low cost makes that a viable route, but maybe a hot-rodded board might be an even better option?
I'm not convinced that a resistor that's been overloaded and raised its resistance over 10X its marked value is still going to obey Ohm's law. But it might. The current through R17 on a healthy board would be about 45mA normally. The idle current for the whole amp is about 60mA.
Having a look at the Cinemag data for the transformer you love in the pdf, are there two versions of it? I ask because it looks like the drawings on the left show a trafo with wires coming out of various colours whereas the two sketches on the right show a slightly larger diameter trafo with 8 PCB pins on it. If there are two variants I'm not seeing two order codes. Nor do I see anywhere the windings-to-pins diagram that's needed to create a PCB footprint for the right-hand version. Any hope of getting the missing info out of Cinemag do you reckon?
Hi Richard,
Love? More like a blind date, set up by yourself : )) Either way, I am ready to mingle! No idea, the staff said they are super busy at the moment so replies to mails are thin the ground, still enquiring about custom or similar un advertised designs.
My gut leans into them being the same transformer with a different connection out, for flexibility, therefore packaging differs for the footed version. It would make sense that they use the same 'footprint' part over several models.
I will certainly ask in the next mail, others are welcome to contact them too, a tactical offensive may bring them out the trenches.
I gave that a try, and it's dead silent. Just for the sake of testing I also tried Kubelik in place of DecaDAC using the included regulator board, still had static. It seems as though I am in need of the buffer you are working on 😁
On a side note, I am also interested in the "to 11" version being proposed. I am curious if the boards could be used with a balanced input instead of the trafo, or would this defeat the whole purpose?
Ben - I had a long look at your amp layout yesterday and scratched my head a lot. I do have a couple of questions arising from that :
1. Is the power for the DAC originating from an external transformer? I see a pair of wires trailing to what might be a socket at the rear.
2. Have you double checked the connection integrity of your 0V wires between the SMPSUs and regulator board? I ask because putting two wires into one of those terminal blocks IME sometimes doesn't connect well to both.
Without knowing what's the issue here I'd hesitate to recommend my up-coming buffer board as a fix to the problem! I'm not clear on what you mean by 'balanced input' - do you mean you just want to supply a balanced signal direct to the TDA8932? That's quite a low signal level (approx 300mVRMS) due to the high gain of the chip so might run into noise problems (both thermal and stray pick-up).
The amp-to-11 is coming along, wifey is creating new footprints for the PCB. It doesn't look like we can accommodate some of the totally crazy capacitor suggestions within a 10*10cm constraint. If height isn't a problem we might consider a plug-in board for jumbo-sized parts along the lines of the filter boards for Deca DAC, but its early days yet.
@Shertzy - if you get continued radio silence from Cinemag mention it on the thread and I'll send them a question on the variants of trafo and pinout.
1. Is the power for the DAC originating from an external transformer? I see a pair of wires trailing to what might be a socket at the rear.
2. Have you double checked the connection integrity of your 0V wires between the SMPSUs and regulator board? I ask because putting two wires into one of those terminal blocks IME sometimes doesn't connect well to both.
Without knowing what's the issue here I'd hesitate to recommend my up-coming buffer board as a fix to the problem! I'm not clear on what you mean by 'balanced input' - do you mean you just want to supply a balanced signal direct to the TDA8932? That's quite a low signal level (approx 300mVRMS) due to the high gain of the chip so might run into noise problems (both thermal and stray pick-up).
The amp-to-11 is coming along, wifey is creating new footprints for the PCB. It doesn't look like we can accommodate some of the totally crazy capacitor suggestions within a 10*10cm constraint. If height isn't a problem we might consider a plug-in board for jumbo-sized parts along the lines of the filter boards for Deca DAC, but its early days yet.
@Shertzy - if you get continued radio silence from Cinemag mention it on the thread and I'll send them a question on the variants of trafo and pinout.
Yes, the DAC is powered by an external transformer. I have two different ones that I tried, one AC and one DC. Didn't seem to make a difference.
Yes, I have double and triple checked those connections. I did find a few poor connections in other places while going over it. I tried every combination of connecting 0Vs I could think of.
Not in the picture, but I did also try with wires soldered directly to the board, then to a bridged header connector to avoid having multiple wires in the terminal block.
That's ok, it seemed like it might be worth a try since I have no issues with with amps or DAC on their own with other equipment. I just can't get them to play nice with each other. Which is not a deal breaker, but it is a little frustrating given that DAC>Amps is a proven solution.
That's what I was thinking. I have a preamp with balanced outputs and wondered if it could go directly to TDA8932 to save on Cinemas on the amp-to-11. Sounds like it would be asking for trouble though.
That didn't take long. second R17 replaced with a wire link and all good, music playing through both MonoAmp boards now. Both yellow LEDs equally bright and no sign of the red LEDs flickering so all seems rock steady.
Is there any downside to removing R17? As for the cause of the malfunction, I'm not sure how it might have done it but the fault definitely occured when I used the SMPS brick that was faulty?
I'm only using my test/sacrificial speaker so can't form any subjective view on the sound quality but it seems pleasant enough at the moment. I'll try it with some proper speakers a bit later.
Thanks for a nice little project and your support with fixing the problem Richard.
Is there any downside to removing R17? As for the cause of the malfunction, I'm not sure how it might have done it but the fault definitely occured when I used the SMPS brick that was faulty?
I'm only using my test/sacrificial speaker so can't form any subjective view on the sound quality but it seems pleasant enough at the moment. I'll try it with some proper speakers a bit later.
Thanks for a nice little project and your support with fixing the problem Richard.
The role of R17 is as part of a low-pass filter to reduce HF content prior to the LM317 regulator. Normally when fed with a SMPSU there's appreciable high frequency ripple and 3 terminal regs aren't very good at rejecting that. I don't know if deleting the resistor will be audible though. I'll introduce a change on future boards where I replace the 2R2 with an inductor. Hopefully an inductor's more resistant to abuse, it'll also make a better filter at the frequencies of SMPSU ripple (40kHz and up).
Good work btw in getting these modules back on their feet!
I have some PCBs for the ACA filters that Guglielmo linked to in post #111
https://www.diyaudio.com/community/...w-8r-mono-amp-kits.359193/page-6#post-6879305
So maybe that would be a good solution. I don't really want toapply the soldering iron to the R17 bads a couple more times as I can see it ending in tears.
https://www.diyaudio.com/community/...w-8r-mono-amp-kits.359193/page-6#post-6879305
So maybe that would be a good solution. I don't really want toapply the soldering iron to the R17 bads a couple more times as I can see it ending in tears.
I've been having a more extended listen this morning using an old pair of Mission 773 floorstanding speakers - you know, this is a pretty good little amp, very easy to listen to with nothing that draws attention to the amplifier. Not surprisingly, given the value for money proposition the MonoAmps represent, the sound falls a little short of what my best amps (300B and 6C33C SE-OTLs) can do but I happily listened for over an hour and only stopped because I was told 'It's Christmas day and you're being unsociable!'.
The parts for the ACA filter should be here next week so let's see what that does. I can't help wondering about what a hot-rodded version mght deliver.
Thanks for this little project Richard, very enjoyable.
The parts for the ACA filter should be here next week so let's see what that does. I can't help wondering about what a hot-rodded version mght deliver.
Thanks for this little project Richard, very enjoyable.
Happy belated Christmas Ray, Richard et al.
I recently came across this little circuit for improving an LM317 output to seriously low noise. It was developed on a russian forum and was shared by traktorist3d on the Miro AD1862 thread. He also does a dual rail version.
The transistors Q1 and Q2 are actually sot32 and are mmbt3904 and 3906. I'm struggling to find the D45H11 in stock anywhere I use.
Maybe one to consider for the low current draw rail on the amp?
I recently came across this little circuit for improving an LM317 output to seriously low noise. It was developed on a russian forum and was shared by traktorist3d on the Miro AD1862 thread. He also does a dual rail version.
The transistors Q1 and Q2 are actually sot32 and are mmbt3904 and 3906. I'm struggling to find the D45H11 in stock anywhere I use.
Maybe one to consider for the low current draw rail on the amp?
Hi Jim. I have some D-Noizator PCBs but I think they would be overkill for Richard's little amp and if I wanted to upgade from the LM317 I would be more inclined towards something like this;
https://www.ebay.co.uk/itm/255168965838?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649
Let's see what comes to pass with the souped-up MonoAmp.
Oh, and festive good wishes to you.
https://www.ebay.co.uk/itm/255168965838?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649
Let's see what comes to pass with the souped-up MonoAmp.
Oh, and festive good wishes to you.
Yes, I've seen there are cheaper regs available but i choose to buy from Alexey at LDO because I know what I'm getting. I've bought a few regs from him before, plus he's very helpful.
I'll have a peek inside my amp a bit later - just taking a short coffee break from soldering up the Xen I/V boards.
I'll have a peek inside my amp a bit later - just taking a short coffee break from soldering up the Xen I/V boards.