Great job and execution GCL, your build is such an inspiration. We need more SX builds, and yours came through very nicely! When you have more time, please post your subjective review versus any other amps you have in your arsenal. I'm gearing up to build one myself in the future.
Bonsai, don't forget to update the BOM in the SX build doc!
Best,
Anand.
Bonsai, don't forget to update the BOM in the SX build doc!
Best,
Anand.
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Very nice gcl!
Let us know how it sounds once you have finished it completely.
Wrt the transformers, I'd just go with what you have right there.
Very glad it's quiet and worked first time!
🙂
Let us know how it sounds once you have finished it completely.
Wrt the transformers, I'd just go with what you have right there.
Very glad it's quiet and worked first time!
🙂
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Anand, yes. I have to redo the BOM from scratch since I can't over paste with updated info like I've done before.
Thank you Bonsai, I have listened again for an hour or so and it's very enjoyable. It has plenty of bass strength with this set up. The clarity is noticeable.
On checking, it turns out that it’s not simple with the transformers. I am running off a variac at the moment at about 210v ac to set the dc at exactly 21.5v. BTW I chose 35v capacitors for the PS main caps. On 240vac the dc supplies are +/-25v. This increases dissipation by approx. 10W/channel. If I keep Iq of 1.4 A I would think it would be OK to run with these. Of course if it gets too hot I would rethink this. After a couple of hours with the open chassis the heatsinks are 44C in the centre. Or is this a bad idea for some reason?
Thanks
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You can try running your amp at +-25V. However, I would then dial the standing current down to say 1.1A to manage the heatsink temperature.
44C in the middle of the heatsink is a good temperature - so it looks like you are ok on that front (1.4A at +-21.5V)
With the specified 1.4A standing current, the sx-Amp will deliver about 28 W peak in pure class A into 8 Ohms. So dialling it down to 1.1 Amps to cater for the additional supply voltage will still give you 20W peak in class A before the amp transitions to class AB. Then you can keep your existing transformers.
44C in the middle of the heatsink is a good temperature - so it looks like you are ok on that front (1.4A at +-21.5V)
With the specified 1.4A standing current, the sx-Amp will deliver about 28 W peak in pure class A into 8 Ohms. So dialling it down to 1.1 Amps to cater for the additional supply voltage will still give you 20W peak in class A before the amp transitions to class AB. Then you can keep your existing transformers.
Thank you for your quick reply. I'll try various things and see how it goes. It will be a while before I report back, also can't resist listening to it now.
Thanks! it is an enjoyable build. Seems to be an excellent amplifier if the power is enough for your situation. It appears to have plenty of guts for my set up in a small room.
As Anand says up top we need more SX builds.
@Bonsai
I built the SX amplifier along with one of my friends and enjoyed every bit of the setup and tweaking. May be took me close to couple of months to build it as I used to use my spare time on the weekends to get this done. Now my setup is like Soekris R2R DAC -> DCB1 - SX -> Frugal Horns (MA CHR70A rated at 86db). Prior to the SX I was using a vintage Rotel 890BX power amp rated around 100+100W and for low volume listening pair with the AmpCampAmp (tweaked for 6+6W class A).
Everything was fine but since couple of months I was hearing the right channel was playing louder compared to the left channel and I thought that could be with the DCB1 which I had some issues with the PSU. But last week couple of my friends had come over for the listening and we had a longish session running to couple of hours with my setup and everybody (including me) felt that the right channel and left channel were giving different gains (in volume). We tried all sorts of completely switching off the right speaker and left and also swapping the input/signal outputs (interconnects between pre and SX) and also the speaker outs left/right swapping on the SX but the loudness remains on the right channel. So the issue is definitely with the right channel of the SX and we even swapped with the AmpCampAmp as well as my Rotel and it was perfect dead center sound imaging but with the SX it wasn't.
So I opened it and we did the checks for any loose connections but nothing of that sort and did the current at 1.4A and the DC offset on both the channels. After I did this we heard it again but it was still the same but the difference now was less compared to earlier. Not sure whether there is any issue with my build of the SX as well as I did not do the suggested closely matching of the transistors but I believe the matching does not result in the gains being mismatch. My friend who also build the same SX along with me with similar set of BOM parts has not heard it so keenly but nevertheless I requested him to do the swapping and see if he also gets the same difference.
Let me know how to go about it on resolving this difference, otherwise it plays damn good with superb punch and takes the life out of my frugal horns. The tiny 4" drivers produce so much base that my other power amps do not produce.
Thanks
I built the SX amplifier along with one of my friends and enjoyed every bit of the setup and tweaking. May be took me close to couple of months to build it as I used to use my spare time on the weekends to get this done. Now my setup is like Soekris R2R DAC -> DCB1 - SX -> Frugal Horns (MA CHR70A rated at 86db). Prior to the SX I was using a vintage Rotel 890BX power amp rated around 100+100W and for low volume listening pair with the AmpCampAmp (tweaked for 6+6W class A).
Everything was fine but since couple of months I was hearing the right channel was playing louder compared to the left channel and I thought that could be with the DCB1 which I had some issues with the PSU. But last week couple of my friends had come over for the listening and we had a longish session running to couple of hours with my setup and everybody (including me) felt that the right channel and left channel were giving different gains (in volume). We tried all sorts of completely switching off the right speaker and left and also swapping the input/signal outputs (interconnects between pre and SX) and also the speaker outs left/right swapping on the SX but the loudness remains on the right channel. So the issue is definitely with the right channel of the SX and we even swapped with the AmpCampAmp as well as my Rotel and it was perfect dead center sound imaging but with the SX it wasn't.
So I opened it and we did the checks for any loose connections but nothing of that sort and did the current at 1.4A and the DC offset on both the channels. After I did this we heard it again but it was still the same but the difference now was less compared to earlier. Not sure whether there is any issue with my build of the SX as well as I did not do the suggested closely matching of the transistors but I believe the matching does not result in the gains being mismatch. My friend who also build the same SX along with me with similar set of BOM parts has not heard it so keenly but nevertheless I requested him to do the swapping and see if he also gets the same difference.
Let me know how to go about it on resolving this difference, otherwise it plays damn good with superb punch and takes the life out of my frugal horns. The tiny 4" drivers produce so much base that my other power amps do not produce.
Thanks
Hello manniraj,
Glad to hear you like your amp!
Re your problem, it is highly unlikely that you are hearing different gains between the channels due to transistor mismatches or differences in gain if they were originally working ok.
Please check that the front end jumper (J2 IIRC) is in place on both channels.
Did you check your input and output connectors for corrosion etc?
Only other potential problem I can think of at this stage is that your feedback resistors may be damaged (also unusual - they are well rated for the job at 5 X 0.5 W.
Glad to hear you like your amp!
Re your problem, it is highly unlikely that you are hearing different gains between the channels due to transistor mismatches or differences in gain if they were originally working ok.
Please check that the front end jumper (J2 IIRC) is in place on both channels.
Did you check your input and output connectors for corrosion etc?
Only other potential problem I can think of at this stage is that your feedback resistors may be damaged (also unusual - they are well rated for the job at 5 X 0.5 W.
Thanks Bonsai, yes on both the boards the J2 jumpers are soldered properly as I had to do the check during the dc offset last week. I have used a very good quality speaker connectors as well as RCA jacks of CMC and they are all gold quoted. In fact I have even replaced the solid silver cables for the output signal connectors on the SX with the Mogami coaxial shielded cables as I noticed some hum with the transformer being closer to the output side. With the change of the shielded cables the hum disappeared.
I wanted to bring to your notice that me and my friend earlier used a 18+18V 7A rated toroidal transformer and the PSU was outputting pretty high voltage (around +/-28V compared to the ideal +/-24V if I am not wrong) and damaged couple of 1A and 5A fuses during the initial setup. In fact I ran with this trafo for almost a month or so before moving to a 15+15V 7A toroidal which brought the temperature and the current/voltage down as per your manual. The bridge rectifiers had given a problem with the high voltage and I had to remove them from the PSU and mount on the heat sinks running solid silver cables from the rectifiers to the PSU board. Not sure whether this would have resulted in the feedback resistors being damaged with the higher voltage transformer.
Can you point out the feedback resistors (naming) that I need to cross check to be sure?
Thanks
I wanted to bring to your notice that me and my friend earlier used a 18+18V 7A rated toroidal transformer and the PSU was outputting pretty high voltage (around +/-28V compared to the ideal +/-24V if I am not wrong) and damaged couple of 1A and 5A fuses during the initial setup. In fact I ran with this trafo for almost a month or so before moving to a 15+15V 7A toroidal which brought the temperature and the current/voltage down as per your manual. The bridge rectifiers had given a problem with the high voltage and I had to remove them from the PSU and mount on the heat sinks running solid silver cables from the rectifiers to the PSU board. Not sure whether this would have resulted in the feedback resistors being damaged with the higher voltage transformer.
Can you point out the feedback resistors (naming) that I need to cross check to be sure?
Thanks
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Its R12, R13, R14, R15 and R16 - if you measure across there you should get 200 Ohms.
Check that R11 is 15 Ohms. There should not be any differences between the two amps beyond about 2%.
Check that R11 is 15 Ohms. There should not be any differences between the two amps beyond about 2%.
Good luck with your amp 🙂 Hopefully it will work out fine.
I am also running soekris dac but direct into the Ovation-SX. Using the built in volume control in the dac. I have a dcb1 at hand which I will try to tap PSU from to the dac.
Sounds great.
I am also running soekris dac but direct into the Ovation-SX. Using the built in volume control in the dac. I have a dcb1 at hand which I will try to tap PSU from to the dac.
Sounds great.
Have you tried the usual suspects? Switching input cables left to right, and then speaker cables to rule those out? Also, measure DC voltage from the emitter of each output transistor to output. This may rule out a bad emitter resistor or even bad output transistor. Also check voltage at the base of each output transistor.
Yes I suspected the same initially and switched the input cables and also speaker cables but still the right channel sounds more volume compared to left. I have not checked the DC voltage from the emitter of each output transistor. I will check these, thanks
hi Andrew
in post #1790 you replaced the parts as this :
1. For Q7 use KSA1142Y in place of KSA1381
2. For Q6 use KSC2682 in place of KSC3503
3. For Q12, use KSC2690 in place of KSC3503
4. For Q13, use KSA1220 in place of KSA1381
my problem is KSA1142Y and KSC2682 also not easily found for near hfe values to be matched is there any other possible replacements
in post #1790 you replaced the parts as this :
1. For Q7 use KSA1142Y in place of KSA1381
2. For Q6 use KSC2682 in place of KSC3503
3. For Q12, use KSC2690 in place of KSC3503
4. For Q13, use KSA1220 in place of KSA1381
my problem is KSA1142Y and KSC2682 also not easily found for near hfe values to be matched is there any other possible replacements
Hello VinDiesel,
If you can get the 1381 and the 3503 then you can use those.
I offered these other parts so it would be easier to source.
If you can get the 1381 and the 3503 then you can use those.
I offered these other parts so it would be easier to source.