aussievintage 3,859 Posted October 21, 2020 Share Posted October 21, 2020 6 minutes ago, JoelG said: Hi all, just after a good technician to repair one of my vintage marantz mono blocks. One amp is running way hotter than the other... Not sure if it's the hot one or cool one that's the problem though, as both sound fine and they always ran hot. Anyway any recommendations for a amp guru in Melbourne would be much appreciated. Joel Hopefully just a bias adjustment. I had an stereo amp that had one channel running hotter than the other. Yes, still sounded fine in both channels. That's all it was, just needed the bias reset. 1 Link to post Share on other sites
JoelG 1 Posted October 21, 2020 Share Posted October 21, 2020 1 minute ago, aussievintage said: Hopefully just a bias adjustment. I had an stereo amp that had one channel running hotter than the other. Yes, still sounded fine in both channels. That's all it was, just needed the bias reset. Ok, I'm not very tech savvy but I kinda thought class A was just full on all the time so bias doesn't come into it? Happy to be wrong about this and if it's just a simple adjustment I will be stoked 👍 Link to post Share on other sites
aussievintage 3,859 Posted October 21, 2020 Share Posted October 21, 2020 14 minutes ago, JoelG said: Ok, I'm not very tech savvy but I kinda thought class A was just full on all the time so bias doesn't come into it? Happy to be wrong about this and if it's just a simple adjustment I will be stoked 👍 No, class A still has a bias setting. It's just set a lot higher than for class A/B to ensure all output devices never turn off - hence the "full on all the time" thing. The only difference in design is the ability to have that much adjustment on the bias, and to have much bigger heatsinks and cooling Also, some amps that call them selves class A, are only class A up to a certain output power, then behave as class A/B at the top end of their capabilities. 1 Link to post Share on other sites
andyr 5,895 Posted October 21, 2020 Share Posted October 21, 2020 11 minutes ago, JoelG said: Ok, I'm not very tech savvy but I kinda thought class A was just full on all the time so bias doesn't come into it? 👍 AIUI, yes, Class A is "on" all the time - but, if it's a tube amp then 'bias' is involved. And I believe that while the Class A circuit draws a constant current from the PS ... the amount being wasted in heating the heatsinks reduces, as the signal level goes up. So driving the spkrs hard actually results in the amp getting less hot than when the volume is low. Andy Link to post Share on other sites
JoelG 1 Posted October 21, 2020 Share Posted October 21, 2020 2 minutes ago, aussievintage said: No, class A still has a bias setting. It's just set a lot higher than for class A/B to ensure all output devices never turn off - hence the "full on all the time" thing. The only difference in design is the ability to have that much adjustment on the bias, and to have much bigger heatsinks and cooling Also, some amps that call them selves class A, are only class A up to a certain output power, then behave as class A/B at the top end of their capabilities. Ok, that's good to know... Hopefully it's an easy fix then. 🤞 Thanks, Joel Link to post Share on other sites
aussievintage 3,859 Posted October 22, 2020 Share Posted October 22, 2020 1 minute ago, andyr said: And I believe that while the Class A circuit draws a constant current from the PS ... the amount being wasted in heating the heatsinks reduces, as the signal level goes up. So driving the spkrs hard actually results in the amp getting less hot than when the volume is low. What really is happening is that the output devices spend more time away from the max power rating curve. See below. The loadline (purple-bluish) is the sloping straight line. The curved line shows 25 watts dissipation, in this instance. As the amplifier outputs a sinewave, it 'travels' up and down the loadine. You can see in this example, it even exceeds 25 watts for a short time. At small, or zero signal, it sits in the middle at the biased operating point and will get hottest. As the magnitude of the signal increase, it spends more and more time towards either end of the load line, and so power dissipated, on average, is less. Another example for triodes with a couple of loadlines Link to post Share on other sites
JoelG 1 Posted October 22, 2020 Share Posted October 22, 2020 16 minutes ago, aussievintage said: What really is happening is that the output devices spend more time away from the max power rating curve. See below. The loadline (purple-bluish) is the sloping straight line. The curved line shows 25 watts dissipation, in this instance. As the amplifier outputs a sinewave, it 'travels' up and down the loadine. You can see in this example, it even exceeds 25 watts for a short time. At small, or zero signal, it sits in the middle at the biased operating point and will get hottest. As the magnitude of the signal increase, it spends more and more time towards either end of the load line, and so power dissipated, on average, is less. Another example for triodes with a couple of loadlines Ok, I actually unplugged everything from the amp and ran them to eliminate any variables and one was hot one cold so not sure, does your diagrams depend on having a load , being the speakers or is that the amps internal bias ? Anyway I can see how it can be a variable load. Thanks, Joel Link to post Share on other sites
aussievintage 3,859 Posted October 22, 2020 Share Posted October 22, 2020 1 minute ago, JoelG said: Ok, I actually unplugged everything from the amp and ran them to eliminate any variables and one was hot one cold so not sure, does your diagrams depend on having a load , being the speakers or is that the amps internal bias ? Anyway I can see how it can be a variable load. Thanks, Joel Yes, there must be a load. In a valve amp, you can damage them without one. The curves happen to be for a valve amp, but the principle is the same. The load is represented by the straight line. Changing bias will just shift that line up and down, while remaining parallel to itself. Without signal, the amp sits at one point on that line, usually about in the middle. This is known as the operating point, and is what one sets when the bias is adjusted. Link to post Share on other sites
aussievintage 3,859 Posted October 22, 2020 Share Posted October 22, 2020 5 minutes ago, JoelG said: having a load , being the speakers or is that the amps internal bias ? oh yes, meant to say. Yes the load is the speakers, or their reflected impedance via an output transformer for valves, mostly. Link to post Share on other sites
JoelG 1 Posted October 22, 2020 Share Posted October 22, 2020 4 minutes ago, aussievintage said: oh yes, meant to say. Yes the load is the speakers, or their reflected impedance via an output transformer for valves, mostly. I see, so without a load the operating point might be out. A load will just relatively change the relationship based on the starting point... And adjusting this bias will do the trick 👌 Link to post Share on other sites
aussievintage 3,859 Posted October 22, 2020 Share Posted October 22, 2020 2 minutes ago, JoelG said: I see, so without a load the operating point might be out. A load will just relatively change the relationship based on the starting point... And adjusting this bias will do the trick 👌 Bottom line, if the amps sound good, even with the temperature difference, I don't think you'll find much wrong. Hopefully just a tune-up. 👍 1 Link to post Share on other sites
rt3m 2 Posted November 10, 2020 Share Posted November 10, 2020 Hi there, i have Monitor Audio subwoofer which is not powering on, looking for recommended repairer in Sydney area, thanks! Link to post Share on other sites
rockeater 743 Posted November 30, 2020 Share Posted November 30, 2020 On 22/10/2020 at 7:34 AM, JoelG said: kinda thought class A was just full on all the time so bias doesn't come into it? All active devices (like transistors and valves) are non-linear. They have their most non-linear area closest to the 0 (crossover point into the negative part of signal curve) and become more linear as the voltage and current increases. To offer better performance, in Class A, these active devices are biased high, so that they are always in their most linear area. Another words, they are driven hard even when there is no signal. Hence increased power consumption and heat. They use the same power whether the music is playing or not. 2 Link to post Share on other sites
ozmatchbox 6 Posted December 8, 2020 Share Posted December 8, 2020 Hi all, am a newbie with hi-fi gear and recently bought the following used Sansui gear (to start off with my hi-fi journey) 😁 and needs servicing AU-417 - volume knob is loose TU-417 - working so far during demo test SC-1330 - doesn't play, rwd or fwd Would anyone here be able to recommend an electronics/vintage hifi repair/service shop in Sydney? Preferably near the lower north shore area? Would be great if you've used their services before to work on your Sansui gear. Appreciate your help on this. 😊 Thanks. Link to post Share on other sites
SONDEKNZ 12 Posted December 13, 2020 Share Posted December 13, 2020 Hi guys! I have a friend who needs his STEREO REMOTE CONTROL repaired. It's a pretty simple device, but is absolutely essential to the entire operation of his beloved (and rare) CLASSIC amplifier - so he can't afford any screw-ups. So I'm looking for a trusted repairer that won't disappoint. Preferably in EAST AUCKLAND. Can anyone make a recommendation please? Appreciated. JINGLE BELLS! Link to post Share on other sites
muon* 3,020 Posted December 13, 2020 Share Posted December 13, 2020 @SONDEKNZ Might help to mention the amplifier model and make. Link to post Share on other sites
SGS 112 Posted December 18, 2020 Share Posted December 18, 2020 NAD M25 fault, fans, possibly channel failure. Would you use a local repairer who seems quite good or take to a NAD specialist 2 hours away or arrange for NAD Australia to repair and ship it? NAD Au want $99 includes pickup but I don't have box. Local want $55 upfront to inspect. Don't know about other option. Chatting to a guy from NAD Au, he seemed strongly recommending authorised due to being Masters series. Link to post Share on other sites
ag47 1 Posted January 6 Share Posted January 6 EAD Powermaster 2000 which recently has some buzzing coming through. Any suggestions for someone that will know how to handle it perfectly (Sydney, Au)? The sound out of this amp is amazing and I would like it to stay that way... Link to post Share on other sites
MattyW 2,239 Posted January 6 Share Posted January 6 (edited) Brisbane Electronics did wonderful work recapping my Victor TT-Y5 as well as installing quality RCA sockets + a banana plug for the earth wire. It should now last another 40 years and will work with any interconnects I should want to run. https://www.briselec.com.au/ Edited January 6 by MattyW Link to post Share on other sites
vagrahb 11 Posted January 7 Share Posted January 7 Hi Guys, Happy New year!. I'm looking to get my Parasound A51 amplifier serviced and could any Brisbane folk recommend a good technician locally. Thanks. Link to post Share on other sites
candyflip 3,858 Posted January 13 Share Posted January 13 (edited) The big problem I'm finding at the moment is the wait times to get in to see anyone... upwards of a month just to get something on the benches around Melbourne, because the queue of repair jobs they already have to do is so long. JLS are quoting a wait time of 5-6 weeks just to have something appraised, before the repair starts. Of course given COVID, this is completely understandable. Just frustrating is all. Edited January 13 by candyflip 3 Link to post Share on other sites
mud_shark 24 Posted January 13 Share Posted January 13 (edited) 1 hour ago, candyflip said: The big problem I'm finding at the moment is the wait times to get in to see anyone... upwards of a month just to get something on the benches around Melbourne. Of course given COVID, this is completely understandable. Just frustrating is all. Am definitely feeling this. Given the wait to get in, and then for the actual service time... half makes me want to buy a second TT for such emergencies 😁 Edited January 13 by mud_shark Typo 1 Link to post Share on other sites
MattyW 2,239 Posted January 13 Share Posted January 13 (edited) 3 minutes ago, mud_shark said: Am definitely feeling this. Given the wait to get in, and then for the actual service time... half makes me want to but a second TT for such emergencies 😁 Yeah, not many people willing to work on them these days. Most places don't have the knowledge or skillset. That and because so few people actually get gear repaired there are not many repairers to start with. It's that whole throw away mentality I've 2x spare tables though the Victor TT-Y5 is the best of them in my mind. That said my Victor TT-71 based tables with Fidelity Research tonearms are not far behind. Edited January 13 by MattyW Link to post Share on other sites
static 51 Posted January 13 Share Posted January 13 CVE Electronics in Pascoe Vale South have done good repair work on two old amps for me recently. Couple of weeks turnaround. I found them from other recommendations here. Link to post Share on other sites
Timoth 0 Posted January 15 Share Posted January 15 Hi, Can anyone recommend someone to service my Luxman SQ 505X Amp? I'm in Sydney. Thanks, Tim Link to post Share on other sites
dneco 24 Posted January 20 Share Posted January 20 Given that the amount of backlog repair techs have right now might be a very long wait here in Melbourne. I have a cd player where the disc won't spin so i'm assuming its a relatively straight forward fix with a replacement motor if anybody knows how to do that? Located in Melbourne's North Thanks Link to post Share on other sites
ag47 1 Posted January 24 Share Posted January 24 On 20/01/2021 at 5:00 PM, dneco said: Given that the amount of backlog repair techs have right now might be a very long wait here in Melbourne. I have a cd player where the disc won't spin so i'm assuming its a relatively straight forward fix with a replacement motor if anybody knows how to do that? Located in Melbourne's North Thanks I don't know if you've opened it up already, but the motor usually runs a belt that looks like a rubber band. Check that it hasn't come off / isn't broken as your first check. 1 Link to post Share on other sites
rockeater 743 Posted January 24 Share Posted January 24 4 hours ago, ag47 said: On 20/01/2021 at 2:00 PM, dneco said: its a relatively straight forward fix with a replacement motor if anybody knows how to do that? I don't know if you've opened it up already, but the motor usually runs a belt that looks like a rubber band. Check that it hasn't come off / isn't broken as your first check. Unless it is a belt driven C.E.C. this is never the case. These belts that @ag47 talks about normally drive CD trays and clamps, not TT motors (C.E.C.s excepted). The fact that CD does not spin is virtually never a motor fault. The fact that the motor does not spin, means that one of the number of things that need to happen before you get to spinning CD, did not happen. It could still be a belt which did not close the tray properly or CD is not fully clamped. But most likely some limit switch is not activated and servo simply does not know that everything is already in place. Most likely it is a matter o finding it and cleaning it. Hope it helps. Link to post Share on other sites
Wilco 73 Posted February 20 Share Posted February 20 On 13/01/2021 at 1:25 PM, candyflip said: The big problem I'm finding at the moment is the wait times to get in to see anyone... upwards of a month just to get something on the benches around Melbourne, because the queue of repair jobs they already have to do is so long. JLS are quoting a wait time of 5-6 weeks just to have something appraised, before the repair starts. Of course given COVID, this is completely understandable. Just frustrating is all. This. I dropped stuff off start of 11th Jan, 3 speakers and 1 integrated amp, and still not done. I had made one call 2 weeks later, and they were kinda onto it. Not planning on calling until 1st March I guess. Has anyone had any experience with Class A Audio and repairs (I know they are a seller here and they regularly list on other platforms), just curious if anyone has had experience with them regarding repairs: https://www.classaaudio.com.au/content/7-hifi-repair-service 1 Link to post Share on other sites
BuzzzFuzzz 3,918 Posted Sunday at 07:10 PM Share Posted Sunday at 07:10 PM G'day Folks. I have a Denon AVC-A1, which has started dropping out in one chanel. It's a 20 year old amp. I'm looking for recommended repairers in either Sydney or Melbourne. I've enquired with The Factory in Canberra... and, though they have been recommended here... I've also heard negative feedback about them. Looking at options. Regards. Ant. Link to post Share on other sites
ozmatchbox 6 Posted Monday at 01:02 AM Share Posted Monday at 01:02 AM 5 hours ago, BuzzzFuzzz said: G'day Folks. I have a Denon AVC-A1, which has started dropping out in one chanel. It's a 20 year old amp. I'm looking for recommended repairers in either Sydney or Melbourne. I've enquired with The Factory in Canberra... and, though they have been recommended here... I've also heard negative feedback about them. Looking at options. Regards. Ant. Hi Ant., Try Dr HiFi in North Sydney. Google the details. He was highly recommended when I had my Sansui amp & tuner serviced. He does a detailed smoke test (over 48 hrs I think) and sends you details on work he's done. He's not cheap but his work speaks for itself. 1 Link to post Share on other sites
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