I have recently acquired a Pioneer SA9900 amplifier which is in excellent condition apart from the fact that it hums. The hum is quite loud and seems independent of volume setting. If you set the amp to operate in separate pre/power mode the hum decreases but is still there. The hum can be heard through speakers as well as headphones. It is present no matter which input is selected. Has anyone had this problem with the amp - could it be power supply issue? - either failed joints or failing caps? any information would be welcome
Pioneer SA9900 hum
- Thread starter memu51
- Start date
I have just played the Pioneer SA9900 preamp through a Sansui AU9700 power amp - yes it still hums the same
Playing it the other way round ie Sansui preamp to Pioneer power amp there is still hum but greatly reduced - but a little to loud to be acceptable
Heaving this lot about has given me a good workout!
Thanks for your ineterst
Playing it the other way round ie Sansui preamp to Pioneer power amp there is still hum but greatly reduced - but a little to loud to be acceptable
Heaving this lot about has given me a good workout!
Thanks for your ineterst
Last edited:
I'd dig up a service manual and check the power supplies, the main one and also any secondary regulation in the amp. Don't forget to look for bad solder connections and broken stuff.
http://www.hifiengine.com/library/pioneer/sa-9900.shtml
http://www.hifiengine.com/library/pioneer/sa-9900.shtml
Last edited:
Pioneer SA9900
Hi
I have replaced 8 of the 12 caps on the main power supply board and it still hums! ( waiting to get hold of the other 4) There are two large 22,000uf 63 V caps next to to the mains transformer - are these likely to be leaking?? - is there a way of checking? - I want to try and make sure they need replacing before i buy replacements as they will be expensive
Hi
I have replaced 8 of the 12 caps on the main power supply board and it still hums! ( waiting to get hold of the other 4) There are two large 22,000uf 63 V caps next to to the mains transformer - are these likely to be leaking?? - is there a way of checking? - I want to try and make sure they need replacing before i buy replacements as they will be expensive
I have now replaced all capacitors on the two power supply boards and the two large 22000F 63V filter caps. I have adjusted the idle and junction point as per service manual but now the relay on power up does not operate and there is no sound from the speakers. There is feint transformer hum and the heat sinks at the rear of the amp get slightly warm. I made sure that I had correct polarity with all caps changed and there were no pops or bangs on power up. Could the new caps have caused some other problem ??
Cogsinister
Super Member
Hi
Measured some voltages from the supply board and discovered a broken wire on one of the terminals. I have soldered back and now relay operates as it should and all voltages OK - only problem - it still hums - loud when connected as integrated and quieter as a power amp - I note that the hi=um does increase in volume - any ideas??
Mark bazinet
the world is awesome today..
Did you ever figure out your hum on your SA. I just bought one... Thanks Mark
Hums can be caused by just about "anything". You need to work out what case yours is so you need basic symptoms as above,
- as integrated, hum in both channels?
- hum increases with volume?
- hum when SA acting as preamp/connected to another power amp
- hum when SA acting as power amp/connected to another preamp
Typical causes are power supply failure/degredation(caps/rectifier/voltage regulators...).
Bad solder connections is another one. If you can follow a schematic you should trace the earth wire connections to the various boards
and maybe measure resistance from earth wires to chassis(with amp powered off/unplugged).
First up, provide the basic symptoms/4 points above.
- as integrated, hum in both channels?
- hum increases with volume?
- hum when SA acting as preamp/connected to another power amp
- hum when SA acting as power amp/connected to another preamp
Typical causes are power supply failure/degredation(caps/rectifier/voltage regulators...).
Bad solder connections is another one. If you can follow a schematic you should trace the earth wire connections to the various boards
and maybe measure resistance from earth wires to chassis(with amp powered off/unplugged).
First up, provide the basic symptoms/4 points above.
Mark bazinet
the world is awesome today..
All caps and filters were replaced, power, driver, etc.. even the 22's
All the 1451's that were on the pioneer have been removed.
Slight hum on right as volume is marked lower if switching from left to right.
Never considered separation of pre-amp and amplifier as a fault,
It threw a fit and popped a main fuse twice I obviously stopped replacing them.
Ergo enter my phono pre-amp ( a Project usb v separate pre-amp (mc / mm) into my aux 1 position as I was not satisfied with the sa's phono stage ?
Sound got progressively worse, I began to adjust the tone controls, (when adjusting the bass (15 hz) that's when it threw the tantrum.
two of eight output transistors were shorted, checked with curve tracing scope.
zero hum now.. I am currently running the externals that were hooked up to the sa on my ta 30 tube amp. Zero issues there.
Sent it back to the tech as this well beyond my abilities. : ( any thoughts
Thank you for your reply
All the 1451's that were on the pioneer have been removed.
Slight hum on right as volume is marked lower if switching from left to right.
Never considered separation of pre-amp and amplifier as a fault,
It threw a fit and popped a main fuse twice I obviously stopped replacing them.
Ergo enter my phono pre-amp ( a Project usb v separate pre-amp (mc / mm) into my aux 1 position as I was not satisfied with the sa's phono stage ?
Sound got progressively worse, I began to adjust the tone controls, (when adjusting the bass (15 hz) that's when it threw the tantrum.
two of eight output transistors were shorted, checked with curve tracing scope.
zero hum now.. I am currently running the externals that were hooked up to the sa on my ta 30 tube amp. Zero issues there.
Sent it back to the tech as this well beyond my abilities. : ( any thoughts
Thank you for your reply
Short answer, WTF! Hums don't normally leed to the carnage you've described, maybe you have other issues.
Also question if hum was in L and/or R channel, again a local channel issue or power supply common to both.
If hum increases with volume then source is probably before the volume control.
bad solder connection at RCA??? dunno...
Not a fault, just trying to localize the problem as being in the preamp, power amp or common to both suggesting power supply.
Also question if hum was in L and/or R channel, again a local channel issue or power supply common to both.
If hum increases with volume then source is probably before the volume control.
The idea was to remove the pre-out main-in links and then connect an exteral preamp. Hard to say how this led to a short, interrupted earth path?
bad solder connection at RCA??? dunno...
Amp started to oscillate???
Mark bazinet
the world is awesome today..
My time with my vintage sa was short, pardon the pun. Given the circumstances I was unable to separate the process side from the amplified side. BTW are you able to use process side of the integrated by way of that switch located on the side. Ass.uming its the amplifier that's faulty can they be run individually with the same power supply. Considering oscillation via cables and speaker connect's, wires are Cambridge , shielded. Turntable is of modest quality a Technics SL1700 c/w Pickering xv-15 1200 e/ phono pre-amp is a Project usbv mc/mm type with external power supply. Speakers are Paradigm Phantom V 2's I am the original owner so no faulty voice coils hear. Low ohms 3.9/4.2 respectively. Simple and effective.They listen well with my ta 30. As to determine the on board sine waves I am unable, as the amp has been sent to my tech. Could the oscillation be caused by an external circuit ? . NO . There are many variables, my external equipment is not one as I enjoy them daily with another amplifier. Sorry for the long winded editorials. Again, thank you for your time.
Your gear is fine, better than most, no suggestion it contributed to blown transistors, the problem is in the SA-9900.
The intention was to run the SA as seperates using the switch and connectors at the side, ie,
Flick switch to seperated then connect external preamp to "power in" RCA's. Speakers connected to SA-9900.
The other test was with SA-9900 acting as a preamp, so RCA connectors from PRE OUT to external power amp, speakers
connected to external power amp.
I fully agree that the amp needs to be looked at by a tech. While the amp can be run as seperate preamp I think it deserves
to be repaired/restored. Maybe the SA-9800 sounds better but the 9900 is worth the effort of a restore.
The intention was to run the SA as seperates using the switch and connectors at the side, ie,
Flick switch to seperated then connect external preamp to "power in" RCA's. Speakers connected to SA-9900.
The other test was with SA-9900 acting as a preamp, so RCA connectors from PRE OUT to external power amp, speakers
connected to external power amp.
I fully agree that the amp needs to be looked at by a tech. While the amp can be run as seperate preamp I think it deserves
to be repaired/restored. Maybe the SA-9800 sounds better but the 9900 is worth the effort of a restore.
A quick note on the above: If the hum goes up/down with the volume, that does not isolate it to the preamp. In the SA-9900 the volume (gain) acts simultaneously in the preamp stage and the amplifier stage.
Mark bazinet
the world is awesome today..
Jeff I have the pioneer M 25 amplifier to connect the pre amp to, I also have the C 21 pioneer processor to connect to the amp side either way we'll be able to discern the two stages. They are original never touched. All though the C21's gain controls are stiff, won't be for long. It's on my bench now.
Mark bazinet
the world is awesome today..
There are many who would bark and bite about SA-98 vs SA-99 It's not about that, Separation is the key here. If we were able to connect the M-25 pioneer amplifier to the pre amp and hook into a scope, Hence, it would be nice if the sine wave in the drive section was rounded. Not withstanding replacing every component on the driver board. Which it was btw. The amp is going to a very qualified tech in BC. No easy task to send, its a heavy unit and I get a uneasy sending it out. So I assembled a box to send it in. I think when all those redundant output transistors are pulled, it will fire up. Cross your fingers xx for no internal component damage. I also have the C21 to hook in the amp side so we'll see when I get it back. I'm in no hurry. I ran the M25 through a Anthem avm 30 pre-amplifier. You want to talk about transistors look inside that unit. Layers and rows of them. I'm hoping that those two faulty shorted transistors caused all that ruckus. I need to get some "better" drivers.4 ohm.
I like my paradigms however, they tend to lean in the bass side. Not what I want or need. It would be interesting to see if we did separate the two and slip another fuse in it. There are two boards that would need to be scoped prior to power up, I do not have enough experience for that. I'm considering taking a course in electrical theory with some hands on. I'm retired so why not.
The SA-9900 is a nice amp and has ample power. Mine was in good condition with no evidence of overheating. However, I have seen some photos of pretty scorched power supply boards from these. I don't think that people always buy the 100W+ integrateds to run them lightly, and the Class-A adds heat. On top of this they had the power for 2 sets of speakers or a set of large 4-ohm speakers, then some put them in stacks or semi-closed cabinets. I think that the only real shortcoming of this amp is that it could use a fan to run at or near full output, especially if running 4ohm loads (which it is rated for, but at the same 110wpc as on an 8ohm load IIRC), the combined heat from the output stages and power supply just doesn't get out well IMO.
