Hi everybody,
1st post. Unfortunatly I do not have the technical know how of many people here, but I much appreciate the input on my problem.
I just had the SA/1s recapped and looked over by a well respected tech in the industry. Amps came back and sound great, but they have a hissing problem.
power caps were replaced with 47000 Epcos 100v
Amps were previously modded with power filtering.
Issue:
Power on, no RCA input connected = no hiss, dead quiet.
As soon as I connect RCA from various sources and different cables I am getting a hiss in both speakers. Tried from preamp, directly from 2 DACs and each one provides hiss. All upstream components have been used with other amps and there was no issue.
What have we tried:
1) Disconnect small yellow parallel caps ( value of the caps and brand unknown as they were installed years ago)
2) tried grounding the RCA input to star
3) move pcb ground away from power filter in the back.
no impact on hiss.
These amps sound spectacular even compared to my modern amps. Without the hiss I would be in sonic heaven. I would appreciate any input you can provide.
1st post. Unfortunatly I do not have the technical know how of many people here, but I much appreciate the input on my problem.
I just had the SA/1s recapped and looked over by a well respected tech in the industry. Amps came back and sound great, but they have a hissing problem.
power caps were replaced with 47000 Epcos 100v
Amps were previously modded with power filtering.
Issue:
Power on, no RCA input connected = no hiss, dead quiet.
As soon as I connect RCA from various sources and different cables I am getting a hiss in both speakers. Tried from preamp, directly from 2 DACs and each one provides hiss. All upstream components have been used with other amps and there was no issue.
What have we tried:
1) Disconnect small yellow parallel caps ( value of the caps and brand unknown as they were installed years ago)
2) tried grounding the RCA input to star
3) move pcb ground away from power filter in the back.
no impact on hiss.
These amps sound spectacular even compared to my modern amps. Without the hiss I would be in sonic heaven. I would appreciate any input you can provide.
Attachments
If amp is quiet with grounded RCA input (or just no input) then amp itself is quiet.
It seems when you connect a preamp to the amp the power-amp just amplifies the "hiss" from the preamp or whatever you have connected?
Normally hiss occurs when the gain in the chain is too high compared to the sensitivity of the speakers.
Do you have very sensitive speakers? ....and what is the total gain in the chain?
It seems when you connect a preamp to the amp the power-amp just amplifies the "hiss" from the preamp or whatever you have connected?
Normally hiss occurs when the gain in the chain is too high compared to the sensitivity of the speakers.
Do you have very sensitive speakers? ....and what is the total gain in the chain?
Speakers are 88db into 4ohm. Preamp output gain per manual 50ohm / 200mA rms max. My other ss amps have 47k ohm input impedance and are completely quiet.
The aluminium plate that are used for grounding for the caps.......is good electrical contact ensured by using shims that "bites" into the aluminium?
If amp oscillates it should be easy to see using a fast scope at speaker out?
If amp oscillates it should be easy to see using a fast scope at speaker out?
Hi, yes, there appears to be very good contact. In regards to measurements I do not have the equipment to check that.
Define "hiss": is it a continuous low frequency "hum" (correct term), or is it some random statics like on a radio between stations?
If it's "hum", it may be a ground loop problem: disconnect both RCA cables from the source, it should go away. A temporary fix is to remove the ground pin of your power plug, and a permanent fix is to have someone install a ground breaker inside the amp.
If it's "hum", it may be a ground loop problem: disconnect both RCA cables from the source, it should go away. A temporary fix is to remove the ground pin of your power plug, and a permanent fix is to have someone install a ground breaker inside the amp.
You can measure using a DMM set to Ohm (or beep) if you have "zero" between all the cap screws and also to the center ground screw.
I would have used star-shims that "bites" into the aluminium to be sure it penetrates the oxidation of the aluminium.
I would have used star-shims that "bites" into the aluminium to be sure it penetrates the oxidation of the aluminium.
No, you have to crank it all the way up.
Definitely not "hiss", but a "hum" with a surprisingly large harmonic content for a ground loop.
Still worth trying the ground pin removal. Att.!!! This can be illegal in some countries as it may kill you!!!
Definitely not "hiss", but a "hum" with a surprisingly large harmonic content for a ground loop.
Still worth trying the ground pin removal. Att.!!! This can be illegal in some countries as it may kill you!!!
Was the hum present before the well respected tech recapped the amp?
I don't have the skills to tell you how to fix the problem, but I can tell you this: If they were mine, I would remove all the mods (rectifiers, filter and truckloads of xtra wiring) and bring it back to stock.
You would still be in sonic heaven.
I don't have the skills to tell you how to fix the problem, but I can tell you this: If they were mine, I would remove all the mods (rectifiers, filter and truckloads of xtra wiring) and bring it back to stock.
You would still be in sonic heaven.
Attachments
Amps were running last 3 years ago. I don't recall hum at that time. The power mods were done 15 years ago by someone else. I ordered a Humx plug to see if this is a grounding issues. Should be here tomorrow.
Fully agree with Baejisman,
I just renovated a set of SA/1, new caps, replaced the tantalum just for good measure. The old electrolytics were still alive but the ESR of course had increased significantly. While in pristine condition there was some surprises which needed attending to.
Some of the small VU meter lamps had increased impedance - just enought to prevent the lights to turn on.
They have the nicest little sockets - so it's an easy fix 🙂
I have previously on an S200 experienced a hum problem which eventually became really noisy - it turned out to be a poor connection at the switch.
Easy fix. On the SA's the switch connections are soldered - but the internal contact points themselves do arc and the connection had degraded after many years of use. This will only become worse with bigger and newer caps. I opened up and cleaned the contact points - but that is not a job for everyone...
These are the non self-cleaning type so carbon eventually do build up also as pitting becomes worse.
It can be seen as an fluctuating current consumption. The SA switches also have an internal peak current protection, but it is not an inrush limiter - which is adviseable to install for installations with RCD and also when increasing the capacitance - upgrading to a similar sized can e-cap will easily get you x3 in capacity ;-)
The input filter looks suspiciously old and the Rifa's on the - bridge? looks like the Rifa type commonly known as "fire crackers" this could of course be a newer and improved model....
I just renovated a set of SA/1, new caps, replaced the tantalum just for good measure. The old electrolytics were still alive but the ESR of course had increased significantly. While in pristine condition there was some surprises which needed attending to.
Some of the small VU meter lamps had increased impedance - just enought to prevent the lights to turn on.
They have the nicest little sockets - so it's an easy fix 🙂
I have previously on an S200 experienced a hum problem which eventually became really noisy - it turned out to be a poor connection at the switch.
Easy fix. On the SA's the switch connections are soldered - but the internal contact points themselves do arc and the connection had degraded after many years of use. This will only become worse with bigger and newer caps. I opened up and cleaned the contact points - but that is not a job for everyone...
These are the non self-cleaning type so carbon eventually do build up also as pitting becomes worse.
It can be seen as an fluctuating current consumption. The SA switches also have an internal peak current protection, but it is not an inrush limiter - which is adviseable to install for installations with RCD and also when increasing the capacitance - upgrading to a similar sized can e-cap will easily get you x3 in capacity ;-)
The input filter looks suspiciously old and the Rifa's on the - bridge? looks like the Rifa type commonly known as "fire crackers" this could of course be a newer and improved model....
Thanks for all the feedback. After trying various possible solutions as outlined here and many other threads the conclusion was a ground loop that only occurred with some cables and when specific components were plugged in. An Emotiva cmx-2 fixed the hum/hiss. Amps are fine.
I have one more last question. I have read from previous owners that they used the bridge caps on top. I don't know what the yellow ones are, but they put more emphasis on the mids and make the amp sound warmer. What types of caps would one use use to experiment with the sound? What would give clearer highs or a punchier bass if this is even possible?
I have one more last question. I have read from previous owners that they used the bridge caps on top. I don't know what the yellow ones are, but they put more emphasis on the mids and make the amp sound warmer. What types of caps would one use use to experiment with the sound? What would give clearer highs or a punchier bass if this is even possible?
Post a pic of the markings on the current caps so we know what we're up against.
Usually, a good starting point is the cheap WIMA MKP before the $$$ exotics.
Let us know your findings.
Usually, a good starting point is the cheap WIMA MKP before the $$$ exotics.
Let us know your findings.
