I have an older Kenwood amp that I pulled out of storage to test an active speaker I'm building. It works well enough but there is a constant hiss coming from the speaker and it's really audible when there is nothing playing. I was just wondering if there is something in general that would cause that or is it one of those things that could be caused by many different things. If it where cheep and easy I might try and fix it for shots and giggles but if it is a big ordeal to diagnose then it's going to the amp grave yard. So I'm seeking some guidance here. I don't know to much about the internal workings of class AB amps so I was hoping someone here might be able to enlighten me.
Could be dried out power supply electrolytic capacitors. Probably not the transistors.
Use shorting plugs in the amp input sockets to be sure it is not noise pickup.
At least burn the amp in for a few days to see if it gets any better.
Use shorting plugs in the amp input sockets to be sure it is not noise pickup.
At least burn the amp in for a few days to see if it gets any better.
Amplifiers produce a certain amount of noise as part of their design and relates to the laws of physics and the gain structure of the amplifier. In an active speaker system there is no passive attenuation applied to the tweeter so a low noise amplifier is even more critical. The higher the sensitivity of the tweeter the more audible the intrinsic noise of the amplifier will be.
It isn't just the amplifier though it's whatever is before it too. The amplifier obviously provides gain and the active crossover will also have a certain level of noise. This noise will get amplified by the amplifiers gain and then sent to the speakers.
Time is unlikely to solve this problem, but as rayma says, short the inputs of the amplifier and see if the noise is still there. Shorting the inputs means connecting the middle pin of an RCA/phono connector to the grip/outside of the connector. If the hiss goes away then the problem is with the combination of the amplifier and the active crossover. Either the active crossover is quite noisy or the amplifier has too much gain. Is this a power amp or an integrated?
It isn't just the amplifier though it's whatever is before it too. The amplifier obviously provides gain and the active crossover will also have a certain level of noise. This noise will get amplified by the amplifiers gain and then sent to the speakers.
Time is unlikely to solve this problem, but as rayma says, short the inputs of the amplifier and see if the noise is still there. Shorting the inputs means connecting the middle pin of an RCA/phono connector to the grip/outside of the connector. If the hiss goes away then the problem is with the combination of the amplifier and the active crossover. Either the active crossover is quite noisy or the amplifier has too much gain. Is this a power amp or an integrated?
Hiss is a Reality of Life.
Nothing is hiss-less although it certainly can be below hearing threshold sometimes.
Nothing is hiss-less although it certainly can be below hearing threshold sometimes.
My stereo is hiss-less. Pre half dial, there is nothing but blackness. I haven't been beyond it to really say, I could suffer hearing damage. Its really quiet by the design. -80 db (r 1w). I will be trying true balanced connectors more out of curiosity than chasing a quieter background.
"Nothing is hiss-less although it certainly can be below hearing threshold sometimes." I have a little hiss with my Sansui S-X1130 when I am using an EQ with it.
The amp is a stereo amp not a receiver and I'm using a Dayton Audio DSP for a cross over connected to my computer as a preamp/source. I have another stereo Sonance amp running right next to it and it runs completely silent. These are not the final amps I will be using in the end only what I'm testing the speaker with in a test box. I'm waiting on my order from Icepower right now. Should be here in a couple of days. I have one of their 1500s PSU's and 4 of their 400A amp modules coming that I will be assembling once I get them into a chassis that I should also be receiving in a few days that I ordered here at the diyaudio shop. I might need some assistance with that project when I start putting it all together. So I might be asking some questions. I will start a build thread when I get around to putting it all together.
I will try shorting inputs and see what happens but I already know it is the amp that has the problem as I am very familiar with the rest of the system and it's all good. This is not really one of Kenwood's better amps. I do have the matching receiver and I have to say it is dead silent though. It's not being used right now but it has been a surprisingly good bit of kit. This amp was intended to add a center channel and a passive sub to the receiver. I picked it up from Good Will and it's the first time that I have actually used it even though I've had it for some time. There is no way to adjust the gains from the out side of the amp but there is a bass volume pot on the rear of the amp that I guess could be technically considered a gain adjustment but it is only on one channel and the hiss is in stereo. It's coming out of both the mid and the tweeter.
So could this be a problem with the gains being set wrong or is it more likely an issue of aging electrolytic caps? Or could it be just a cheap noisy design that Kenwood didn't put much effort into? In a couple of days I will be pulling it out of my system and packing the drivers away until the final boxes are built and likely will never use the amp again but If I can fix it I figure it could be a good learning experience and I might just fix it for that reason but in the end it will likely be going back to Good Will and some one else can have it. I already have to much gear I don't use.
I will try shorting inputs and see what happens but I already know it is the amp that has the problem as I am very familiar with the rest of the system and it's all good. This is not really one of Kenwood's better amps. I do have the matching receiver and I have to say it is dead silent though. It's not being used right now but it has been a surprisingly good bit of kit. This amp was intended to add a center channel and a passive sub to the receiver. I picked it up from Good Will and it's the first time that I have actually used it even though I've had it for some time. There is no way to adjust the gains from the out side of the amp but there is a bass volume pot on the rear of the amp that I guess could be technically considered a gain adjustment but it is only on one channel and the hiss is in stereo. It's coming out of both the mid and the tweeter.
So could this be a problem with the gains being set wrong or is it more likely an issue of aging electrolytic caps? Or could it be just a cheap noisy design that Kenwood didn't put much effort into? In a couple of days I will be pulling it out of my system and packing the drivers away until the final boxes are built and likely will never use the amp again but If I can fix it I figure it could be a good learning experience and I might just fix it for that reason but in the end it will likely be going back to Good Will and some one else can have it. I already have to much gear I don't use.
Another thing worth noting is the hiss is unaffected by turning up the volume on my computer when there is no music being played. The hiss is at a steady volume. Just loud enough to annoy the hell out of you and definitely above the noise floor. It is audible when playing back music at low levels.
What does that mean? Short the inputs and leave it running for a couple of days? Is that what you are suggesting?
Hiss generally means a poor choice somewhere in the system gain structure. Somewhere there is a powerful output driving a sensitive input and it has been made to work by attenuating the input, leaving the system noise exaggerated. My guess is that you have a +20dBm computer output driving a 0dBm amplifier input. There is no point being able to drive your amp beyond clipping. Assuming the amp does not hiss (much) with no input (disconnected), you need to attenuate the amp input signal.
https://www.prosoundtraining.com/2017/10/20/gain-structure-made-easy/#:~:text=Gain Structure 1 Feed the waveform into one,sensitivity down, and then turn it on.
https://www.prosoundtraining.com/2017/10/20/gain-structure-made-easy/#:~:text=Gain Structure 1 Feed the waveform into one,sensitivity down, and then turn it on.
I think the idea is to suspend believe in physics for a few days and see what happens. If your hearing deteriorates in the meantime you'll most likely hear less hiss.
So if I understand it correctly, the signal path is computer - DSP crossover - amplifier - loudspeaker drivers? That is, the amplifier is temporarily used as the amplifier of your active speaker.
If so, it would indeed be interesting to find out what happens with the amplifier inputs shorted. If you still hear hiss, it must be due to the amplifier and solving it would then probably require a redesign of the amplifier. If not, you could check if an attenuator between the crossover and the amplifier helps.
You could then also try a low-pass filter that filters off ultrasonics between the crossover and the amplifier, as one of the possible causes would be intermodulation between the frequency components of the out-of-band quantization noise of the DAC of the DSP crossover filter. It's a bit far fetched because the DSP crossover itself is supposed to attenuate that sufficiently, but you never know.
Ok disconnecting the dsp from the amp did away with the hiss and replaced it with a hum. I will short the inputs but have to configure something to do it with first. I'll get back to you tomorrow it's to late tonight but thanks.
Been there done that. No thanks. I fully embraced CD technology when it was introduced back in the 80's but it took a while to design CD players that could withstand the daily abuses of being installed in a vehicle so I was forced to keep using cassette tapes for quite a while longer then I wanted to. Considering I was a teenager back then my only real stereo was in my car. It was useless to have one at home because I couldn't listen to it without my parents telling me to turn it down and I was hardly ever home anyways. Today my entire music library, and it's quite extensive, is digital and stored on my computers hard drive and backed up on a removable drive and parts of it are on usb thumb drives for playback in my vehicles. I still have a ton of CD's somewhere in storage but never use them since I ripped everything to my computer years ago.
Ha ha - I had a friend who wanted a cassette player repaired a few years ago. If it wasn't for the owner being a friend I most likely would not have done it. But after decades since disposing of my Nakamichi and tapes, I was gobsmacked by the sound of cassettes - whatever the hiss, rumble and wow and flutter, they sounded ORGANIC in a way that CD just does not. I now regularly repair and upgrade cassette decks. One from the 1980s I have in the workshop now sells around >US$10,000 on the secondhand market. I wish I could get that for a vintage CD player.
PC caps will cause HUM, not hiss. Hiss, or white noise is a principal of physics. Look up "Johnson noise" Look up "signal to noise ratio"
Older equipment was noisier as the transistors were noisier. Basically all parts were. We are spoiled with S/N ratios of 100 dB now, but back in the 790's it was more like 70 dB. Remember, the surface noise of an LP is only 65 dB.
Older equipment was noisier as the transistors were noisier. Basically all parts were. We are spoiled with S/N ratios of 100 dB now, but back in the 790's it was more like 70 dB. Remember, the surface noise of an LP is only 65 dB.
I had a hiss like this two days ago. After re-wiring the entire audio system for two hours, I found the problem was only there if my CD player was grounded. Lifting it solved it. You could try isolation transformers on the audio lines from the DSP to the amp to break any loops.
If the hiss is there while shorted, it's most likely the preamp transistors.
If you have a scope, see what the output looks like. Sometimes hiss can manifest from a higher frequency oscillation in the 100's of kHz.
If the hiss is there while shorted, it's most likely the preamp transistors.
If you have a scope, see what the output looks like. Sometimes hiss can manifest from a higher frequency oscillation in the 100's of kHz.