RIAA amplifier trouble - Page 1
Forum section: electronics / beginners

author: jawa_master
author_rank: Contributor
timestamp: May 27, 2017, 08:59:58 am
content: Geetings.Acouple of weeks back i bought this RIAA amplifier of ebay:http://www.ebay.com/itm/400244739310?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT(it's rated at 9-15vDC. The listing also offers a schematic without any values. If you need them to help me solve this, let me know, and i'll send a picture of the circuit)Sadly it has a couple of flaws. From the moment you plug it in, there is a high pitched peeping sound. But it doesn't end there. After two or three songs, the sound quality starts to degrade gradualy. It sounds as if you were listening on a terrible fm connection. The highs and lows starts to completely dissapear, until you're only left with some distorted drumsounds.Luckily, the problem is easily fixed by turning it off and on, but it's kind of bothersome to do this every two songsMy powersuply is a 220vAC to 12vDC converter. However, i have also tried running it on a 9v battery, so i don't think this is the problem.I have put the entire thing in a metal box, So i have also tried shorting the ground and the input ground on the circuit to the metal wall via diferent capasitors. This removed the high pitched sound i mentioned, but the audio degrading thing still remains.So, if any of you can figure out what i'm doing wrong here, i would love to hear it. In advance, thanks.

author: Andy Watson
author_rank: Super Contributor
timestamp: May 27, 2017, 09:24:05 am
content: Quote from: jawa_master on May 27, 2017, 08:59:58 am"a220v ...a9v battery ..." This sounds very singular! Is that a typo or are you really using only one power-supply?

author: jawa_master
author_rank: Contributor
timestamp: May 27, 2017, 09:34:56 am
content: Quote from: Andy Watson on May 27, 2017, 09:24:05 amI'm sorry, but i don't think i understand your question. I'm not a native english speaker, nor in any way an electro engineer. Would you care to put it other terms

author: Andy Watson
author_rank: Super Contributor
timestamp: May 27, 2017, 09:37:55 am
content: You appear to be saying that you are usingonepower-supply. This design requires two/dual power supplies.

author: jawa_master
author_rank: Contributor
timestamp: May 27, 2017, 09:47:19 am
content: Quote from: Andy Watson on May 27, 2017, 09:37:55 amWhere does it say that? There is only one "power supply" on the schematic.

author: NottheDan
author_rank: Frequent Contributor
timestamp: May 27, 2017, 09:53:01 am
content: Quote from: jawa_master on May 27, 2017, 09:47:19 amV-GNDV+How are you connecting it so you are getting -9V, +9V and a Ground in the middle out of a single battery?

author: sokoloff
author_rank: Super Contributor
timestamp: May 27, 2017, 09:53:16 am
content: Quote from: jawa_master on May 27, 2017, 09:47:19 amWith positive and negative rails...Said differently: how did you connect up the two terminals of the 9V battery to the 3 terminals: V-, GND, and V+ ?

author: Andy Watson
author_rank: Super Contributor
timestamp: May 27, 2017, 09:54:51 am
content: The power socket is labelled -V, Gnd and +V. Perhaps it would be clearer if it were labelled -V 0v +V. Also, the ebay listing says :QuoteI read that as plus and minus 9V to plus and minus 15V.

author: jawa_master
author_rank: Contributor
timestamp: May 27, 2017, 10:30:27 am
content: Quote from: Andy Watson on May 27, 2017, 09:54:51 amAhhh, i see. I'll try it out

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 27, 2017, 11:32:20 am
content: Most circuits that use op-amp integrated circuits operate on TWO power supplies. A positive power supply, and a negative power supply. That is why there are THREE connections for power.You could use TWO 9V batteries, one for positive, and one for negative.Or you could use a bi-polar power supply such as the one suggested in the Ebay listing. However that power supply suggested on the Ebay page requires a power transformer with two outputs which is also rather expensive.A modern alternative would be a power supply that generates both the positive and negative power voltages from a single input. There are many of these on Ebay. For example:http://www.ebay.com/itm/272321462327http://www.ebay.com/itm/182089091186http://www.ebay.com/itm/311502086620http://www.ebay.com/itm/182089091186

author: Zero999
author_rank: Super Contributor
timestamp: May 27, 2017, 12:22:36 pm
content: Quote from: jawa_master on May 27, 2017, 08:59:58 amThe problem is the lack of a dual power supply, as mentioned above.Use two 9V batteries and connect the circuit as shown below.

author: jawa_master
author_rank: Contributor
timestamp: May 27, 2017, 07:40:15 pm
content: Hey again.Despite all odds, i had another one of the powersupply i was using laying around. I coupled them up like you said, and it works like a charmThanks to everyone who replied

author: Zero999
author_rank: Super Contributor
timestamp: May 27, 2017, 09:13:52 pm
content: Quote from: jawa_master on May 27, 2017, 07:40:15 pmGood.Another option to two power supplies or a DC-DC converter, is a rail splitter. A simple potential divider could be used, but this is generally not recommended, as the output impedance is high and the 0V point will shift as the current draw from the positive and negative rails changes. The easiest way is to use a rail splitter IC such as the TLE2426, which has a low output impedance.https://tangentsoft.net/elec/vgrounds.html