Connect vintage turntable with amplifier to another amplifier? - Page 1
Forum section: electronics / beginners

author: Larzzon
author_rank: Newbie
timestamp: November 30, 2019, 01:00:21 pm
content: So i have repaired a Sanyo G-2312 Portable turntable, it works fine, but with modern technology of small and powerfull speakers i would like to be able to get more sound from the player. My idea is to remove the soldered speaker cables and install 3.5mm mono-jacks and 3.5 mono-plugs on the speakers. This should not be a problem, but getting back to modern speakers, lets say i buy a speaker with 3.5mm aux input then i assume it has an built in amplifier of some sorts, can i connect my two mono jacks (speaker output) with an mono-mono to stereo adapter to the aux input of a portable speaker (like the ones you use with your phone) or an aux input of an amplifier? I would believe that the signal out from my player would be to strong, maybe not strong enough do destroy anything, normally i like the "Learning by burning" but this time i dont want to risk it, i am having a hard time believing i am the first to want to do this so there should be a nice solution to this problem.Another solution could maybe be to connect an aux cable before the amplifier, but once again i don't know if that would work, is the signal strong enough?I need some help figuring out what signal i can use.Best regardsStefan Larsson

author: mariush
author_rank: Super Contributor
timestamp: November 30, 2019, 01:16:12 pm
content: I would encourage you to find the output of the pre-amp , before the sound is amplified for the speakers.Can't find a free schematic online so maybe if you take some clear pictures of the circuit boards inside, someone could give you some pointers here?

author: Larzzon
author_rank: Newbie
timestamp: November 30, 2019, 01:29:31 pm
content: Ok, so it is after the preamp i should connect, i haven't either found any schematics for this player unfortunately. But i will take a look and if i can't figure out where the preamp is (which i likely wont) i will try to take good pictures and post it here.Best regardsStefan Larsson

author: Larzzon
author_rank: Newbie
timestamp: November 30, 2019, 02:19:07 pm
content: I figure that the small card is the amplifier. Maybe the input to the potentiometers for volume would be the after the preamp?

author: Gyro
author_rank: Super Contributor
timestamp: November 30, 2019, 02:28:17 pm
content: Wow, that's a little one!Yes, the small board with the aluminium strips clamping the 4 transistors is the speaker amp.It inputs to it are the two screened cables (one grey, one brown), They are probably coming straight off the volume control but tone controls might be involved too, it's hard to see.If you tap off on those, you will at least be bypassing the speaker amp distortion.

author: Larzzon
author_rank: Newbie
timestamp: November 30, 2019, 02:49:10 pm
content: I do think that the tone control are the yellow and white. Do i need these or can i just ignore them for this project? and then to my 3.5mm stereo jack (i have decide to put two stereo jacks, one for the speakers and one for aux), i tap of the brown and grey and use the screen as common ground.Hopefully in a couple of days i would be able to buy all the jacks and plugs i need to try it out.Best RegardsStefan Larsson

author: mariush
author_rank: Super Contributor
timestamp: November 30, 2019, 02:56:59 pm
content: I agree it's those two pairs.The point where several wires come together is the ground (star grounding) or common.You could get a stereo extension cable and just cut one connector and you have your jack. ex:https://www.amazon.com/AmazonBasics-3-5mm-Female-Stereo-Audio/dp/B01CNAUYBY/Or get a stereo to RCA cable and cut the rca jacks :https://www.amazon.com/UGREEN-Adapter-Compatible-Smartphones-Tablets/dp/B00QUWDUMC/Or buy and you can add the two RCA jacks on the back of the unit, then use a RCA -> stereo cable to plug into the Line-In of your sound card.example:https://www.amazon.com/VONOTO-Connector-Chassis-Amplifier-Terminal/dp/B07BFQCLSL/rca to stereo cables are cheap:https://www.amazon.com/s?k=rca+to+stereoedit: i don't see the power wires going into that circuit board... could it be those yellow and white wires are positive and negative voltage for the amplifier and not tone control? I only see a thicker red wire connected to ground besides these wires.

author: Larzzon
author_rank: Newbie
timestamp: November 30, 2019, 03:41:25 pm
content: In the last picture the blue cable in the bottom left corner is connected to the capacitor, so i figured that is posetive and the little thicker red is negative.I dont want to make any holes so i will install two chassi mounted 3.5mm where the cables enter the chassi from the speakers, so it will be possible to restore it to orginal condition if i want to in the future.Best regardsStefan Larsson

author: Gyro
author_rank: Super Contributor
timestamp: November 30, 2019, 05:55:54 pm
content: Quote from: Larzzon on November 30, 2019, 02:49:10 pmIf the Yellow and White are from the tone control then it is implemented on the speaker amplifier board, downstream of the two screened cable pick-off points (another good thing).Quote from: Larzzon on November 30, 2019, 03:41:25 pmIf the blue wire comes from the cap then yes, it probably is the supply. You should be able determine the supply polarity from the capacitor - the output transistors look to be Germanium, so I wouldn't be surprised if they were PNP and using a -ve supply (Blue) with +ve (Red) ground (that would account for the wire colours).Be very careful about using 3.5mm sockets, these normally short as you insert the jack - which could kill the amplifier output stage! Also you may accidentally cause a ground loop where they are screwed into the chassis.

author: Larzzon
author_rank: Newbie
timestamp: December 02, 2019, 06:00:31 pm
content: I decided to go with RCA plugs, to avoid the 3.5mm as you suggested. And i taped of the signal before the volume potentiometers (it was kind of a misstake but when i was done soldering i figured i would try it out.)I have tried it out and it kinda works, the thing i notice was that i get a very low volume out from my soundbar, normally when listening on my soundbar i have volume 16 and to get equally sound volume on the turntable i needed about 30-35.Is this because it is not built for it and the signal is to low. The problem is that the speakers starts "humming" when getting that high and can clearly be heard when the music goes down a bit in the song.The speakers only "hums" when the 2xrca - 2xrca cable is connected even without the turntable. Could this be because i bought a cheap cable (which i did, the cheapest they had, length 3meter)? The cable i used to install the new rca sockets is an ordinary speaker cable about 25cm.(the "humming" sounds quite alot as when you had your phone close to speakers and got a message or something).Is there an easy fix? It would work if i could get a bit more sound from the turntable without the need to turn up the volume as much.Best regardsStefan Larsson

author: Gyro
author_rank: Super Contributor
timestamp: December 02, 2019, 08:22:45 pm
content: I wondered if that might happen (although in the opposite direction) hence suggesting tapping after the volume control, so that the level could be dropped if necessary.It's unfortunately a consequence of a unit with no line-level connections, it doesn't need to meet any 'standard' so there is nothing defining what the line level at the volume control actually is. In your case, the level is very low and most of the gain is in the speaker amplifier.I would hesitate to try to pick up a higher level in the early stages of the speaker amplifier without a schematic. The two alternatives I see are either use the speaker outputs and see how good/bad the quality is. The other is to build or buy a small preamplifier board to increase the level.I would obviously try the first one and see how much distortion the speaker amplifier actually has. Poor frequency response is the other potential issue. The speaker amplifier has transformer coupled output stage drivers and was designed to drive small, low frequency limited speakers.Only trying it will tell you whether the quality is degraded too much (compared to what you have heard, tapping at the volume control).