Amp + speaker and Log pot selection/wiring?

[reuben911]

Hey all. First time posting here, I hope this is the right place. I'm working on stereo setup for a classic car. Basically the dash needs to be empty with the exception of a single knob used for stereo on/off/volume. All other control will be from my phone. So I found this blue tooth receiver + 200w amp on amazon and hid it behind the dash:

Amazon.com

^mostly as an experimental proof of concept. The audio quality is not great so I am open to recommendations for a higher quality unit that will work for my application.

I've got only 2 door speakers to power:

https://www.crutchfield.com/p_109CT631/JBL-631.html?omnews=13416192

So I've made several failed attempts at wiring in a logarithmic pot as a volume knob between the head unit and the speakers. I've done some research but both pots I tried sparked and smoked when I tried to test vol function so I assume they are wrecked now. Either they were sized wrong or installed wrong, or both. I have successfully been able to wire in the 12v power and get the on/off function to work well though. Small win.

Log pots I tried:

Panel Mount 10K Dual Log Potentiometer w/ On-Off Switch

This Panel Mount 10K Dual Logarithmic Potentiometer w/ On-Off Switch is a two-in-one; you get a dual-ganged potentiometer and an on-off switch. For the potentiometer-half, ...

www.adafruit.com

Can someone please confirm the pot I need? And explain or draw a wiring diagram for me like I read at a third grade level? thanks.
Also open to any other equipment suggestions that will produce a higher quality sound without changing the aesthetic goal.

 

[audio_tony]

You can't use a conventional pot between amp and speakers. You need to control the volume before the amp.

You could use a wirewound pot, however finding something suitable (that can handle the power) will prove to be tough.

Also - any pot in between the amp and speakers will affect sound quality (particularly bass) and is not recommended anyway.

Bottom line; the audio level must be controlled before the input to the amp for best quality and reliability.

 

[reuben911]

good info thanks. So my current setup is no good for what I'm after then. Sounds like I've got to find a stand alone blue tooth receiver, add a volume knob, then an amp?

 

[audio_tony]

That is correct. BT receiver -> volume pot -> amp.

 

[reuben911]

ok. A quick search and I find these two:

https://www.amazon.com/DS18-Bluetooth-Streaming-Receiver-Waterproof/dp/B07BV578YG?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A2O35ZQF0HWQ2Q&gQT=1

Amazon.com

So I would need to wire the pot into the red/white input wires before the amp? Is that all I would need?
Is the 10k pot the correct size?

 

[audio_tony]

There is a screen on each cable - you can join those on one side of the (stereo / dual) pot.

Then take the center conductor and connect that to the other side of the pot (left and right) - then take the output from the center connections on the pot to left and right inputs no the amp. You also need to connect the screen from the pot to the amp (the screened part of the RCA socket).

For this application I would use a 50k pot (or even 100k) as I suspect 10k will give limited control at low volume.

Note that the ground is on the right hand side of the pot (with the shaft facing you). If you connect the ground to the wrong side, the pot will be turning anticlockwise to increase the volume, which I'm sure you don't want!

 

[kiwifi]

Try one of these...

PAC LC-1 Passive Volume Control Review

This is the review and detailed measurements of the PAC LC-1 passive attenuator. It was kindly purchased new by a member and costs just $9.50 including shipping from Amazon. I must say for such a cheap device, the RCA cables feely nice and supple. And volume control itself is smooth. Inside...

www.audiosciencereview.com

 

[reuben911]

and pair that with the bt receiver + amp above? I would have to find one that I can dash mount and fit the matching knob onto though.

 

[reuben911]

Alright I'm finally circling back to this project and dialing it in. now trying to select the correct AMP for my speakers.

Speakers -just 2 in doors JBL 631 https://www.crutchfield.com/p_109CT631/JBL-631.html?omnews=13416192
Potentiometer - PC865, Philmore 100K Ohm Audio Taper Potentiometer w/Switch
BT receiver - NVX VUBT2 universal bluetooth receiver 4.0

and then Amps...I believe I need a 200w amp? capable of powering 3ohm jbl speakers. preferably the smallest+lightest unit. Right now i am looking at:

Sound Storm (SSL) EV2.200 Evolution Series 200 Watt 2 Channel Power Amplifier with High-Low Crossover

Class A/B Amplifier200 Watt MaxSoft Turn-On CircuitChrome-Plated RCA Connectors & Screw Terminals

www.qualitymobilevideo.com

thoughts? and when I install should I wire to the high input or the standard RCA input???
Again, I'm not looking for top tier audio performance, just a viable and hidden bluetooth radio in a 45 year old car.
thanks.

​

 

[DVDdoug]

It's probably too late but you can buy car stereos that look vintage.

I believe I need a 200w amp? capable of powering 3ohm

That seems about right. But given the price I don't really trust that it can put-out 200W (although you may not need all of that power). Most manufacturers "fudge" a bit.

and when I install should I wire to the high input or the standard RCA input???

The high-level input is for connecting to speaker outputs. The RCA input is for line-level or headphone-level signals.

 

[reuben911]

thx @DVDdoug but in my application there will be no visible stereo on the dash, only a single Pot for on/off/vol. see my junk pic in 1st post - will be much different with upholstery. feel free to follow the car build on IG 911.sc.83

ok so wire to the high level input from the potentiometer. thx.

anyone have recs on a diff compact amp for this application? reasonably priced is a +

 

[Ropeburn]

You already found out you can't use a regular pot for any speaker connection - that's not what they're intended for. Those pots are rated 1/8 or 1/4 Watt or something around that, and will of course go up in smoke as soon as you try to push considerable power (high current) through them.

You can just use the existing pot on the amp board in your first post. De-solder it, mount on the dashboard, wire it to the board just like it was before so it's electrically identical, just with wire.

If it's too small for mounting, find a physically bigger one with the same specification, and do the same.

 

[reuben911]

that does seem like an obvious solution, not sure why I didn't think of that.

but the sound quality on this little amp board is really flat so I don't mind upgrading