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Car Amp on the desk "Pioneer GM-40" and tune level making ?

Mika

New Member
Hi everyone,

I want to start a little project.

Actually I want to readapt my car amp, the GM-40 Pioneer as a simple enough desk amp.
First of :

- Wich supply should look for, because there is a ground cable with it. So maybe something safe anough for me to put the red wire on (+) and the ground cable on the (-) .

- Also, the fact is I don't have any inputs on this (one RCA should be enough), nor have I a tune level. Or a volume turn button, that could be nice too.

- And maybe a nice on/off button.... well... we'll see about that.

Those are my expectations.

My question to you guys is "Is it possible " ?

I will try to come with as much answers as possible, but I'm far from a good electronician. Don't worry, I am a good worker ; )

Cheers.
 

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Diver300

Well-Known Member
Most Helpful Member
That amplifier is supposed to work with a car audio player, so it doesn't have a volume control. The volume control would be in the car audio player.

You need a power supply that has a voltage between 12 V and 14 V. It should have current rating of 4 A or more. You just connect -ve to black and +ve to red.

What sound source do you want to use? Have you got speakers?
 

Mika

New Member
Diver300, hi,

The volume control would be in the car audio player.
Yes indeed, I thought for a second to use an old cassette/jack device (See what I mean ? ) but I want something a bit more... , and the cassette player has loudness, dolby, bass...

This is why I need some new tune level, Actually I'm thinking to take the tune level out of one of my dead real amps (Technics, SU-C04) as it has a dead side, ((or find something more adapted and easier to make ? I'm afraid it wouldn't be a good idea...) You guys here are from afar more aware of the difficulties, so I will listen to your advice a bit )

Ok for the supply, I'll start looking.

What sound source do you want to use? Have you got speakers?
I'll just hook up my laptop, smartphone, portable cdplayer on it. Laptop may or may not have a sound card hooked up as I'll probably start a little (little) home music studio. Meaning : At least an RCA entry on the car amp, maybe with a jack. I'd have to work on some design one day or another.


For the speakers I have some lovely 4 Ohms , ITT "TL250 Compact" . I can give you the specifications if you like.
 
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Mika

New Member
Nigel,

Yeah I like them ! ! They're so cuute :)

A bit dusty though, they will get some attention later.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Nigel,

Yeah I like them ! ! They're so cuute :)

A bit dusty though, they will get some attention later.
In the UK KB (Kolster Brandes) were rebranded as ITT in the mid-70's - KB were famous for making 'hand built' TV's, not using PCB's years after everyone else had long since moved to PCB's.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
For a volume control, you will need a dual audio potentiometer. https://www.amazon.com/Dual-Potentiometer/s?k=Dual+Potentiometer 10K is probably OK.

You could use a pre-amp.

One of my early amplifiers was a home-built car amp and two potentiometers, Volume L and volume R.

The common is an end tab when the resistance is near 0, with the pot CCW,
The middle tab goes to the amp.
The common tab goes to the amp and the signal source.
The other side goes to the amp,

You don;t want a linear potentiometer.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
For a volume control, you will need a dual audio potentiometer. https://www.amazon.com/Dual-Potentiometer/s?k=Dual+Potentiometer 10K is probably OK.

You could use a pre-amp.

One of my early amplifiers was a home-built car amp and two potentiometers, Volume L and volume R.

The common is an end tab when the resistance is near 0, with the pot CCW,
The middle tab goes to the amp.
The common tab goes to the amp and the signal source.
The other side goes to the amp,

You don;t want a linear potentiometer.
Or, if you're got a linear pot, see figure 8 in this article - how to make a better log pot.


The claimed sensitivity of the amp is 70mv, so hopefully a preamp won't be needed?.
 

Mika

New Member
KeepItSimpleStupid, Hi ,

I have indeed come to the conclusion, after reading the service manual of my SU-C04, that it wouldn't be any easier to take a part of an existing amp. I thought it would just be some steps like
-take the volume, bass and balance buttono's PCB out
-hook them up
-listen to the music
... haha !!

So I'll dive into making from scratch my own volume and balance ; left and right channel volume is a very good idea.
For a volume control, you will need a dual audio potentiometer. https://www.amazon.com/Dual-Potentiometer/s?k=Dual+Potentiometer 10K is probably OK.
Such a shame, I can't even take out the variable resistors. They are 100K Ohm on the Su-C04 Meh, I'll buy it then.

The claimed sensitivity of the amp is 70mv, so hopefully a preamp won't be needed?.
If not needed, would it be useful if I want to add bass and treble control though ? Or is it unrelated ?


So if I'm right (I didn't make any research yet) I'll have to look for some potentiometers and that's it ? (in the case I don't make a preamp)

+ looking for the right connections on the Pioneer .

I'm a lot working on my personal company lately, but I'll see you gals soon.

Thank you for your help. Much


M.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
At a minimum you need a power supply, two volume controls, fuse and wires and connectors.

A pre-amp generally does
Selection
Volume
Balance
Loudness compensation
Mute
Tone controls
Provides a headphone amplifier
it might have turn-on suppression in it. Usually the amp does.
Interface to whatever your connecting it to; e.g. Bluetooth receiver
Sensitivity is typically 1v RMS for consumer equipment, I think.
Tape loops/dubbing (obsolete) The tape loop is at a higher level (Signal processor loop)
Phono EQ and type MM/MC/Ceramic (obsolete)

There are some IC's that will convert a linear analog signal to volume.

The first device I ever had was a.
A phono pre-amp
Two volume controls
A home made car amp from a NE570

Then I picked up an integrated amplifier (White elephant table) with a very poorly designed amp and used that as my first pre-amp.

My very first (MONO SYSTEM) was a Fisher model 50A valve amp (I threw it out). Ran a drill through the innerstage transformer.
A Heathkit valve preamp that got it's power from an octal tube socket modded into the 50A
A 45 only changer.
 

audioguru

Well-Known Member
Most Helpful Member
Amazon and its seller do not explain what is in their Dual potentiometer kit maybe because they do not know anything about audio or have a translation problem.
The "Taiss 10k Linear Dual Taper Audio B Type Potentiometer, Volume Control Potentiometer B10k" says both "Linear B type" and says the opposite "Audio Volume Control" type. A volume control must be an Audio A Type not a Linear B Type. Guess which type this junk is.

Most of the other Amazon potentiometers also say the wrong B Type.
 

audioguru

Well-Known Member
Most Helpful Member
You mean you never use RS Components??
:D:D
I am not in the UK. In North America we had a store called Radio Shack that sold audio products and electronic parts at very high prices.
I bought some speakers on sale:
1) The Minimus 7 speakers were good sounding small bookshelf speakers rated at 40W. They had a cast aluminum enclosure, a 4" woofer and a dome tweeter.
The woofers failed after a few years so I bought replacements that also failed after a few years. They were marked 5W Korea.

2) Speakers with sealed wooden enclosures, 6.5" woofers that sounded good and cheap little 2.5" shriekers pretending to be tweeters. They had a very low clearance price. I measured the TS specs of the woofers and they were perfect for a ported enclosure so I designed and added ports, a proper crossover network and a good dome tweeter. Now they sound great.

3) I bought an audio cable to connect my stereo to my TV for 15 dollars. Then I saw exactly the same cable at The Dollar Store for 1 dollar so I bought one there and returned it to Radio Shack and got my 15 dollars back.
 

picbits

Well-Known Member
My parents still have my pair of Minimus 7 speakers I bought from Tandy (Radioshack in the UK back then) as faulty back in the mid 1980's and fixed - I was unofficially working fro the store at that time so got replacement parts at cost. Despite spending years in my various cars as back shelf speakers, they are still working nicely.
 

audioguru

Well-Known Member
Most Helpful Member
An old single-ended car radio operating from a 12V battery (13.8V to 14.4V) produced only 2.3W into the 8 ohms "'40W rating" of a Minimus 7 speaker. A new bridged amplifier produces 7.9W. The average power with voices or music is 1/10th.

I removed the tweeter from a Minimus 7 speaker and added a port so that it was used as the sub-woofer in my audio system at the beach and it sounded much better than an expensive ghetto blaster.
 

Mika

New Member
Hello,

so I've tried to keep up. And indeed have to keep it simple. Electronics and math seems not to be my strength.

I'll go for an already made (or kit) pre-amp. I want volume and a bit of tones, and if possible balance.

If correct I need

- AC/DC 230V to 12V-14V ; 4 or 5 Amp power converter

power supply from electric_4you or Power converter from Txhang_fans

-a pre amp :D

the one Rjenkinsgb proposed, I don't quiet understand. Why is there 3 entry points for 12V ac ?? Does the 230V come directly in, and then converted on the board ??

I found this one, and still am working to get the details of entries. But the fact it has direct entry points suits me.
Besides, I'm a bit concerned by the price... too cheap too fragile ?

Also, I've come up with a schematic of connections.

maybe I got it all wrong :

I've hooked up the power supply with pre-amp and Pioneer, and am not sure if the ground from the 8points cable should be hooked up on the preamp too. I think not.


Let's see If I can go home, or go on.

Cheers !!
 

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rjenkinsgb

Well-Known Member
Most Helpful Member
I don't quiet understand. Why is there 3 entry points for 12V ac ??
It needs a centre tapped "12-0-12" transformer.

The one you link to to needs the same transformer. It looks to have a lot more power supply smoothing, but otherwise similar.

Re. your drawing, note that those preamps use a split supply, the will not work from a single 12V supply.

With a two-terminal power connection, they are often labelled + and - but once connected are 0V or ground / common and positive supply.

A lot of analog and audio gear needs dual or split supplies, with both positive and negative relative to the ground or common point.

eg. Those preamps are running on somewhere around 24 or 30V, arranged as positive, ground, negative; +12, 0V, -12 or +15, 0V, -15.

See the battery diagram in this picture, it may make the idea clearer:

split_supply.jpg
 

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