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Sun Jun 12, 2022 4:14 pm

Just bought a 74 tintop, previous owner had it for a few decades and assumed the Sapphire XXV in it was junk.
Got it working on my test bench today but the volume even at full is laughable. Any ideas? Been scouring for information and there's not much on these OEM units. Only thing I saw was possibly the antenna is the problem, touching it does nothing to increase volume.
I would really like to keep it as it's original, branded and anything else is gonna look out of place besides overpriced (In my opinion) modern recreations.

Also, not sure if this is the appropriate place for this thread as it may be better suited elsewhere. Apologies in advance

Sun Jun 12, 2022 5:24 pm

zbealeo wrote: Just bought a 74 tintop, previous owner had it for a few decades and assumed the Sapphire XXV in it was junk.
Got it working on my test bench today but the volume even at full is laughable. Any ideas? Been scouring for information and there's not much on these OEM units. Only thing I saw was possibly the antenna is the problem, touching it does nothing to increase volume.
I would really like to keep it as it's original, branded and anything else is gonna look out of place besides overpriced (In my opinion) modern recreations.

Also, not sure if this is the appropriate place for this thread as it may be better suited elsewhere. Apologies in advance

What speaker are you using? I have had this issue before....many years ago. Trying to jog my memory of what causes it. Ray

Ray

Sun Jun 12, 2022 5:27 pm

raygreenwood wrote: zbealeo wrote: Just bought a 74 tintop, previous owner had it for a few decades and assumed the Sapphire XXV in it was junk.
Got it working on my test bench today but the volume even at full is laughable. Any ideas? Been scouring for information and there's not much on these OEM units. Only thing I saw was possibly the antenna is the problem, touching it does nothing to increase volume.
I would really like to keep it as it's original, branded and anything else is gonna look out of place besides overpriced (In my opinion) modern recreations.

Also, not sure if this is the appropriate place for this thread as it may be better suited elsewhere. Apologies in advance

What speaker are you using? I have had this issue before....many years ago. Trying to jog my memory of what causes it. Ray

Ray

Using some old sparkomatic sk693 speakers
I can try one of my bookshelf speakers I have as well to see if it just doesn't like that model. I couldn't actually test sound quality until I got it in the bus since I don't have another antenna or even a metal coat hanger.

Sun Jun 12, 2022 5:33 pm

you need a speaker of likely 4 to 8 ohms, Once you put an antenna on it you most likely have to trim the antenna at about 1300 - 1600 on the AM dial but I don't know where the trim is on that unit. Some are in the dial front, some are in the back, and some are electronic but most of that period required trimming to the antenna on AM. Make sure everything is properly hooked up. It is stereo so there should be 3 or 4 leads for the speakers.

manual per a google search. I haven't read it but if you haven't, here it is.

https://www.google.com/url?sa=t&rct=j&q=&a...tjJY2Og_VB

Sun Jun 12, 2022 6:08 pm

SGKent wrote: you need a speaker of likely 4 to 8 ohms, Once you put an antenna on it you most likely have to trim the antenna at about 1300 - 1600 on the AM dial but I don't know where the trim is on that unit. Some are in the dial front, some are in the back, and some are electronic but most of that period required trimming to the antenna on AM. Make sure everything is properly hooked up. It is stereo so there should be 3 or 4 leads for the speakers.

manual per a google search. I haven't read it but if you haven't, here it is.

https://www.google.com/url?sa=t&rct=j&q=&a...tjJY2Og_VB

Ah appreciate the info. I saw the wiring diagram but not this manual. I just ordered some door speakers within spec and we'll see.
The bookshelf speakers unsurprisingly were also very quiet

Sun Jun 12, 2022 6:59 pm

did you connect the speakers per the wiring diagram with the three wires as shown? I would think anything that is larger than a free standing 6 x 9 would take too much energy to drive. Most of the speakers for those units were 4" or 5" free standing or ported speakers. Some bookshelf speakers are air tight, they are an air suspension type speaker rather than a ported speaker, and they take considerable more power to drive them.

Mon Jun 13, 2022 11:37 am

SGKent wrote: did you connect the speakers per the wiring diagram with the three wires as shown? I would think anything that is larger than a free standing 6 x 9 would take too much energy to drive. Most of the speakers for those units were 4" or 5" free standing or ported speakers. Some bookshelf speakers are air tight, they are an air suspension type speaker rather than a ported speaker, and they take considerable more power to drive them.
So the sparkomatic I used to test is a 3 ohm 6x9
I attached it to the left channel only, here's a video of it being very quiet at full volume
https://photos.google.com/share/AF1QipP-1uVVK3mDj0...Jjb0lUUmNR
Not sure it's going to really show much

Mon Jun 13, 2022 11:56 am

did you set the balance to the middle?

Mon Jun 13, 2022 11:58 am

Note the information in the link indicates that this is a stereo unit, needing two speakers. Note the speaker connections. A single speaker connected between the two stereo outputs will be mighty quiet.

Schematic:

Mon Jun 13, 2022 11:59 am

Don’t think you have a speaker issue. Likely the amplifier circuit in the radio is no longer functioning.

If I were you, I would get a 12v amp board for a couple of bucks from Amazon and feed that amp baord speaker signal you are getting now and drive the speakers off that board. Those boards are 2x2 inches and will fit inside the radio.

Alternatively, just gut the electronics out of the radio, replace with a Bluetooth receiver an amp board. The radio will look original with all modern insides. That’s what I did on a Sapphire V in my 67. Still looks original factory. https://www.thesamba.com/vw/forum/viewtopic.php?t=769052

Mon Jun 13, 2022 12:11 pm

This should help:

Mon Jun 13, 2022 12:56 pm

his wires (in the photo) show that he was connected on one side of the system but the photos show a setup in a bus, not on a workbench. I'd set it up on the bench with a 12V regulated PS (not a battery charger that has lots of ripple) and try it there. The system shows two speakers and without analyzing the circuit, there could be voltage issues when only one speaker is connected. There is also a balance control and it has to be set to the middle. In general, running early transistor equipment without a load is a good way to damage it. I can remember many folks bringing equipment in for repair in the 1970's where they either ran a radio without a load or shorted the output. The protection circuits that everyone has the luxury of today did not exist in lots of equipment back then.

Looking I do not see a balance control on the right hand side. Looks like it should be a double knob.

speaker connection in the photo

Mon Jun 13, 2022 6:27 pm

Thanks again for all the input!
I ended up opening the unit, cleaned it up as well as I could and resoldered some connections that had seen better days.
And to my pleasant surprise it works! New video with the added bonus of it being audible while running! https://photos.google.com/share/AF1QipNoxB88FC_ERV...pfYVdMdWdn

Now to figure out the best Bluetooth method and probably realize all this was in vain :lol:

AirHead1966 wrote:
Alternatively, just gut the electronics out of the radio, replace with a Bluetooth receiver an amp board. The radio will look original with all modern insides. That’s what I did on a Sapphire V in my 67. Still looks original factory. https://www.thesamba.com/vw/forum/viewtopic.php?t=769052
You did an awesome job with that one! I may see if I can get my hands on a broken one and do this.

Tue Jun 14, 2022 5:00 am

I Googled this radio and it shows a user manual PDF with circuit schematics. And driving two parallel pairs of 3.2 ohm speakers. So it should manage a fair power output.

Tue Jun 14, 2022 8:14 pm

SGKent wrote: In general, running early transistor equipment without a load is a good way to damage it. I can remember many folks bringing equipment in for repair in the 1970's where they either ran a radio without a load or shorted the output. The protection circuits that everyone has the luxury of today did not exist in lots of equipment back then.
While generally correct, this particular radio has a trick up it's sleeve: note the bias resistor on the output pull-down transistor is connected to the speaker side of the output capacitor. With the speaker disconnected, operating bias is removed from the output stage, effectively disabling it. No load, no operation. Kinda clever...