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Getting sound out of a Model 1 TRS-80

Hi Dave, I seem to have had conflicting measurements. After a few re-tries the result is as in pic.
 

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I've bought a Loadmouse pc speaker

I've googled for this and haven't really gotten any sensible hits?

In my experience it's really pretty non-critical what you use for this; back in the day I hacked together a speaker by using one of a pair of amplified Walkman speakers. (The speakers in question each had their own set of 4AA batteries and were connected to the Walkman by a Y-cable that had a stereo 3.5mm plug on the walkman side and mono 3.5mm plugs on the speakers. This meant the TRS-80's cassette out could just be plugged directly into them; the "hacking" part was I wired a volume knob I salvaged from somewhere between the amp board and the speaker because otherwise it was *waaaaay* to loud. Granted it was probably pretty dumb to put the resistor on the output of the amp instead of the input, but, eh, it worked.) More recently I've gotten sound out of my Model I by:

A: Hooking it up to one of those dumb disco-ball party speakers:
Screen Shot 2023-03-17 at 4.14.29 PM.png
B: Plugging it into the front-panel Mic input on my desktop computer, starting up Audacity, and turning on the recording monitor so it plays the Mic input out the speakers.

(The latter method is what I'm using to CSAVE programs instead of actually using a cassette deck, to load them I of course hook the cassette input to the headphone output.)

Unfortunately all the amplified PC speakers I have lying around have captive cords so I can't connect a set up to the TRS-80 without either a gender changer or making a cable, but I can't think of a good reason why there would be any problem at all using them. Do you still get this mysterious hum if you *don't* have the Cassette deck hooked up at the same time as the speakers via your Y cable? I can't say I ever tried having a cassette deck and a speaker hooked up at the same time, I've always just swapped the cable.
 
I've googled for this and haven't really gotten any sensible hits?

In my experience it's really pretty non-critical what you use for this; back in the day I hacked together a speaker by using one of a pair of amplified Walkman speakers. (The speakers in question each had their own set of 4AA batteries and were connected to the Walkman by a Y-cable that had a stereo 3.5mm plug on the walkman side and mono 3.5mm plugs on the speakers. This meant the TRS-80's cassette out could just be plugged directly into them; the "hacking" part was I wired a volume knob I salvaged from somewhere between the amp board and the speaker because otherwise it was *waaaaay* to loud. Granted it was probably pretty dumb to put the resistor on the output of the amp instead of the input, but, eh, it worked.) More recently I've gotten sound out of my Model I by:

A: Hooking it up to one of those dumb disco-ball party speakers:
View attachment 1254319
B: Plugging it into the front-panel Mic input on my desktop computer, starting up Audacity, and turning on the recording monitor so it plays the Mic input out the speakers.

(The latter method is what I'm using to CSAVE programs instead of actually using a cassette deck, to load them I of course hook the cassette input to the headphone output.)

Unfortunately all the amplified PC speakers I have lying around have captive cords so I can't connect a set up to the TRS-80 without either a gender changer or making a cable, but I can't think of a good reason why there would be any problem at all using them. Do you still get this mysterious hum if you *don't* have the Cassette deck hooked up at the same time as the speakers via your Y cable? I can't say I ever tried having a cassette deck and a speaker hooked up at the same time, I've always just swapped the cable.
The cassette deck I have is a Radio Shack CCR-81, which I didn't know but cuts the speaker when the input jack is plugged, so no audio. The hum is there with or without the cassette deck connected. I've ordered a mono splitter 3.5mm for the deck and TRS-80 and a 3.5mm stereo to mono adapter for the stereo Loudmouse input plug. Hopefully it might be better. That disco ball is pretty RAD. Would be cool with my Amiga A1200 Icedrake setup but the TRS-80 is a spaceship grey theme for me. Loudmouse pictured.
 

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I don't really see how more connectors will actually help to be honest...

Can you draw out the schematic of how you go from the cassette data output jack to the cassette unit and the amplifier. Let's see how the whole lot is cabled up.

I will do a bit of calculation tomorrow on the resistor network and see what voltage we are getting out of the cassette port.

Dave
 
I've tried a stereo female to female 3.5mm from trs-80 out to speaker in so far (with hum). The picture is my planned alternative.
 

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So, can you use your multimeter and work out the internal wiring of the Y cable at the cassette end and the cable to the speaker.

EDIT: I see this is your planned configuration, so I assume it doesn't exist yet.

I assume that all of these units ate connected to the mains power, but that you are using a single, mains socket for the power feed?

By disconnecting the cables, at what point does the hum go away?

If you have used a cable directly from the TRS-80 to the speaker, and this gives you hum, but it goes away when the cable is disconnected - then this is almost certainly to be a ground loop.

Dave
 
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HI Dave. Yes all the units are in some way connected to the same outlet via a Belkin Surge protected board.

The hum isn't there when the speaker input is disconnected from the stereo jumper I'm currently using to the TRS-80 output (Direct No Cassette) I thought a mono adapter there might be an answer. Otherwise is there some sort of ground-loop filter on the market? I don't really have other mains outlet options.

Richard
 
First a big thank-you to all respondents. Update is the first stereo "Y" adapter arrived and it fixed the problem. No hum. It is between the TRS-80, Cassette deck and speaker. I now have an extra ground loop isolator, mono splitter and stereo/mono plug (all 3.5mm) coming in the mail but seem now not to be needed. Reduced video attached.
 

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Excellent.

So, it would make sense to me (for completeness) to use your multimeter on the 'faulty' cable and the 'working' cable to identify what the connection differences are.

This is to leave a 'record' for future readers with the same problem...

Dave
 
Thanks Dave. It seems the "Y" cable is working by way of the mono input jack on the cassette deck. This mono input jack seems to balance both channels in the stereo "Y" adapter and indeed the speaker to gnd. The previous attempt was a direct stereo link from the mono TRS-80 to stereo speaker where the Right? channel was disconnected? and causing the amplifier to hum. I will test later.

Richard.
 
After further inspection, the mono audio from the TRS-80 is carried on the Left channel of the stereo "Y" adapter to the mono jack of the cassette deck. The stereo "Y" adapter is also connected to the stereo speaker input.
Although the humming has stopped I might be grounding the right channel of the speaker which is maybe not wise. So...
For the speaker to enact both channels, this input needs a mono->stereo plug adapter, to pick up the mono signal, carried on the left channel of the "Y" adapter and display in tandem

Another option is to use a mono 3-way plug (2xFj+Mp) and an adapter (stereoFj+monoMp) + speakers input. These are in the mail so I might try it but 3 pugs in line protrude from the cassette deck a fair way.
 
Yes, that would be the only scenario that would make sense with the right channel open circuit and a (relatively) long cable from the amplifier right channel that is not grounded or connected in parallel to the left channel.

There is absolutely nothing wrong with connecting the amplifiers input to GND. But it does mean you are loosing some additional volume you can obtain from driving both channels of the amplifier.

How good is your soldering? I would have thought the best thing would be to make up your own cable?

Gnd (sleeve) to gnd (sleeve) at the amplifier.

Signal (tip) to left signal (tip) and right signal (ring) at the amplifier.

I will post you an image of what you need later...

Dave
 
I can solder ok. but not snappy yet. I've actually ordered previously a plug to do the job. For me It'sa 48km road-trip to Jaycar, the components store for jacks etc so an ebay order has been easier.
 
My cousin lives in the Northern Territories. The 'weekly shop' [sic] is a plane ride away!

Here is a picture of what you need:

1679396178360.png

On the left is your stereo amplifier connector and on the right is your mono cassette 'Y' lead.

The cable you require is single core screened cable.

The screen is identified as the black wire.

The central core is identified as the red wire. The core needs to be connected to the tip and ring at the AMPLIFIER end.

Hope this helps? If not to make a lead up - to ask the supplier whether their lead has the same connections or not.

Dave
 
Thanks Dave. I've never been to the NT but:
With my current "Y" cable and plug on order, this pictured will be the arrangement.
 

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So it looks like from your drawing that your amplifier has a TRS male plug (on the right).

I am happy with the mono (ts) to stereo (trs) adaptor in the middle. That should connect the mono signal to both the left and right signals of the amplifier.

I am not sure what the connector is on the left though. is this on your cassette? If so, you will be shorting out the 'right' channel to ground by the action of inserting the mono part of the adaptor into the left-hand side connector.

Dave
 
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