Frox Optical Speaker System

I just noticed the serial number: 01362. Unless they serialized them randomly, it would appear they made quite a few. From prior post it seems like there may have been a lot of unfinished parts. I am interested in firing up this system, but with an amp. that only has 3ea. connections. I will need your help. I will also need to find out if my amp. has volume control over the three connections.
Almost definitely not, see my response above. You typically see only one optical out, it's meant for digital recording. And it will probably only output from digital inputs. Connecting it to your speaker is IMO a bad idea - it will be at full volume, and I don't see any volume controls on the speakers.

It's actually unfortunate that these only have digital inputs, since you will be converting your signal from digital (unless it's a turntable) to analog, then to digital again to drive the speakers, then the speakers convert the signal to analog again.

If it was me I'd probably try to insert an analog input in the speaker circuitry between the DAC and the amp.
 
Given that there are a couple of Lattice Semi GALs next to it, I'm guessing that labelled device is a mask ROM DSP, rather than a logic ASIC. Either that or they screwed up the ASIC design, and had to add some GALs to sort it out...

Mask ROM processors are a bit cheaper than full or semi-custom ASICs (which I was designing at the time).

I couldn't have said that better. Really, I couldn't have.

;)
 
I just noticed the serial number: 01362. Unless they serialized them randomly, it would appear they made quite a few. From prior post it seems like there may have been a lot of unfinished parts. I am interested in firing up this system, but with an amp. that only has 3ea. connections. I will need your help. I will also need to find out if my amp. has volume control over the three connections.

Unless the S/N range started at 1350, may have happened...
 
If it was me I'd probably try to insert an analog input in the speaker circuitry between the DAC and the amp.

That's what everyone did that converted them to stereo use. You go in after the DAC and crossover sections.

IIRC gain was set in the crossover sections while the amp was set at unity.
 
cpt_paranola, Sorry, way over my head. If pictures would help you guys, I will try to send some more to you. Honestly, I think it's obvious (at least to me) that I have reached my level of understanding here. Some of you guys are probably engineers and you have already left me inhaling smoke (lol). I'm fine with assisting you and your curiosity. Personally, I just want to see if I can set this system set up and see how it sounds. Also, to remind you guys, there is another board that is being covered up by the smaller one, so, I have not as yet sent any pictures of it.
 
My amplifier does have 3ea. separate set up features for the digital coaxial inputs, so hopefully they should each be able to set the volume independently.
 
switchsler, I sure don't want to set these speakers up at full volume. I wonder what amplifier they were using for thee speakers back in those days?
 
Trying to insert an analog input in the speaker circuitry between the DAC and the amp. sounds a lot like engineering to me. When they were designing this system, what could they have been thinking? I do have a couple of turntables that I use but the amplifier is a solid state Mac Mc 250, and a Mac MCD 7000 CD player that is analog which of course neither have any optical connections on them.
 
Personally, I just want to see if I can set this system set up and see how it sounds.

How much of the system do you want to get working?

If all you want is the amp and speakers, then you'll need to find out how the DAC board connects to the amp; i.e. which wires carry the analogue signal. I can only see the ribbon cable, so that probably has two conductors (or maybe three: ground either side of signal). Then rest will be power, and, since I can't see the optical connector on that board, the serial digital stream. Once you've found the signal wires, you can remove the DAC board and inject an analogue signal to the amp. One way to find the signal wires is to touch each signal with a finger; you'll hear the injected hum when you find the signal wires... Make sure there are no mains voltages around (that's unlikely, I think; looks like a low voltage DC board).

If you want to try the full DAC and amp, you'll need to give it a volume-controlled digital stream; a PC running a media player should do this, using the player's volume control.
 
I do have a friend who is an electrical engineer, He is used to working on vintage items such as Juke boxes and old radios, but he does not like to work on anything without a schematic. I will never see a schematic for this system.
 
Wow, this would be a heavy duty computer system, not no speakers on the desk set up. I would still have to figure out how to connect the speakers to my computer? I do not see a volume control on the disc player so I would have to buy one with a volume control. What quality sound would I get from a computer? Also, I would or would not be able to set up iTunes and have the ablility to control the volume? I guess if I could get this set up and running, I might be able to get an online EQ to just sound?
 
but he does not like to work on anything without a schematic.

That's unfortunate. Given the modular nature of the system, it really shouldn't be that hard to figure out the connections between the DAC and the amp. You could even trace the signal from the analogue output pins of the DAC; easy to find and download the datasheet; it's a PCM17-something (ribbon cable is obscuring the part #). Possibly the PCM1700 to pair with the DF1700 upsampling filter.
 
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I would still have to figure out how to connect the speakers to my computer? I

You will need a computer with an optical SPDIF output*, and a media player like MediaMonkey or MusicBee. And some ripped CDs.

* mine has a coax SPDIF, and it's a bog-standard HP desktop, nothing special.

I could even use one of my little £30 Android media boxes, which has an optical SPDIF output, and run a media player such as BubbleUPnP, using its volume control on the SPDIF o/p.
 
I have an IMAC computer with the CD drive that came with it (if that helps). Like I said I can take more pictures if you want and I will call my friend and see what he thinks.
 
Does the iMac have optical SPDIF output? It may be part of a 3.5mm audio output (Apple went for a combined analogue and digital jack, with the optical out in the centre of the jack plug). You'll need a suitable 3.5mm optical jack to toslink cable.

Forget the CD drive, and concentrate on playing ripped files. iTunes should do that. You may have to fiddle with some settings to make sure the optical output isn't fixed level audio, and responds to the iTunes volume control.
 
Smoke-libr8r said he was interested in more pictures

Thanks for the panel pictures. When you post pictures of the subwoofer board, please include a close-up of its connector panel.

What does everyone think? The full/sub set to "full" if you aren't running a sub, "sub" otherwise? This "sub" position enables a sub/sat crossover? The bi/mono seems self-explanatory. The "A/B" could be setting the left versus right speaker?

It doesn't look like the sub has an optical input, but does have what looks like a port similar to the I/O on the sat. Could a cable connecting the two be how the sub gets its music signal?

They were thinking about a pure, digitally-connected system, not about making individual, versatile components.

I think you are on the right track with the advice to hook them up to a PC that has a volume controlled TOSLINK.

What quality sound would I get from a computer?

The quality of the sound would be largely determined by the quality of the DAC in the speakers. I'd guess that it will be pretty good. The next thing would depend on the quality of your digital music files. The optical link should transfer the data on a bit for bit basis so there isn't any loss (I'm leaving out some caveats for sake of simplicity).

It would be pretty cool if these could be fired-up the way that Frox intended.

Keep in mind at this point in time I could have gotten a soundmotor chip spun up. The ASIC* business was booming and every chip mill offered this.

Yep, but having a custom chip made isn't trivial (or cheap). It is definitely a step or two beyond building a custom board with off the shelf parts. For some reason I was under the impression that Frog Designs was more about making the product and packaging pretty/trendy than doing in-depth electronics design. Apparently, I was mistaken.

That's what everyone did that converted them to stereo use. You go in after the DAC and crossover sections.

Why did people convert these? Was there a shortcoming in the optical interface?
 
I just got off the phone with my friend and said that it shouldn't be a big deal putting a volume control on each speaker so they can be adjusted individually. I looked at the manual for my amp. and it has 3ea. digital optical input connections but only one digital optical output connection. He said that he thought that because my receiver was already set up for digital optical output that my volume control should work. Problem I see with either computer or my receiver is if they both only have one output, then either way all I will get is mono coming out to all speakers. My best deal would be to find out if any company is selling an amplifier that has stereo digital optical output connectors and from what I have learned so far, I doubt it. Maybe in another 20 years.
 
Wow, seems like every time I am typing you guys are brain storming. Only wish I understood half of what your saying. My computer must already be set up for stereo, they sell stereo speakers for it. And from what I'm getting from you guys is, that the digital music I'll get from iTunes or a CD player should plenty good. So, my guess is after I get volume controls on each speaker for adjustments, I will need a splitter for left and one for right. Does that sound right? I am curious what the power on these amps. are rated at.
 
I think you are on the right track with the advice to hook them up to a PC that has a volume controlled TOSLINK.

There are a few potential drawbacks with that approach though.

We're assuming they used SPDIF via their TOSlink connector. I'm not sure when SPDIF was developed; wiki not being helpful...

Basic SPDIF is only 20 bit, so, using a 16-bit source, that only gives 4 bits of volume control before you would start to lose sound quality. With the extended 24-bit version, you'd get 8 bits, so potentially 256 levels without losing quality. Hard to know if this speaker would support 30 or 24 bit protocol.

You'd have to be sure that the pc volume control does use the full range of SPDIF resolution available, rather than just attenuating the 16 bits of red book CD.
 
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