Smithers XKR
Well-known member
Transistors use low voltage 45v or so and higher current than valve tech so why the bigger Caps? Is it some sort of hybrid?
Barrier strip outputs- HELP
- Thread starter racer
- Start date
The portastudio, being essentially a cassette recorder will I think operate at -10dBV (0.316V ) whereas that Altec unit will be 'studio' levels of +4dBu (~1V) but also probably capably of much higher levels of 10 V or more. Recipe for some very nasty distortion! Add to that the fact that compressors need to work at the level they need to work at IYSWIM and that means you will likely need some attenuation between comp out and portastudio in. I doubt the latter is balanced so a 10k pot in a tin is the easiest solution. Put it at the recorder end.
The Altec output is 'floating' transformer balanced so I would not ground the screen at that end but tie screen and 'cold' together at the pot.
Can do a scribble if you want.
Dave.
The Altec output is 'floating' transformer balanced so I would not ground the screen at that end but tie screen and 'cold' together at the pot.
Can do a scribble if you want.
Dave.
bouldersoundguy
Well-known member
I think it has a pot built in.
[Edit] Then again, if it's the fixed threshold type where you drive the input into the threshold then dial back the output, you might run out of attenuation. If it's the variable threshold type of compressor, it's pretty likely that just running the output a bit under 12:00 will do the trick.
[Edit] Then again, if it's the fixed threshold type where you drive the input into the threshold then dial back the output, you might run out of attenuation. If it's the variable threshold type of compressor, it's pretty likely that just running the output a bit under 12:00 will do the trick.
Last edited:
TalismanRich
Well-known member
According to the manual, the output of a 1612A is variable from 0 to +27dBm which is pretty hefty! With a 600ohm impedance, that's about 25V.
Have you got a link to that manual Rich? I could not find one. Also should have said, OP should IMHO use the 150 Ohm winding.
Dave.
TalismanRich
Well-known member
Here's the docs for the 1612A. They are available on ManualsLib.com.
I am obliged Rich. I still think the output will need to be attenuated because the meter is driven from the output circuit and so will be pretty useless if the compressor is operated at a lower than normal level?
The resolution of that schematic is just not quite good enough for me to read the type number of that output amplifier. Anyone got younger, better minces?
Dave.
The resolution of that schematic is just not quite good enough for me to read the type number of that output amplifier. Anyone got younger, better minces?
Dave.
TalismanRich
Well-known member
It looks like it might be a Peerless 15769 or 16769. If you look at the transformer in the gut shot, it's stamped on the top. Schematic says 150 - 600 Ohm.
TalismanRich
Well-known member
I didn't think I could find anything but I finallly found a discussion on Gearspace from 2017 showing it's an LM380 op amp. 2.5w audio amp IC.
Good searching that man! I have used those before, they make a cracking headphone amp and if you run them from just a couple of AAs they overload with a guitar very nicely.I didn't think I could find anything but I finallly found a discussion on Gearspace from 2017 showing it's an LM380 op amp. 2.5w audio amp IC.
Dave.
rob aylestone
Moderator
On the screening front - it's simple. Tiny levels in a circuit might well be compromised by external interference, so you wrap them in a conductive tube connected to ground. Once the levels get up to line level and over, it's less vital and by speaker level unimportant. In things like guitars, then it's one conductor in the centre and a common ground and conductor. Telephones were sent miles without any screening between the exchanges, but once levels become really low - preventing outside interference entering an audio circuit is a good idea.
Yus, there are several factors involved here. The source impedance must be as low as possible. Many decades ago we ran mic lines hundreds of feet using twin twisted lamp cable without a screen but the microphones were 30 Ohms and fed a good quality transformer and the grid of a Triode. We got no hum because the system was balanced and radio frequency interference did not arise until taxis got radio transmitters!
RFI continued to be a problem especially with the advent of the Silicon transistor because even 'audio' types such as the venerable BC109 still had lots of gain at 50M Hz and beyond (Triodes don't you see) The problem has largely been licked these days but mobile phones put out a pretty intense pulse and will 'chirp' into almost any kit if they are within a yard or so of it.
But of course, with 'screens' come ground loop issues and they have to really be tackled on a one-off basis.
Dave.
Hi Dave, can you please do a scribble? Thanks!
I hope the attached is clear to you? It is drawn as two mono jacks in a tin with a 10,000 Ohm log volume control pot'. The view is of the back of the pot.
The jack lead to the compressor will have a 2 core cable with 'hot ' to the tip and screen and cold connected to the sleeve.
At the comp' end just the two core wires connect. to the barrier strip. I have shown the cable screen twisted out because you might find you need to take that to the compressor's chassis but that is very unlikely. (i.e. might hum) Ignore the actual terminal connection I have shown, go as marked in the manual. Since you are attenuating the signal you might as well go for the full fat 600 Ohm connection.
I have shown a metal case but you could probably get away with an ABS box? Certainly you could 'lashup' the circuit 'naked' for a test.
Have fun!
Dave.
The jack lead to the compressor will have a 2 core cable with 'hot ' to the tip and screen and cold connected to the sleeve.
At the comp' end just the two core wires connect. to the barrier strip. I have shown the cable screen twisted out because you might find you need to take that to the compressor's chassis but that is very unlikely. (i.e. might hum) Ignore the actual terminal connection I have shown, go as marked in the manual. Since you are attenuating the signal you might as well go for the full fat 600 Ohm connection.
I have shown a metal case but you could probably get away with an ABS box? Certainly you could 'lashup' the circuit 'naked' for a test.
Have fun!
Dave.