ANYONE HELP!!! Helios line input
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mitsos
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I'm not familiar with the rest of the schematic, but your line in is definitely wired wrong. As it is, you are grounding your line in signal, so you at least want to flip hte connection around.
But you really need a shorting jack for this (also called switching or normalling). With this kind of jack (wired properly), when nothing is inserted, the signal from the transformer secondary passes through the jack to the amp, but once you plug a line signal into it, the shorting connector is lifted and breaks the connection from the trafo so the line input goes to the circuit.
Sorry, I doubt I explained it clearly, but I'm sure google will have pics/examples.
But you really need a shorting jack for this (also called switching or normalling). With this kind of jack (wired properly), when nothing is inserted, the signal from the transformer secondary passes through the jack to the amp, but once you plug a line signal into it, the shorting connector is lifted and breaks the connection from the trafo so the line input goes to the circuit.
Sorry, I doubt I explained it clearly, but I'm sure google will have pics/examples.
AP carrier
Active member
gemini86 said:
I had one which was built diy from veroboard. It sounded great but made some weird splat sounds when overdriven. Did you ever have this effect with the real ones?
Also the sowter transformer for the helios pre I have has two taps. One 10:1 balanced for the mic pre and the other 1:1 unbalanced for the tape level. Never tried it 'line in' without the transformer though.
Andrew
0dbfs
Well-known member
Hey these look pretty cool. I'm still on the fence about which circuit to use for a little channelstrip / EQ / summing project I am collecting parts for but this might be useful for a number of reasons.
Do you know what type of level these see before reaching the "over-driven" stage? Also, what kind of output-drive capabilities does something like this have?
Thx,
jonathan
Do you know what type of level these see before reaching the "over-driven" stage? Also, what kind of output-drive capabilities does something like this have?
Thx,
jonathan
gemini86
Well-known member
The debate is still out on the output drive. Some say it's meant for 5k but the channel schematic shows 10k. I made up a sample and it was hooked up to an la2a and it instantly fell on its face,as expected. It does clip fairly early, I have noticed. But it takes a while for it to transition from 2nd to 3rd harmonic. I think the layout is key to getting the original sound. They start oscillating at the highest gain setting and just go bonkers. Can be a really cool effect. I had circuit boards made that followed the original layout closely so I have the same "d efects " (I call it character ) . Once I get a proper scope, i'll do some measuring. But that will be a while. I do know my client is very happy.
The 1:1 tap was actually hooked up as a "-20 db" pad if you look at an original front panel. We actually ended up going for the lustraphone clones by Cyril at Raindirk Audio. They won hands down in listening tests.
AP carrier said:
The 1:1 tap was actually hooked up as a "-20 db" pad if you look at an original front panel. We actually ended up going for the lustraphone clones by Cyril at Raindirk Audio. They won hands down in listening tests.
gemini86
Well-known member
Look at the gyraf g9 for a nice clear example. Instead of bypassing the mic transformer, why not put line input through a 20db pad and then the mic transformer, like the g9 does?
0dbfs
Well-known member
Yes. Some of the older neve modules do that as well. I think 1061.
So, in the channel-schem are card 1 and card 2 the same ckt's? Looks like ckt feeds the EQ and there is makeup in card2. Insert appears to be unbal out between this input stage and the EQ.
Man, these consoles were something else eh?
Cheers,
jb
So, in the channel-schem are card 1 and card 2 the same ckt's? Looks like ckt feeds the EQ and there is makeup in card2. Insert appears to be unbal out between this input stage and the EQ.
Man, these consoles were something else eh?
Cheers,
jb
gemini86
Well-known member
Yeah, the same circuit, but apparently they started with the 15c1 circuit (-24V supply, transistors positions swapped) then the 2181 circuit (+24v then transistors as they are here), then the 22113 circuit, which added a small handful of transistors and other parts to make it drive low impedance inputs on outboard gear. The history and other details is hazy, at best but that's what I've gathered from all my reading and research. There's a pretty lengthy thread over on psw forum about the helios desks.
0dbfs
Well-known member
gemini86 said:
I'll have to read through that one again too.
Igor's Type-69 EQ appears to use a similar input stage but the output stage is ba283 style.
Are you using just this portion for your pres or do you have a different output stage?
Thx,
jb
gemini86
Well-known member
Just the input portion into a 10k load works great.
0dbfs
Well-known member
That's sweet. Looks like it can be quite small... With minimal parts. To drive say... A passive mixer w/10k inputs...
Very affordable too except for maybe transformers...
Is there normally a 1:1 on the output?
Does that really do 70dB of gain? Wow!
Thx,
j
Very affordable too except for maybe transformers...
Is there normally a 1:1 on the output?
Does that really do 70dB of gain? Wow!
Thx,
j
gemini86
Well-known member
Good except r7 says 1-2k... should be 1.2k or 1200ohms.
The originals were direct out unbalanced, I imagine they went to a fader and mixing network from there.
The originals were direct out unbalanced, I imagine they went to a fader and mixing network from there.
gemini86
Well-known member
Yes it does 70db but not cleanly. I added a 10 pot after it as an output attenuator. Simple and effective.
gemini86
Well-known member
Not that I see.
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