Advice needed on modding a 1567a
andrew montreal
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#1
28th December 2012
Old 28th December 2012
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Advice needed on modding a 1567a

So I have just bought a 1567a and have read alot about possible mods... which all seem to rid the unit of its original tone. What I was thinking would be interesting would be to create a two channel unit, with one channel having a line input as well. Let me know if this makes any sense:

- keep the 4722 in the first channel which would be sent to the second channel.
- use a 15095 in the second channel making it an output. Possibly using the second channel's pot as an output control.
- keep the 4722 in the third channel as my second mic input.
- have the fourth channel be a line level input.
- the third and fourth channels would still be sent to the original master output of the unit keeping its tone control and metering.

Doesn't this seem doable with some internal modding? Or am I WAY OFF?

Thanks.
andrew montreal
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28th December 2012
Old 28th December 2012
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Does anyone know anything about modding this unit? Or perhaps know someone who would know?

Thanks.
#3
29th December 2012
Old 29th December 2012
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Richard Crowley's Avatar
 

Not sure what you are asking here. The Altec Lansing 1567A is a monaural (one-channel) mixer. If you want to turn it into a two-channel (stereo) mixer, you would be better off starting from scratch. Please clarify exactly what you are trying to do here?

You can see from the schematic diagrams that it is a pretty straightforward circuit. Four input channels with half of a 12AX7 triode amplifer in each input. Annother 12AX7 for summing and tone controls, and both halves of a 6CG7 connected in parallel for the output amp. Not sure exactly what people are referring to as "its original tone"? Most of whatever they are hearing is likely either decaying capacitors or the sound of the input and output transformers, not the basic circuit.

If you want to make a fire-bottle stereo mixer, I think you would be better off selling the vintage 1567A and start from scratch.
andrew montreal
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29th December 2012
Old 29th December 2012
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Quote:
Originally Posted by rcrowley View Post
Not sure what you are asking here. The Altec Lansing 1567A is a monaural (one-channel) mixer. If you want to turn it into a two-channel (stereo) mixer, you would be better off starting from scratch. Please clarify exactly what you are trying to do here?

You can see from the schematic diagrams that it is a pretty straightforward circuit. Four input channels with half of a 12AX7 triode amplifer in each input. Annother 12AX7 for summing and tone controls, and both halves of a 6CG7 connected in parallel for the output amp. Not sure exactly what people are referring to as "its original tone"? Most of whatever they are hearing is likely either decaying capacitors or the sound of the input and output transformers, not the basic circuit.

If you want to make a fire-bottle stereo mixer, I think you would be better off selling the vintage 1567A and start from scratch.
Thanks for the response R.,

I honestly don't know very much about electronic circuitry but your answer did confirm a few things I understood about about the set-up of this unit. I do believe the "tone" of the unit comes from the input and output transformers of the unit.

Your response has also made me consider another variation on the mod:

Would it not be simple enough to keep the two first inputs (transformers and their shared tube) as is, having one of those channels feeding the output section of the unit, again as is, while the second input feeds a second 6CG7 (which would be put in the place of the 2nd 12AX7, which in turn would feed a second 15095). In terms of more expensive components, all I would need to purchase is a second 6CG7 and another 15095 transformer.

Of course, I wouldn't be doing this myself. I would get a skilled technician to do it.

Does this not make any sense? Would it not be a great option seeing as I would rarely see myself actually mixing signals within this unit?
andrew montreal
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29th December 2012
Old 29th December 2012
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Ohh, to clarify... what I meant by changing the tone is that some felt that by modding the unit, one would be taking away from what makes this unit special as is. I am trying to find a way where I can get a second channel from it while still keeping some of its original tone, which I understood came from the input and output transformers as well as the simple EQ section. Perhaps I am wrong to assume that.
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29th December 2012
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I just can't see a way to justify such major surgery to something that has something of a "vintage reputation". So many changes would be necessary, (where to put the additional controls/knobs, second VU meter?) it would pretty much destroy the basic unit. Especially the front panel which is much of it's "charm". I just can't see it.

If you really like the sound, it really would be simpler to just make a new stereo unit from scratch IMHO. And since the input and output transformers are plug-in, it is pretty trivial to mix-n-match and try it with and without, etc.

When I built my first from-scratch mixer, I shamelessly copied the appearance, using a similar shade of green and the same knobs, etc. Although it used UTC transformers and IC op-amps for the mic inputs.
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29th December 2012
Old 29th December 2012
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If I am reading your post right, it sounds like you are thinking that the 15095 tx creates an output wherever it is plugged in? If that is your thought process it is not correct, the 15095 is called an output tx because of it's intended purpose, noot because of what it does electrically. The reality is that if you want 2 channels of the 1567a circuit, then you either need 2 1567s or you need a custom built clone of the circuit with 2 channels. It is not as simple as slapping a few extra transformers on it and calling it a day. I have a 1567 that i recently had modded and restored, i have to admit i was disappointed with the unit when i got it back. Even with new signal path and psu caps and an eq bypass switch, its really is more of a distortion box than a "fat tone-licious box of preamp awesomeness" that i thought it would be. I need to experiment with different tubes, i hear that 12au7 tubes will give it a little less gain but more girth and better noise specs. Dont forget that one mans trash is another mans treasure, you might be really into noisy trashy preamps and think that that is "character" but my def of character is vastly different. If your unit is operational then try to listen to it before going too far downthis road, it might be just the ticket for you but it also might not.
#8
29th December 2012
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Mr Crowley and Sha-zam are right, rather than spend a small fortune trying to turn this thing into something it's not (a stereo Mic pre), you would probably be better off selling that 4722s and tubes separately and then the pre itself for as much $ as possible and then getting a stereo pre that you like. Or buy a second altec and hope they somewhat match.

Some of the solid state altec pres can be modded easily to have a couple more inputs with their own outputs that skip the master volume and eq but I think that its a lot easier done with a different version.

sent from my m-3500 using the gearslutz app
andrew montreal
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29th December 2012
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Though as has been pointed out to me that hum could be an issue seeing as we are bringing the output section into the input section (and I say "could"), the idea I had is not that crazy. I would be retaining the tonal quality of the unit for one channel and the second channel would only lose the EQ section. And none of the front plate would be destroyed. Actually, there would be no need for any modding of the body at all.

The first channel would feed the EQ section and master output as is. This would not be changed.

The second channel (and second half of the first 12AX7) would feed a 6CG7 which would be placed where the unneeded second 12AX7 is. It in turn would feed the newly placed 15095 on the third channel, whose volume control would now be a output control for my second channel.

The second channel would not have tone control or a meter... but it would have the 4722, the 6CG7, and the 15095 in its path. Not a bad idea, no?

I must admit that I'm not concerned about resale value. I am looking for tone, not money.

On the other hand, you're all probably right. Is this really worth the headache?
#10
29th December 2012
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I'd buy the transformers and build something new, since parts responsible for most of the sound are all available. Hell, build multiple channels in a smaller package, reducing each channel to a purely mono signal path, eliminating the mixer part. People will eventually be pissed that you hacked an original into something different, after all if it still works now, it's not in the category of disposable equipment. It immediately becomes a less desirable and non-original device once you change it, and it's ultimately why this stuff is 'rare'; bad karma. As a tech I absolutely hate it when customers want arbitrary cosmetic or unicorn chasing modifications that change historically significant equipments.
#11
29th December 2012
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seems like it would be easy to 'try' the sound by jumping out the tones stack and pulling the second 12ax7 .. to see what it would sound like...

but .. before you start modding you should try some different tubes and get a pad for the output so it can be operated up in the sweet spot and not melt your next stage... this seems to lower the s/n ratio a lot for me as well ...but hey its yours.... all you will do is make mine more valuable
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andrew montreal
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29th December 2012
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For now I'm simply going to have a tech look at it and make sure all the parts are working as is. I'll see if I can find another 1567a without the transformers and tubes and simply put the parts I'm not using into it. I happen to have two 15095's already.

Or would anyone know which other unit has the same set-up but with fewer inputs. I don't actually need a 1567a... I just need something that will allow for a 4722 to feed a 12AX7 -> 12AX7 for EQ -> 6CG7 -> 15095.

Thanks.
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29th December 2012
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Quote:
Originally Posted by andrew montreal View Post
For now I'm simply going to have a tech look at it and make sure all the parts are working as is. I'll see if I can find another 1567a without the transformers and tubes and simply put the parts I'm not using into it. I happen to have two 15095's already.

Or would anyone know which other unit has the same set-up but with fewer inputs. I don't actually need a 1567a... I just need something that will allow for a 4722 to feed a 12AX7 -> 12AX7 for EQ -> 6CG7 -> 15095.

Thanks.
Altec made a mono tube chan that used the same trannies called the 1566 .. also there are several mixers in the 1567a format from that era...
andrew montreal
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30th December 2012
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Originally Posted by rogerbrain View Post
Altec made a mono tube chan that used the same trannies called the 1566 .. also there are several mixers in the 1567a format from that era...
Thanks. The search has begun.
#15
1st January 2013
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Actually Andrew, I kind of liked your idea. Your 2 in/2 out mod could be way more useful to some folks than 4 in/1 out. It also surprised me how many folks were against modding a 1567 which was designed and sold as PA equipment (same as the 436 compressor which *everyone* mods). If you have a good tech who won't butcher it, go ahead and experiment!
andrew montreal
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2nd January 2013
Old 2nd January 2013
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Originally Posted by mjrippe View Post
Actually Andrew, I kind of liked your idea. Your 2 in/2 out mod could be way more useful to some folks than 4 in/1 out. It also surprised me how many folks were against modding a 1567 which was designed and sold as PA equipment (same as the 436 compressor which *everyone* mods). If you have a good tech who won't butcher it, go ahead and experiment!
After quite a few conversations about the issue, I've decided to use the extra pieces in another bare unit. The amount of modding that would be needed doesn't really make sense when I could simply find myself another simpler and less expensive unit that doesn't have the tubes and transformers and simply put them in it. Also, this way if ever I wanted to do a mono drum recording (for example), I would simply have to put back the transformers into my 1567a.

Thanks for your support though. It's appreciated.
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