Recent builds: Altec/Spectra Sonics, Gssl.

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jamesfei

Well-known member
Joined
Nov 8, 2004
Messages
70
Location
Oakland
Here are my two recent builds: the top is a gssl. The gain reduction meter is external so I can put it next to my console meters and use the large Orion "Catwisker" (it has a very stylized pointer and great ballistics).

AltecSpectraGssl_640.jpg


The bottom is 2 channels of Altec 9475 and 2 channels of Spectra Sonics 101, used for mic pres as well as makeup gain for passive eq's. Both have 20db input pads. The Altec outputs goes to a bridged-T attenuator (20db in 1db steps). The Spectra uses HS-56's for input, and go direct/unbalanced out. The gain switch adjusts gain in 3db steps from 35db to 50db. I had to clamp one of the HS-56's down inside because somebody had hacked off the mounting posts.

AltecSpectra2_640.jpg
 
Nice! If you could mount that meter on a desk lamp arm, it would be so mad scientist. And those knobs on the attenuators.... whoa! Really like the way your panel engraving accentuates them.
 
Thanks for the comments! The Spectras were re-capped with Nichicon Muse (I picked up a bunch when I was in Japan). I think they are the KZ series but can't remember without opening the box again. I also re-capped the power supply cap in the Altec.

If anyone is interested, I used a 6 position gain switch for the Spectra 101 and the values are below. You can use finer steps, but the gain range is limited to 35db to 50db. With the 20db input pad, this gives you a range from 15 to 50db, pretty usable for most situations.


gain--total resistance--resistor

35db= 5.6k 5.6k
38db= 8k62 3k
41db= 12k6 4k
44db= 18k8 6k2
47db= 28k8 10k
50db= 46k2 17k4


[quote author="rattleyour"]Very cool!

We finished four SS 110's a while back but haven't re-capped them yet-- what are those black caps you used?[/quote]
 
[quote author="jamesfei"]Thanks for the comments! The Spectras were re-capped with Nichicon Muse (I picked up a bunch when I was in Japan). I think they are the KZ series but can't remember without opening the box again. I also re-capped the power supply cap in the Altec.

If anyone is interested, I used a 6 position gain switch for the Spectra 101 and the values are below. You can use finer steps, but the gain range is limited to 35db to 50db. With the 20db input pad, this gives you a range from 15 to 50db, pretty usable for most situations.


gain--total resistance--resistor

35db= 5.6k 5.6k
38db= 8k62 3k
41db= 12k6 4k
44db= 18k8 6k2
47db= 28k8 10k
50db= 46k2 17k4
[/quote]


Hi James,

Well done on this project, looks great :thumb:

I do have a question about the SS101 gain switching. I've tried this myself as have others and found you get a 'pop' when swithing? Are you getting this, if not I'd love to know what switch you are using.

Thanks

Matt
 
Hi Matta. Yes there is the pop since the gain is set using the dc output. You should be able to get around that by blocking dc to the switch (you can try taking the audio out to the switch instead of the DC out--pin H instead of pin K). Your switch would also have to be "pot-like", like the one I described, and non-shorting, so the gain won't "jump" going from step to step.

What kind of switch are you using right now?

I ended up living with the pops so I would have one less cap in the signal path. The amp mostly lives in the studio and I usually don't need to fuss with the levels once they're set.

James

Hi James,

Well done on this project, looks great :thumb:

I do have a question about the SS101 gain switching. I've tried this myself as have others and found you get a 'pop' when swithing? Are you getting this, if not I'd love to know what switch you are using.

Thanks

Matt
 
[quote author="jamesfei"]Hi Matta. Yes there is the pop since the gain is set using the dc output. You should be able to get around that by blocking dc to the switch (you can try taking the audio out to the switch instead of the DC out--pin H instead of pin K). Your switch would also have to be "pot-like", like the one I described, and non-shorting, so the gain won't "jump" going from step to step.

What kind of switch are you using right now?

I ended up living with the pops so I would have one less cap in the signal path. The amp mostly lives in the studio and I usually don't need to fuss with the levels once they're set.

James
[/quote]

Hi James,

I've tried both shorting and none shorting with a DC blocking cap but to a lesser or greater degree I ended up with some popping and decided to forgo it and fixed the gain at 55dB's and put a variable pad in front amp, works well for my needs but was interested to see what you did.

Cheers

Matt
 
How was the switch wired? If you did as on the JLM diagram posted earlier, using single resistors for each gain setting, then the gain may be jumping around too much momentarily even with a shorting switch. For example, switching from 10k to 20k (40db to 45db), the resistors will be in parallel for a moment in between detents, dropping from 10k to 6k7, then up to 20k. I'll have to check mine next time.

James


Hi James,

I've tried both shorting and none shorting with a DC blocking cap but to a lesser or greater degree I ended up with some popping and decided to forgo it and fixed the gain at 55dB's and put a variable pad in front amp, works well for my needs but was interested to see what you did.

Cheers

Matt
 
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