30904 attenuator works!

[BillWojo]

Anybody that has been following my antics with my HeathKit AS101's knows that I'm on an upgrade path to make them sound the best that they can.
Yesterday I installed my 902 drivers with new aluminum diaphragms from GPA along with the adapters I made to go from 7/8" throat to the 1" inlet 811b horn. After installing them I found the midrange to be very hot but I could hear potential in the sound quality.
A few months back I found a set of 30904 attenuators on ebay for cheap. So today I grabbed my friend that got me into this whole Altec mess and we got to work on them. Before I did anything I let him play some music and he agreed that they needed a bit of work.
So we opened the speakers back up and installed the attenuators. Right away we could hear the difference, much smoother with no peaky midrange, overall very very nice. I could live with these just as they are now, they have never sounded better.
I remembered that I had a CD with a very slow frequency sweep so I played that. I've played this before in the past while they were fairly new to me and found that the higher midrange was very bright, so much so that I would turn the volume down so I wouldn't damage the diaphragms. I could hear the dips and peaks in the volume as the frequency increased. After today's modifications there were no noticeable dips or peaks till my hearing gave out.
My friend Dave is 28 years old and has always taken good care of his ears. As we played the sweeps I looked at him and when it became silent I said "I'm Out". He could hear it to 20KHz and tell me it stopped. Said it dropped off somewhat at the higher end but was nice and smooth.
We continued playing music for quite some time and chatted about Altec stuff. We spent a little time checking out the 291-16K drivers that I picked up, he was surprised at the great condition that they were in. Thanks to elitopus1 on the board, I have a set of Symbiotik diaphragms coming in later this week.
When they arrive I'm going to install them and drop by his place for some Altec fun. He has a huge set of EV fiberglass horns, about 3 foot across that will fit up to the Altec drivers. Also has a set of large JBL 15" bass bins. I dropped him off with a Rane crossover to check out, it was intermittent and I fixed a few cracked solder joints on the board. So next weekend if he is up to it we should be cranking out some tunes large format style. Should be fun.

BillWojo

[bowtie427ss]

Sounds like you and "Rex" are havin a blast. Anxious for you fellas to relate your impressions of those giant radial horns.

Just gotta get you guys turned on to Ashly amplifiers now.

[Elitopus1]

Just gotta get you guys turned on to Ashly amplifiers now.

Man you shouldn't say things like that publicly! I only have 4 Ashly amps! Now the price is gonna go up again

Don't buy Ashly amps

[bowtie427ss]

I have a set of Symbiotik diaphragms coming in later this week.
When they arrive I'm going to install them and drop by his place for some Altec fun.

You need a spider shim to install them. Once a diaphragm has been shimmed, it can be removed and replaced in the SAME driver, in the SAME orientation with no special procedures or shims.

If you're importing diaphragms from one large format driver to another, you should follow the procedure for installing a NEW diaphragm.

http://www.greatplainsaudio.com/LgDrvrDiaRepl.pdf

Man you shouldn't say things like that publicly! I only have 4 Ashly amps! Now the price is gonna go up again

Don't buy Ashly amps

Did you know Ashly built amps that look like this?

They're MOSFET too.

[Elitopus1]

Did you know Ashly built amps that look like this?

They're MOSFET too.

What?!?

I did not know that

[bowtie427ss]

They appear on ebay now and then. I don't think they were made in large numbers. But, they are out there, we've even discussed them here briefly.

[gdmoore28]

Anybody that has been following my antics with my HeathKit AS101's knows that I'm on an upgrade path to make them sound the best that they can.
Yesterday I installed my 902 drivers with new aluminum diaphragms from GPA along with the adapters I made to go from 7/8" throat to the 1" inlet 811b horn. After installing them I found the midrange to be very hot but I could hear potential in the sound quality.
A few months back I found a set of 30904 attenuators on ebay for cheap. So today I grabbed my friend that got me into this whole Altec mess and we got to work on them. Before I did anything I let him play some music and he agreed that they needed a bit of work.
So we opened the speakers back up and installed the attenuators. Right away we could hear the difference, much smoother with no peaky midrange, overall very very nice. I could live with these just as they are now, they have never sounded better.
BillWojo

Bill, thanks so much for posting your experience with the 30904 eq. I'm planning to use it in my next build, but I've never heard the effect it has on Altec horns. Good to know that that ear-splitting midrange is going to be attenuated enough to be worth the effort!

GeeDeeEmm

[GM]

So we opened the speakers back up and installed the attenuators. Right away we could hear the difference, much smoother with no peaky midrange, overall very very nice. I could live with these just as they are now, they have never sounded better.

Said it dropped off somewhat at the higher end but was nice and smooth.

Kind of surprised since it's designed for a somewhat lower efficiency woofer, so in theory would be shelving down the horn too much.

Regardless, reduce C1 to 'let through' more of the extreme HF. Way back when we were young and spinning vinyl, tapes, 0.1-1.0 uF was the norm depending on the system, so probably a bit more for modern CDs.

GM

- - - Updated - - -

Does anyone know what the 30904 attenuation curve looks like and what varying the components in the attenuator does to that curve? Thanks.

No beyond that the three resistors act as a fixed version of the adjustable attenuator [L-pad/voltage divider] and C1 is a HF bypass cap, so if you already have good Altec attenuators, then you just need to set it with no regard for how rolled off the HF is, then experiment with different caps to 'lift up' the HF to flatten it out to 15-20 kHz or whatever sounds best overall.

GM

[BillWojo]

I,m not to worried about the highest frequency's on my system after helping my friend Dave set up my 291-16K drivers on his EV HR9040 horns. At my request we did a frequency sweep after getting everything all wired up. He used a program on his computer and much to my dismay as I watched the digital readout as it did a slow sweep, my hearing fell out at about 10K.
To many years of working in loud machine shops, racing motorcycles and driving with the windows open really took it's toll on me.
Thank God the midrange on my Altecs are so sweet, I still enjoy listening, that won't stop. Still kind of bums me out though.

BillWojo

[GM]

I,m not to worried about the highest frequency's on my system........

To many years of working in loud machine shops, racing motorcycles and driving with the windows open really took it's toll on me.

Me neither for same/similar reasons, but I try to post for the public at large , though if there's others [especially females] with good HF hearing that will be listening, they tend to want to hear it.

GM