Quad Eight 712 Graphic EQ

[MikoKensington]

So I recently acquired a pair of Quad Eight 712 Graphic EQ's for a great price.  They're going to need some recapping at the very least.  Also, the faces had Dymo labels indicating non-original frequencies.  So I may have to tweak the L/C's to get them closer to stock. 

But perhaps most crucial to the sound of these EQ's, are the round fader knobs.  One unit is missing 3 knobs.  Which means it's probably going to sound terrible.  So, I'd like to find some replacements to obtain the best performance from both of them.

I tried affixing Rolo's.  But I ended up getting chocolate all over my fingers, and everything else on my bench.

I've been researching some transistor subs, just in case.  Anyone have any experience with these?  Any info/pitfalls/wisdom would be welcomed.

 

[strangeandbouncy]

Miko,



  I have had plenty of experience with Rolos, and in my experience, there is NO substitute!


      ;D ;D ;D ;D


    MErry Xmas!


  ps nice find!

 

[sunnen1]

i love Rolos  ;D

 

[QUEEF BAG]

i admit rolos are pretty good, but but + & - 26V may be a little high...
zener down to + & - 18V to keep the chocolate from melting.

 

[swimslowly]

i love these units, they sound really great, you'll enjoy them I'm sure!

 

[jsteiger]

I believe that Tubemooley (aka Dana Walcott) also just snagged a pair of these from evilbay. I am not sure if has received them yet or not but he was pretty pumped to say the least. Maybe they are all from the same source?

To bad the Rolo's didn't work out. Well...work out as fader knobs. I'm sure they worked out just fine for other things.

 

[swimslowly]

if anyone ever makes PCB's of this module I will certainly buy some...it'd be a great/easy DIY project if there's a decent source for the inductor values...

 

[MikoKensington]

Someone was selling some later black ones on ebay for $550 each.  They had 6 for sale and sold through all of them.  I got mine from a surplus store on ebay for 19.99 each.  Needless to say, I was excited.

They need some work for sure.  At least one inductor has been replaced, and I don't know where to source a proper fit to put it back to stock.  I can see some other small changes have been made, so I'd like to see another to compare.  

The other downside is they're big.  Side by side, they're too wide for a Par-Metal enclosure.  I've never been a fan of faceplate racking, so I'm carefully considering my options.  

 

[swimslowly]

The ones I had came with small side panels that made two fit perfectly into a 19" rack. Ken @ Orphan Audio might have these parts as well as the inductor you need, as he has many original QE parts. I'm attaching a photo of mine so you can barely see what I'm talking about...

 

[MikoKensington]

Thanks for the pic.  I might just put them in one rack case each.  We'll see.  I may contact Ken about the inductor.  

 

[okgb]

Don't the Rolo's prevent you're fingers from slipping
or is that the pre celestion version ?

 

[MikoKensington]

Depends on doping and the color of back cap.

 

[Tekay]

For a more beefy sound try meatballs as knobs

Saw that R9 and R21 are marked different? should be the same like 100R.

Happy holidays

 

[MikoKensington]

Good eye!  I'll check the actual unit when I open it up, for exploration. 

Link to full-size schematic.  If you'd like to get a better look.
http://farm6.static.flickr.com/5206/5278034584_ae17c367ce_o.jpg

 

[Tekay]

The ampstages are also used in the MM100 modul with 100R resistors. Neve BA226 is more or less the same amp stage but mirrowed, the diff stage uses pnp instead.

 

[hobiesound]

looking at the schematic right now, but aren't C14-C17 supposed to go somewhere? like ground/OV? or am i just too tired to get it. And i know i'm tired allright.

This looks very similar to the API 553. another stupid question but this is swinging input eq isn't it?

greetings,

Thomas

 

[haima]

looking at the schematic right now, but aren't C14-C17 supposed to go somewhere? like ground/OV? or am i just too tired to get it. And i know i'm tired allright.

i'm tired too... and no expert - but i'd say there is a line missing below that group of caps, connecting it to 0v...?

this is  a swinging input eq isn't it?

Sure looks like it to me  

There's two "discrete opamps" used. The bases of the NPN pairs are the inverting & non-inverting inputs.

BTW: check out the neat use of those 5k trimmers to center the faders null point...

Thanks for reminding me to buy some Rolos Miko  ;D

 

[Tubemooley]

Someone was selling some later black ones on ebay for $550 each.  They had 6 for sale and sold through all of them.  I got mine from a surplus store on ebay for 19.99 each.

Just like Jeff mentioned, I bought two of those black ones on eBay. They are actually brown. You bought a pair for 40 bucks? That's insane. Holy fruck. I wish I had seen those. My pair will fit in our QE Pacifica. There are some empty module spaces right next to the master section. I'm pretty certain they will fit right there with a little extra metal to mount them. I plan to put a bridging trannie on the inputs to make them balanced. I'm gonna' check with Ken at Orphan first to see what he recommends. These things are supposed to totally rock. DW.

 

[Tubemooley]

Miko - I just read your posts a little closer. Ken will probably have that inductor. One of my 712's looks to be completely unused. I can take a few photo's of the component side of the circuit boards and send them to you so you can compare to yours. See how your high band is labeled 8200 Hz? You have the music version. I have the dialog version and that band is at 6400 Hz. I will probably change C17 and make them the music version. Schweet. DANA.

 

[MikoKensington]

I'd love some pics!  I can tell almost every band in mine has been changed.  Mis-matched parallel caps, random types of caps, etc.  I'm going to start a shopping list, so looking at stock types of components will be a big help.  Now if I could just get a few days off work...