Quad Eight 712 Graphic EQ

[MikoKensington]

When you going to crack open one of yours, Dana? 

 

[Tubemooley]

It's the holidays and I'm on vacation and I've been sick too. How about them for excuses? Give me a couple of hours and I'll post some photo's. Ya' know.... I never have posted photo's successfully. Let me give it another try. DANA.

 

[Tubemooley]

I just took a few photo's of the 712. I removed four screws and flipped over the circuit board so you can see all the components. But the forum will only allow 300Kb attachments per post and I don't have a dithering program to make these files smaller. Miko, send me an e-mail to tubemooley_at_yahoo.com and I will send you the photo's. I'll send them to the groupdiy e-mail account too. You guys know how to access that? DW.

 

[jsteiger]

Yo Dana, Happy Holidays my friend!

Why don't you just use photobucket or one of the other freebie hosting sites? Just post a link so the rest of the class can also enjoy.    8)

Best, Jeff

 

[Ptownkid]

The inductors in the schem have me confused...are those values really in Henries?

 

[emrr]

Interesting there are two versions, with two sets of freq, and an odd freq selection at that.  Implies they were not worried about maintaining flat group response anywhere other than at unity.  Usually graphics combine for flat in-band response when all set to same gain. 

 

[jsteiger]

The inductors in the schem have me confused...are those values really in Henries?

The skiz is not drawn in order of the frequencies. If you look at the cap labels and the chart it will make sense.

 

[MikoKensington]

I'm about to start my capacitor shopping list for these.  I'll probably go with BC's for the electrolytics.  They look like fairly standard values.  The filter section starts to raise questions for me.  Since mine have been modified, there's a strange mix of film caps here.  So, I wonder what might be the best type in this application.  225P Orange Drops?  Panasonic?  Mallory? 

Also, .062uf and .39uf aren't very common values.  Would .068 and .33 take me far off the mark?  Or should I use a couple values in parallel to get where I need to be?

 

[Ptownkid]

The inductors in the schem have me confused...are those values really in Henries?

The skiz is not drawn in order of the frequencies. If you look at the cap labels and the chart it will make sense.

You lost me...I'm talking about the inductors...

 

[jsteiger]

The inductors in the schem have me confused...are those values really in Henries?

The skiz is not drawn in order of the frequencies. If you look at the cap labels and the chart it will make sense.

You lost me...I'm talking about the inductors...

Yes, I know. I only assume you mean the values don't make sense when reading the skiz left to right? Otherwise, they seem pretty standard fare.

.055H = 6.4k or 8.2k
.125H = 4.5k
.24H = 2.2k
.4H = 1k
1H = 400Hz
2.5H = 160Hz
6.35H = 65Hz

 

[Ptownkid]

Cool, thanks. I just wanted to make sure that the values were actually in Henries. 6.35H seemed high that's all...where does on find such values? Roll my own?

 

[jsteiger]

Carnhill has a few inductors that get close. Colin should have them IIRC.

 

[Ptownkid]

Yeah, i looked there but there's no data for any of them on their site...

 

[MikoKensington]

I'll bet Reichenbach made the originals.  Cinemag might whip them up. 

 

[haima]

Last time i was in LA i got a handful of similar looking inductors from OPAMPLABS in Hollywood, across the road from the Record Plant....

They had a variety of values. Cheap. PCB mount...

They were surprised when i rocked up asking about inductors - "do people still want these things?"

Nice folks - Still hangin' in there....  :'(

EDIT: here's the link to the page on their website: http://www.opamplabs.com/87.htm obviously not the same values - but handy anyway...

 

[Igor]

Just saw this, tasty EQ schematic, thanx! I had some experience with MM405 modules, sweet EQ.

 

[haima]

Is that what you're basing your 500 series LC EQ on Igor?