REDD EQ, Helios 69 and Dick Swettenham

Gearsix said:

Ian, have you found the 7h inductor for bass?
I have made a little search but for those values I have seen inductors similar to transformers

Click to expand...

Yes, there is a Carnhill inductor with a 7H tap, the VTB9043. It is the very small values I am having trouble finding.

Cheers

Ian

Great Ian, I can't wait to see this circuit!

In the last schematic posted by Ian there are 3 multi tapped inductors (considering that the 7H one is in a multi tapped inductor) ... not really cheap ... but if it sounds like I expect ...

Several people have asked about using the REDD EQ with the REDD 47 mic preamp. Like my other passive EQs, this one does need some gain make up and there is no easy way to fit the EQ within the existing REDD 47 circuit because it is all tied together via negative feedback. So you really need a separate gain make up stage.

One way to solve this is to remove the output transformer and drive the EQ direct from the output of the E88CC then add another E88CC stage for gain make up after the EQ (you will need to modify it to increase its gain). You can then fit the output transformer here instead of after the first E88CC.

Or you could use the poor man's tube gain make up stage or something similar.

Cheers

Ian

Hi Ian. The additional E88CC would probably be easier to do as it could run off the identical power supply or lightly modified?

Cheers,
Bojan.

baadc0de said:

Hi Ian. The additional E88CC would probably be easier to do as it could run off the identical power supply or lightly modified?

Cheers,
Bojan.

Click to expand...

Yes, that is true. There is only a small increase in HT and heater currents.

I checked out the REDD 47 schematic and the E88CC stage as it is has a gain of about 13dB so it is almost ready to use (the REDD EQ has an insertion loss of about 15dB). The 330K that goes to the anode of the EF86 would instead go via a capacitor to the output of the EQ. A 1uF 400V orange drop would be fine.

Cheers

Ian

Gearsix said:

In the last schematic posted by Ian there are 3 multi tapped inductors (considering that the 7H one is in a multi tapped inductor) ... not really cheap ... but if it sounds like I expect ...

Click to expand...

There are 3 inductors in this design and the values are rather non-standard so I think I will ask Chrion to do a quote for a set.

Cheers

Ian

I am making good progress with the PCB layout. I have arranged the three main level switches Treble, Brilliance and Bass on one inch centres on the PCB. The frequency select switch for the Brilliance control will be off board and connected via a 10 way header.

At the moment I am assuming all three inductors will be Carnhil/Chrion types/sizes. However, the ones for the Brilliance cut are quite small in value, ranging from 12mH to 47mH and not available in any of the standard Carnhill types. So I have started a separate thread in the drawing board asking if anyone has had experience of using small leaded inductors in EQ circuits:

http://www.groupdiy.com/index.php?topic=51380.msg652961#msg652961

Cheers

Ian

Great work Ian!
I have not experiences with these small inductors but I know someone used them for Pultec eq with good results
Eventually it works, you could use a small single inductor for the bass instead of the big one that is more expensive (it may be good for those like me who want to realize more channels)

Fablab said:

Great work Ian!
I have not experiences with these small inductors but I know someone used them for Pultec eq with good results
Eventually it works, you could use a small single inductor for the bass instead of the big one that is more expensive (it may be good for those like me who want to realize more channels)

Click to expand...

The trouble with the bass inductor is that it is 7 Henries and you can only get that amount of inductance in something fairly large. However, I am sure Chrion would be able to make one for a lot less than the Carnhill price.

Cheers

ian

I have just had delivery of some small inductors to try in the brilliance cut part of the EQ. I'll build a test circuit and see how it performs. If it works OK I'll build it into the PCB layout.

Cheers

Ian

I just lashed up the 10KHz brilliance cut circuit using a small 10mH inductor and measured the response. I did not have the exact resistor values to hand so the cut is only just over 8dB but the response looks about right to me. I will try the other frequencies next.

Cheers

Ian

I bought some more small  inductors, worked out the values needed to be wired in series to get the values we want, calculated the correct cap values and how to make them with paralleled pairs and built the brilliance cut EQ around a Lorlin switch. I then tested all four frequencies on my Lindos test set. The results are here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/REDDEQ/swtests/

Click on any .htm files to get the results in your browser. I did not change the pot values so we still have 8dB cut rather than 10 but it is the same for all four frequencies which is encouraging.

I am happy with these results. The Q seems right as does the overall shape of the plots so I am going to start the PCB layout on the basis of using this circuit and these values. I'll tweak the resistor values on the bench to get the right cut values.

Cheers

Ian

I have just about finished the PCB layout for the REDD EQ using the small leaded inductors made by EDCOR for the Brilliance cut. It is fairly tidy and I have checked the ground plane integrity so any changes now would be mostly cosmetic like moving component idents. I need to check it thoroughly against the schematic and then it will be ready to be made. I am expecting the Helios PCBs made by Iteastudio any day now and if these are good I'll most likely get 10 of the RED EQ boards made by them as well as their prices are very reasonable - unless it turns out lots of people want one.

Cheers

Ian

Well, this is shaping up to be pretty awesome! One small inquiry / request though, since probably a few of us will be using this to augment our existing REDD47 preamps, would an extra PCB that does the E88CC makeup section be feasible? If small enough, maybe that could be added as an extra section that you can opt to use or not on the existing EQ PCB? Sorry for chiming in so late with this idea.. just thought to throw it out and see if anyone likes it!

As I realised, this is not 51X compatible. Will there be a 51X design available.
Thanks !

Marc Duchesne said:

As I realised, this is not 51X compatible. Will there be a 51X design available.
Thanks !

Click to expand...

It is at least partially 51X compatible. It is only 100mm high so it will fit inside a 51X slot but is does not have a 51X connector or input and gain make up circuits. There are ways of doing this that were discussed earlier in the thread using readily available parts.

Cheers

Ian

baadc0de said:

Well, this is shaping up to be pretty awesome! One small inquiry / request though, since probably a few of us will be using this to augment our existing REDD47 preamps, would an extra PCB that does the E88CC makeup section be feasible? If small enough, maybe that could be added as an extra section that you can opt to use or not on the existing EQ PCB? Sorry for chiming in so late with this idea.. just thought to throw it out and see if anyone likes it!

Click to expand...

I am trying to keep the number of versions to a manageable number, preferably one!! The current format is ideal for builders of the EZTubeMixer and can also, with a little effort be built into a 51X compatible module. It is also fine for rack mounting module builders as you can use any gain make up you fancy. If you want a tube gain make up stage then you could always use my poor man's tube gain make up stage which uses an E88CC either as a mu follower or SRPP stage. I gues what you would really like it to be the same as the E88CC stage in the REDD47. Let me have a look at the current poor man's tube make up PCB layout and see if it can be built as the REDD 47 E88CC stage.

Cheers

Ian

It is at least partially 51X compatible. It is only 100mm high so it will fit inside a 51X slot but is does not have a 51X connector or input and gain make up circuits. There are ways of doing this that were discussed earlier in the thread using readily available parts.

Cheers

Ian

........

Cool, I can then manage to fit it in a 51X, do you happen to know if anybody designed a 500 front panel already...
Thanks Ian

-marc