REDD EQ, Helios 69 and Dick Swettenham

[ruffrecords]

There are no caps as big as 68uF in the Helios EQ. There is a 68nF and the biggest is a 680nF. For just about all the capacitors in this EQ I use ones made by Panasonic that are available from Farnell and its clones.

Here is an 18nF:

http://uk.farnell.com/panasonic/ecqv1h183jl/cap-film-pet-18nf-50v-rad/dp/1669203

and here is a 68nF:

http://uk.farnell.com/panasonic/ecqv1h683jl/cap-film-pet-68nf-50v-rad/dp/1744827

Cheers

Ian

 

[mus1k_freak]

That make sense on the silk screen there was a u68 and a u18 everything else  was n. So I'm guessing that's 680?

 

[ruffrecords]

That make sense on the silk screen there was a u68 and a u18 everything else  was n. So I'm guessing that's 680?

That's right. There's only room for three characters  on the silk screen so u68 is used for 0.68uF por 680nF. u18 is 0.18uF or 180nF.

Cheers

Ian

 

[ForthMonkey]

How can i combine Redd eq with Redd mic pre to building mixer with line input?

 

[ruffrecords]

How can i combine Redd eq with Redd mic pre to building mixer with line input?

I am not sure what you mean. Do you no longer need the mic input?

Cheers

Ian

 

[ForthMonkey]

How can i combine Redd eq with Redd mic pre to building mixer with line input?

I am not sure what you mean. Do you no longer need the mic input?

Cheers

Ian

Now i'm designing solid state recording/mixing console.I've converted Redd pre to fet preamp.It's working really good.I breadboarded it and i liked sound.I want to use this redd eq or only low&high bands with this preamp(It has mic&line inputs).With no transformers.But I can't figure it out how can i add eq?

Circuit like this;

Mic&Line Balanced Input Module->FetRedd Preamp->Balanced Output Module

 

[ruffrecords]

URL="http://www.mediacollege.com/audio/processing/limiter/"]http://www.mediacollege.com/audio/processing/limiter/[/URL]

Now i'm designing solid state recording/mixing console.I've converted Redd pre to fet preamp.It's working really good.I breadboarded it and i liked sound.I want to use this redd eq or only low&high bands with this preamp(It has mic&line inputs).With no transformers.But I can't figure it out how can i add eq?

Circuit like this;

Mic&Line Balanced Input Module->FetRedd Preamp->Balanced Output Module

OK, now I understand. Post a schematic of what you have showing where you want to put the EQ and I'll see if I can help.

Cheers

Ian

 

[ForthMonkey]

PMed

 

[goetzmd]

Please excuse me if this is a stupid question but I'm pretty new to electronics.

Have I got this right?
This is a passive EQ which means I could hook it up directly to my +4dBu line input and output of my audio-interface and it will work without any power supply. The downside would be the non-symetrical in- and output and a 10dB loss.

Cheers,
Goetz

 

[ruffrecords]

Please excuse me if this is a stupid question but I'm pretty new to electronics.

Have I got this right?
This is a passive EQ which means I could hook it up directly to my +4dBu line input and output of my audio-interface and it will work without any power supply. The downside would be the non-symetrical in- and output and a 10dB loss.

Cheers,
Goetz

Basically yes, but it is not ideal. Driving it direct with +4dBu from a regular audio interface is no problem. Feeding its output into a regular 10K bridging input is not ideal. The REDD EQ output impedance is a nominal 5K ohms but it varies over a wide range depending on the EQ settings. It works best when loaded by a high impedance input like a tube or FET op amp.

By all means try it but you will find all the boosts are increased, the top cut and mid cut will be reduced. The bass cut will be unaffected. The extra boost is caused by the loading. This also increases the loss in the EQ.

Cheers

Ian

 

[goetzmd]

Thanks Ian!

I'm going to order 2 pcbs and read up more in impedance and opamps!

Would it be a quick and dirty fix to hook up the output to the hi-z input of an audio interface?

Thanks and all the best,
Goetz

 

[ruffrecords]

Thanks Ian!

I'm going to order 2 pcbs and read up more in impedance and opamps!

Would it be a quick and dirty fix to hook up the output to the hi-z input of an audio interface?

Thanks and all the best,
Goetz

Yes, that would be fine.

Cheers

Ian

 

[goetzmd]

I received my boards (thanks Ian) and ordered all switches and the single value inductors from Farnell. They were all in stock for EU shipping but pretty expensive.

Since I'm building a 500 series version I have limited space for extras. I'd love to have a transformer – but there's only room for one. What would be the historically correct transformer or something similar that's available today? Also, would make more sense - an input or output transformer?

For example a blue Carnhill VTB 9071 10k:10k as input transformer has the right dimensions…

FYI: I also want to add a fet opamp to match the level and output impedance, a bypass switch and a +- 10dB output trim. (At least I think that this makes sense…  )

I'm a real newbie so any suggestions are highly appreciated! 

Cheers,
Goetz

 

[ruffrecords]

I received my boards (thanks Ian) and ordered all switches and the single value inductors from Farnell. They were all in stock for EU shipping but pretty expensive.

Since I'm building a 500 series version I have limited space for extras. I'd love to have a transformer – but there's only room for one. What would be the historically correct transformer or something similar that's available today? Also, would make more sense - an input or output transformer?

For example a blue Carnhill VTB 9071 10k:10k as input transformer has the right dimensions…

FYI: I also want to add a fet opamp to match the level and output impedance, a bypass switch and a +- 10dB output trim. (At least I think that this makes sense…  )

I'm a real newbie so any suggestions are highly appreciated! 

Cheers,
Goetz

The individual inductors are quite cheap, the only problem is that you have to buy at least 5 of each from Farnell but at least you need 3 of the 10mH ones. perhaps REDD EQ builders could pass on their spare inductors to others??

The Carnhill 10K:10K will be fine as an input transformer. the original would have had a 200:200 transformer or it might have been balanced throughout in which case it would not have needed a transformer at all. Either way, my version is intended to be fed from a 10K:10K transformer and Carnhill is about as good as you can get.

FET OPA for gain make up and trim sounds fine to me. Bypass can be done with a DPDT switch. You can wire it up much the same way as it was done for the PMEQP1A:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png

Just substitute the REDDEQ where is says PMEQP1A. The pad is already on the REDD EQ PCB. The 470K was nedded for the PMEQP1A. You can leave it out for a FET OPA and just use the OPA gain setting to get the overall gain right.

Cheers

Ian

Cheers

Ian

 

[goetzmd]

The individual inductors are quite cheap, the only problem is that you have to buy at least 5 of each from Farnell but at least you need 3 of the 10mH ones. perhaps REDD EQ builders could pass on their spare inductors to others??

The individual inductors are in fact cheap – I'll offer the additional ones I've bought when they arrive. I meant  that the switches are expensive, especially since I had to substitute the Lorlin with another Grayhill to fit it all into a single 500 modul.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png

Thank you Ian! That helps a lot!! 

Any particular reason why you trim the bypassed signal and not the actual eqed signal?

Also, do you have any suggestions regarding the output. I'm pretty sure I can't fit a full size output transformer in.
This is an option but I'd rather use not an IC:
http://store.diyrecordingequipment.com/balanced-output-building-block/
Or would this be a sensible option:
http://www.neutrik.com/en/accessories/transformers/nte1

Cheers,
Goetz

 

[ruffrecords]

The individual inductors are quite cheap, the only problem is that you have to buy at least 5 of each from Farnell but at least you need 3 of the 10mH ones. perhaps REDD EQ builders could pass on their spare inductors to others??

The individual inductors are in fact cheap – I'll offer the additional ones I've bought when they arrive. I meant  that the switches are expensive, especially since I had to substitute the Lorlin with another Grayhill to fit it all into a single 500 modul.

Ah, now I understand. Yes , the Grayhill switches are not cheap but they are very good quality.

Any particular reason why you trim the bypassed signal and not the actual eqed signal?

So it is universally applicable. Each EQ has a different insertion loss. To set it up you set the controls to flat and then adjust the gain make up for overall unity gain. Then you swtich in the pad to bypass the EQ and adjust the pad for the same output. This works with any passive EQ no matter what the insertion loss.

Also, do you have any suggestions regarding the output. I'm pretty sure I can't fit a full size output transformer in.
This is an option but I'd rather use not an IC:
http://store.diyrecordingequipment.com/balanced-output-building-block/
Or would this be a sensible option:
http://www.neutrik.com/en/accessories/transformers/nte1

Cheers,
Goetz

Semiconductors are not my area. There are lots of options and I am sure there are others here much better qualified to make recommendations.

Cheers

Ian

 

[goetzmd]

So it is universally applicable. Each EQ has a different insertion loss. To set it up you set the controls to flat and then adjust the gain make up for overall unity gain. Then you swtich in the pad to bypass the EQ and adjust the pad for the same output. This works with any passive EQ no matter what the insertion loss.

That totally makes sense! Thanks, Ian!

For the output I'm looking into really small transformers...
http://www.neutrik.com/en/accessories/transformers/nte1

All the best,
Goetz

 

[ruffrecords]

For the output I'm looking into really small transformers...
http://www.neutrik.com/en/accessories/transformers/nte1

All the best,
Goetz

The trouble with small transformers is they cannot take high signal levels. The NTE one you linked to for example is specified for a maximum level of  -3 dBu (@ 50 Hz, 1% THD). Not much good if you want a +4dBu output level. The obvious way to save space if you are using a semiconductor gain make up stage is to make it electronically balanced. The trouble with the 500 series format is that by the time you have fitted and input and output transformer there's not much room left for anything else.

Have you thought about making it a double width module?

Cheers

Ian

 

[goetzmd]

The trouble with small transformers is they cannot take high signal levels. The NTE one you linked to for example is specified for a maximum level of  -3 dBu (@ 50 Hz, 1% THD). Not much good if you want a +4dBu output level. The obvious way to save space if you are using a semiconductor gain make up stage is to make it electronically balanced. The trouble with the 500 series format is that by the time you have fitted and input and output transformer there's not much room left for anything else.

Have you thought about making it a double width module?

Thank you for pointing that out Ian! Neutrik has another small transformer which I already used in building the Studer EQ: http://www.neutrik.com/en/accessories/transformers/ntl1  It can do 5V (@30 Hz, 1% THD) which should be around +16 dBu… at least if my math is correct.  ;D I simply was looking for an alternative since this one is 50 € a piece….

I thought about a double width module but I feel that part of the 500 format charm is the limited space. Also my rack is nearly full…  :'( 

Cheers,
Goetz

 

[ruffrecords]

The Neutrik specifications are confusing  to say the least. It says "NTL1 is a line transformer intended to balance amplifier outputs for line driving up to +24 dBm". The it says it can drive 6V rms into 600 ohms at 30Hz which is just over 17dBu. The strange thing is the primary inductance is a whopping 150 Henries and the primary dc resistance is 100 ohms. YThis says to me that this is really intended as a 10K:10K line input transformer.

I am definitely not a transformer expert but for a line output transformer driven by an op amp you need a lot less primary inductance so you can use a lot fewer turns and hence have a larger signal level before saturating the core. A 15 Henry inductance has an impedance of 1884 ohms at 20Hz which would be more than OK.

Cheers

Ian