REDD EQ, Helios 69 and Dick Swettenham

[ruffrecords]

Hi Ian,

Do you know wich amp is in the RS127? Tube? Germanium? Transistor?

Thank's

It did not have an amp. It was 100% passive. It did not contain a gain make up amp and so it had an insertion loss, probably around 10 to 15dB. In those days everything was 600 ohms in and 600 ohms out (or 200 in the case of EMI) and they were just plugged together and a REDD47 pre added at the end to restore the gain.

Cheers

Ian

 

[ruffrecords]

So a poor mans tube gain make up stage might be wise.

Yes!

Cheers

Ian

 

[ruffrecords]

I have finished updating the schematic and filled in all the values as well as correcting the bass cut circuit error. Next I will begin the PCB layout.I am going to start with a Eurocard sized PCB so it is compatible with the EZ Tube Mixer.

Cheers

Ian

 

[Fablab]

Hi Ian,
have you plans to realize the circuit with all the controls off PCB so it si possible to adapt the board in API module?
Have a nice weekend!
Fab

 

[ruffrecords]

Hi Ian,
have you plans to realize the circuit with all the controls off PCB so it si possible to adapt the board in API module?
Have a nice weekend!
Fab

I don't know. It would be nice if it could be used in a variety of places;  EZ Tube Mixer, 500 series or 19inch racks.

I am not sure how mounting the controls off the PCB would help that. At the moment I have the bass, brilliance and treble level controls on the PCB (Grayhills) and the brilliance frequency select off board. You could easily wire an off board switch to the Gray hill pads.

Cheers

Ian

 

[Strawtles]

In a API 500 format I am sure it becomes a best seller!

 

[buildafriend]

I would like as much as possible to be on the PCB, I also prefer the grayhill switches. Small enough to fit in 500 format is a great idea. 

 

[ruffrecords]

The PCB is currently 100mm tall and a 500 series card is about 114mm high so this PCB will definitely fit in a 500 format. The only question is how will you do the input and gain make  parts?

Cheers

Ian

 

[Fablab]

Hi Ian,
what do you think about the possibility to include in the PCB a small stage for gain with 2 or 3 transistors (es. BC184) similar to Neve output stage?

 

[ruffrecords]

Hi Ian,
what do you think about the possibility to include in the PCB a small stage for gain with 2 or 3 transistors (es. BC184) similar to Neve output stage?

To be honest I am very reluctant to do that because all my designs are vacuum tube based. I don't do transistor designs any more and I don't really want to go back to them. Unfortunately the 500 series format does not really lend itself to vacuum tubes (I have looked into it in some detail) so there is little incentive for me to develop 500 series boards. I know the 500 series is very popular and if my designs appeared in a 500 format they would probably be very popular but I am not in it for popularity or money - I do it because it is fun.

A lot of people have built my EQ designs into rack mounting units and that is fine because there are plenty of available gain make up amps you can use in that format but it is not so easy for 500 series. I am happy to do them in eurocard height format and these should fit into a 500 series module but you will have to sort out your own gain make up.

On the other hand, this is a bit of a special case because I don't think there is a 500 module available with this EQ. I guess it deoends on just how many people would want a 500 series card with this EQ.

Cheers

Ian

 

[mylesgm]

I would be happy to do this eq in 500 and I'm sure there are many more people interested too.  The easiest way would be to create the eq board in such a way that it can use an existing interface like this: http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=128

Then the builders can decide what opamps/tx they wish to use or can create their own interface if there is enough space left in the 500 footprint.

 

[Fablab]

It seems the right solution

 

[buildafriend]

if it is made as a 500 series card :'(, I would greatly appreciate some terminal block pads for input and output so that it can be integrated in a normal rack mount chassis, as you had originally intended.

thanks regardless

 

[Biasrocks]

http://classicapi.com/catalog/product_info.php?cPath=84_86&products_id=147

if it is made as a 500 series card :'(, I would greatly appreciate some terminal block pads for input and output so that it can be integrated in a normal rack mount chassis, as you had originally intended.

thanks regardless

 

[ruffrecords]

I would be happy to do this eq in 500 and I'm sure there are many more people interested too.  The easiest way would be to create the eq board in such a way that it can use an existing interface like this: http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=128

Then the builders can decide what opamps/tx they wish to use or can create their own interface if there is enough space left in the 500 footprint.

That looks to be an interesting option. Does anyone have exact dimensions for this PCB?? I printed off the bare PCB from the web site and guestimated its depth as 68mm. Given the 500 series total depth if 150.8 mm that leaves about 82mm in which to squeeze the EQ which is half the depth of a Eurocard and rather tight.

The other thing I am not clear about is what do you use for metalwork if you don't buy a kit?

Cheers

Ian

 

[Strawtles]

Another solution may be this one

http://www.audiomaintenance.com/acatalog/blank_pcbs.html

 

[shabtek]

whoa there Strawties;

;Dnobody would know what to do with that (;D cheeky)

 

[Strawtles]

You can mount the circuit on the 500 Board and then build a small gain preamplifier on the remaining part (the Neve circuit in this page may be a good example)
The JLM Audio circuit is really nice, but for a loss of 10/15 dB perhaps it is too  ;D

 

[ruffrecords]

It seems there is a range of options for those keen to put this into a 500 series module. What I will do is keep it 100mm high with standard 3U module fixing holes, but also try to keep it as shallow as possible so 500 series fans can use it too.

Cheers

Ian

 

[Gearsix]

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