Ferrograph PREAMP project - HOW TO ?

[EvLoutonian]

Hi Ferro-folks!

As I'm sure many of you have probably already noticed, the British-made "Ferrograph" reel to reel preamp units can be removed and modified to operate as standalone units - and apparently results can be pretty good.  Some people have added balanced mic input stages, and balanced line out, as well as other possible features.

I have had a couple of these modules sitting around here for the past four years and I've been slowly slowly trying to work out how to do at least the most basic of mods to get them up and running.

So my question is basically, who has done this to any degree, and what modifications and tweaks are required to get it working? 

Also, what additions do you think are worthwhile on top of the basic functions?

I realise a power supply is required for the high tension and filament voltages, which could presumably be done most easily if you already have the original power supply section from the base of the deck itself, or you could make up a new one from parts, or repurposed from another surplus device.

Are there other additional connections or changes that need to be made on the amplifier chassis itself, or any parts of the circuit that need to be removed (or switched out) to optimise for standalone use?

Which of the components would you replace in terms of resistors or cap's, and where would you leave them as stock (presuming everything is in tact)?


Here's the Ferrograph 5 circuit diagram:
http://www.morphet.org.uk/images/ferro/ferro-5man/circuit_diagram.gif

 

[EvLoutonian]

The modules look something like this (with some variations, depending on the series ie. 4, 5, 6)

and the original deck:

More pic's here:
http://www.ukaudiomart.com/details/649083069-ferrograph_tube_mic_pre_amp_amp_amp_vintage_british/images/632504/
and here:
https://www.gearslutz.com/board/attachments/low-end-theory/231297d1303307540-just-bought-50-60s-valve-preamp-did-i-get-ripped-off-foto0558.jpg

and some nicely racked examples from Analogue Addicts, UK:

 

[ruffrecords]

Ferrograph made very robust, good quality tape recorders for their day. Some even found their way into professional audio - I used some Series 7 types when recording music for BBC Radio Nottingham in the 70s. I am disappointed that there are a number of unscrupulous traders repackaging these as vintage professional mic pres and making outlandish claims for them and selling them at inflated prices. You can often pick up a complete machine for less than £50 on eBay. I have a high speed (15ips) stereo Series 5 with balanced ins and out that I got for about this price.

That said, there is no reason why you could not make a nice little two channel mic pre/mixer from an old Series 5 such as you have. V1 is the head preamp with equalisation. By removing the EQ and using a 1:10 input transformer you could make this into a mic input. V2 is the original mic input . Adding a 1:10 transformer to the input of this would make a second mic pre. The outputs of these two could be passively mixed and further amplified by V3. V4 is intended to drive a speaker. By changing the transformer you could convert this into a 600 ohm output. V5 acts as a meter buffer amp and you could keep it for that purpose to monitor the output. You don't have the power supply so you don't have V6 and V7.

Nice little project that should give you a nice couple of tube mic pres. Things to watch for include the fact that that all the stages use pentodes. These tend to be noisier than triodes so don't expect a very quiet mic pre although the EF86 tubes used at the inputs are perhaps the quietest pentodes available. Remember that in those days you were lucky if the tape recorder achieved a 50dB signal to noise ratio. It also uses ac heaters and you typically get hum at about -60dBV at the putput. Good enough in those days but dc heaters can improve that a lot.

Good luck and if you need more help just ask.

Cheers

ian

 

[snod_donkey]

We have several of the analogue addicts re-boxed units and have to say they sound stunning. Up against our V72, V76 as well as other units they perform equally as well and in most cases actually are far better! I can honestly say any "claims" that are made regarding the quality are actually from the people that have purchased and recorded with the units. If they are good enough to be used at Air Studios, Miloco then they must be doing something right...

Drop Ian a message here as i am sure he would be able to help out
https://www.facebook.com/pages/Analogue-Addicts-uk-Vintage-Valve-Mic-Preamps/500996753243751

These are some tracks that were done with several of these
https://soundcloud.com/analogue-addicts-uk/testing
https://www.youtube.com/watch?v=EN_ur0k5OpM
https://soundcloud.com/deadsvilledf/come-awake#new-timed-comment-at-209448
https://soundcloud.com/animalnoise/alright