by cipher <nospam@[EMAIL PROTECTED]
>
Oct 9, 2008 at 11:40 AM
Ian Thompson-Bell <ruffrecords@[EMAIL PROTECTED]
> wrote in news:gcl4de$rpc$1
@[EMAIL PROTECTED]
> cipher wrote:
>> Please continue the discussion and correspondance with me..
>>
>> This subject is still relevant as I still record quite frequently and
>> have found that the "commercially available" products out there just
>> dont tickle my fancy
>>
>> I am not a troll.
>>
>> -Cipher /Tynan
>>
>
>
> Hi Tynan,
>
> I recently purchased a DVD containing the manuals for a range old RCA
> and other tube based broadcast mixing consoles. One interesting aspect
> was that the earlier ones all had mic pres which were transformer
> balanced *out* as well as in. Mixing took place using 200 ohm bridged T
> stepped rotary channel faders connected to these transformers and the
> resultant mix fed into another transformer and amplifier. This meant a
> lot of expensive transformers and faders.
>
> A later model in the same series (RCA BC-6 series) dispensed with the
> output transformer on each mic pre, included a 100K (stepped) pot half
> way down the mic pre as a channel fader and a cathode follower output
> feeding 22K mixing resistors. The mix was amplified by the same basic
> mic pre topology with the group fader replacing the channel one.
>
> The mic pre was interesting also because it used a pair of 12AY7 tubes
> on a PCB. The first 12AY7 is wired with global NFB giving 26dB of gain
> and incidentally they used selected 12AY7 tubes for this stage for
> lowest noise. The second 12AY7 was wired as a triode stage with local
> NFB followed by a cathode follower. The two tubes together give a total
> gain of 48dB which with a 10:1 transformer gives a maximum channel gain
> of 68dB. With a 20dB pad on the transformer the first stage has a gain
> of 26dB and can produce +12dBV at negligible distortion (simulated)
> which means a max mic input level of -14dBV can be handled.
>
> Since the 12AY7 is hardly common today so I re-jigged the circuit to
> work with 6N1P tubes which have a similar mu but higher gm and lower ra
> and this gave even less distortion. The pair of tubes is capable of
> delivering +12dBV into 22K at less than 0.1% harmonic distortion most of
> which is 2nd harmonic.
>
> So simulation seems to suggest this is quite a good design so I am now
> off to build one and put it through its paces. I'll let you know the
> results.
>
> Cheers
>
> Ian
>
Sir, thank you for continuing the work, please let me know how it goes.. I
really want something to materialize here.
