EMI TG mic preamp schematic

[Strawtles]

Hello, I am interested to the EMI TG console preamp  schematic. Is it possible that someone has it?
A good weekend at all

 

[Strawtles]

No one can help me?

 

[Fablab]

I'm looking for this circuit for a long time
In particular I'm interested in the input stage, eventually someone has it

 

[ruffrecords]

There are several threads here and at other boards asking the same question and none of them was successful. It is well known that EMI prefers not to publish them. However, Chandler have brought out authorised clones, one in 500 format. If someone has one of these it would be relatively easy to recreate the schematic.

Cheers

Ian

 

[Strawtles]

Here a photo of the 500 format circuit ... it seems not too complicated

 

[Liutmod]

I love Abbey Road machines.
For me the REDD 47 preamplifier is the most beautiful valve preamplifier ever made and I love the TG 12413 compressor, too but after reading an interview with Geoff Emerick where he speaks very badly of the EMI TG console (and preamps) I am not too sure they are really great preamps

 

[ruffrecords]

Looks to me to have about six transistors - two in the mic pre and four in the output stage. Looks like they have tried to obscure the markings on the two power transistors.

Cheers

Ian

 

[Fablab]

Yes, there are two transistors in the input stage (originally BC109 and BCY71 now BC184 and BC214) and a four transistors output stage that it is the same output stage they used in other projects.
It would be interesting to understand how the first stage is done.

 

[ruffrecords]

From what I have been able to gather from various snippets on the internet, the input amplifier consists of:

1. An input transformer with a 1:3.16 ratio i.e 10dB of gain

2, This followed by a 12 step attenuator with each step equalling. 5dB

3. The attenuator is followed by a type D amplifier with a nominal gain of 25dB. The fine gain control operates in the feedback loop of this amplifier to allow the gain to be varied from 20dB o 30dB

4. Nominal output level of the type D amplifier is -10dBV where  EMI's 0dB is about 0.44V ( a left over from their 200 ohm days I think)

The attenuator therefore spans input levels from +20dBV to -50dBV (why I have no idea. Chandler porbably changed this).

I have not seen a schematic of the type D  amplifier but the only description I have come across describes it as a three transistor circuit so it looks like we are a transistor short. Strangely, the description is very similar to that of the standard Neve three transistor amplifier.

Cheers

Ian

 

[pucho812]

If it's anything like the Neve 3 transistor amplifier, then  they read the same wireless world article that others did.  Apparently the 3 transistor amplifier used was borrowed from a wireless world article. They were not the not ones to use it.

 

[ruffrecords]

If it's anything like the Neve 3 transistor amplifier, then  they read the same wireless world article that others did.  Apparently the 3 transistor amplifier used was borrowed from a wireless world article. They were not the not ones to use it.

That is the second time someone has mentioned a Wireless World article. I am not inclined to believe it unless someone can produce the actual article.

Back to the main topic, since this is a stand alone device, there is strictly speaking no need for the emitter follower since the preamp drives a single well defined load. So maybe the topology was changed slightly for this product. It would not be hard to do.

Cheers

ian

 

[Fablab]

Hi Ian, attached you can see the second stage schematic (I found it in this forum about 10 years ago )
What is missing from the mic preamp circuit is the first stage with  two transistors (BC184 and BC214) and the 12 steps attenuator.
Unlike the Neve this circuit works with a +28/-28 Volt power supply

 

[wlinart]

The schematic of amplifier D is posted here: https://groupdiy.com/index.php?topic=61769.msg782841#msg782841

 

[ruffrecords]

The schematic of amplifier D is posted here: https://groupdiy.com/index.php?topic=61769.msg782841#msg782841

Yes, that is almost identical to the Neve gain block.

Cheers

Ian

 

[Strawtles]

The input stage is different from TG 2 mic preamp that has a couple of BC184 and BC214 as confirmed in this article:

http://www.soundonsound.com/reviews/chandler-limited-tg2-500

 

[ruffrecords]

The input stage is different from TG 2 mic preamp that has a couple of BC184 and BC214 as confirmed in this article:

http://www.soundonsound.com/reviews/chandler-limited-tg2-500

It is probably a version of the very standard two transistor gain block (attached). The base gain is set by the ratio of  R2 and R3 which can be increased by setting R4. It was common to use the PNP in the first position because of its lower noise.

Cheers

Ian

 

[Strawtles]

This schematic seems to be compatible with the number of components in the TG 500 module.
It remains only to know the right value of resistors.
For the gain we can use a pot intead of R4?

 

[analogguru]

For the experts:
How does it come that the Chandler TG2 uses four transistors in the input stage ?

 

[warpie]

maybe two stages for more gain?

 

[Strawtles]

it is possible that the 500 format and the rack version are different circuits ... what's the original one?