Hi everybody!
This thread is about the Focusrite 110 preamp topology with its special output transformer.
My question will be, if there is a possibility to use another output transformer in this topology.
But first the background information:
This "pumpkin" toroidal output transformer used in the ISA 110 has a second output winding which is used to send a feedback signal back into the output stage; I guess to cancel out distortion. Here is the schematic:
You can find this schematic (in a bigger and more readable version) and more information at Kevs very nice webpages (called the DIY Factory; thumbsup for Kev!); at the following URL there is that special page about building a 110 based preamp:
http://www.diyfactory.com/projects/diy110/diy110.htm
As you can see there, forum member Okko has built some 110-type preamps using these pumpkin output transformers.
There also has been a discussion here at the prodigy forum regarding that special output topology:
http://www.groupdiy.com/index.php?topic=4485
Now to my "problem":
Two weeks ago I bought 4 of them pumpkin output transformers here at the black market. The seller claimed that they would be perfect for a Focusrite 110 project, so I thought the transformers would have the second output winding for the tertiary feedback topology.
Waiting for the transformers to arrive, I made the PCBs for four channels, and stuffed and finished two of them.
When the transformers arrived, I discovered that they did NOT have two secondary windings - so no winding for the feedback! Of course I have been disappointed... :sad:
(BTW: everything is cool with the seller; he has just not been aware that the pumpkins for a 110 preamp have to have that second output winding; and he will take back the transformers if I don´t want them anymore).
The transformers I got are on a NEVE EV11381 card (out of a serie 66 console, as the seller said).
Now to the question:
Can I just use them in this circuit, and leave the feedback connection open? Can anybody tell me what will happen soundwise (I´m sure it won´t explode :grin? Or do I have to modify the output stage?
Cheers and thanks for your help; Christoph
This thread is about the Focusrite 110 preamp topology with its special output transformer.
My question will be, if there is a possibility to use another output transformer in this topology.
But first the background information:
This "pumpkin" toroidal output transformer used in the ISA 110 has a second output winding which is used to send a feedback signal back into the output stage; I guess to cancel out distortion. Here is the schematic:
You can find this schematic (in a bigger and more readable version) and more information at Kevs very nice webpages (called the DIY Factory; thumbsup for Kev!); at the following URL there is that special page about building a 110 based preamp:
http://www.diyfactory.com/projects/diy110/diy110.htm
As you can see there, forum member Okko has built some 110-type preamps using these pumpkin output transformers.
There also has been a discussion here at the prodigy forum regarding that special output topology:
http://www.groupdiy.com/index.php?topic=4485
Now to my "problem":
Two weeks ago I bought 4 of them pumpkin output transformers here at the black market. The seller claimed that they would be perfect for a Focusrite 110 project, so I thought the transformers would have the second output winding for the tertiary feedback topology.
Waiting for the transformers to arrive, I made the PCBs for four channels, and stuffed and finished two of them.
When the transformers arrived, I discovered that they did NOT have two secondary windings - so no winding for the feedback! Of course I have been disappointed... :sad:
(BTW: everything is cool with the seller; he has just not been aware that the pumpkins for a 110 preamp have to have that second output winding; and he will take back the transformers if I don´t want them anymore).
The transformers I got are on a NEVE EV11381 card (out of a serie 66 console, as the seller said).
Now to the question:
Can I just use them in this circuit, and leave the feedback connection open? Can anybody tell me what will happen soundwise (I´m sure it won´t explode :grin? Or do I have to modify the output stage?
Cheers and thanks for your help; Christoph