API 212/215 hybrid

[Zebra_PD]

Hi,

So I would like to combine these to classic modules into one. A 212 preamp with a 215 discrete HP/LP Sweep Filter. Will try to design a couple of prototypes and hoping to provide some boards and perhaps kits with hard to find parts in the EU for the DIY community later on.

The 212 is prob no stranger to most on this forum but not a lot have been said about the 215.

http://www.apiaudio.com/product.php?id=115

But basically is a discrete HP/LP Sweep Filter with following features:

Wide range 6 dB per octave LOPASS control
Wide range 12 dB per octave HIPASS control
Balanced input stage
Passive filter design for smooth tone
Unity gain throughout
Hard Wire BYPASS switch
Transformer Coupled Output to +28 dBu
All Discrete Design

It uses a 2010 all dicrete OPAMP for the input and a 2025 for the output (same as 212) and a transformer (prob AP-2623?).


Will post the schematics of the 215 (still tracking em down) later on. So still is a bit unclear around the details of design of it.

So basically my idea is that both "units" will be fitted on one board and share the same output amp.  Alternative the option to put the 215 input amp to a separate board for those that don't need the all decrete input.

Things I haven't made up my mind around or figured out and where need the help of you guys:

- Just add the HP/LP Sweep Filter part of the 215 in the chain after the 212 input vs add the 215 input stage and separate line-in TRS/XLR to the design to use the filter with other preamps or as a outboard mixing tool.

- the effect on the sound/function of the input 2010 OPAMP to the overal 215 design? (Info on the 2010 https://groupdiy.com/index.php?topic=44073.0 )

- Other european subitute for the transformers besides the Sowter 9820 and 9825?

- subitute  the 2010 OPAMP or recreate it?

- any other challenges or things  I haven't thought that might be a problem down the road.

And thoughts or feedback are highly appreciated.

 

[PRR]

1pFd caps make no sense. Find a similar design and steal values.

 

[Zebra_PD]

1pFd caps make no sense. Find a similar design and steal values.

Can't guarantee that schematics of the 2010 is a 100% accurate. Found it in the thread linked above.

Still in the process of tracking down some schematics for the 215 module. Hoping to shed some light on the 2010 design as well.

Perhaps anyone that have build a 225/2500 type compressor have any incite?

Perhaps Jeff of CAPI is lurking around somewhere here and could provide some info. Found an old GS post of his that he was working on implementing a API style filters to some of his design a couple of years ago, probably the CAPI 553F, in a GS thread about the 215.

The CAPI 553F have the HP/LP on separate cards so for a first test run I might try to order 2 sets of those just to see if the hole 212/215 hybrid idea works as well in reality as in my head. Just wire those cards on to some 212 boards prior to the output amp

Also having my eyes on the ML12 cards from
Whistle Rock that implement a all-discrete input option, either passive or FET based. Haven't had a chance to compare the schematics of the M12 and the 212 yet though.