Home theater bypass

If you want to use the Mac 275 for both stereo and HT duty, there will be two ways for connections:
1. Use a line level source selector connect to Mac 275 input to select the output from cj preamp or Onkyo 805.

2. Connect the Onkyo 805 front R/L preout to cj pv1 one of the line level input (not the phono) and set the cj volume control to unity gain position during HT playback.

To find the cj volume control at unity gain position:
connect the cj preamp main output to Onkyo 805 one of the analog input (i.e. CD input),
connect the cj preamp monitor or tape out to Onkyo 805 another analog input (i.e. AUX1 input),
connect a cd player to the cj preamp to play some test tone,
switch between the two input on Onkyo 805 and adjust the volume control on the cj preamp until both input getting same loudness/SPL.
Mark that volume control position on the cj preamp front panel, it’s the unity gain position.

If connect the Onkyo 805 front R/L preout to one of the line level input on cj pv1 and set the cj volume control to a fixed position during HT playback, the cj preamp act as a pass-through and the Onkyo 805 do all the control (i.e. select input source, surround mode, volume ...)

http://daveayers.com/Audio_Diagrams.htm

perhaps easier method from a practical standpoint is to use the 12:00 position on your CJ as the reference point for the input from the AVR and then use the AVR to set the correct volume levels for each channel.  This method doesn't find unity gain for the CJ, but it avoids having to mark the proper volume level on the faceplate of your stereo preamp

+1 soix

https://www.computeraudiophile.com/uploads/monthly_2013_09/58cd96b7e0681_HomeTheaterBypass.JPG.02904...
In the schematic, CDP is a compact disc player (CD player), passive pre is the cj and amp is Mac 275 and receiver is Onkyo 805.

Maybe this schematic give you a better idea:
http://daveayers.com/Audio_Diagrams.htm

To operate either system all units must be on ?

For stereo playback, only the source (CD player, turntable or tuner), cj preamp and Mac power amp need to be on, the Onkyo receiver can be off.
Before any playback using Onkyo receiver at the first time, you need to set the cj preamp volume to 12 o’clock and re-calibrate the speakers level setting via automatic speaker setup or adjust the front R/L speakers manually (see page 55-59 of Onkyo TX-SR805 Owner’s manual).

I have a Mac C48 preamp that only goes into bypass mode by a 12v trigger from a processor. I have been working around this as my Oppo 105 that I use as a processor has no 12v trigger.

Another idea would be to get one of those 12V wall wart DC power adapters, chop the end and solder it into a 1/8" male mono plug. Use that as the 12V trigger for C48 and then just plug it in when you want to trigger the C48 into bypass mode.

Same idea with some refinement :
Use a 12V wall wart DC power adapters with inline on/off switch and a 3.5mm Male to 5.5x2.1mm Female DC Adapter.
https://www.amazon.com/Gxilee-100-240V-Converter-Household-Electronics/dp/B01FXF6AEQ
https://www.ebay.com/itm/3-5mm-Male-to-5-5x2-1mm-Female-DC-Adapter-Converter-Jack-Power-Plug-CCTV-DV...
Turn on the inline switch if you want bypass.

So now I am about to set up my new 205 which has a trigger to put the C48 in bypass, but what if I just want to play a CD and not HT, how do i control that, if every time I turn on the 205, the C48 goes into bypass.

https://www.amazon.com/RDL-ST-ACR2-Line-Level-Audio-Controlled/dp/B01D96JVFG
Connect the RDL input to center channel or LFE output of 205, connect the RDL relay switch between 205 trigger output and C48 trigger input.
The HT bypass will be done automatically.

the DVD player is connected to the receiver with a hdmi and connected via the audio outs to the preamp inputs. The receiver preouts are connected to the preamps tuner inputs. The preamp is connected to the Mac then the speakers Maggie 1.7.

@audiomaze -- what input on the CJ are the audio outs from the DVD player connected to?

The tuner.

How many tuner input on the cj preamp?