Hi,
I recently purchased a AWA 400 Wall Telephone that is in excellent condition.
I have now connected it to a Grandstream 801 and can receive and make calls when connected to a modem, the bell also rings.

But...volume is very low, I can barely hear or be heard.

There are settings in the Grandstream to increase Gain, but it has made very little difference.

I also purchased a NOS handset receiver and transmitter from Old Phones in Perth, just tested them now and the result is still the same, very low volume.

The wiring for the handset going to the terminal block is clean.

There were 3 wires originally in a 605 plug I have removed that and installed an RJ11 plug using the 2 centre pins.

The original wires were Blue,White,Red.
Everywhere i've read said the red wire is not needed so it is not connected, only the Blue and White wire.

Any suggestions in improving the volume?

I've never done anything like this before so my knowledge is very minimal.

Thanks

See the terminal block for line connections:

#1 White (Green - RJ11)
#2 Red (only needed if an extension bell is required with link between #1 & #2 removed).
#3 Blue (Red - RJ11)

Is there a circuit diagram inside the phone?

Yes there is a circuit diagram inside
I'll also add photos of the terminal block.

I have since emailed Brad to add photos to this post.

The photos are.

Wiring diagram from inside the phone

The 605 plug original , the added text in the photo is what I thought was the Tip, Ringer and Bell

Terminal Block, with white and blue wire connected to terminal 1 and 3 , red I did not use in the RJ11 plug.

The two centre wires in a RJ11 connector are red & green.

https://satmaximum.com/rj11-vs-rj45-what-is-the-difference.html

https://archive.goughlui.com/wp-content/uploads/2017/12/2017121917361528.jpg

EDIT: Disregard my first post and the image link above.

The green wire replaces the blue and the red replaces the white. We still use landlines at work - I just checked.

The image below is more like it:

https://archive.goughlui.com/wp-content/uploads/2017/12/2017121917421537.jpg

Your attached link of the 605 plug with red and green wires matches the original 605 plug on my phone, each wire connected to the prongs at each end of the plug but my phone has an additional red wire connecting to the middle prong, which confirms it does not need to be used/ connected

But the original wires on my phone are blue and white ( contained in the original 605 plug) they are also connected to the terminal block.

I can also confirm white goes to terminal one and blue is in terminal 3

The white and blue wires then are spliced into the red and green wires of an RJ12 plug
Not a RJ11

I’ve read if the tip and ring wires are swapped they can still work but not as good as the correct wiring.

I have tried switching the tip and ring but same thing, everything work but just very low volume
I’m happy to be corrected if I’m wrong on this

Yes your update link shows a 605 plug to RJ11 convertor
I've tried one of those also but ended up completely removing the 605 plug and convertor and went with just splicing the two wires into the RJ plug

Photos uploaded to Post 3.

On the 600 series plug the white wire goes to terminal #2. The photo shows it going to terminal #1. The corrosion on the red & green wires may be a problem.

The handsets leads goes to:

Green #6
Red #7
Blue # #4
White #5
(although the way there are currently shouldn't affect the working)

Everything else appears in order.

Are those two grey wires going to a key lock?

I’ve done a bit of wire switching and cleaning to see if there’s any difference, handset and tip and ring wires, no change at all.
I did just notice that terminal one and 2 has a metal bridge? connecting them together.
The terminals that appear rusty I think are ok, it might be the clear plastic original sheeting has yellowed.
The grey wires go to a white press button switch that is between the hook switch, is that a party line button??
I’ve pressed that white button whilst in a call and it does not appear to do nothing, no disconnection
I’ve gone back to the Grandstream which allows “gain” to be raised from “0” which is default to “12db” which is max, no change in volume even at max.

I think I’ve figured it out, I don’t want to speak too soon though.
I have zero knowledge with these telephones.
Let me see if I can explain it.
I found 4 brass prongs inside the phone where the hook switch works, when the receiver is replaced it pushes the two outer plates away from the centre plates and cuts the call.
The two outer plates, those that are pushed apart and cut the call touch two inner plates when in a call, one of the plates has a slight bend in it so it does not touch the inner plates, on one side it does
When I place a call and push the plate inwards my voice can be heard.
The only issue I have now is bending that plate so it makes its own connection, without me damaging the plate
Does this make any sense?
I call the rotary phone with my mobile and then set my mobile to record, and it records my voice loud and clear, but I have not tested any one calling me to see if I can hear them

Hope this all makes sense

If it does, can anyone explain what the plates are connected to the hook switch?

You can easily tell if the hook switch is not working by using a test lead with alligator clips between terminals #1 - #16 and #11 - #15.

Refer to the schematic.

You have to be careful not to foul the dial leads when putting the phone back together. This could cause the hook switch contacts to bend.

Schematics, I have no experience in understanding them unfortunately.

I've asked Brad to attach a new photo of the culprit hopefully to give a clearer picture.

The hook switch was working fine, but it is an internal switch inside the hook switch that seems to have been affecting the sound.

One side when pressed in I hear the phone bell ring for a second, so this is the power?

The other side when pressed in I can hear the handset crackle, maybe its power to the handset, i'm not sure.

My description may be confusing, i'll hopefully be able to explain it further when the photo is uploaded.

But yes, at present one of the hook switches was bent, it did not affect hanging up call, but did have an affect when in a call.

So now there is a huge difference in volume, totally normal now.

Thanks for the advice so far.

Actually it can be seen in my third photo, left hand side, directly under the conical plunger that pushes the contacts apart, in-between the longer contacts there are 2 internal contacts, left hand side seems to affect handset if not always touching, mine has slight outward bend

Photo (#4) uploaded to Post 3.