Mofo

[Max N]

I have long had a hankering to hear a jensen 990 discrete op amp or one of its descendants...or maybe I already did but have forgotten...I'll get my coat

[Max N]

https://www.jensen-transformers.com/wp- ... 1-bmcf.pdf

[Max N]

https://www.jensen-transformers.com/wp- ... 1-bmcf.pdf

Impressive numbers but what would it sound like….

[simon]

How does the dual rail PS become dual rail? Does the PS gnd need tieing to the -ve IN? Otherwise it's just a single rail supply as far as I can see.

Is the answer to this that when the ground rail is tied to the PS ground the -ve pin is pretty much at ground?

Assuming a maximum voltage in of 2V RMS, 5.66V p-p, a gain of 2 would give a maximum voltage out of 11.32V. So at the -ve pin there would be 3.8V. Near enough ground.

[Nick]

That PCB layout looks like a single rail so I would ignore it. Your diagram in https://www.audio-talk.co.uk/phpBB3/vie ... 22#p200222 looks right, just need decoupling on the -ve rail. You have a power supply with -15v 0v and +15v, the 0v is the input ground (and the output ground) and the power rails are decoupled and connected to the op amp power rails.

[steve s]

I've been going to build a second mofo based amp for the last year, I've had all the parts for at least 18 months

I've had old eddystone receiver case in the garage for years, at leat 10, which I took in a couple of weeks ago to be powder coated, it has a lovely cast alloy front that looks quite something..

I eventually collected it yesterday and spent last night deciding how I could fit things in, today's job is to cut the various mounting boards so I have some flexibility.

I'm planning on using another 30s valve to drive it, I took my valve data book to bed, but could not find anything that seems more suited than what I have in other amplifiers
For me my priorities are gain between 7× and 15 x, built in the 30s, low impedance ( driving an interstage ), and known sound quality.

Px25 is the probably the best suited but it's going to be a squeeze to get those in, so I'm still very much undecided.. idh valves are much easier

I'll get a pic up of the case so you can see where I'm heading.

[simon]

Sounds interesting Steve, looking forwards to a photo.

I'm still undecided if I need any gain at all. I haven't used all the volume pot yet, but I haven't had a loud listening session yet either.

I did have a scratch around for some bits and breadboarded the op amp gain stage. I ran out of time yesterday but intend to try it with a 24V SMPS with a divider ground for +12V 0V -12V supply. I'm not expecting the breadboard bit to work...

20221105_123504.jpg (112.32 KiB) Viewed 3149 times

[pre65]

OK, this gain problem has been bugging me for a few days, so as my memory is suspect, and I seem to have forgotten what has been done by myself (MoFo wise) I've gone back to basics.

Now, the Audionote (copy) pre amp WILL give, in my room, loud enough listening volumes with the volume control a few clicks away from maximum.

So, I apologise for my demented ramblings trying to solve a problem that does not seem to need solving.

[steve s]

20221105_130801_copy_640x480.jpg (219.94 KiB) Viewed 3143 times

20221105_130753_copy_640x480.jpg (214.42 KiB) Viewed 3143 times

The two half's are loosely together the fit is rather tight after the powder coat but I'm sure it will be fine.

[Ray P]

That looks really nice Steve.

[pre65]

Looks really good Steve, I'm envious.

[simon]

That's a result Phil!

Looks like retro microwave Steve?

[pre65]

That's a result Phil!

After a while I was able to back the volume down a bit, ended up 4 clicks down, and still loud enough.

[steve s]

That's a result Phil!

Looks like retro microwave Steve?

I see what you mean simon.. it does look like our black microwave !

Its probably more like a slow cooker in use though.

[steve s]

The empty case weighs about the same as our microwave before I start filling it !