Inovonics 375

[Dmichel123]

http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Inovonics%20Model%20375%20Instruction%20Manual.pdf

Trying to get a couple of these going. I don't think they need repair so much as I'm probably not connecting things right. These came with an Ampex 300 transport we picked up a few years ago. We were never able to get them to Record. I have one connected to a 351 transport now, and I'm having the same issue.

Would this need to be connected to a headstack to get the electronics to go into "record" mode and make the light come on? We definitely had it connected to heads on the 300 transport. I'm wondering if there's a connection on the 10-pin "power" connector that needs to be made to make the relay click over.

Thanks,
Danny

 

[radardoug]

RTFM. Theres a record logic line which needs to be controlled.

 

[Dmichel123]

RTFM. Theres a record logic line which needs to be controlled.

I've RTFM. I just RTFM again. Maybe you can screenshot the page that explains it, because I don't see it in TFM.

 

[radardoug]

Follow the  lines back from the record relay.

 

[Dmichel123]

Follow the  lines back from the record relay.

R49 390ohm. Looks and measures fine.

 

[radardoug]

No, I mean follow the relay control line, and follow it through the logic that drives it. You will come to a pin marked 'record logic' or similar. If you want me to do it for you, then I have to charge you. I've pointed you in the right direction.

 

[Dmichel123]

No, I mean follow the relay control line, and follow it through the logic that drives it. You will come to a pin marked 'record logic' or similar. If you want me to do it for you, then I have to charge you. I've pointed you in the right direction.

I've looked at the schematic for hours and hours. Record logic goes to "P". There is no "P" anywhere else in the manual. Perhaps you have a different manual than the one I posted? The record switch is in the chassis of the Inovonics, not external. Wherever it is that "P" or "record logic" goes, it should still be connected as built. I can't see any evidence of modifications to this unit.

 

[radardoug]

The unit has a set of cards, one for repro, one for record, and possibly others. I would suggest the P is on the record card edge connector. There is a later drawing showing the relationship of the cards. This only has numbers. So you need to investigate where the wiring goes. Take out the record card and trace from the components on the card to the edge connector. That will be P.
Follow the wiring on the other side. PCB connectors are often made with numbers on one side and letters on the other side.
It is clear to me that you do not have the faultfinding skills to do this if you cannot follow the drawings provided. Maybe find a tech who has those skills.

 

[radardoug]

If you look at the last page of the manual, it shows the interface cables for various machines. All interfacing is on a 10 pin Jones plug. The P on the record card is pin 13 on the overall interface drawing, record card pinout, and goes to the record pin on the Jones plug.
Couldn't be much clearer with a bit of study. When can you send my fee? Hehe!

 

[Dmichel123]

The manual I'm looking at doesn't have a page showing cable diagrams for different transports. I'm sure I would have figured out cabling if I had a diagram showing cable wiring.

My manual also shows P/21/Record logic going to 10, not 13, on the power PCB. I'm fairly certain both of my units are still wired this way, stock. I see no signs of modifications, but can take another close look tomorrow.

 

[radardoug]

You will find that manual on the Inovonics website.

 

[Dmichel123]

You will find that manual on the Inovonics website.

Thanks. That makes it much easier. For some reason, that page was missing from the manual I have.

 

[Dmichel123]

Would changing the uA748 Op amps in this thing to 5534s be a good upgrade for improved fidelity?

 

[radardoug]

So does that mean you have got the units going? You need to bear in mind that the distortion off tape is 3% at peak level, and probably around .5% at normal operating level. So changing the opamp is probably not going to have a major effect. The designers at Inovonics knew what they were doing, even though constrained by an older opamp.

 

[Dmichel123]

I have them going, but haven't recorded anything on them yet. I'm just going off of what I've read: that they measure low distortion but sound pretty horrible.

 

[radardoug]

I believe Inovonics sold quite a lot of these, so I'm sure they dont sound that horrible. The cap changers and op amp changers of this world often exaggerate.

 

[gridcurrent]

I have them going, but haven't recorded anything on them yet. I'm just going off of what I've read: that they measure low distortion but sound pretty horrible.

Neil Muncy configured many of the 375 electronics onto rebuilt 300 transports.
Functions are useful, flexible eq, sync though hardly necessary on a 2 track.
Spent time with them, easy to work on,  good workmanship.
In my opinion, they play back better than they record.
The repro section is a good candidate for distillation and "improvement". 
Replace the ic based line amp with the discrete, trendy op-amp of your choice. 

 

[radardoug]

Neil Muncy configured many of the 375 electronics onto rebuilt 300 transports.
Functions are useful, flexible eq, sync though hardly necessary on a 2 track.
Spent time with them, easy to work on,  good workmanship.
In my opinion, they play back better than they record.
The repro section is a good candidate for distillation and "improvement". 
Replace the ic based line amp with the discrete, trendy op-amp of your choice.

If they play back better than they record, why would you change the playback side? Surely you would change the record side.
But this OP does not have high electronic skills, why not leave it as it is?

 

[Dmichel123]

If they play back better than they record, why would you change the playback side? Surely you would change the record side.
But this OP does not have high electronic skills, why not leave it as it is?

You're a swell guy, Doug. I don't have high electronic skills, because the manual I have is missing a page. Funny, I've rebuilt probably 100 guitar amps, 25 mic pres and consoles, several Ampex recorders, designed and built guitar effects pedals, etc. I've gotten a lot done for being a retard.

 

[Dmichel123]

How will I EVER figure out how to remove and replace 8 pin op amps?!?!?