RFZ V742dy
« on: May 13, 2020, 04:23:57 PM »
Sorry for cross-posting, this is also in the Preamplifiers section.

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Hello everyone, I hope your collective wisdom could help me with a couple of RFZ V742dy isolation/line amps I have:

I got a pair of these cheap, allured by the split transformer balanced outputs, and to see if I could use it for general utilities at least/modification to the input transformer for greater gain at best (?). I understand the +24v referenced to ground and 0v to '-24v', so I have them working, that's all fine (I have V781s also). But I am a bit confused by them both.

Firstly, the main Leitungs Ausgang (line output) works OK, but that's about the extent of it's use.. the problems are as follows:

- Main line out DOES work, but with what sounds like a fixed HPF at around 200hz or thereabouts.. (both units behave same)

- Secondary output DOES NOT work despite being connected on those pins from the internal view, and I have checked the switch, seems to be fine (both units behave similarly)

- Abhörausgang (monitor output) DOES NOT work despite being connected on those pins from the internal view (both units behave similarly)

- I have recapped one of the amplifier PCBs, had replaced C4 (separate to the amp pcb) from a 25v 220uf Frolyt axial to a 63v 220uf Nichicon radial and it exploded after 20 mins! Why could that be?

I would really appreciate some help to get the splits functioning, otherwise I will gut it and use the transformers for something (open to suggestions..)

Some docs attached


Re: RFZ V742dy
« Reply #1 on: May 13, 2020, 04:34:02 PM »
page 2

mjrippe

Re: RFZ V742dy
« Reply #2 on: May 14, 2020, 12:00:45 AM »
- I have recapped one of the amplifier PCBs, had replaced C4 (separate to the amp pcb) from a 25v 220uf Frolyt axial to a 63v 220uf Nichicon radial and it exploded after 20 mins! Why could that be?

Either it was a faulty cap, or you put the cap in backwards.

As for the HPF, try removing C1, C2, R1.  It is drawn oddly and I'm having allergies right now and can't think straight but that looks filter-y to me.
« Last Edit: May 14, 2020, 12:06:15 AM by mjrippe »

Re: RFZ V742dy
« Reply #3 on: May 15, 2020, 08:30:23 AM »
OK, I have made progress. Stupid me, I actually had the polarity on the DC reversed! So dumb I didn't double check it!

Anyway, explains why the caps were popping! It's sounds absolutely fine now, but I am still confised why I receive no signal on the ST2 A3/B3 and ST1 A4/B4.. I sent an input signal to the relevent contacts on the switch and the signal from there is OK, it's just not getting to that point?

Re: RFZ V742dy
« Reply #4 on: May 15, 2020, 04:32:29 PM »
Hey guys, I am really begging for help here, it is driving me nuts!

I am staring at the schematic, and cannot understnad why I get no signal on those extra outputs!

The transformer set-up is quite unusual, is the signal being passed from TR2 to TR3?

Someone please help me  :-[

moamps

Re: RFZ V742dy
« Reply #5 on: May 15, 2020, 05:49:25 PM »
TR3 is obviously  auto transformer so you should connect B3 to B4 an A3 to A4 on B connector to get signal at  ST1 A4-B4.

Re: RFZ V742dy
« Reply #6 on: May 16, 2020, 12:30:04 PM »
MOAMPS THANK YOU SO MUCH!

tommia

Re: RFZ V742dy
« Reply #7 on: May 18, 2020, 11:56:24 AM »
don't remove c1 c2 r1 these are rfi filter

Re: RFZ V742dy
« Reply #8 on: May 18, 2020, 02:53:06 PM »
When they didn't impact the sound I put them back :)

mjrippe

Re: RFZ V742dy
« Reply #9 on: May 19, 2020, 12:27:10 AM »
don't remove c1 c2 r1 these are rfi filter

Yeah, I thought the values looked wrong for audio band but I was not feeling well enough to figure it out.  Thank you!


 

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