Can't claim credit, Tom is the one who posted this. I've currently got a 2230 on the bench now giving me heartburn. Now it's the tuner I'm dealing with.
Phono "motorboating" solved(?)
- Thread starter Steven Tate
- Start date
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I’ll be home tomorrow and can get you voltages or scope pix if it helps!
Thanks Randy! Might be taking you up on it. I'll PM you later and fill you in on my tale of woe.
Please do! Misery loves company!Thanks Randy! Might be taking you up on it. I'll PM you later and fill you in on my tale of woe.
JD Harvey
Galvanized Ear
Looks right. 47 ohm and traces cut.
RyeGuy859
Well-Known Member
Wanted to leave a comment on this.
Have a 2270 i fully restored, Played it for months on Aux sounded great. Decided to do some records and got the motor boating. The phono board was rebuilt according to to leestereos guide. The only transistors replaced were the 458s with 1845s. It did it even when the record player was off, and only stopped when i unplugged the rca’s. Also tried a reverse Phono adaptor i have for my phone and got the same result.
Swapped the 1845s with 1815s i had and happy to say not a single issue 3 hours later.
Have a 2270 i fully restored, Played it for months on Aux sounded great. Decided to do some records and got the motor boating. The phono board was rebuilt according to to leestereos guide. The only transistors replaced were the 458s with 1845s. It did it even when the record player was off, and only stopped when i unplugged the rca’s. Also tried a reverse Phono adaptor i have for my phone and got the same result.
Swapped the 1845s with 1815s i had and happy to say not a single issue 3 hours later.
That is a great suggestion and I’m going to try it as I have the same issue. But I can use. Aux and phono 1 and 2 without a problem but if I connect anything to the tape loop, that’s when I get the rhythmic thumping. I’ve been chasing this issue for quite a while.
John H, you should start a new thread, detail everything about your unit, what's been done, circumstances etc. Post a few pics of the boards, etc.
That's the best way to get some of the smart people to weigh in, the more info the more likely they can help you. Good luck. By the Way, that really sounds like a strange issue?
That's the best way to get some of the smart people to weigh in, the more info the more likely they can help you. Good luck. By the Way, that really sounds like a strange issue?
I Can Verify This Fix
After fighting the dreaded motorboating on my Marantz 2270’s P700 phono board, I can confirm this simple fix completely solves it.
This oscillation or thumping started after I did a complete recap of the unit and installed the two new transistors that came with the kit in the phone on board the KSC1815s
In my case, the amp would start pulsing the moment anything was plugged into the Tape 1 or Tape 2 jacks — even if the tape loop wasn’t engaged — but only when Phono 1 or Phono 2 was selected as the source. The problem came from using modern low-capacitance transistors (like KSC1815s) in place of the original 2SC458s.
The cure: solder a 10 pF C0G/NP0 ceramic capacitor between the base and collector of (I did this on the underside of the board as they are pretty tiny) H705 and H706. That’s it. The phono stage is now totally stable, even with my reel-to-reel deck connected to both Tape 1 In and Out.
If your rebuilt 2270 motorboats when tape gear is attached and a phono input is selected, this tiny two-cap fix works wonders. Somebody mentioned that I should’ve posted some pictures before and after, but here is a picture of the phone board, and the two transistors that are in between the blue electrolytic capacitor, and I added the small disc capacitors on the bottom of the board underneath sorry I didn’t take a picture.
Attachments
I also swapped the original 22 µF decoupling caps for 470 µF ultra-low-ESR Panasonic FM electrolytics, each bypassed with a 1 µF film cap. That gives the phono stage a cleaner, more isolated power feed and filters noise coming from the rest of the preamp. But I think 470 µF might be a little bit excessive, but it is working just fine
I added a small 33 Ω resistor in series with the DC + feed, forming a simple RC filter with the new cap. Together these changes lower background noise, tighten the low end, and keep the phono stage rock-solid even with tape decks or long cables connected.
The only side effects are a slightly slower voltage rise at power-on and a tiny bit more inrush current — both completely harmless.
Have you done any sweep testing to verify riaa?
That’s a good question, but at this point, I have not done any test testing on the RIAAA equalization circuit. But the modifications that I made with the exception of adding the 10 pF capacitors is the only thing that could influence that equalization circuit (in a good way as it puts back the capacitance that was removed with the modern transistors). The larger decoupling capacitor are just on the DC power rail, and resistor on the DC+. They do not go anywhere near the signal chain. Although I could be wrong as this was just my solutions to this general problem. Also, there are a lot of iterations on the phono boards Marantz models. And I am definitely not an expert..
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Most of us aren’t experts. But your contribution to a fix could be helpful to others down the road and is what AK is all about. I was thinking this could be done with a signal generator and multimeter and excel. More easily done on a hp 8903 b or one of the fancier lcd screen testers that display in real time. Thanks for sharing!
Leestereo
Super Member
The 22uF capacitors at C703/704 are in the signal path; they are the high pass filter for the RIAA equalization. See here for more details: https://audiokarma.org/forums/index...pgrade-of-a-marantz-2270.793805/post-10982411
Thanks for the detailed explanation! In my unit, those 22 µF capacitors were replaced with higher-value electrolytics that are bypassed with small film capacitors, not full film replacements. I had thought they were just part of the DC supply, but it makes sense now that they’re tied into the RIAA feedback network and influence the low-frequency response. That also explains why stability changed after the transistor swap — everything’s solid now after adding the tiny base-to-collector caps on the diff pair.
Just finished another 2230 phono board and got motorboating on the left channel only. On this one, I recapped, replaced the diodes and only replaced H705 and H706 (2SC458) with KSC1815Y, both with hfe of 151. I left the 4 x 2SC1000s in place since i didn't have any hiss. As before, it only happened when i have a tape deck connected to the Record Out jacks. With nothing connected to the Record Out jacks, it's fine.
I added the 2 x 47Ω resistors inline with the outputs and the motorboating disappeared . . . . should have just added them while I was in there, but i thought it was a good chance to revisit this issue on another receiver to have more data. If that didn't cure the problem, I would have gone for the Miller caps next.
I added the 2 x 47Ω resistors inline with the outputs and the motorboating disappeared . . . . should have just added them while I was in there, but i thought it was a good chance to revisit this issue on another receiver to have more data. If that didn't cure the problem, I would have gone for the Miller caps next.
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