Rotel RX-600A Weak Channel

[ScooterMcTav]

Think I'll need to do some surgery on my dumpster rescued RX-600A. However, as I'm pretty ham handed with a soldering iron, I'm not sure the patient will survive.

Recently, the right channel has gotten weaker, and I have:
- confirmed dc offset
- made sure all buttons and pots are clean and not affecting balance
- tried multiple sources and cables

I normally would not invest time or money on an old piece like this (just replace it) but the wonderful sound this receiver has generated over the past few years is absolutely superb, and I'd hate to give up on it. It's chameleon ability to sound good with every set of speakers I've paired it with (JBL, Mission, Wharfedale, and my valued Soliloquies) makes it worth saving.

So, any likely culprits? Caps? Where should I start?

And as a side note (not sure if related) it did make an odd noise on power-up. Best I can describe it is a sound like losing a life on an Atari game.

 

[ScooterMcTav]

Hi all,

Any ideas? Anyone?

 

[zebulon1]

Run it through another Amp or Pre
It has the "Pre Out", "Main In" RCA jacks.
See if you can narrow it down to the Pre amp or main amp.

 

[ScooterMcTav]

Run it through another Amp or Pre
It has the "Pre Out", "Main In" RCA jacks.
See if you can narrow it down to the Pre amp or main amp.

Thanks Zeb,

Overlooked "troubleshooting 101". Funny as I thought about this when making my bump post today - will check this tonight and report back.

 

[zebulon1]

I'm betting on the pre amp.
I know you mentioned cleaning the pot's but I might remind you that Deoxit and follow-up Fader 5 are the best accessible products to use on the pots and switches. The signals run through every switch and pot, so - all controls should be Deox'ed and later, lubed.
Several applications might be needed.
The strange sound is intriguing.

 

[ScooterMcTav]

Ok, so let me see how many ways I feel stupid this evening.

#1 - Removed the system from the rig it was in to set it up on the bench. And noticed that a bad stripping job meant that my 8' run of 16 ga was closer to an 8' run of 24 ga at the speaker terminals. This was feeding 12 ohm speakers....errrm
#2 - But get it to the bench anyways, hook up a pair of Mission bookshelves, hook my iPhone directly to the power amp in jumpers, and proceed to deafen myself as the iPhone volume was set to full.
#3 - I proceed to deafen myself as I play with the useless volume control, only realizing after what felt like 5 hours (likely 2 sec) that I needed to lower the signal feed
#4 - Power amp is fine, now that I'm listening at normal levels
#5 - Jumpers back in, and receiver is working fine

So, guessing the weak channel was likely due to a bad wire. Oh well, at least it gave me an excuse to go buy my Luxman R-1050.

I wonder if the srange noise may have been caused to my cell being in close proximity to the receiver itself. I belive it may have been sitting o nthe receiver when I turned it on and it made the noise.

 

[zebulon1]

Cleaning the jumpers might be all it was.
Also, you don't want to feed to much gain into the amps. Look in the Service Manual and see the line level signals are only around 250mV's. The head phone jack in the phones are well over a volt and more!
I use a ipod dock from Belkin and or a Bluetooth stereo receiver connected to the AUX input (Great for Streaming). This is the best and least distorted method of listening to the vintage equipment.

https://www.amazon.com/Belkin-F8Z492TTP-Bluetooth-Music-Receiver/dp/B0047T79VS

https://www.google.com/chromecast/a...mpaign=audio&gclid=CIjBzoLtxc8CFYqIfgodmN0LAg

http://www.ebay.com/itm/Belkin-Audi...903867?hash=item3f2b5497fb:g:g~sAAMXQL99ScJYm

 

[ScooterMcTav]

Appreciate the tip Zeb. If I read your post correctly, I will be introducing distortion to my music by pinning the volume on my iPhone via RCA cables? If so, great tip. It would also explain why the better a system I listen to, the worse my digital music sounds. Funny enough, I had a thread about this in digital sources; I was unhappy with the sound from my phone, and although a lot of my issues appear to stem from compressed DR, I wonder if this is also an issue.

You suggest bluetooth, but my experience with my Marantz AVR is that Air Play maintained quality better. Maybe I'd be better off using an old Apple TV?

Edit: Wow, just looked at the input specs of my three vintage receivers in current use:
Rotel RX-600a - 130mV (as per Hi-Fi Engine)
Luxman R-1050 - 150mV
McIntosh MA-6100 - 300mV

Looks like we could use some signal damping on all three to improve sound quality.

 

[patrick_l]

I once had case of Yamaha AX-500 amplifier playing only one channel. After checking all possible trace that exist in that amp, turned out, I just needed to pull out/ pull in "receive" to "send" jumpers few times. After that amp was perfect (and I felt stupid why I haven't checked that jumpers first)

 

[ScooterMcTav]

Yah, once had an old NAD and was getting the soldering iron ready...until I realized the pre out-power in jumpers were missing.

Good thing I dropped it a few times to test out the cold welds first.

 

[ScooterMcTav]

Cleaning the jumpers might be all it was.
Also, you don't want to feed to much gain into the amps. Look in the Service Manual and see the line level signals are only around 250mV's. The head phone jack in the phones are well over a volt and more!
I use a ipod dock from Belkin and or a Bluetooth stereo receiver connected to the AUX input (Great for Streaming). This is the best and least distorted method of listening to the vintage equipment.

Hey Zeb,

Here's a question, as you've had me thinking about the gain issue. So I've been looking for some time at a Teac CD-P650, as it's attractively priced right now, and also has a USB input and internal DAC for iDevices. However, I noted in its specs that it has a 2V output! Yikes!

I mean I know CD outputs are hot compared to Casettes, but wouldn't a 2V output from a CD player have the same issues as a 1V output from the iPhone, or is the quality of the signal fundamentally different?

 

[zebulon1]

I think you use the proprietary cable, plunging it into the USB. This is different than using the head phone jack on the iPod.
I'm not sure where you are seeing that in the spec's.

 

[ScooterMcTav]

http://www.teac.com/product/cd-p650/specifications/

So even if using the USB on the CD player (or even using the CD player to play a CD), it's analog signal to the receiver is at 2V!

Found this discussed on a different forum (SH) where they suggest either adding an attenuator to the signal between the CD player and the input, or finding a vintage CD player (Sony multi-disc suggested) that has a volume pot that controls its output level. Came with a very good waveform analysis showing dynamic peaks on too hot a signal clip. With voltage attenuated down to 500mV-1V, the clips disappeared.