My 2019 Update Thread - My final system I think.

[Gazjam]

Cheers Alan.

Did some housekeeping on it before plugging it in and leaving it to warm up.
Exposed fresh copper on the mains cable and fitted a new silver plated 13A plug with a decent fuse.
New speaker cable connections too, don’t think it’s been switched on in Months since it was tested as working in January.
So a couple of days before I make up my mind on it.

From first test at switch on though, quite different sounding than before, much better at the low end.
Which is what I was after, great.

Some pics:
Compared to the smaller amp from the 2nd system, showing the difference in size.
All about the power supply in the amp, in comparison a lot bigger and higher rated.


After a Bit of a clean up the amps almost like new, been lucky with this one.
Can tell its been well looked and was handed in as a Trade in.
An older amp though, so wanted to open it up and check for any swollen caps or brown outs on resistors.
Clean as a whistle, a good result.
Massive transformer, beefy power supply caps and the thing weigh’s a ton. Exactly what you’d want in a power amp.



Is this 10K uF rating indicative of a strong power output? I’ve read the amp can punt out a constant 30 amps.
Four internal glass fuses...Some room for improvement then.

Dual Mono construction, and able to bridge it to a monoblock with a lot more than it’s 130 watts in stereo mode.


Looks the biz in the system rack, sounding good so far, a big jump in quality particularly in the low end over its little brother the RB-971.
Just let it do its thing in the background for a couple of days then I’ll sit down for a proper listen.



So a good result so far, think it’s been a good punt!

I have had some experience of checking over the really hi-end Japanese amplifiers of yesteryear, they are quite impressive.
Also updating some of the phono amps with modern capacitors.

Good stuff Gaz

[Gazjam]

Hmnn..
Bit more background hiss than I’m used to.
Think the old gain structure with efficient speakers Scenario is kicking in.
My Pre has a valve input stage, wondering if I’m hearing tube noise...

Do Rothwell attenuators work to lower amp gain? Thinking -10dB or so.
Wondering if they affect Sound quality or just lower amp gain.

Anyone any direct experience of using ‘em to lower background hiss?

thanks.

[AJSki2fly]

Great looking amp, should do the business, these old beasts were well respected when new. I suspect your hiss may be coming from what’s in front of it, maybe time to do some front end swaps to try and find the cause , if you can.

[Puffin]

If the gain of both amps is the same you could bridge them and then the fun really starts! Any difference in WPC is irrelevant.

[Gazjam]

Front end swaps...you mean everything from the Preamp backwards Adrian?
Suspect its the Pre, as even with nothing connected Im still getting the hiss on all inputs, RCA and XLR.

Thats why I was thinking attenuators, reduce the gain between Pre and power.
Never had to tackle this before an interesting problem!

Great looking amp, should do the business, these old beasts were well respected when new. I suspect your hiss may be coming from what’s in front of it, maybe time to do some front end swaps to try and find the cause , if you can.

[Gazjam]

Cheers Rob,

So you saing if the gain in the same one channel wouldnt be quieter than the other given ones quite a lower watts per channel?
New to me this stuff!

If the gain of both amps is the same you could bridge them and then the fun really starts! Any difference in WPC is irrelevant.

[Ali Tait]

You using the PS Audio as a pre?

Does it not have adjustable gain?

[Gazjam]

Its a PS Audio Preamp I use Ali yeah,not the Dac as a digital volume straight into the power amp.

Volume at zero onPre still hiss, but of course gain and volume are different

[Firebottle]

Rather than use external attenuators why not reduce the gain of the amplifier itself?

Alter R651 and 652, 18K, I suggest tacking an additional 18K in parallel with each one.
Don't use in monoblock mode unless you do the same with R561.

[Gazjam]

Whoa...

way above my paygrade Alan!