• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Can Someone Model This --- RIAA Curve

jheu02

jheu02

AK Subscriber
Subscriber
I have the scat for the phono section of a Scott A-436 I've restored to give to my brother. He's gotten back into vinyl, so I'd like to make it have the best curve possible. So, if anyone can model this for me and see how close it is and whether component values could be changed to make it closer it would be VERY much appreciated. The Qs have already been replaced by matched KSC1845Fs (around 425hfe if that matters). Signal path caps have been replaced by UKL series. Current board pic with replaced components and then scat. SM states +1 / -3dB for the RIAA curve, 60dB S/N, 47K input impedence.

index.php


Scott Phono Scat.jpg
 
Last edited:
Register to hide this ad
It would make a lot more sense and would give you much better performance to buy an outboard pre, such as the Schiit Mani.

A Daewoo will never be a Porsche.....
 
I see what you're saying, but that's not the point. I brought this back from the land of dead amps. So, I just want it to be this. He's just got a basic TT and some BPC right now, so this will definitely be an improvement. If I can make it even better, all the more so. And to your analogy, a Porsche can only shine on the autobahn. If it's restricted to city speeds, it's just another car.
 
does this have a selectable tape head / phono EQ? There appear to be 2 sets of components there for an EQ curve. Tape head / phono makes sense but just confirming. Also assuming they connect to the output of the amp via a switch to select which set of bits is involved?

Most likely the 2 caps and 2 resistors are your RIAA stuff, the single cap and resistor are for tape head. I forget the turnover points but if I remember right RIAA has 2, NAB has 1.
 
gadget73 said:
does this have a selectable tape head / phono EQ? There appear to be 2 sets of components there for an EQ curve. Tape head / phono makes sense but just confirming. Also assuming they connect to the output of the amp via a switch to select which set of bits is involved?

Most likely the 2 caps and 2 resistors are your RIAA stuff, the single cap and resistor are for tape head. I forget the turnover points but if I remember right RIAA has 2, NAB has 1.
Click to expand...
I don't believe so, but not at the computer to check the SM. Will look later.

EDIT:
I don't see evidence of "tape head", though there is a DIN connector on the back panel. No switch for selecting between tape/phono.
 
Last edited:
jheu02 said:
I see what you're saying, but that's not the point. I brought this back from the land of dead amps. So, I just want it to be this. He's just got a basic TT and some BPC right now, so this will definitely be an improvement. If I can make it even better, all the more so. And to your analogy, a Porsche can only shine on the autobahn. If it's restricted to city speeds, it's just another car.
Click to expand...
Fair, that's a good point, but then just leave it be.
 
ivandezande said:
Fair, that's a good point, but then just leave it be.
Click to expand...

I will, IF there's nothing more that can be squeezed from the basic design. But since Scott farmed this out to Korea (which at the time wasn't quite to the standards of MIJ), bean counters are notorious for skimping on parts, and I saw no evidence of specific attempts to optimize signal path with LL caps etc, that's what I've focused on after getting it running again. Rebuild thread here. I know it will never be on par with TOTL from other manufacturers, but it's in the sweet spot at 42WPC, it has meters(!), a silver face, and rack handles. I'll most likely also give him the pair of Avid 100s it's currently driving.
 
Assuming I've read the schematic correctly, and it's more than a bit fuzzy, the response is pretty good. I wouldn't mess with it. I do always check my RIAA circuits with a physical inverse network, just as shown in the model. (edit- can't seem to upload a better image but response is within plus/minus 0.5 dB)
ScottRIAA_2.jpg
 
Last edited:
ConradH said:
Assuming I've read the schematic correctly, and it's more than a bit fuzzy, the response is pretty good. I wouldn't mess with it. I do always check my RIAA circuits with a physical inverse network, just as shown in the model. (edit- can't seem to upload a better image but response is within plus/minus 0.5 dB)
View attachment 2550380
Click to expand...
Your image is even more than a bit fuzzy. Maybe post the circuit and the results separately?
 
Thanks for going to the trouble. It sounds pretty good, and with this confirmation, I guess there's nothing more to be gained. So, now to schedule a trip to deliver the goods. :music:
 
In case you're curious, based on the formulas published by Stanley Lipshitz, the Scott network works out to a 41 Hz bass shelf, 2,192 Hz treble cut and 496 Hz turnover/bass boost. RIAA standard is 50 Hz, 2,122 Hz and 500 Hz respectively. Hagerman's reverse network works out to 50 Hz, 2,095 Hz and 510 Hz.

In reality close enough is good enough by the time you factor in other variables such as loudness taps, tone controls, speaker frequency response and room acoustics.
 
Great community here. Thanks for all the interest in helping out a fellow AKer in not only resurrecting, but even bettering a piece of gear that was destined for the dump.
 
It is now. Did you take a look at how they were when I started?

I'm now in the process of putting new grill cloth on the Avids. They were pretty rough when I found them, and haven't done anything for the grills til now since I'll be giving them along with the amp and tuner.
IMG_20220427_103342190.jpg
 
You must log in or register to reply here.
Back
Top Bottom