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SLO100 Capacitor Question

8/20/2000 11:04 AM
SLO100 Capacitor Question
Hello all,  
I am preparing to build a SLO clone and would like to know the actuil type of Mallory caps used in a real SLO100.  
I know the small value caps are ceramic. Are ceramics essential for the correct sound or can I use mica or polystyrene in place of these? Does the type make much difference? They are not used in too many places throughout the circuit.  
Thanks everyone  
8/20/2000 4:10 PM
frank #2
Hi Craig,  
In a slo 100 that i've seen, the coupling caps where the mallory PVC-400v types!  
The 22n has the number 412 stamped on the body!  
I would not use silver-mica in such a high-gain amp  
because it can make the high-end sound a bit to hash  
( just my 2 cents!!??!!)  
Good luck,  
Regards, Frank#2
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8/20/2000 4:26 PM

Ive built a SLO clone and Im very happy with it after some experimentation. First off, I tried the silver mica and it added a bit of hi end harshness so I used the ceramic disc and it added just the right amount of hi end with a bit of graininess to the sound. Also If your building off the schematic on the blue guitar site there are some errors on the schematic. If you want to look at a actual insides of a SLO, here is a site from a friend of mine.  
8/20/2000 9:12 PM
Craig D
Re: SLO100 mods
Thanks Mitch,  
I am aware of the errors from previous posts, but I have a question regarding the clean channel bright switch. I was looking at the schems for the X88R, which seems to have the SLO clean channel in it, and the 470pF bright cap is actually switched in parallel with the 470k resistor, not in place of it as shown in the SLO schem. Is this also an error in the SLO schem?  
Craig D
8/21/2000 9:07 PM
Rick Erickson

"the 470pF bright cap is actually switched in parallel with the 470k resistor, not in place of it as shown in the SLO schem. Is this also an error in the SLO schem?"
Yes it is. The 470K resistor should be in circuit at all times and the cap switched across it for bright as you noted.  
8/20/2000 6:20 PM
Joe L
Re: SLO100 Capacitor Question
No flames here Craig! Capacitors are cheap enough to grab a few types in each value and play around. And yes, they have a different sound depending on which type they are! The differences do depend on their position in the signal path with direct coupling being the most affected by type and bypassing of cathode or plate resistors being the least affected.  
For instance, that .001 bypassing the plate cap of the third SLO Lead channel. I tried poly, mica and ceramic and could hear no difference. However, the .0022 bypassing the 470K right before the Lead OD Volume pot is very dependant on type. A 500v ceramic here (higher voltage ceramics are a bit more linear and don't roll highs off as much) will blur the signal and roll off highs. It is not an unpleasant thing at all and tends to make the distortion a bit smoother.  
My recommendation is to use what is in the SLO which is 1000v ceramics for all capacitors valued .0022uF and less. Save the money and spend it on the best output transformer you can find.  
Now, to answer your question. The Poly type caps in the SLO are all Mallory PVC series which are Polyester/Foil types which are probably identical to the Sprague 418P series. The exception is the 1uF caps used in cathode bypass and the coupling to the effects loop. These are a type "MKT" Philips 1uF/250V. I have found a couple of these in a switching supply and they nothing special and can be substituted by any good polyester/polypropolene type. I use a CDE brand in this position with a Mouser Electronics part number of "5989-250V1.0".  
For the rest of the PVC types I just use Spraque 715Ps which are a tiny bit more hifi than the Mallory PVC series.  
Let us know if you have any further questions on the SLO. And watch the layout of that section around the second and third Lead gain stages. Keep them shielded and away from the input circuitry of V3 unless you want bleedover into the clean channel and tone uglies!  
..Joe L
8/20/2000 7:27 PM
Randall Aiken

Joe, you should post a link to your excellent SLO build and soundfiles. This is quality workmanship, folks!  
Randall Aiken
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