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Design of SLO preamp

2/21/2005 9:14 PM
Dan Design of SLO preamp
I have a question about the SLO schems floating around in that zip file. I have an SLO and Ive been helpin out a few guys who are interested in doin an SLO OD channel preamp. It gets a little wierd because the Normal channels stays active when the OD channel gain stages are added in. Theres that common input stage then the 1 normal channel gain stage is parallel to 2 OD channel gain stages then joining up at the tone stack (eliminating the tube buffered loop.) Now I dont think the active clean gain stage interacts that much since the clean/crunch switch, bright switch and normal volume control dont seem to cause more then an extremely subtle effect when you mess with them when using the OD channel. It looks to me like with the normal volumes turned all the way down the normal channel is out anyway and yet there is barely any effect to the tone of the OD channel. So would it be safe to assume I could eliminate that clean gain stage without any real change in the tone of that amp when just using the OD channel?
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2/22/2005 5:34 AM

I heard about people who did it, and they said the tone change was subtle. In my SLO clon if I use he OD channel and turn the clean channel volume all the way up I hear a diference, similar to turn a little the presence control up.  
I remember I had read somewhere in a question to Mike about it, he said that it would change the tone a little because the clean channel is in opposite phase and OD signal levels is mich higher.  
Hope it helps
2/23/2005 1:30 PM
Ian Anderson

Think of it this way - the Dual Recto is a knock-off of the SLO100 and it doesn't have the clean channel. That should give you an idea of the tone difference (ish).  
... Ian :)
2/23/2005 8:22 PM
But with the Normal channel volume all the way down whatever it is that normal gain stage was doing is off at that point right? I hear a difference but its not that great a difference. Isnt the 2 gian stages parallel to it on the OD side going to give you a signal thats huge in comparison?
2/24/2005 6:31 AM

1. The clean channel is in oppossite phase to the OD channel. The clean signal is very little in comparison, so with all the clean vol down, the difference will not be noticeable.  
2. Puting another opto in the path of the clean channel will help. Try it and use your ears. This is similar to the post that asks what will happen with the slo tone if the fx loop is removed. The answer is "try it and judge for yourself". There will be a change in the tone, but how much and how important is in your ears.  
2/24/2005 7:06 AM
Ive bypassed the Loop on my SLO to great effect but I havent installed a switch. Im not trying to mod my SLO to take out that out of phase stage when on the OD channel. I rather like what it does when the normal volume is turned up. My entire concern in this post revolves around that out of phase Normal channel gain stage since the preamp being designed will most likely leave it out which, also eliminating the loop, looks almost exactly like the high gain channel in the X88R. What Ian said concernes me but Im not sure whether too take it too seriously or not (no offense Ian) because of that fact that the parallel stages on the overdrive are so large by comparison that the one parallel out of phase Normal channel gain stage will have an extremely subtle effect which is pretty evident in the fact that messing with the normal volume causes a very subtle change in the OD sound, though a nice one. That small cut in bass can be acheived by other means right.  
So I guess my main concern Alex was to make sure Im not overlooking something in assuming that when on the OD channel, turning the volume all the way down on the Normal channel will sound the same as completely removing that out of phase Normal channel gain stage all together as it is in the X88R. If it is thats a change I can live with for the sake of this preamp design.  
Thanks for your help  

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