TIS 98 (comparison clips added)

[jnewlyn]

I've got my EPos-3 all torn apart and ready to swap out the TIS 58 for the TIS 98. But I need to know the difference between the Base/Emitter/Collector and Drain/Gate/Source. I have the pin out for the TIS 98 but need to know where the legs go. For example, would the 24 VDC be the Collector or Emitter? I'm pretty sure the guitar signal in, is the Base but that's all I know. I'll post the results in this thread once I get this.

Oh, and do I bias this the same way I did the TIS 58?

[jnewlyn]

CRAP. Tried both and this doesn't seem to work. There's no drive or gain going on. The only sound I get is like you'd get if you just barely cracked the volume pot on your guitar. Just a very quiet clean thing. No drive or volume. The other way is about the same except when you hit the strings real hard, you get a more clipped sound and it quickly just mutes out to nothing. Some ting wong. Where's GoodGuest?

[leadguy]

http://forum.metroamp.com/viewtopic.php?f=16&t=25988" onclick="window.open(this.href);return false;

Quotes from sosecho

"The input stage is almost exactly like stage q3 with the exception of the 1K emitter resistor which is instead 3.3K. The collector voltage is 14.3V with 20.8 on the 35uf cap."

"A note of interest might be that this is a echoplex with TIS98 input not TIS58 jfet and it has the compressor board. The compressor board was correctly installed after the record level pot, I don't know if this was done at the factory or by a tech. But the TIS98 input looks original."





So the TIS98 gets hooked up as above but with a 3.3k emitter resistor instead of the 1k emitter resistor up above, and then the output goes to the compressor board.



ie just change the above FET circuit to the above TIS98 circuit and use a 3.3k emitter resistor instead of a 1k emitter resistor.

It's all pretty straight forward I think.

When you had the TIS58 connected to the compressor and then got a lot of noise from the compressor, isn't right somehow.

Compressors are not that noisy.

So I would say there is still something wrong with the compressor part, maybe in power supply.

[jnewlyn]

It is. Already have the 3.3K resistor. In fact, it's a 5K trimmer so I can monkey with it. However, the above is also showing a 470K resistor at the input that bypasses the transistor, to the 22K at the VDC supply. This I don't have and probably need to try. Awesome post leadguy.

[Good Guest]

The collector resistor probably isn't the problem as it works with a wide range of values but follow the pinout correctly with the schematic........

Using a trimpot isn't really necessary the transistor should work flawlessly with the correct values...it's not as finicky as the FET in that regards...22k collector ...etc.


I think a lot of people are looking for too much gain and overdrive with these ep3 preamps.....they weren't designed as boosts and overdrives ..that's just the hypers and bottomfeeders trying to get $$$$ .Tone color, compression , 180 degree phase inversion, and a pre driver for the compressor that's pretty well all one should really expect..if you luck out tho and get a transistor that boosts more than others ..good on ya but doesn't necessarily mean EVH tone.

tis98Pinoutep.jpg (31.21 KiB) Viewed 1306 times

[jnewlyn]

OK, so some progress has been made here. I first had the Collector and Emitter reversed because I didn't realize that the Echoplex schematic was describing the pin out from the "bottom" view. So I got that OK now but the 470K resistor that connects the Base and Collector points, does have to be there or it doesn't work. I also had to dial the 5K trim pot on the emitter side all the way to 0 resistance just to realize a unity gain. It still does cut some just a hair when comparing it in bypass (at which only the MXR 6 band is in front of the amp) I am working with the voltage supply on the other side (25K trim pot instead of 22K resistor) and it seems when I go pretty low (4VDC) I get some gain increase. Not that I'm looking for boost but at the very least, the same as when it's bypassed like I mentioned.

More to come soon.

[Good Guest]

now but the 470K resistor that connects the Base and Collector points, does have to be there or it doesn't work. )

That resistor in this context or circuit can be referred to as the gain resistor ...the higher it goes ..so does the gain..the lower it goes so goes the gain..470k is a good choice.

[jnewlyn]

now but the 470K resistor that connects the Base and Collector points, does have to be there or it doesn't work. )

That resistor in this context or circuit can be referred to as the gain resistor ...the higher it goes ..so does the gain..the lower it goes so goes the gain..470k is a good choice.

You got it. And in doing so, I also tried a 1 meg in there and got just about dead nuts equal drive. Maybe a hair more but nothing of significance in terms of boost. Now that I've got this going, I find myself with a big smile when I play along with VH. Something about it seems to sound even better. I really like it. I don't really know how to explain it but it's just soothing even though it has all sorts of hair and rasp. Like more musical distortion. I think of thin light water boiling vs. a simmering thick soup. Both have heat and steam but the soup has some tasty, tonal flavor with creamy thickness.
OK, kind of a stupid analogy definitely an improvement to my ears. And this is without the compressor. Speaking of compressor. That's next but I'm gonna try and make a clip with just the transistor change for some A/B comparison.

[jnewlyn]

Since I've already done a clip with the TIS 58, I just did a short clip of the everything the exact same except for the transistor change. Both just short and bone dry for comparison. I might be losing it here but these are really really close. I think the TIS 98 sounds a little sweeter though. What do you guys think?

http://www.soundclick.com/bands/default ... ID=1214336" onclick="window.open(this.href);return false;

[rgorke]

James,

Sounds sweeter and smoother to my ears. Nicely done!

Roger

[uiovbged332]

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