THAT 1510/1512 preamp chips

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Amo Audio

Member
Joined
Apr 12, 2005
Messages
24
Location
Vancouver, BC
I just stumbled on these on the web and I'm now interested in replacing the SSM2017's on my TLA compressor's mic pres with these to try them out.

Here's the site

The site says if possible to choose the 1512 because it has better specs, but I'm not sure which is an appropriate replacement for the SSM2017 in this case... The only difference I can see on their site between the two chips is the "Gain Equation" secion (which I'm not smart enough to understand...)

Anybody able to shed some light on this for me? Any other mods or upgrades that come to mind would be very much appreciated as well! I'm going to leave 1 channel untouched at first so I can A/B the upgrades.

Here's the TLA schematic. In case it helps, you'll find the chips-to-be-swapped at IC1 and IC3 on page 3 of the pdf.


Thanks!! :thumb:
 
I've done one channel in an old German Behringer PreQ. I haven't had time to sort out all the issues the box had, (gotta get my tracing happening) but the That 1510 combined with some other mods raised by Rossi has given the circuit balls. Again.... do a search.
 
I tried searching before I posted here, and I tried for a while after as well, but I can't find anything on these chips in the forum... Am I blind?

Where'd you get your 1510's? I'm having a hard time finding a place that sells them in small orders (I need only 2 of them...)
 
Thanks so much mediatechnology for the info. It will be used for the mic and line inputs of the TLA, but I'm not too worried about a little more noise. Is there anything else that might go wrong with using the 1510 in a mic/line circuit? The gain resistor is 5k indented, will I have to change this do you think so that the indent is at unity (0db when in line mode)? I'll probly go ahead and order some from you!

Thanks again.
 
Ah yes, thanks for all the invaluable info! I'll be placing my order shortly! Can't wait to see how much of a difference this mod will make. I'll post some audio when I get around to it. I'm also going to be replacing the output IC's and next i'll replace the more important caps as you suggested.

Do you know a specific brand/type of cap that would be considered "the best". Anything to steer me in the right direction would be much appreciated.

This is my first real DIY attempt and I've already learned so much!
 
> the "Gain Equation" secion (which I'm not smart enough to understand...)

Break it down.

You know that Gain, Av, for a Mike Amp is normally large. Rarely less than 20dB which is Av=10, sometimes as much as 60dB which is Av=1,000.

See that "1+"? Forget it! If you want a gain of 1,000, who cares if it is really 1,000 or 1,001? Even at Av=10, Av=11 is "same-as for all practical purpose".

Then the equation is 10K/Rg. Lookit Fig 2, Basic Circuit. Rg is a resistor you tie to two pins RG1 and RG2. If you want a fixed gain, you figure it.

For Av=1,000, you find a number Rg which makes 10K/Rg= 1,000.

Try, oh, say, "1". 10K/1 is 10,000 which is more gain than you want. Try "10". 10K/10= 1,000, what you want. Rg is a 10 ohm resistor.

Now figure Av=10. Turns out that 10K/1000= 10, Rg should be a 1,000 ohm or 1K resistor.

A little further fooling says for Av=100=40dB, you want Rg= 100 ohms.

So for a 20dB/40dB/60dB gain control, you need a variable resistor that is 10 ohms at one end, 100 ohms in the middle, and 1,000 ohms at the other end. A linear 1K resistor is good at one extreme. At the other extreme, resistance goes (nearly) to zero, gain goes to infinity, which is not nice; but we can stick a 10 ohm fixed resistor in series and get 1,010-10 ohms. Problem: the middle of a 1K linear pot is 500 ohms, or 510 ohms with the 10 ohm fixed resistor, and we wanted 100 ohms. Answer: "audio taper" pots give about 10%-20% resistance in the middle, instead of linear 50%. So we get total 110 or 210 ohms in the middle, tolerably close to our 100 ohm goal. However, to get the knob "turning the right way", it has to be a reverse audio taper.

As for the difference between 1510 and 1512... 1512 has half the gain. Or: we need an Rg of half the value for the same gain. At very high gain, that actually increases distortion (but it is all point-oh-oh stuff). At low gain, the very large Rg values needed, like 1K, become smaller, like 500 ohms, which reduces noise. However, the 60dB gain needs Rg=5 ohms, an uncomfortably low value. The stray resistance of many common pots is higher than 5 ohms already, and very unpredictable.

I think to get full high-gain use of 1512, you need Custom Pots. If you are needing 40dB-0dB, the 1512 is a clear winner; if you need 60dB-20dB, the 1510 may be easier to harness. (You certainly need Custom Pots to get more than about 40dB of range on one pot. I have "60dB gain trims" but the end is too twitchy to use.)

I wonder how they call this a "tube compressor".
 
Thanks PRR for the info. I'm fairly new to electronics and DIY so I really appreciate you explaining that for me.

[quote author="PRR"]I wonder how they call this a "tube compressor".[/quote]

:shock: How dare you!

Actually yes I have heard this said about this unit before and to make matters worse, silk-screened on the front panel is "dual valve pre-amplifier/compressor" which is even more ridiculous seeing as though the preamp has absolutely nothing to do with any "valves" (as far as I can tell). I knew this before I bought the unit however and didn't pay anything close to the inflated price TLA is asking for it.

I'd used the C1 before and I bought it because I quite like how it compresses. Although the sound of the unit is a little "hazy" it is my go-to box for certain sources. I hope the mods I'm planning for the box can remove the slight hazyness that I've had to live with up till now when using this compressor so perhaps I can go to it more often.

having said that, do you know what the tube is actually doing in the circuit (if anything)? Is it just thrown in there so they can write "valve" on the faceplate, or does it actually perform some meaningful task in the design?
 

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