Modding Pre-Amp Board on MTX TA81001D...

[HsOffRoad]

I just picked up a pair of MTX Thunder TA81001D amps, and according to the engineers at MTX there is no way to disable the subsonic filter or bypass the built in EQ in the pre-amp board (which is a crock). The TA92001, TE4001, and TE1501 units all have a button to bypass all of this garbage, but no such button exists on the TA81001. If you take the pre-amp board out, you can clearly see a spot on the board for the bypass switch - Labeled as "S102". MTX refuses to give me a schematic or instructions on what needs to be jumpered, removed, etc. to
eliminate the EQ and Subsonic filter pieces. I'm about to tear into it myself, but figured I would ask here first. If anyone has experiencing modding these out, or access to to schematics for the TA92001, TE4001, or TE1501 pre-amp boards, It would be most appreciated.

Thanks Guys,

Hans

[I Am An Idiot]

You say you can clearly see S102. Is this just the white silk screen, or can you see the traces and holes to mount the switch to? If there are traces and mounting holes, are there any jumpers or traces connecting any switch terminal to any other switch terminal?

[Perry Babin]

I agree with IAAI. Try that first.

I tried bypassing the preamp board on a 4601 and it was not happy with the high frequency signals. With driven full range, the amp drew excessive current even without a load. The current draw increased when loaded. In the newer amplifiers, there may be a circuit mod that allows you to bypass the crossovers without damaging the amplifier. I believe that the 4601 would self destruct if I ran it like this for any significant period of time.

When driven from the subwoofer output of the head unit, it didn't draw excessive as it did with the full range signal. It essentially performed normally (but with significanly lower gain -- a 2v head unit could not drive it to full power).

If you try this, do NOT run it higher than 100Hz. If you do, you run the risk of destroying the amp. Sometimes, when these amps fail, they do so dramatically (melted aluminum and severely charred fiberglass).

The following image shows the jumper positions I used on the 4601. These may not correspond to the same connections for your amp. Doing this on your amp may cause it to fail.

http://www.bcae1.com/IMG_3478b.jpg

If you try this, insert a 15 or 20 amp fuse in the B+ line feeding your amplifier. If there is a problem, the small fuse may help prevent damage to your amp.

[ppia600]

I understand the bypassing the subsonic filter part.. but why are you wanting to bypass the eq, are you talking about the crossover or bass boost? I wouldn't think the ouput design of this amp would be designed to play high frequencies. Just curious.

[Nick Tanner]

I saw that OffRoad (I think that was his name) may have the schematics for the 801 D. If so, I REALLY need them.

My email is: ntanner@wavecable.com

Thank you SO much if you can provide this. In particular, I need to know what size capacitor goes in the C19 spot on the board.

Thank you,

Nick

[Perry Babin]

You should start a new thread or ask a moderator to move this.

I have photos of the 801d but the capacitors are covering the circuit board designations. If you can tell me where it is, I'll see if I can read its value in the photo.

[I Am An Idiot]

Hey Perry, what's the matter with your picture software? Just a couple weeks ago you removed a clamp to expose the transistors beneath it. But you can't remove a cap to read the silk screen on the board? I am Soooo disappointed.