No input caps on Charlize

[Radian]

Hello folks,

I found this post from LeoK at the Klipsch forum.
He has build a Tripath amp without the input caps.
His amp is called the Waltham Integration. He send me the full schematic on request.
My question to the experienced amoung you is,
can this mod be done to the Charlize (TA2020)?

Here is his description of the mod:


Posted by leok ( A ) on May 03, 2002 at 02:40:20

I have designed, produced, and distributed (including a few sales) a small stereo amplifier based on the Tripath TA1101B. My design is taken directly from the Tripath application scematic in the TA1101 data sheet. I have made one very important change in the input, and learned a few things about which components should be optimized.
My application is driving Klipsch Forte, RB-5, and RF-7 loudspeakers. I generally use a fraction of a watt .. never more than two or three Watts. I have done some work with tubes: currently I have a design that uses KT66s, PP, triode, no feedback. The tube amp is nice, but the Tripath is very very nice.

The input:
see Tripath's TA1101B Data Sheet:
"Application/Test Circuit" at Tripath.com
There is a 2.2uF electrolytic (C1) on each input because the input amp is biased at something like 2.5V. That cap has a huge impact on the sound. To get rid of it:
Observe static electricity protection rules. Until this circuit is complete, the Tripath input is floating and very vulnerable.
1) Use a floating, non grounded, 12V power supply. They are readily available.
2) Isolate audio input ground from the 12V ground and connect it directly to the TA1101B-pin 14.
3) Connect the audio signal directly to the resistors: R1. Now the audio is connected differentially to the input amps.
4) Bypass the audio ground (now connected to pin 14) to the circuit 12V ground. I use a 22uF electrolytic and 0.1uF ceramic. + connects to the audio ground. This step limits common mode noise which otherwise totally swamps the input circuit.
5) Insert a 7 or 8 volt zener diode between the audio and 12V grounds, cathode to audio gnd, to protect the chip input, esp pin 14.
6) Put big rf beads on all power, input, and speaker wires (you really should do this anyway with this amp). A single bead for each +/- pair is fine .. that's 5 beads total.
That's it. it makes a BIG difference.
Other tips:
1) rf beads (I already said it, but it's important).
2) nice 1.5 amp torroid output inductors
3) nice (mylar or better) output caps. I use .22uF because my speakers
are 8 Ohms.
4) nice 2200 uF electrolytics for VDD1/2 instead of 180uF

[BWRX]

This mod can be done to any of the Tripath chips that have access to the non inverting input pin of the input op amps. Just make sure your souce ground is completely floating. You will need good bypassing from the non inverting input to power ground otherwise you will get noise. Doing this will also have an effect the DC offset on the outputs.

[Pano]

Originally posted by BWRX
Doing this will also have an effect the DC offset on the outputs.

Yes it will. For the brave only.

A high qaulity film cap in that spot is a good idea.

[Radian]

Thanks guys,

Yes it will. For the brave only.

Why do you think so? Is it brave to run the amp like that?
Leo sold a few of those amps and they seem to work fine.
I really would like to implement the mod on my bords for the TA2020.
I also want to run the chip with a clean external 5V supply. Do you think the sound would benefit enough to do it.
I would really appreciate it if you guys could take a look at my bord. Please tell me what you would do different.

Thanks, Klaus

[surya]

Hi

I read somewhere to remove input caps you must connect the source ground to biascap pin.
The bias cap itself connect to GND.
Do I have to remove the bias cap or simply solder the ground source to the cap ?

thanks b4

[Lostcause]

Hi Surya, you just need to connect the source ground to the pin or if that's too fiddly then the pin side of the bias cap.
DO NOT REMOVE THE BIAS CAP.
Also, you need to ensure that the source and the amp are running on seperate (isolated) power sources.
Generally this means that you must run one or the other off a battery.

[surya]

Hi Lostcause,

Thanks for the info

Any tweak suggestion to improve this little amp ?

Surya

[Lostcause]

No problem.

Not much to do with Charlize, she doesn't require much tweaking at all.
Direct coupling without input caps was the one mod that made a big difference to me.
If you dont have the air coils then that is a worthwhile mod... but I did change mine to toroids..... just my preference

Cheers
Lee