Potentiometer

[locky]

Hi Jan,
Could you give me a few pointers regarding adding a potnetiometer to the AMP1, ie... Is this possible? Where should it fit into the circuit? What capacity would work best?
Thanks!
Dave L

[tom]

Hi,
maybe this could give you a little advice:
http://www.dact.com/html/passive_preamp.html

Tom

[mleghorn]

I have the same question. Tom, your response suggests the use of a passive pre-amp, in the form of a low impedance volume control. However, I noticed that on the Tripath site, the TA2022 chip is designated as an integrated amp. Does this mean that there is a pre-amp and an amp on the chip, and a volume control can be inserted between the pre-amp and the amp? If so, that would be an ideal solution for me.

I’ve become very interested in the Tripath amps because I recently bought the Sonic Impact T-amp (for $30!) and upgraded with a better volume control and connectors, and was amazed by the sound quality. If a small $30, 5 watt amp sounds this good, I wonder how good their “bigger” amps sound. The chip that comes with the T-amp is also designated as an integrated amp on the Tripath site.

Thanks,

Mike

[tom]

Hi mleghorn
That`s a very interesting question cause I am going to use my AMP3 also only with a volume pot. Maybe Jan could say something about that.

Tom

[Jan]

Hi,

In the Tripath chips there is an analogue input section that is an opamp. The signal input resistor and feedback resistor are external on most chips, including the TA2022 but not on all Tripath chips. The outputs from this opamp is not available, other than the feedback path. So for volume you would normally have either a plain pot or an additional separate preamp. The advantage of a separate preamp would be more flexibility, possibly adding tone controlls, and possibly protection of the Tripath chip from what users can do on the inputs. An other advantage with a separate preamp is that you can implement inputs with different sensitivities; inputs from different source levels, even low level signals like phono or microphones, having more or less the same output plevel to the power amp.

As the feedback/inpt resistors are external, you can adjust the input gain; increase it a bit for compensating the loss in a pot or decrease it a bit if you have a preamp with a high output level. In the kits there are few extra resistors included so you can adjust the gain. Also for the TA2022 the power stage gain can be adjusted with external resistors. You should be able to find a suitable sensitivity for any active sound source, like CD player, computer sound card, MP3 player etc, with just a pot for the volume.

I have written elsewhere about how to select the gain/sensitivity of the amp. Optimally, the input stage sould be adjusted to have an output signal that is maximum 4V ptp while the main stage gain should be adjusted so that maximum input signal gives an output voltage to the speakers that is close to the supply rail voltage.

If you need other resistor values and have a supplier that provides 0805 size SMD resistors in small quantity, get some low noice thin film or metal film resitors and try to find values where the amps is clipping a bit when your volume is at maximum. Or let me know when you order a kit and I may be able to provide these as a bonus. If you order them separately, I'd have to charge shipping.

As far as I understand the term Integrated Amp, as used by Tripath, it is referring to the integration of input/modulation/output transistors in one chip. This in contrast to some other Tripath chips where the input / modulator is in one chip, while the MOSFET driver is in a separate chip, and for the highest power versions, also the MOSFETs are external. So it's not an integrated amp in the conventional system sense.