Recommended diy Pre for T-amp

t.

Member
2003-05-26 1:35 am
notts
Hi,

I've recently built an Amp3 module
After reading various posts it seems the class-T amps sound best when used with an active pre.

Does anybody know of any diy design that suits these amps? tube or solid state, linedstage or buffered etc :)


Cheers!
 
t. said:
Hi,

I've recently built an Amp3 module
After reading various posts it seems the class-T amps sound best when used with an active pre.

Does anybody know of any diy design that suits these amps? tube or solid state, linedstage or buffered etc :)


Cheers!



I have been using a variation of a nice dc coupled discrete buffer. Look in the Solid State forum for either Tao buffer or eight part harmony.
The resistors in the output shown are sized for using it as a headphone amp. I use 80 - 90 ohms for low power draw (batteries) and 50 ohm for active supply. With 50 ohm resistors it runs at about 30 ma.
I have tried several, opamp and discrete, and this is the cleanest and most transparent so far. The frequency respsonse is way more than needed.

George
 

t.

Member
2003-05-26 1:35 am
notts
Re: Re: Recommended diy Pre for T-amp

Panelhead said:




I have been using a variation of a nice dc coupled discrete buffer. Look in the Solid State forum for either Tao buffer or eight part harmony.
The resistors in the output shown are sized for using it as a headphone amp. I use 80 - 90 ohms for low power draw (batteries) and 50 ohm for active supply. With 50 ohm resistors it runs at about 30 ma.
I have tried several, opamp and discrete, and this is the cleanest and most transparent so far. The frequency respsonse is way more than needed.

George

Thank you George:cool:

I'll check it out.
BTW these little T-amps are not bad at all really, I was pleasantly surprised.
I'm hoping to turn mine into a nice little amp, the Amp3 is currently being run by a 12v 7aH battery
 
Direct Coupling

t. said:
I guess its this one George http://www.diyaudio.com/forums/attachment.php?s=&postid=264145&stamp=1068704031

I need to find a suitable transformer:)
I'll now have a look to see if I can find the other parts


The input transformer is not needed, a 15 - 25K pot can be used for R1.
Used 70 ohm for R2, a 25 ohm between it and the lower transistor, and a 90 ohm resistor for R3.
Also built one with a 40 ohm, 20 ohm pot, and a 56 ohm resistor.
The pot allows for cancelling out dc. Just take the output off the wiper.

George
 

t.

Member
2003-05-26 1:35 am
notts
Re: Direct Coupling

Panelhead said:



The input transformer is not needed, a 15 - 25K pot can be used for R1.
Used 70 ohm for R2, a 25 ohm between it and the lower transistor, and a 90 ohm resistor for R3.
Also built one with a 40 ohm, 20 ohm pot, and a 56 ohm resistor.
The pot allows for cancelling out dc. Just take the output off the wiper.

George

Ok, Thanks again George:)
 
I had timing problems with the T-Amp on my 4Ohm 96dB speakers. By accident I found out that this can be fixed more or less by using a 100mA current limit. Somebody told me that this works as a compressor in first line. I didn`t have the timing problems with 8Ohm 96dB speakers. Probably I used the T-Amp at too low voltages with my 4Ohm speakers. Now I ask myself whether it is possible to use the T-Amp fully-driven and do the volume control with a double power-potentiometer at the output. One condition for that would be that there is constant impedance over the whole frequency range, and I think it is met with my Ciares. But it would also depend on the output filter of the T-Amp. Is it C or LC, and is the output filter within the feedback loop or outside?


Oliver
 
el`Ol said:
I had timing problems with the T-Amp on my 4Ohm 96dB speakers. By accident I found out that this can be fixed more or less by using a 100mA current limit. Somebody told me that this works as a compressor in first line. I didn`t have the timing problems with 8Ohm 96dB speakers. Probably I used the T-Amp at too low voltages with my 4Ohm speakers. Now I ask myself whether it is possible to use the T-Amp fully-driven and do the volume control with a double power-potentiometer at the output. One condition for that would be that there is constant impedance over the whole frequency range, and I think it is met with my Ciares. But it would also depend on the output filter of the T-Amp. Is it C or LC, and is the output filter within the feedback loop or outside?


Oliver


Could you elaborate on the 'timing problem'? Also, the T-amp in it's stock form is optimized for a 6 ohm load (based on the output capacitor filtering). If you know you'll be using 4ohm or 8ohm speakers, you may want to change the filter capacitors to the appropriate value. (check the other SI threads on here)
 
With "timing problems" I mean that everything sounds like moving a spoon in honey an rhythmical details are swallowed. This becomes especially evident with Jazz an Barocque music.

Another method of using a digital amp fully driven is adjusting the volume by changing the voltage for the output stage, like it is done in the Tact Millenium. Is this possible for the T-Amp?
 
Well, I haven't experienced your "timing" problem. Not sure where that might be coming from.

You can't adjust the T-amp by changing the rail voltages (that I'm aware of). The amp has a fixed gain, and works similarly to any standard amplifier.

If you haven't looked at all the mods, I would suggest trying them out to see if it helps your problems. There's a lot of room for improvement over the stock SI.

My speakers aren't all that efficient (only 90db 1w/1m or so), but the T-amp drives it very well and to levels that would probably annoy the neighbors. Perhaps your speakers are efficient enough that more of the switching harmonics are audible.