Nuuk Buffered Passive Preamp Issue

[Nuuk]

Be very interested to see what you think.

You may have to wait a while Phil as my T-Amp audition is for a review I will be writing 'elsewhere'!

For now suffice to say that for the money, and given the quality of pot and input caps, it's not bad! 😉

 

[dsavitsk]

Would a lower value of R3 reduce brightness or would that be very system dependant.

A good quality carbon film instead of a metal film in R4 (and/or as an input resistor if you use one) may also tame some brightness/harshness. Try either a Riken or a Kiwamee.

-d

 

[Hara]

Whats the series resistor and attenuator (12 step) values using this buffer and the t-amp charlize? I'm also curious of the calculation work. According to the data sheets the gain on the TA2020 is...

TA2020 Amplifier Gain
The gain of the TA2020-020 is set by the ratio of two external resistors,
RI and RF, and is given by the following formula:

V_O/V_I = -12 * (R_f / R_I)

where VI is the input signal level and VO is the differential output signal
level across the speaker.

I'm not sure of the values on the board. So what would be the gain of the charlize and the preamp?

Also, the R at the end of some resistor values is just plain Ohms right?

Thanks

 

[Nuuk]

Hara, if my memory serves me correctly, Charlize has input and feedback resistors of around 20K. This would give a gain of -12db.

The gain of the three-transistor buffer is unity, ie 1, so you don't increase the gain (of the system) by using the buffer.

Now, a slight problem. Those that have tried the buffer will tell you that there is some DC on the input. This manifests itself as a click when you adjust the attenuator. With a 10K attenuator, the clicks are very small and I can easily live with them.

If however, you need to use a higher value attenuator, as you may for instance if you use a NOS DAC like the Monica2 or DacKit, then these noises are a bit louder.

I used a 25K attenuator, and again I was prepared to live with the clicks rather than add another capacitor between the attenuator and input of the buffer (which cures the problem).

I have since moved on to use Pedja's discrete Jfet buffer and more laterly, my valve pre-amp. (BTW Audiodigit tell me their valve pre for the class-T amps, and their class-T/valve integrated amp, should be available around Christmas time).

While we are on this subject, I have found that the relationship of gain in the pre and power power amps does affect the presentation of the sound. I'm still experimenting to find the best combination (if there is one) but I am convinced it lies somewhere between the extremes. Does anybody else have experience of this phenomenon?

 

[Hara]

Yeah I'm going to have to experiment with those different pre's a lot of them look simple and do-able.

Thats good info about the clicking noise! Thanks

I checked out the site for the valve pre's, they look really nice.

http://www.autocostruire.com/catalo...d=267&osCsid=79a38dcec0dceada6ec68764e7129487

 

[Nuuk]

I checked out the site for the valve pre's, they look really nice.

They do! The reason for the delay is that they want to get them 'perfect' and it's good to hear that from a supplier who is obviously putting quality before commercial interests (although the two are (or should be) linked!). 😉

 

[Andypairo]

I have since moved on to use Pedja's discrete Jfet buffer and more laterly, my valve pre-amp.

Hello Nuuk,
can you post more details about it? Or it is just the buffer for the VBIGC?

Cheers

Andrea

 

[Nuuk]

can you post more details about it? Or it is just the buffer for the VBIGC?

Anything to oblige Andrea (well we are nearly in the festive season). 😉

Full details here . Next job is too build a DC supply for the heaters as I have a small amount of hum. Gain is probalby too high as it is but I'm not sure how to reduce it!

Yeo also has a few interesting designs on his site!

 

[carlosfm]

While we are on this subject, I have found that the relationship of gain in the pre and power power amps does affect the presentation of the sound. I'm still experimenting to find the best combination (if there is one) but I am convinced it lies somewhere between the extremes. Does anybody else have experience of this phenomenon?

I definitely prefer to have some gain on the preamp.
Between 2 and 3x gain.
LM power amp chips at gains up to 22x, no more.
They sound better IMO at lower gains.
I use ~20x gain with the LM3886, 2.8x gain on the pre.
Always use the power amp on the lowest gain range and use the rest of the gain you need on the pre.
The pre is usually (or should be IMO) higher bandwidth, lower noise. It's advantageous to use some of the needed gain here.

 

[Nuuk]

I definitely prefer to have some gain on the preamp.

I thought that question would wake you up Carlos! 😀

Have you ever tried varying the gain on both pre and power to see what happens?

From what I have tried so far, the higher the gain on the pre compared to the power amp, the 'nearer' the sound is to the listening position. And the imaging seems larger too.

 

[carlosfm]

I thought that question would wake you up Carlos! 😀

Have you ever tried varying the gain on both pre and power to see what happens?

Yes, I had more gain on the power amp, and also on the pre.
There's a point where the volume control becomes too sensitive and you know you have too much gain for your speakers' sensitivity.
I settled on this overall gain because it matches my speakers well, and the power amp sounds better at lower gains, with a some help from the pre.
The point I was making it that it sounds better to have gain on the pre ('normal' gains are between 2 and 3, but it can be higher) , not just a buffer, and lower gain on the power amp.

From what I have tried so far, the higher the gain on the pre compared to the power amp, the 'nearer' the sound is to the listening position. And the imaging seems larger too.

I have better imaging with my pre/power than any other integrated amp I made, either with 'passive' pre or with buffers.
Give the pre a more important role, it pays

 

[Nuuk]

The point I was making it that it sounds better to have gain on the pre ('normal' gains are between 2 and 3, but it can be higher) , not just a buffer, and lower gain on the power amp.

Yes, I agree, it pays to have some gain in the pre!