Setting up TA2020 kit for use with Valve pre-amp - diyAudio
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Old 3rd September 2005, 11:58 AM   #1
johnm is offline johnm  United Kingdom
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Default Setting up TA2020 kit for use with Valve pre-amp

Hi everyone!

Just received the TA2020 kit from Autocostruire.

I'm going to set it up as a power-amp, and wish to use it with my Ming da MC-7R valve pre-amp. However I'm in the dark as to which resistor combinations to use to correctly set the gain/feedback on the TA2020 board.

The pre-amp puts out from 100mv-22v depending on volume pot position. The output inpendence of the pre-amp is 100k.

The Autocostruire manual lists the following combinations to set gain on the TA2020 board:

Rin / Rf gain dB
20k 68k 40.8 32.2dB
20k 36k 21.6 26.7dB
20k 20k 12 21.6dB
47k 10k 2.55 8.14dB
120k 10k 1 0dB

Does anyone know which I should select, and how is this worked out?

Cheers!

- John
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Old 3rd September 2005, 02:09 PM   #2
ac2005 is offline ac2005  Hong Kong
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I am also using a tube pre for my Autocontruire TA2020 too. It seems that 20k + 20k combination is the best. With this setting, you can turn the volume pot over 9 o'clock position for a normal listening volume. The gain of the stock setting is just too high if you have a pre. You can only turn you volume pot to 7-8 o'clock and people say it sounds bad if the volume pot is below 9 o'clock position.
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Old 3rd September 2005, 06:14 PM   #3
johnm is offline johnm  United Kingdom
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Thanks! I'll give this a go tomorrow and report back!

Cheers,

- John
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Old 4th September 2005, 06:00 AM   #4
garbage is offline garbage  Singapore
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regarding the gain of the ta2020 chip, i am using one such kit, but not from Autocontruire. the gain resistors are the usual 20k/20k as specified in the tripath datasheet.

i found that the gain is very low when used with my 1545a non oversampling dac with passive i/v conversion. my speakers are 93db and i ran the ta2020 with a 12v sla battery.

input volume pot is a 100k alps black beauty. i had to go over 2o'clock for relative loud levels. this is in a room that is medium sized (approximately 7m x 6m, not exact figures). the speakers are slightly more than 3m apart, measured from the insides of the speakers.
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Old 4th September 2005, 06:18 PM   #5
ac2005 is offline ac2005  Hong Kong
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The gain is low coz you don't have a pre. A typical pre normally has a gain of around 10.
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Old 6th September 2005, 08:45 PM   #6
Nuuk is offline Nuuk  United Kingdom
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Quote:
i found that the gain is very low when used with my 1545a non oversampling dac with passive i/v conversion. my speakers are 93db and i ran the ta2020 with a 12v sla battery.
Garbage, am I correct in thinking that your DAC comes from 'just up the road in KL'? If so, I have found exactly the same thing. The output of the 1545 is quite low, and with the low gain of the amp, it's just not enough, even with quite efficient speakers (which I have here).

In fact, I discussed this with the supplier and they agree that a pre-amp with some gain is the solution. They didn't like the idea of increasing the gain of the 2020 (more gain equals more noise) but I have to say that my experience with the 'other 2020' amp that came with a lot more gain was that noise wasn't really a problem.

So, it's either more gain in the power amp, or another stage (pre-amp) with a bit of gain. I have just built a pre-amp with a gain of 3 specifically to use with the 1545 DAC.
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Old 6th September 2005, 09:01 PM   #7
johnm is offline johnm  United Kingdom
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Hi guys.

Just finished building my TA2020 kit - very very pleased with the sound at present, though for the first 4-5 hours it sounded pretty awful!

Using the 20k + 20k resistor combination as input in the TA2020, volume is nearly unbearable barely a quarter of the way around the volume control on the Ming Da MC7R. Obviously I need to change the input resistors again. Next values down on the instruction sheet are 47k (Rin) and 10k (Rf), giving 2.55 gain. Worth giving these a go or can anyone else recommend a more appropriate 'tailor-made' combo for the MC-7R?

The Ming Da does seem to have more gain than usual with x10 - usual value is around x3!!

Cheers,

- John
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Old 6th September 2005, 09:08 PM   #8
Nuuk is offline Nuuk  United Kingdom
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John, my valve pre-amp has so much gain that the last power amp I tried it with only allowed me to use the first couple of steps of the attenuator before it became too loud. I am yet to try it with a class-T amp!

If you don't want to keep changing the resistors (and it can be a bit of a pain with those double sided solder pads), you could try making up a simple voltage divider to put between the pre-amp and 2020. When you find the right amount of attenuation, you can then work out which resistors to put in the 2020.

I'm not sure which values to use in the voltage divider. Perhaps somebodyelse can suggest something for you.
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Old 7th September 2005, 12:45 AM   #9
garbage is offline garbage  Singapore
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Quote:
Originally posted by Nuuk


Garbage, am I correct in thinking that your DAC comes from 'just up the road in KL'? If so, I have found exactly the same thing. The output of the 1545 is quite low, and with the low gain of the amp, it's just not enough, even with quite efficient speakers (which I have here).

In fact, I discussed this with the supplier and they agree that a pre-amp with some gain is the solution. They didn't like the idea of increasing the gain of the 2020 (more gain equals more noise) but I have to say that my experience with the 'other 2020' amp that came with a lot more gain was that noise wasn't really a problem.

So, it's either more gain in the power amp, or another stage (pre-amp) with a bit of gain. I have just built a pre-amp with a gain of 3 specifically to use with the 1545 DAC.
hi Nuuk

yes, the boards came from there.

i just soldered in 39k resistors at Rf of the 2020. have not listened to it yet as it was late (did not want to wake others up).

cheers
garbage
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Old 7th September 2005, 03:02 AM   #10
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hi all

this is yeo from diyparadise.

thx for the interest in monica and charlize.

yes, output from monica is lower than conventional dacs so in some systems, a gain stage is mandatory. i said some as lots of amps out there need only 100mv for full power!

that said, if a gain stage is needed, i always advocate the gain stage in your current stage, usually your preamp. no point adding another gain stage to the detriment of your sonics.

as the gain of charlize, we feel really justified when this customer of ours who hv bought our charlize and various other "ta2020 kits" found that our charlize is of the lowest noise! (RFI, EMI, hiss)

anyway, we'll be working on a tube gain stage soon. it has to be really quiet though...

btw, when is the tnt review out?

donjuan
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