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VTA M-125 mono block kit.
VTA M-125 mono block kit.
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Old 12th November 2016, 04:03 PM   #1
wanders is offline wanders  United States
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Default VTA M-125 mono block kit.

I recently built the Tubes 4 Hifi Sp-14, 6SN7 preamp. (Didn't use the kit.) I'm pleased with the finished product and am now interested in the designers' VTA M-125 mono block kits. I'd appreciate hearing from anyone with experience and views on this product?
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Old 19th December 2016, 07:52 PM   #2
TurvenuijaFIN is offline TurvenuijaFIN  Finland
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This amplifier is interesting. Does anyone know circuit diagram components and their values?

I need only resistors values
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Old 19th December 2016, 10:27 PM   #3
petertub is offline petertub  Sweden
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VTA M-125 mono block kit.
Quote:
Originally Posted by TurvenuijaFIN View Post
This amplifier is interesting. Does anyone know circuit diagram components and their values?

I need only resistors values
Scematics and BOM is inkluded in the kit.
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Old 21st December 2016, 04:12 PM   #4
boatheelmusic is offline boatheelmusic  United States
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I've built the M-125s, a great amp. I found the kit to be very cost effective, especially when you consider that the transformers aren't available elsewhere or alone.
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Old 21st December 2016, 09:10 PM   #5
petertub is offline petertub  Sweden
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VTA M-125 mono block kit.
Quote:
Originally Posted by boatheelmusic View Post
I've built the M-125s, a great amp. I found the kit to be very cost effective, especially when you consider that the transformers aren't available elsewhere or alone.
Whoops, is that so ? Mk-6 ( dynacos 120w used a A-541 transformer or simular)
is'nt that available ?

If indeed the transformers are single-sourced , that is a big nono in my book ...
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Old 21st December 2016, 09:24 PM   #6
gabdx is offline gabdx  Canada
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Quote:
Originally Posted by wanders View Post
I recently built the Tubes 4 Hifi Sp-14, 6SN7 preamp. (Didn't use the kit.) I'm pleased with the finished product and am now interested in the designers' VTA M-125 mono block kits. I'd appreciate hearing from anyone with experience and views on this product?
Hey I built a modified version of the VTA with their MK-3 boards.

I have another unit with the M125 like driver and input.

I seriously do not think that one can improve the sound after this...

I had one issue with the feedback wire picking up AC filament and mains noise.

Except that it works flawlessly. I use only 2 x kt120 per side instead of 4x

I use 100 watts output transformers.

The input stage is very adequate, the bias points great.

The driver stage is a very hifi tube able to drive well a quad of kt120. and the LTP is very well designed.

If you improve that design the result will be marginal...

From the design the things that improved the circuit and the sound I would class in order of most important to least important in percentage:

1. Get the best 12BH7 tube possible with matched sections(70%)
One would think the constant current sink null any imperfections, but a well matched low distortion selected tube will clean up the sound with a dramatic effect on sound clarity.

2. Adjust feedback for your speakers, i suggest a little higher or lower feedback resistor and hear test it, nothing major. (15%)

3. Use film capacitors ( around 100uf ) in the power supply input/driver tubes. (10%) , makes the top end a little more detailed.

4. Get good input tube (5%) , hard to see any improvement

I could not hear any difference much with coupling capacitors as long as they are decent quality film.
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Old 2nd January 2017, 04:27 PM   #7
deepee99 is offline deepee99
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IMHO, the best value in audio today are the M-125 monoblocs. For not much effort you can build the kits yourself;or for another few hundred bucks VTA will build them for you. They are "plain Jane," all business so you're not paying 10 large for blue meters or somesuch. They will drive any speaker known to man, from Maggie IIs to Vandersteens to Tylers. Plus they have a great chat room (Basket). Bob Latino, who in conjunction with Roy Mottram at Tubdes4HiFi designed these amps and are a phone call away. The out-of-the-box components are very good and you can always add a few teaks for that extra 5 percent. I have had my M-125s about three years now and cannot imagine owning anything else. Wouldn't trade 'em straight across for the best Mac or ARC.
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Old 3rd January 2017, 04:18 PM   #8
deepee99 is offline deepee99
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Another advantage I neglected to mention is that the M-125s is that you have a choice of noval (12BH7A) driver boards, which come as standard equipment, or octal (6SN7) driver boards. Bob Latino favours the novals but many M-125 owners, including me, like the wider selection of 6SN7s.
Again, you can't go wrong with this amp.
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Old 3rd January 2017, 05:55 PM   #9
petertub is offline petertub  Sweden
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VTA M-125 mono block kit.
And M-125 already has an IEC input well !! No more broken or dangerous mains cable!
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Old 3rd January 2017, 10:49 PM   #10
dahlberg is offline dahlberg  Sweden
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Quote:
Originally Posted by gabdx View Post
Hey I built a modified version of the VTA with their MK-3 boards.

I have another unit with the M125 like driver and input.

I seriously do not think that one can improve the sound after this...

I had one issue with the feedback wire picking up AC filament and mains noise.

Except that it works flawlessly. I use only 2 x kt120 per side instead of 4x

I use 100 watts output transformers.

The input stage is very adequate, the bias points great.

The driver stage is a very hifi tube able to drive well a quad of kt120. and the LTP is very well designed.

If you improve that design the result will be marginal...

From the design the things that improved the circuit and the sound I would class in order of most important to least important in percentage:

1. Get the best 12BH7 tube possible with matched sections(70%)
One would think the constant current sink null any imperfections, but a well matched low distortion selected tube will clean up the sound with a dramatic effect on sound clarity.

2. Adjust feedback for your speakers, i suggest a little higher or lower feedback resistor and hear test it, nothing major. (15%)

3. Use film capacitors ( around 100uf ) in the power supply input/driver tubes. (10%) , makes the top end a little more detailed.

4. Get good input tube (5%) , hard to see any improvement

I could not hear any difference much with coupling capacitors as long as they are decent quality film.
Thanks for the tip about the feedback wire. Got mine up and running this evening and there is some hum (20mV). I will try to solve that tomorrow

Edit: Other than that it sounds promising.
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Last edited by dahlberg; 3rd January 2017 at 11:15 PM.
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