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Bonzoro

WTB, M1.0t (Non Inv)

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I guess you missed what I said. It would be inside.  And, I asked if anybody had ever done it (add a vol pot), Guess not.  Modding the inside of the amp is done all the time. People are drilling or fabbing all kinds of stuff, adding remote volumes, etc.....AND, it can be removed. You also laughed at my "Sweet Spot"....   What's your issue with me? Couldn't you just say "Never done it, or just ignore me???   

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The only unit I've worked on with a level pot would be the PM1.5.  If you look at that configuration, there is input buffering, followed by a 20K pot, followed by the AC coupled amplifier input. The m1.0t basically starts at the AC coupled amplifier input right on the other side of the input RCA. My point being that if you wanted to do this in a similar manner, you would need to do it right at the input.  You could maybe lift the input capacitor and put something in there to try it. One side of the pot to RCA input, one side to GND, and the pot wiper connected to the input capacitor. Whatever value pot you choose would be the load on your preamp. Can't see what possible harm this would cause, at least as a trial.  Keep in mind that the input board has high voltage, and the components are sandwiched between the board and chassis.  The grounding of the 1.0t is fairly sensitive, so be sure to get a baseline of idle noise level in the speakers before adding the pot, just to make sure you have not changed this with the pot addition.

I believe it would be best to follow the pot with a buffer but that means more circuitry as well as tapping into the 12V supplies...

Edited by jeffs
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Thanks Jeff. It may be more trouble than it's worth. Maybe the passive would be the way to go. 

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If you have the ability to communicate with retired member SteveFord, I put one on an m-500 for him.  He wanted it right on the front panel; taking the drill press to the front panel was a cringe moment.

 

I can't find any pictures here, but iirc I did it as posted above by @jeffs.  I had to use heavily shielded wiring to reach the front panel; if you keep it as tweaker sized holes on the back you can avoid that.

Edited by RichP714
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1 minute ago, RichP714 said:

taking that drop press to the front panel was a cringe moment.

I'm cringing just thinking about it.

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1 hour ago, Bonzoro said:

I guess you missed what I said. It would be inside.  And, I asked if anybody had ever done it (add a vol pot), Guess not.  Modding the inside of the amp is done all the time. People are drilling or fabbing all kinds of stuff, adding remote volumes, etc.....AND, it can be removed. You also laughed at my "Sweet Spot"....   What's your issue with me? Couldn't you just say "Never done it, or just ignore me???   

 

No, I understand what you're trying to do. Whether it is inside or outside, it does the same thing, attenuate the input signal. That's what a passive pre-amp does. All I was suggesting is that a passive does everything you want better than what you can do to the amp itself, with much less trouble.

 

I didn't laugh at your sweet spot, I 'quoted it' because those were your words...I was just quoting your own phrase.

 

It was just a suggestion - like I said, if you really want to add a knob, then there's nothing stopping you. I have added pots to amp inputs - it's very simple. From the TFM-35 schematic:

 

image.png

 

The C-1 in particular has about 1k of output resistance so even a dead short at the M1.0t input won't hurt anything.

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2 hours ago, Bonzoro said:

Thanks Jeff. It may be more trouble than it's worth. Maybe the passive would be the way to go. 

I don't think it's that much trouble at all, at least to try.

I was going down this path (for a m1.5t) and even bought some pots a while back .... changed gears and never followed thru. Pots are very small chassis mount ALPS units with indents. I think 20Kohm ... check when I get home.

There's plenty of room to mount these internally on an l-bracket or similar, or even mount thru the back chassis if you don't mind drilling holes thru the nice diagrams on the back :).

 

I have a dead amp on my bench and Mouser parts expected to arrive today. After I get thru that, I have a m1.0t mkII and can give it a try for you with the pots I have? Let me know - might be a few days before I get to it ....... more than happy to try it out if you would like. 1 beer job, maybe 2 if I do a frequency response test (I used to spend time on some of the motorcycle forums and the HD guys timed a task by how many beers they would drink?)

 

I have a project where I need a bit more amp gain (9dB or so) to drive a subwoofer.  That's more of an issue as active components are involved. As a stop-gap I bought an external cheapo tube buffer with volume control for $31, maybe has  maximum 15dB of gain. Works great, but in the end it's another rectangular box that I'd rather not have. When time permits, I will add a gain circuit internally to eliminate the extra box (once again it's a m1.5t).

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5 hours ago, jeffs said:

I'm cringing just thinking about it.

How about I do that to a face plate off of Ebay????    Keep the original intact???    :)

5 hours ago, jeffs said:

I'm cringing just thinking about it.

Jeff, the Jigsaw would make me cringe.  I won't freak about the imported face plate off the bay.......     ☺️

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2 hours ago, jeffs said:

I don't think it's that much trouble at all, at least to try.

I was going down this path (for a m1.5t) and even bought some pots a while back .... changed gears and never followed thru. Pots are very small chassis mount ALPS units with indents. I think 20Kohm ... check when I get home.

There's plenty of room to mount these internally on an l-bracket or similar, or even mount thru the back chassis if you don't mind drilling holes thru the nice diagrams on the back :).

 

I have a dead amp on my bench and Mouser parts expected to arrive today. After I get thru that, I have a m1.0t mkII and can give it a try for you with the pots I have? Let me know - might be a few days before I get to it ....... more than happy to try it out if you would like. 1 beer job, maybe 2 if I do a frequency response test (I used to spend time on some of the motorcycle forums and the HD guys timed a task by how many beers they would drink?)

 

I have a project where I need a bit more amp gain (9dB or so) to drive a subwoofer.  That's more of an issue as active components are involved. As a stop-gap I bought an external cheapo tube buffer with volume control for $31, maybe has  maximum 15dB of gain. Works great, but in the end it's another rectangular box that I'd rather not have. When time permits, I will add a gain circuit internally to eliminate the extra box (once again it's a m1.5t).

 

 

Jeff, are you going to try it with just the pots or are you going to try it with the buffer circuitry?  I have a couple of the double 20K pots  or single 50K Pots. Thanks

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15 hours ago, Bonzoro said:

Jeff, are you going to try it with just the pots or are you going to try it with the buffer circuitry?

Just the pots.

I got my dead amp up and running last night. I didn't look at the pots I have, but I think they are 10K based on an old Mouser order. I think 20-50K might be a better option, but as was previously mentioned, a pre-amp like the C-1 should not have much difficulty

 

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10 hours ago, jeffs said:

Just the pots.

I got my dead amp up and running last night. I didn't look at the pots I have, but I think they are 10K based on an old Mouser order. I think 20-50K might be a better option, but as was previously mentioned, a pre-amp like the C-1 should not have much difficulty

 

 

 

both my amps will be here tomorrow so I'll get working on #1.     I'll go find my pot stash (Potentiometer's OK? ?) and after, I'll do some experimentation.  The WOPL has 100K pots and I tried 50K's a while back (Not sure which preamp I used) and it didn't like them but on the Carvers and the C-1, I'll start with 20K's and go from there after I baseline with nothing on the input lines. Thanks

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On 10/31/2019 at 8:36 PM, Bonzoro said:

I'll start with 20K's and go from there after I baseline with nothing on the input lines. Thanks

I tried this with a 10K pot on one channel, the other channel got full signal. I did not test for audio quality, etc.... I simply did a freq response test from 20Hz to 20KHz with a function generator connected directly to the amp, no preamp.  Since a C-1 has 200ohm series output resistance, I included 220ohm in series between the func generator and the input on EACH channel, considering this a typical application.

I ran 2 sweeps, one sweep with the pot all the way up, the other with the pot trimmed about 1/2 scale. Output level on the straight thru channel was about 3Vrms, input was at 100mVrms, dummy 8ohm loads on both channels.

 

For the straight in channel, the gain was nominally 29.8dB with a variation of only 0.28dB.  Set at full level, the channel with the pot was nominally 29.2dB with a variation of 0.27dB.  The 220ohm and 10K pot make a voltage divider 10K/10220= 0.978. This would account for some of the difference. Note that the gain in this channel might be slightly less to begin with, I never went back to check without the pot.

 

Set at about 1/2 level the attenuated channel was nominally 23.0dB, so about 6.2dB down from the full scale of 29.2dB.  Makes sense as 1/2=6.02dB. Variation was a bit higher, 0.37dB, still excellent flatness over the audio range.

 

So - from a freq response standpoint - this looks good.

As mentioned, the grounding on these inputs is sensitive, your ears will tell you if the pot adds any noise due to ground loop or the like.

 

Edited by jeffs
added load info.
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I'm doing some listening to this M-1.0t I just modded. It sound excellent. I'm impressed with the sound.  I still have the thump fix and the 5 way jacks to install but wanted to listen to it while I did some work to the Sansui G-7700 I picked up, it needs some TLC (has blown outputs on one channel).  The M-1.0t amp threw me a couple curve balls but I figured them out this morning. Seems that the previous owner had Q107 short out and took a couple resistors with it. He replaced them with the wrong values. Instead of 910 ohm, he used 800 ohm and instead of the 43 ohm, he used 47 ohm. It made a difference since these are the biasing resistors and the transistors refused to turn on.  Guess he used what he had on hand. close but no cigar. 

 

Any body know what offset is acceptable on the speaker terminals?  One is like 13mv and one is about 25mv. I didn't see anything in the Service Manual but maybe I missed it.  

 

Gonna play with these two M-1.0t's  (one is fully modded, one is still stock) and do some comparisons and some testing before I do anything else to them.  Can't wait to get this modded amp in the house and hooked up to the C-1 and the CornScala's. 

 

As I said, very impressed with the sound of these Non-Inverting amps, both stock and modded..

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There is no DC Offset adjustment on the M1.0t.  High Offset is probably do to mismatch in complimentary transistor pairs, or out of tolerance components due to age, or the input opamp, or a difference in the  (+) or (-) low voltages that powers the opamp.  Or a combination of all of the above.  However, I think any Offset between 20mV and 50mV (though not ideal) is acceptable.  There is something wrong if the Offset is above 50mV and requires investigation.   Anything below 20mV is perfectly OK for these amps. 

 

In your case I am not sure I would chase that ghost. 

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2 hours ago, dennismiller55 said:

There is no DC Offset adjustment on the M1.0t.  High Offset is probably do to mismatch in complimentary transistor pairs, or out of tolerance components due to age, or the input opamp, or a difference in the  (+) or (-) low voltages that powers the opamp.  Or a combination of all of the above.  However, I think any Offset between 20mV and 50mV (though not ideal) is acceptable.  There is something wrong if the Offset is above 50mV and requires investigation.   Anything below 20mV is perfectly OK for these amps. 

 

In your case I am not sure I would chase that ghost. 

 

Agreed. +/- 30mv is my “worry point”.

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I did notice it dropped closer to zero when I swapped out the input board from the second amp so it is possible the opamp is off a wee bit.. 

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Noticed right off the bat these opt2 amps run out of gas WAY before a WOPL.  If  (And I mean IF), these will push 400 WPC, they don't do it for long.  Something to do with not having a real transformer.   They sound excellent but have no legs. But, they are cheaper so that must be why they are popular.  Guess I could try them out as Mono's, one on each channel.  Don't know if it was a cost cutting thing or not why they used a gadget instead of a true transformer.  I even returned my Gain Jumper on my C-1 to the normal position due to lower sensitivity (Lower than the White Oak Mod on a Phase Linear 700 Series II).  I'm running a series of tests on my Audio Precision P1P Access, and I'll run both modded M-1.0t's along with 2 WOPL's and see if anything pops out at me.  The THD=N numbers are not as good either.  One amp got new RCA's and 5 ways, the other has not (as of yet) and I'm waiting on the Thump fix FET's for the second amp since it scared the hell out of the dogs AND ME......

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10 hours ago, Bonzoro said:

Noticed right off the bat these opt2 amps run out of gas WAY before a WOPL.  If  (And I mean IF), these will push 400 WPC, they don't do it for long.  Something to do with not having a real transformer.   They sound excellent but have no legs. But, they are cheaper so that must be why they are popular.  Guess I could try them out as Mono's, one on each channel.  Don't know if it was a cost cutting thing or not why they used a gadget instead of a true transformer.  I even returned my Gain Jumper on my C-1 to the normal position due to lower sensitivity (Lower than the White Oak Mod on a Phase Linear 700 Series II).  I'm running a series of tests on my Audio Precision P1P Access, and I'll run both modded M-1.0t's along with 2 WOPL's and see if anything pops out at me.  The THD=N numbers are not as good either.  One amp got new RCA's and 5 ways, the other has not (as of yet) and I'm waiting on the Thump fix FET's for the second amp since it scared the hell out of the dogs AND ME......

 

Heres a handy formula to assist you in your calculations😉

 

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14 hours ago, Bonzoro said:

If  (And I mean IF), these will push 400 WPC, they don't do it for long......

 

Specs from carvermk2.com:

 

  Stock   Mk II   opt 002
Power      
8 ohms 200 watts <0.15% THD   400 watts <0.15% THD   460 watts < 0.15% THD
4 ohms 400 watts <0.15% THD   450 watts <0.15% THD   510 watts < 0.15% THD
At Clipping      
8 ohms 350 watts   450 watts   500 watts
4 ohms 500 watts   520 watts   555 watts
Dynamic      
8 ohms 550 watts   670 watts   700 watts
4 ohms 832 watts   940 watts 1000 watts
2 ohms 928 watts 1250 watts

1290 watts

 

If the amp doesn't throw at least 460W RMS at an 8 ohm load,  and under 0.15% THD, then there is something wrong.

 

The whole point of the magnetic fields coil is that music is NOT a sinusoidal signal; therefore being able to push several hundred watts RMS is a meaningless numbers game (unless you listen to sine waves at full throttle)

 

A musical signal will typically have a 10dB peak to average ratio (20dB with good source material); the extra heatsink and transformer size required to acheive those uber high wattage numbers becomes an unnecessary expense when listen to music.

 

Carver's magnetic field coil is a physical manifestation of Paul Klipsch's comment "what the world needs is a good 15W amplifer"; a 15W amplifier with the headroom to properly amplify a signal with 20dB peak to average ratio would be able to produce 1500 watts on demand.

 

 

3 hours ago, Bonzoro said:

Why Thank you. Don't believe I've ever seen one of those before.

 

That's the Ohm's law pyramid; what might be confusing you is that the variable for Voltage is typically expressed as E (not V); the pyramid should be P=I*E

Edited by RichP714
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