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New Millett Hybrid MiniMAX (what happened to this thread?) - Page 130

post #1936 of 1948
Quote:
Originally Posted by dentaku81 View Post
 

Awesome, im currently building a cmoy to re-learn how to solder, but i will start on the minimax after that.

Sounds like a good plan. ;)

post #1937 of 1948
Will HE500 and LCD2 sounds good with miniMax? Right now I paired them with EF5. Will miniMax gives a significant improvement over EF5? Thanks
post #1938 of 1948
Quote:
Originally Posted by wewewho77 View Post

Will HE500 and LCD2 sounds good with miniMax? Right now I paired them with EF5. Will miniMax gives a significant improvement over EF5? Thanks

Typically, I don't like direct comparisons in the DIY forum section.  We're not really trying to compete against commercial products.

 

What I will tell you - I know nothing about the EF-5 except photos, etc. - is that I am not a fan of single-tube stereo amplifiers.  In my years of testing and matching literally thousands of tubes, the incidence of dual-triode tubes where the triodes are matched is very low.  I'd say one in 20 or 30, probably.  If the triodes are unmatched, you can balance the channels, but the stronger triode will always pump more output with transients, etc.*

 

* With two-tube amps using dual-triode tubes, the triodes of each tube are typically connected in parallel.  That averages the output.  You can have one tube measuring 120/80 and another at 105/95 - theoretically, they are matched because they each average to 100.  It exponentially increases your chances of matching the tubes' output in the amp.


Edited by tomb - 10/24/13 at 3:40pm
post #1939 of 1948
Sorry tom I didn't mean disrespect to anybody here. I used to be sceptical about tubes for their noise issue, old technology etc. But I also realize that tubes has so many faithful fans out there. I thought there's must be something special about them. So I decided to buy this EF5 amplifier for my HE500. And then I finally can understand why so many people loooves the sound of tubes. And my EF5 is so small but sounds so nice to my ears. I wonder if a bigger tube amps will take my setup to a much higher level. I asked around and someone very experienced DIYer suggested to try SSMH or miniMax if I want to have a big step up from my current setup. He said these amps are a steal for their price. So I just want to know your opinion here guys. Maybe I just send you PM than ask in this thread about the comparison between them. I really appreciate your information. Thanks
post #1940 of 1948
Quote:
Originally Posted by wewewho77 View Post

Sorry tom I didn't mean disrespect to anybody here. I used to be sceptical about tubes for their noise issue, old technology etc. But I also realize that tubes has so many faithful fans out there. I thought there's must be something special about them. So I decided to buy this EF5 amplifier for my HE500. And then I finally can understand why so many people loooves the sound of tubes. And my EF5 is so small but sounds so nice to my ears. I wonder if a bigger tube amps will take my setup to a much higher level. I asked around and someone very experienced DIYer suggested to try SSMH or miniMax if I want to have a big step up from my current setup. He said these amps are a steal for their price. So I just want to know your opinion here guys. Maybe I just send you PM than ask in this thread about the comparison between them. I really appreciate your information. Thanks

No disrespect was felt. :)

 

It's a perfectly natural question, but probably best asked in the Head-Fi Amplifier section.  No one's going to object to sound quality comparisons, there.  It's just that DIY - in my opinion - is about offering do-it-yourself designs and support.  (This is the MiniMAX support thread, for instance.)  We're not even trying to compete against each other with most designs.  Most of us, even if we're MOT's, are running on shoestring budgets and do this because of our love of the hobby.  Yes, I'd be untruthful if I didn't say economics plays a large part, but that's simply the reality of buying, selling, and the required investments to do that on a regular basis.

 

Anyway - it's just my opinion and one I try to adhere to.  As I said, no one's going to object to you asking any sort of comparison question over in the Amplifier section.  Besides reviews, that's the almost the whole purpose of that section.

 

There's a comparison review on Head-Fi, but I think he had some dud tubes, or else didn't re-bias with tube changes.;)  The MiniMAX was also sold as a fully-built product by Whiplash Audio for awhile, too.  I believe there are several reviews of the Whiplash Audio MiniMAX on Head-Fi.  The MiniMAX has been around for quite awhile - just google "Millett Hybrid MiniMAX review" and you'll find a bunch - even some youtube videos like this one: http://www.youtube.com/watch?v=kQtTv1qI1Yc


Edited by tomb - 10/25/13 at 7:00am
post #1941 of 1948

Hi all,

 

I was wondering if I may have a hand in troubleshooting my MiniMax.

 

It's been going strong for quite a couple of years now, but unfortunately as I did not use a case for it, dust gathered and the blue smoke escaped.

 

At first i thought the problem was isolated around the burnt QM1 which I've replaced, found out DM1 was open circuit, so replaced that as well. Fuse was a gone as well. I've then verified that the relay now successfully trips and that both relay output coils are switching. TA2L- Gnd/ TA2R-Gnd and TA2L-TB1L/ TA2R-TB2R are biased still correctly.

 

I'm not really where to go from here. Could anyone recommend any other pads i should be testing?

 

Cheers,

Bismar

post #1942 of 1948
Quote:
Originally Posted by Bismar View Post
 

Hi all,

 

I was wondering if I may have a hand in troubleshooting my MiniMax.

 

It's been going strong for quite a couple of years now, but unfortunately as I did not use a case for it, dust gathered and the blue smoke escaped.

 

At first i thought the problem was isolated around the burnt QM1 which I've replaced, found out DM1 was open circuit, so replaced that as well. Fuse was a gone as well. I've then verified that the relay now successfully trips and that both relay output coils are switching. TA2L- Gnd/ TA2R-Gnd and TA2L-TB1L/ TA2R-TB2R are biased still correctly.

 

I'm not really where to go from here. Could anyone recommend any other pads i should be testing?

 

Cheers,

Bismar

Questions:

  • If those points are biased correctly, does that mean that the amp turns on, but you get no sound?
  • What is the voltage setting?
  • Are you using the proper adapter (24VAC)?
  • How about the tubes - have you tried swapping them out?

 

I'm not sure I see the issue from your description.  If the bias points are correct and you can tell that the relay switches in, you should get sound unless the tubes are blown.  Maybe you have a shorted tube?  Just as a check, can you give us the exact readings from your bias points?

post #1943 of 1948
Quote:
Originally Posted by tomb View Post
 

Questions:

  • If those points are biased correctly, does that mean that the amp turns on, but you get no sound?
  • What is the voltage setting?
  • Are you using the proper adapter (24VAC)?
  • How about the tubes - have you tried swapping them out?

 

I'm not sure I see the issue from your description.  If the bias points are correct and you can tell that the relay switches in, you should get sound unless the tubes are blown.  Maybe you have a shorted tube?  Just as a check, can you give us the exact readings from your bias points?

 

tomb,

 

Thanks very much for your help, you solved it! 

 

Its been so long that one pair of tubes has blown I did not honestly think about even swapping them out. Turns out both my previous tubes must have blown in the short.

 

Its such a huge difference being able to use this amp again!

post #1944 of 1948
Quote:
Originally Posted by Bismar View Post
 

 

tomb,

 

Thanks very much for your help, you solved it!

 

Its been so long that one pair of tubes has blown I did not honestly think about even swapping them out. Turns out both my previous tubes must have blown in the short.

 

Its such a huge difference being able to use this amp again!

 

Glad you got it fixed! :)

post #1945 of 1948

MiniMAX Improved Relay-Delay

 

I've meant to document this for a long time, but an e-mail this weekend from a customer finally forced me to do it. ;)  As some of you know, the MOSFET-MAX uses an updated relay-delay circuit.  This circuit uses 24VDC instead of a zener-induced 12VDC supply.  This is accomplished by using a 24VDC regulator - the 78L24 - to establish the voltage to the relay.  The relay, in turn, is a 24VDC rated relay.

 

The result is that the entire relay circuit operates much, much faster.  There are no immediately measurable spikes in voltage on turn OFF, where as the existing circuit had quite a bit.  Turn OFF voltage spikes to the headphone output are caused by the charged capacitors on the PCB and minute arcing between the relay contacts.  You can measure this yourself by applying a DMM to the headphone output while turning the amp off.  The voltage is liable to spike to several whole-number volts before everything dies down.  There is very little to no spikes using the 24VDC relay circuit that cetoole designed for the MOSFET-MAX.

 

So what?  Well, ... it's very easy to implement this into an existing MiniMAX.  You don't need the MOSFET-MAX PCB to do it.

 

Here's the original circuit schematic for the relay-delay used on the original Millett Hybrid MAX and the current Millett Hybrid MiniMAX:

old-relay.jpg

And here's the updated version using 24VDC, the new regulator, and a 24VDC relay:

new-relay.jpg

This can be implemented as it stands on an existing MiniMAX PCB as shown in the photo below:

 

new-relay-PCB-sm.jpg

 

Note that RM2 has been replaced with 2M.  I soldered together two 1M resistors in the pic above, since 2M resistors aren't that common in my toolbox.  Further, there is no DM1, RM1, or QM1 (BD139 transistor).  The 78L24 is soldered into the first two pads of QM1 with the middle leg (pin 2) stretched out to connect to GND at the left pad of DM1.  This is all that's needed to obtain the advantages of the new relay circuit and its improvements.

 

Note that most Millett Hybrid MAXes, MiniMAXes, and MOSFET-MAXes are setup with 27VDC at the power supply adjustment.  This gives sufficient voltage headroom to allow the 78L24 to regulate at 24VDC.  Other amplifier designs that run right at 24VDC or less will probably not work.  JMHO, but I believe the higher voltage - not just the regulator - has a lot to do with speeding up the relay and cutting down on the voltage spikes.

 

Anyway, I hope I've demonstrated that it's pretty easy to implement the new circuit in existing MAXes or MiniMAXes.

post #1946 of 1948

Thanks Tom - but is it entirely necessary to do the mod?

 

In my minimax, I notice a slight click on power on, and also the same at power off.  But it's not painful on the ears or anyway, so I never ever take my headphones out of the socket. Is that ok?

post #1947 of 1948
Quote:
Originally Posted by lordearl View Post
 

Thanks Tom - but is it entirely necessary to do the mod?

 

In my minimax, I notice a slight click on power on, and also the same at power off.  But it's not painful on the ears or anyway, so I never ever take my headphones out of the socket. Is that ok?


No, it is not necessary to do the mod.  The existing relay-delay provides ample protection and I have never unplugged my headphones with a MiniMAX.  However, for those measurement freaks who've applied a DMM to the amp at power off, they may have noticed some voltage spikes that would make them uncomfortable.  These spikes on Turn OFF are not exclusive to the MiniMAX or even a tube amp or hybrid.  They exist in any amp with significant capacitor loading (almost anything with more than a CMoy's 2 x 220uf).  This relay is fast enough to stop most of those spikes.  It is an improvement, nothing more.

 

BTW - I forgot to mention that the BOM should be followed from the MOSFET-MAX.  It also specifies a different electrolytic capacitor for CM3.  It should be a 470uf, 35V cap.  The CM3 normally specified for the MiniMAX (470uf 16V) will blow up at 24VDC.

 

Again, this is only documented for those wishing for a measureable improvement - and especially for those attempting to implement their own relay-delay in other amp designs.  It has been discussed several times before in this thread and the Starving Student thread.  It's just that I never documented how simple it is to install in the MiniMAX.

 

 

P.S. I might have converted to this relay circuit completely in future MiniMAX kits, but the future of the MiniMAX is in doubt.  I'm afraid the market has been saturated and sales have been non-existent lately.  When it comes time to manufacture more custom-machined cases to the tune of several thousands of dollars, it may just be the best business decision to not continue with it. :(


Edited by tomb - 1/4/15 at 7:29pm
post #1948 of 1948

Thank You for still care and developing this project !

Your support is great - photos, details ...

Stay with us :)

Thanx a lot!

edit: I just did it.

 

 


Edited by NuClear235 - 1/12/15 at 9:04am
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