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Millett "Starving Student" hybrid amp - Page 439

post #6571 of 6798
alright one last question and it's about the tube socket wiring... I'm using 12au7 tubes which have a nine pin configuration and am using the modified plans by the equalizer which I am sure you are all familiar with. my question is m the tubes for this have nine pins while the diagram only specifies what to do with eight of then. What do I do with the ninth pin? And they are numbered out of order as I am familiar with pins being numbered radially and sequentially starting with one one the left side of the had. So if anyone can shed Adobe light on how to ruin three tube wiring I works appreciate it .
The nine pin mini of course

http://electriciantraining.tpub.com/14178/img/14178_24_2.jpg


http://diyforums.org/SSMH/schematic/SSMH-origPCB-sm.gif
post #6572 of 6798

Pin 9 is the center-tap of the heater, so it can be used with 6.3 V.

 

post #6573 of 6798

awesome thanks. So how does the pin numbering correspond to the numbering on the schematic? why isn't pin 9 specified in the diagram?

post #6574 of 6798
Quote:
Originally Posted by audi0lurker View Post

awesome thanks. So how does the pin numbering correspond to the numbering on the schematic? why isn't pin 9 specified in the diagram?

 

The pin number on the schematic correspond to the pin number on the socket. They are not in order on the schematic because the part drawing used has them this way, which is common on schematics. Schematics are drawn to be quickly understood, not to match physical components packages.

 

Pin 9 is unused in the SSMH, so there's no reason for it to be shown anyways.

post #6575 of 6798

Indeed, pin 9 is the heater center tap (used in circuits where the heaters are fed in parallel with a 6.3 V source), it is not used  in the SSMH circuit and SHOULD NOT be connected to anything, as there's a voltage present at that point.

 

Sorry about the confusion with the pin numbers, to make it easier to produce a schematic diagram, I simply took the existing 19J6 schematic and relabeled the pin numbers redface.gif. My apologies, I should have been more careful with that detail.

post #6576 of 6798
Quote:
Originally Posted by Goobley View Post

The Equalizer was the first (AFAIR) to implement this mod, then I also added it back when my SS operated at standard voltages.

 

I used a CRD shortly after I built this, some 5 years ago  :P  I did a number of minor mods to it (original SSMH with 19J6).  CRD (0.56mA) on the plate, changed the CRC filter to reduce the voltage drop from increased current, global negative feedback, and removing local negative feedback (cap on the cathode).  I can't recall why I bypassed the cathode.  I actually don't mind the CRD here, just to keep in the goal of a Starving Student.  I did everything on the cheap.

 

Decent amp but still too much gain for my headphones.

 

One thing I have wanted to experiment with was putting the potentiometer after the gain stage, with additional caps to block DC from the voltage divider for the MOSFET.

 

This has to be one of the longest running threads I've ever seen.  Good luck to anyone who can read 6576 posts. :)


Edited by holland - 6/23/13 at 8:25pm
post #6577 of 6798

Hello again.

 

I got a question capacitors C2 and C4.

 

 

 

What is the purpose of these 2 capacitors? Are they used to block the DC?

I currently have 0.22uF ceramic capacitors installed in that place. I believe they're the reason for which I am getting a bass roll-off problem (tested with RMAA).

 

Few days ago I was trying to design my own solid state amp. I used 0.22uF capacitors to block the DC and they were causing a bass roll-off below 100-150hz. Replacing them with polarised 2.2uF fixed the problem for me. I wonder if I can do the same in starving student since I know very little about tubes.

 

So is it safe to replace these capacitors with 2.2uF 63v polarised ones? The positive pin of capcitor must face the MOSFET, right?

 

Thanks.

post #6578 of 6798
Quote:
Originally Posted by ProTofik View Post

Hello again.

 

I got a question capacitors C2 and C4.

 

 

 

What is the purpose of these 2 capacitors? Are they used to block the DC?

I currently have 0.22uF ceramic capacitors installed in that place. I believe they're the reason for which I am getting a bass roll-off problem (tested with RMAA).

 

Few days ago I was trying to design my own solid state amp. I used 0.22uF capacitors to block the DC and they were causing a bass roll-off below 100-150hz. Replacing them with polarised 2.2uF fixed the problem for me. I wonder if I can do the same in starving student since I know very little about tubes.

 

So is it safe to replace these capacitors with 2.2uF 63v polarised ones? The positive pin of capcitor must face the MOSFET, right?

 

Thanks.

 

You can't compare the values of these caps between amplifiers. You also need to take into account the value of the resistor following, in this case R4 and R10.

 http://en.wikipedia.org/wiki/High-pass_filter#First-order_continuous-time_implementation

 

The interstage filter using a 0.22 µf cap has a cut off frequency of 4 hz.

 

What is the impedance of the headphones you're using with the amp? What value capacitor did you use for C3 and C5?

 

If you're using 32 R headphones with 150 µf capacitors at the output, you get a cut off frequency of 33 Hz. This would more likely be your problem.

post #6579 of 6798

For RMAA tests I used 33ohm resistors as a load. C1, C3, C5 and C6 that I am using are 220uF.

 

So if the C2 and C4 are not my problem, then what is?

 

Tomorrow I will make another RMAA test with 300ohm load (since this is what my HD600 are) and see if I will get the same result.


Edited by ProTofik - 6/27/13 at 6:28pm
post #6580 of 6798
Quote:
Originally Posted by ProTofik View Post

For RMAA tests I used 33ohm resistors as a load. C1, C3, C5 and C6 that I am using are 220uF.

 

So if the C2 and C4 are not my problem, then what is?

 

Tomorrow I will make another RMAA test with 300ohm load (since this is what my HD600 are) and see if I will get the same result.

 

You don't need RMAA to test that... any calculator will do, even google.

 

33 ohms and 220 µf: 1/(2*Pi*220*10^-6*33) = 22 Hz

300 ohms and 220 µf: 1/(2*Pi*220*10^-6*300) = 2.4 Hz

 

So with your HD600 there should be no bass roll off due to parts selection. It is more probably due to the character of the tubes themselves.

post #6581 of 6798


All that is very interesting.  One of my motivations for building this was to learn some circut theory and what not(being a 3rd yeach ME wondering why he isnt an EE)

 

So Im wondering if someone could give me the reason to add Capacitors C3a and C5a(.22uf at 250v)  in parallel with the 470uf caps at 63v.  It seems funny to add these.  So Now I have a 470.022uf cap? that seems so insignigigant.  Such a low capacatance and such a high voltage rating.

 

 

 Please, higher minds enlighten me

http://diyforums.org/SSMH/schematic/SSMH-origPCB-sm.gif

post #6582 of 6798

The larger the value the cap, the more inductance it tends to have at higher frequencies.

This can cause some high frequency roll-off.

Adding a smaller value cap in parallel counteracts this effect.

post #6583 of 6798
Quote:
Originally Posted by ProTofik View Post

For RMAA tests I used 33ohm resistors as a load. C1, C3, C5 and C6 that I am using are 220uF.

 

So if the C2 and C4 are not my problem, then what is?

 

Tomorrow I will make another RMAA test with 300ohm load (since this is what my HD600 are) and see if I will get the same result.

 

Your output caps, C3 and C5, are too small.  I used 1000uF, but 470uF is a minimum.  KimLaroux's formula is almost correct.  You need to take into account that the high pass filter is C3 (or C5) interacting with the parallel resistance of 2K and the output headphones.

 

Anyway, the corner frequency, which the equation 1/(2*pi*RC), is about the -3dB point, and it bends about it at 6dB per octave.

post #6584 of 6798
Quote:
Originally Posted by Avro_Arrow View Post

The larger the value the cap, the more inductance it tends to have at higher frequencies.
This can cause some high frequency roll-off.
Adding a smaller value cap in parallel counteracts this effect.
That makes perfect sence. Isn't it wonderful glee the world works out? Do what is the relation to capacitors and low frequencies? ie very low and deep bass. Will larger capacitors discharge more current to drive deep low frequencies? How could I get a bit more low end in theory?
post #6585 of 6798

Hello All, 

  I've been getting into the audiophile ways for a while now, and have decided to tinker my way into the DIY realm.

 

  Thus I'm going to go for the SSHA build.  However I'm looking to add in a bit of protection for the headphones.  I've seen multiple posts on this, and I'm unaware of what the general consensus was.

 

  Thus I have a couple questions that I'd love some input on.  

 

  First is the headphone delay worth putting in?  Lets say I have a friend fire this up while I'm away, I'd rather not lose some nice Sennheisers.

 

  Second, I've been looking at the e12 circuit and the simplified version from the HybridMax at http://www.diyforums.org/MAX/MAXe12.php .  If this is put into the system what then is the current load that the power supply needs to be able to output?  If this goes into the system, are two of them needed, one for each channel?

 

  Third, how well does the diode method of bypassing the headphones at startup / shutdown work?  (Seen here: http://www.head-fi.org/t/319231/millett-starving-student-hybrid-amp/5805#post_7413132)  Do the LEDs continue to blink indefinitely? 

 

Thanks!

-Whil

 

Parts are on the way!

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