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Millett "Starving Student" hybrid amp - Page 41

post #601 of 6814
thanks holland for the info I ask cause I´ve tried to build a power supply for my YAHA and eventough I got rid of most of the noise there´s still a very little hum. I´ll also look around here and diyaudio for some PS schematics.

RDS, I have a couple of reassons to not use the cisco PS unit , one is that me and my familly have a couple of bad experiences with ebay and paypal so I try to use only when theres no way around it. also I live in mexico and the shipping will be more expensive than the actual unit. to make things worse , is that it is really stressful to try to track down a package once it enters costums and the Mexican post service gets in charge ( last time i needed like 20 phone calls and 5 days just to figure if the package had already left customs). so when I order something I make sure its an ammount that has to pay taxes ( belive me it's safer ) and make sure to get a tracking number and insurance.

As for building the ps I do have some experience around power electronics, the problem is that I don´t have experience around audio electronics.

well thank you all for your time

Francisco
post #602 of 6814
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post #603 of 6814
fjc - I could post one to you, but I guess that won`t solve your customs problems.
If it will send me a pm.
post #604 of 6814
Quote:
Originally Posted by tomb View Post
Considering the gain involved, it works pretty well on your SSMH PCB. I went conservative and just added ~50K resistors in line with the 50K pot, but it's a much better adjustment than I expected.
You mean to add 50k resistors to the existing pot right not a separate one for the preamp stage? How many resistors did you use? After you add the resistors is a simple switch between rca outs and hp out is all that is needed?
post #605 of 6814
I should say:
The preamp can be deadly to your speakers
As you are sending that turn on/off thump to your speaker amp, if your amp is powerful enough it may blow your speakers. I think to be safe you should have a relay if you`re going to do a preamp.
post #606 of 6814
Or I can just always turn the amp off first... Current speakers are el cheapos anyways. I was trying to figure out if there would be any way to use an OPT to drive speakers since someone suggested that but I don't think it could work.
post #607 of 6814
I just want to make sure someone doesn`t put a hit out on me after they blow their B&W Nautilus or something.
post #608 of 6814
Quote:
Originally Posted by dsavitsk View Post
I'll agree with rds here. This method will end up with a lower Zin in most cases. The relationship of the voltage divider and pot will need to be 10x which will leave either the input Z too low for some sources, or the second attenuation stage will be potentially large which can be noisy. Either way, it is two attenuators when you only need one. OTOH, putting a resistor in series with the pot essentially lengthens the resistive element of the pot and just keeps the wiper from traveling over the whole thing.
Fair enough, I've just always been cautioned against doing that on the input of an amp.
post #609 of 6814
I started following this thread in the beginning then was away for a month now boom it's 61 pages--which I just finished reading.

I'm looking to build and I've noted some updates, I'm wondering if this is right or have I missed something in this monster thread?

Start with Pete's BOM/schematic
Change c6 to 470uf as per http://www.head-fi.org/forums/4220313-post238.html
Maybe change the output to a 470uf as well.

Is this the "optimum" configuration? There's has been a lot of advice, and since my parts drawer is pretty much empty I'm ordering everything likely using the digikey parts list from tom--mouser's Canadian shipping is absurd.


Thanks!
post #610 of 6814
Quote:
...I've just always been cautioned against doing that (adding series resistance to a pot) on the input of an amp.
Probably the reason people have cautioned against that is because it is not a good idea to have a huge input impedance. Large input impedances make the amp more susceptible to noise.
The solution is to use a lower impedance pot if you want to reduce the gain a lot.
That is why I recommended a 100k resistor in series with a 10k pot.
I've also found using 220k in series with a 50k pot to be perfectly acceptable.
post #611 of 6814
Quote:
Originally Posted by rds View Post
Probably the reason people have cautioned against that is because it is not a good idea to have a huge input impedance. Large input impedances make the amp more susceptible to noise.
The solution is to use a lower impedance pot if you want to reduce the gain a lot.
That is why I recommended a 100k resistor in series with a 10k pot.
I've also found using 220k in series with a 50k pot to be perfectly acceptable.
Thanks for the explanation!
post #612 of 6814
No problem.
Just to complete that explanation the noise problem comes from the source feeding the amp. Any source is going to have a superimposed noise in its output current. A higher impedance means the source outputs less current, and therefore the noise to signal ratio increases. At some point with an extremely high impedance the signal will be completely lost in the noise.
On the other hand if the input impedance is too low the source will have to output a very large current. Too low an impedance will require the source to output more current than it is capable of and therefore will distort.
So like everything there is some point in the middle that is 'just right'.
post #613 of 6814
I've just finished my summer commuting and will have some time for a project in the near term. I can't wait any longer for the SOHA II so I'm going to build a Starving Student. I watched this thread when it first started but haven't followed it for a while and I don't necessarily want to read all 600+ posts. Are there any consensus good-bang-for-the-buck upgrades/replacements to the standard BOM listed on Pete Millett's website?

Thanks,
Vic
post #614 of 6814
I just built an Alien DAC.

The Alien DAC assembly page says about a pair of caps on the output end: "If your amp (or any other device you are going to connect your DAC to) has some input DC protection, do not populate CL and CR. This way you avoid all sorts of problems with coupling capacitors selection and mounting."

So here's the beginner's question: Does the SSMH have "input DC protection"?

Thanks in advance.
post #615 of 6814
Quote:
Originally Posted by royewest View Post
I just built an Alien DAC.

The Alien DAC assembly page says about a pair of caps on the output end: "If your amp (or any other device you are going to connect your DAC to) has some input DC protection, do not populate CL and CR. This way you avoid all sorts of problems with coupling capacitors selection and mounting."

So here's the beginner's question: Does the SSMH have "input DC protection"?

Thanks in advance.
NO, not in the sense that the Alien documentation means, anyway.

For what it's worth, those output caps on the Alien are essentially the only protection afforded to the PCM chip, too. I won't digress into relating the entire sordid story, but suffice to say that I've blown out a couple of PCM chips from messing around with different connections when those output caps were not in the circuit.
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