[Zoide]

Well, if the PPA is one of the more affordable entry models as opposed to a full monty best specs one, would it give very noticeable hiss driving HD580s at medium / low-medium volume?

Also, how much does a STEPS usually cost from one of the DIY builders?

Thanks.

 

[ppl]

The PPA has better Power supply rejection ratio than most conventional Amplifiers. 20dB better than the op amp alone because, of the Jfet rail isolation. Also the Ground Channel removes hum that may be on the Ground from other AC sources and also isolates the ground from contamination of the Load Current spikes. What all this adds up to is an amp that while more tolerant of Bad power sources than other Amps. An example the META42 Hum on an unregulated radio Shack wall wart however the PPA quiet with the PPA. The High resolving powers of the PPA Let you listen way deep into the background so any noise from the AC power supply will be heard. This noise not always is from the supply it self but is actually EMI and RFI coming from the AC mains and passing through the power supply. Good power supplies will lessen this noise by proper filtering. Wall Warts are real bad at passing RFI interference into the Amp since no umbilical cord is present to help reduce and dissipate this noise prior to its entering the Power supply. Some real high quality power supplies such as the STEPs have EMI filtering for the AC Mains and thus reduces this noise to so low of a level that you can no longer hear it.

 

[Zoide]

So I'm using an Elpac with my PPA and HD-580s, and I hear no hiss. Given that hiss is not an issue at all for me, would a better power supply (ie. STEPS) improve anything for me?

 

[ppl]

Ipods PPA replaces the Bass boost switch with a Gain switch this is not an attuator like a volume control it actualy lower the closed loop gain. This results in more Neg feedback whitch in turn lower Distortion noise and widens the Frequency response. Yes while the PPA is more tolerent of bad power sources it is clearly better than amps like the META42 that will hum on anything less than an elPcac. the PPA on this same supply is hum free however the higher resolving power of the PPA requires a first rate power supply.

Most perple do not understand that in spite of the fact the PPA is a DIY Amp it was intended to sound as good as High end Amps costing over $1,000 USD and surly will if built correctly.

 

[Zoide]

So if I understand you correctly, even if there is no hiss in my setup, my PPA's resolving power would improve with a better power supply? What exactly would this mean? (as in, what's resolving power?

)

 

[morsel]

Some PPAs I have come across are not grounded or cased properly, which can result in increased hum or noise. This is one of the drawbacks of buying DIY amps, or building your own. Kurt and I brought a prototype PPA to a Berkeley meet last year which was not properly grounded. Tangent recently sent me a prototype v1.1 which was not properly grounded. So even we of Team PPA make mistakes sometimes. Before investing in expensive power supplies, make sure you follow the wiring considerations at http://elvencraft.com/ppa/ by tying case and pot housing to signal ground.

Another chronic problem is the use of excessive gain with low impedance headphones, often in tandem with OPA637 opamps. Those of you with efficient low impedance phones should have your gain set to 2-4, not 11. This will reduce noise and hum, as well as giving you more useful range of adjustement of volume. If the volume knob is set around 9 o'clock for normal listening, your gain is too high. Ideally, normal listening should be between 12-3 o'clock.

 

[Dane]

Sigh! Tell me about it

Quote:

Originally Posted by morsel Some PPAs I have come across are not grounded or cased properly, which can result in increased hum or noise. This is one of the drawbacks of buying DIY amps, or building your own. Kurt and I brought a prototype PPA to a Berkeley meet last year which was not properly grounded. Tangent recently sent me a prototype v1.1 which was not properly grounded. So even we of Team PPA make mistakes sometimes. Before investing in expensive power supplies, make sure you follow the wiring considerations at http://elvencraft.com/ppa/ by tying case and pot housing to signal ground. Another chronic problem is the use of excessive gain with low impedance headphones, often in tandem with OPA637 opamps. Those of you with efficient low impedance phones should have your gain set to 2-4, not 11. This will reduce noise and hum, as well as giving you more useful range of adjustement of volume. If the volume knob is set around 9 o'clock for normal listening, your gain is too high. Ideally, normal listening should be between 12-3 o'clock.

 

[adhoc]

Quote:

Originally Posted by morsel Another chronic problem is the use of excessive gain with low impedance headphones, often in tandem with OPA637 opamps. Those of you with efficient low impedance phones should have your gain set to 2-4, not 11. This will reduce noise and hum, as well as giving you more useful range of adjustement of volume. If the volume knob is set around 9 o'clock for normal listening, your gain is too high. Ideally, normal listening should be between 12-3 o'clock.

then what would i do if my main phones are both a low impedance and high impedance phone? set my gain to a midpoint level like, say, 6? lower my source output if it is capable of doing so (like most soundcards are)?

and just to clarify, the 'problem' is due to pots being unable to track accurately for both channels at low levels or an opamp-related issue specific to the opa627/637? and if it is the latter, why?

 

[morsel]

Quote:

what would i do if my main phones are both a low impedance and high impedance phone?

Set your gain only as high as needed for adequate volume with your high impedance headphones at 12-3 o'clock volume knob setting.

Quote:

and just to clarify, the 'problem' is due to pots being unable to track accurately for both channels at low levels or an opamp-related issue specific to the opa627/637? and if it is the latter, why?

The OPA637 is unstable at gains of 5 or less. This makes it a poor choice for use with low impedance headphones. Pots track less accurately at the low end of their range, and excessive gain is bad because the pot must excessively attenuate the signal to compensate for the excessive gain, thus reducing the signal to noise ratio.

Improper grounding is a more serious problem than excessive gain.

 

[adhoc]

thanks for that detailed reply morsel.