Pimenta trouble - Ety-4p's won't work?

[fincherr]

Just finished wiring my first Pimenta, (with stacked buffers, AD8620/10 soldered to the bottom of the board, ALPS pot, class A bias, ZNR/FET, and all of the caps).

Following Tangent's testing steps, I first plugged in a pair of cheap headphones, which sounded great at all volume levels. Then I tried my desk headphones, a 10 year old Sony MDR-V600. Sound was even better!

I then moved to the ETY4p's, which had terrible static and very low volume. What is happening here?

I get a very loud thump/click when I switch the amp on, (without a source connected to the input). The system is not in a case yet, and I'm using two 9v batteries.

 

[Garbz]

Well the ER-4Ps are a very low impednace earphone. Background noises which are present will be much louder through these, however this would be described as white noise at low levels.

The thump/click is due again to the low impedance which makes them much more suseptable to poweron thumps as low impednace phones need less voltage to move the diaphram generally.

The crap sound is a harder problem to track down. An educated guess would be that the amp is unstable because of the hard to drive load, but i've not yet played with pimetas. Do the chips get hot?

 

[fincherr]

Quote:

Originally Posted by Garbz Well the ER-4Ps are a very low impednace earphone. Background noises which are present will be much louder through these, however this would be described as white noise at low levels. The thump/click is due again to the low impedance which makes them much more suseptable to poweron thumps as low impednace phones need less voltage to move the diaphram generally. The crap sound is a harder problem to track down. An educated guess would be that the amp is unstable because of the hard to drive load, but i've not yet played with pimetas. Do the chips get hot?

The thump occurs with all three headphones. The buffers get hot with use, but stay cool if the amp is on but no input. Evetything else stays cool.

 

[mono]

Did you put jumpers or resistors in the R8 (resistor) spots on the board? I suggest resistors if it's jumpered.

 

[fincherr]

Quote:

Originally Posted by mono Did you put jumpers or resistors in the R8 (resistor) spots on the board? I suggest resistors if it's jumpered.

Thoese are jumpered. I thought r8 was only to reduce hiss?

 

[m0nKeY bUsiNeSs]

Are you using a 1/8 to 1/4 inch adapter with the etys? sometimes those don't make the best of contacts with the 1/8inch plug and can cause problems.

 

[Garbz]

The adapters are normally associated with poor sound not hiss static buz or whatever.

R8 is there to raise the load seen by the amplifier. The idea is that since the etys present a very difficult load for an amplifier to drive stably being something like 25ohms, putting a small resistor like 75ohm or 120ohm in the R8 position may stabalise things.

Are the buffers warm when the er-4ps are plugged in and when there's no sound?

 

[fincherr]

Quote:

Originally Posted by Garbz The adapters are normally associated with poor sound not hiss static buz or whatever. R8 is there to raise the load seen by the amplifier. The idea is that since the etys present a very difficult load for an amplifier to drive stably being something like 25ohms, putting a small resistor like 75ohm or 120ohm in the R8 position may stabalise things. Are the buffers warm when the er-4ps are plugged in and when there's no sound?

The buffers do get warm when any headset is plugged into the output jack. I also get the loud clunking noise when the jack is inserted into the output plug.

I'm wondering if I installed Tangent's jfet's improperly? (all four have the same part number, so it would be an easy mistake). Could that cause this problem?

 

[mono]

Quote:

I also get the loud clunking noise when the jack is inserted into the output plug.

It is good to get into the habit of not plugging/unplugging the 'phones while it's turned on. A loud thump might even damage them. If you don't want to permanently add the R8 to the circuit you could try putting a couple in series on an "adapter" dongle, just a male/female short extension cord essentially. That's not technically as good as having it inside the feedback loop but will still work.

 

[nikongod]

heres the real question, does sound (music, when hooked upto something) come through the etymotics?

how big is your dc offset?

 

[fincherr]

Quote:

Originally Posted by nikongod heres the real question, does sound (music, when hooked upto something) come through the etymotics? how big is your dc offset?

Sound does come through the ety4's, it is very faint and scratchy.

Your right, I've got a dc offset problem. I'm reading 5.5 VOLTS, (not millivolts), between the output ground and the output left and right. I'm also seeing 5.3 V offset from input ground to output ground.

(I should have seen this before, however when the meter went into over-range on the millivolt scale it shows a 1 value, which i mistook for 1 millivolt).

 

[fincherr]

Quote:

Originally Posted by fincherr Sound does come through the ety4's, it is very faint and scratchy. Your right, I've got a dc offset problem. I'm reading 5.5 VOLTS, (not millivolts), between the output ground and the output left and right. I'm also seeing 5.3 V offset from input ground to output ground. (I should have seen this before, however when the meter went into over-range on the millivolt scale it shows a 1 value, which i mistook for 1 millivolt).

Problem was poor solder joins on pins 2 & 3 of the ground amp, (-IN and +IN). After re-soldering I had to add the ground wire to the Alps pot to remove static when the control knob was touched. The buffer chips run much cooler now also. Now the DC offset is 0.1 millivolts between the output ground and the output left and right; and 0.0 from input ground to output ground.

Thanks again to everyone for their help, (and do they still make the big black analog Simpson meters?)

 

[nikongod]

so, i guess everything is going well?

 

[fincherr]

Quote:

Originally Posted by nikongod so, i guess everything is going well?

Everything is going well; now I just gotta correct the low battery power LED circuit problem, add an external power supply jack, change-out the temporary jacks, do the casework, find a battery drawer, decide if I want a rechargeable system, figure out a way to add a portable graphic equalizer ...... I think I'll let everything burn in for a few days first!

 

[Garbz]

Ummmm... Are the ER-4Ps fine ? 5.5V is a lot of DC for a small cannelphone!

Also mono I have to disagree. I personally believe that unless you have output protection circuit, plugin and unplug the headphones AFTER turnonn and BEFORE turnoff. The minor short of the output circuit is nothing compared to the DC thumps of some of the common amp designs on these boards. Plus a few buffers are cheaper to replace than headphones. If they still thump when you plug / unplug them then there's got to be DC on the rails, nothing else would cause that thump.