or Connect
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › A Very Compact Hybrid Amp
New Posts  All Forums:Forum Nav:

A Very Compact Hybrid Amp - Page 120

post #1786 of 2213
I have no idea what happened..but while I was trying to measure the output pin 6 of the opamp on turn on to see its behavious I accidently shorted the Vcc pin 7 to pin6 with the probe tip.
Voila!..it seems to work just fine now. I have 12.01 volts between OL->SG and OR-> SG

Weird i tell you. Going to wire up and the amp and see if it all works fine.

Edit:

I hooked up the wires and set up the amp..it works great. THough with the shunt mod of 33.2k ohm resistors and a 50k ALps pot the amp E12 mutes the output very quickly not to mention not enough travel available on the Volume knob. I will revert to a more standard pot wiring to see if it alleviates the problem. Thanks for the help Alex. It just baffles me what was wrong though. That spark seemed to fix the E12 problem like that . Haha
post #1787 of 2213
I've read a lot here that Grados need a low impedance amplifier, but I find my rs1i sound great from this amp (with r18 = 110 ohms).
I wonder if Grados really do need low impedance?
post #1788 of 2213
Thread Starter 
Quote:
Originally Posted by sachu View Post
Edit:

I hooked up the wires and set up the amp..it works great. THough with the shunt mod of 33.2k ohm resistors and a 50k ALps pot the amp E12 mutes the output very quickly not to mention not enough travel available on the Volume knob. I will revert to a more standard pot wiring to see if it alleviates the problem. Thanks for the help Alex. It just baffles me what was wrong though. That spark seemed to fix the E12 problem like that . Haha
I am wondering if the opamp was not seated properly and if one of the pins was not actually making contact until you sparked through the oxidation. Other than that your guess is as good as mine.

rds, the output impedance of the amp is not as important for headphones as it is for speakers. Headphones are mostly a resistive load and so the damping is not terribly important. The "voicecoil" of the headphones does not generate much, if any, back emf into the amp. At least so far as I know. Since it doesn't the series resistors matter only for the gain of the amp.

OTOH, maybe it's just a great amp.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #1789 of 2213

Is it normal?

I finished building my cth two weeks ago and its sounds fantastic, but i have two questions:

1.) When i switch of the cth, i hear a click in my Headphones. It seems that the protection ciruit ist switching not fast enough.
Is it normal?

In operation, Output DC-Offset is below 15mV. After replacing the TL082 with an LT1057, Offset is below 2mV.

2.) Can i change Q1P to an ZTX451 (80V, 1A, NPN, TO92)


Thank you in advance.

CM
post #1790 of 2213
The brief, sharp click you hear @ pwr-off is considered normal for the CTH. It is the tiny delay between the pwr-off & the relay release.

You are hearing a fraction of a second of the start of offset caused during pwr-off & only hear it because its getting abruptly interrupted. In other designs that should have the feature but don't, you don't notice their DC offset swings as much because they proceed uninterrupted (to the detriment of your headphones).

Don't know about your Q1P sub suggestion (runeight could comment) but BC337 should be sufficient. Interesting observation WRT TL082 --> LT1057.

BTW another behavior, depending on source & tube, is that CTH's e12 circuit will kick & then re-enable @ connected source's pwr-up.
post #1791 of 2213
I noticed, that e12 will kick on very loud and heavy basses.Is it possible that the DC-Servo swings at low Freq. wich will trigger the e12?
post #1792 of 2213
Don't think anyone is experiencing that (if so, chime in).
Are you using any parts other than those in the latest BoM (Parts List -> Full Excel BoM)?
post #1793 of 2213
I am using only BOM-Parts and it happens only once so far. I play a bassheavy Title from Feuerhake (TickTack) it´s a Trance Track, and Volumepot was at 1pm Position. I´m using a E88CC (6922) Tube. On all other Titles everything is ok. Source was a cheap USB-DAC.
post #1794 of 2213
mhhhh -cth-kit arrived today (thanks bill!), but when powering on, q1p starts to become really hot, smoke. any suggestions? (need additional infos?)

greets, dennis.
post #1795 of 2213
dennis,

Remove the regulator LM7824 chip, replace Q1P and then power up.

Check voltage at pin 1 or input of the voltage regulator IC. See if Q1P smokes out again.

If it does then you have a problem in your power supply section preceding Q1P, else you might have some fried transistors in the buffer and/or splitter circuit.
post #1796 of 2213
Thread Starter 
Wow. Many possibilities. THere is probably a short on the 24V side of the regulator which is drawing too much current and then burning up Q1P.

I know that the CTH is a tight board, but check all of the transistor polarities and make sure they are in the right places. Check the opamps to make sure they are in the right sockets and oriented correctly.

Check for solder bridges on the board anywhere.

Let us know what you find.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #1797 of 2213
Thread Starter 
Quote:
Originally Posted by acmemr View Post
I noticed, that e12 will kick on very loud and heavy basses.Is it possible that the DC-Servo swings at low Freq. wich will trigger the e12?
This is possible. The servo is definitely very subsonic though and shouldn't do this at any bass frequency that you can hear. Nevertheless, we have seen that some builds exhibit very unexpected e12 trips.

You can slow down the e12 or make it less sensitive if you want to do that with a few resistor changes.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
Reply
post #1798 of 2213
ok - q1p replaced and lm7824 removed, voltage between pin 3 and pin 1 is 33,4V, no smoke

btw: do r18l and r18r have to be present?
post #1799 of 2213
yes..R18L and R18R are your output resistors.

No smoke means your Power supply section is alright.

I would suggest removing all your splitter transistors (Q1S-Q6S) except for the TLE2426 splitter chip.

Then install a new LM7824 (use the old one if you don't have another). Power it on and check for voltage at pin 3 of the splitter opamp/ IC1S.
post #1800 of 2213
enough soldering for today...i'll try it tomorrow. thanks for your help!
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › A Very Compact Hybrid Amp