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A Very Compact Hybrid Amp - Page 122

post #1816 of 2213
Quote:
Originally Posted by sachu View Post
No..always measure with respect to SG (star ground).Since you have tombstoned the two diodes, D1p and D3p (they are right next to each other i believe), very carefully with the red probe on the exposed lead on top of the diode and the other black probe on SG..measure the voltages at these two diodes.

ahhh, ok 34,5v! (both)
post #1817 of 2213
ok..if both D1P and D3P are measuring that and you are not getting similar voltage at pin 1 of LM7824 regulator (chekc to make sure u are measuring pin1) then your Q1P and Q2P transistors need to be swapped out.

If that isthe case, swap those transistors out and then remeasure at pin 1 of regulator.
post #1818 of 2213
ok, i'll swap them ... is there a electronics-friendly way to discharge the caps faster than waiting?
post #1819 of 2213
Quote:
Originally Posted by speedbasslenny View Post
ok, i'll swap them ... is there a electronics-friendly way to discharge the caps faster than waiting?
lick your finger and bridge the contacts
post #1820 of 2213
Naughty Naughty Smeggy..
post #1821 of 2213

It Lives!

Well my CTH is up and running. Being a newbie it took me about 2 days off and on working on it to get it put together. Started with the Spruce Canyon kit with upgraded caps. Started on the first try (made sure to check, re-check, and then check one more time all parts) and sounds great. First impression is that my D10 with topkit is now relegated to DAC duty (he's not happy but that's tough). Incredibly three dimensional sound. Currently have a 6DJ8 Bugle Boy in it and enjoying the powerful bass.

Question: I have a CBS 7730 to try but want to make sure that this will use 6V heater setting. Is this correct?

Also, what have you guys experienced with burn-in times, especially with the upgraded Sonicaps?

Looking forward to many hours of listening.
post #1822 of 2213
Thread Starter 
Great!!!! It's a nice little amp in a very small package.

I think that 7730 is a 12au7 equivalent which means 12V heater setting. Perhaps someone else can verify.
Dr. Cavalli gained notoriety with his first DIY amplifier projects. His success has blossomed into Cavalli Audio, a world leader in amplifier design.
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post #1823 of 2213

Hum

So I've got a little hum issue. When the amp is on with no music playing I hear a bit of hum. If I crank up the volume the hum gets louder. When I touch the pot or the 6/12v heater switch the hum drops a bit. Also, it sounds like it's coming from the left side (about 11 o'clock on the soundstage). I've got SG grounded to the case and the pot grounded to the same point. I'm wondering if I should have shielded the coupling cap leads. I'm using upgraded Sonicaps here tombstoned and I'm thinking that these long leads (around 1 inch) are picking up some interference?

Thoughts?

Edit: it happens with all tubes (both 6 and 12V). I used teflon covered silver wire throughout. Should I have used shielded?
post #1824 of 2213
I have been reading both this thread and the EHHA thread here. I know a number of posters here have built both amps. I realize this is sort of a David versus Goliath comparison, but I am trying to decide which amp to build to power my AKG K-501's and Fostex T50RP (not modded - yet!). I realize I could build the CTH first and do an EHHA down the road.

There seems to be about a 3X cost difference between the 2 amps, once you add even a modest case into the EHHA cost. I guess my question is - is the cost difference worth it in terms of sound quality? The CTH has the portability going for it, which would be nice, but I can live with the EHHA size, IF the SQ is so much better that it makes it worth the cost difference. I can use it with my main stereo rig pretty easily.

I listen to mostly classical (symphony orchestra, concertos, etc.), pop / rock (John Mayer, Sheryl Crow, older Genesis, Split Enz, Lucia Micarelli, Sting), some Jazz (Weather Report, Wynton Marsallis, etc.).

So, can anyone comment on their perceptions of the real sound difference? Is the EHHA really 3X better? Thanks in advance. Oh, you can PM me if you would rather keep this thread less busy.
post #1825 of 2213
Quote:
Originally Posted by stringgz301 View Post
Well my CTH is up and running.

Question: I have a CBS 7730 to try but want to make sure that this will use 6V heater setting. Is this correct?
Quote:
Originally Posted by runeight View Post
I think that 7730 is a 12au7 equivalent which means 12V heater setting. Perhaps someone else can verify.
Congrats stringgz301. Your going to love this amp.

Yes, the 7730 is an instrument grade 12AU7. Some versions were made with gold pins, some not. Enjoy.
post #1826 of 2213
Quote:
Originally Posted by CYoung234 View Post
I have been reading both this thread and the EHHA thread here. I know a number of posters here have built both amps. I realize this is sort of a David versus Goliath comparison, but I am trying to decide which amp to build to power my AKG K-501's and Fostex T50RP (not modded - yet!). I realize I could build the CTH first and do an EHHA down the road.

There seems to be about a 3X cost difference between the 2 amps, once you add even a modest case into the EHHA cost. I guess my question is - is the cost difference worth it in terms of sound quality? The CTH has the portability going for it, which would be nice, but I can live with the EHHA size, IF the SQ is so much better that it makes it worth the cost difference. I can use it with my main stereo rig pretty easily.

I listen to mostly classical (symphony orchestra, concertos, etc.), pop / rock (John Mayer, Sheryl Crow, older Genesis, Split Enz, Lucia Micarelli, Sting), some Jazz (Weather Report, Wynton Marsallis, etc.).

So, can anyone comment on their perceptions of the real sound difference? Is the EHHA really 3X better? Thanks in advance. Oh, you can PM me if you would rather keep this thread less busy.
I would say in general ($/SQ ≠ 1) spending twice as much on an amp doesn't mean you'll get twice the SQ... especially once you build any decent amplifier like you find mentioned on the forum (even a CMoY). I would say that even with the cheapest, simplest amp design your 80%+ there in terms of SQ.

Many times amps also just "sound" different and match better with different headphones, so it's more of a personal preference. The only major differences I've heard going from a CMoY to a SOHAII is that the latter has better bass control (bass is tight and not boomy) and there's better separation in instruments and highs have more clarity. I would say start small and simple and build from there... once you've heard it and a few other amps you'll know the sound your after.
post #1827 of 2213
Thread Starter 
Quote:
Originally Posted by stringgz301 View Post
So I've got a little hum issue. When the amp is on with no music playing I hear a bit of hum. If I crank up the volume the hum gets louder. When I touch the pot or the 6/12v heater switch the hum drops a bit. Also, it sounds like it's coming from the left side (about 11 o'clock on the soundstage). I've got SG grounded to the case and the pot grounded to the same point. I'm wondering if I should have shielded the coupling cap leads. I'm using upgraded Sonicaps here tombstoned and I'm thinking that these long leads (around 1 inch) are picking up some interference?

Thoughts?

Edit: it happens with all tubes (both 6 and 12V). I used teflon covered silver wire throughout. Should I have used shielded?
Does the hum level change if you move the amp to different loctions? Or closer and farther from line cords, wallwarts, etc?? If yes, then it could be the cap leads. If not, it's probably something else.

If the amp is inside the hammond enclosure you shoudn't need to use shielded wire on the inside.

If the hum is not coming from outside the amp then we have to debug the internals and the grounds and the solder joints, etc.
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 #1828 of 2213
@ CYoung234 - Others may come in & give you some thoughts on the amps you've asked about. But I did want to sort of echo bmwpowere36m3's comments... Think cost of equipment vs perceived SQ is a diminishing returns thing, like a non-linear curve where you pick your spot. And perhaps move up it, esp if you go to meets & hear other things.

If you like to build & have the ability, you'll be building more than one amp & the FS forums are very active here, so no decision needs to be final
post #1829 of 2213
Quote:
Originally Posted by cfcubed View Post
@ CYoung234 - Others may come in & give you some thoughts on the amps you've asked about. But I did want to sort of echo bmwpowere36m3's comments... Think cost of equipment vs perceived SQ is a diminishing returns thing, like a non-linear curve where you pick your spot. And perhaps move up it, esp if you go to meets & hear other things.

If you like to build & have the ability, you'll be building more than one amp & the FS forums are very active here, so no decision needs to be final
Thank you for your reply and to bmwpower36m3 as well (nice car by the way - I drive an e39 5 series myself). Your answers mirror what I suspected I would hear.

I suspect I will start with the CTH and go from there. I am actually not building this - my twin brother (Pars on this forum), will be. He was the one who originally suggested an EHHA. I have listened to his Gilmore and a few other headphone amps as I have been buying headphones. However, I am a big fan of hybrid amps. My home stereo uses a Counterpoint SA-220 hybrid power amp with an Audible Illusions Modulus 2D preamp, driving Apogee Centaurus ribbon hybrids.
post #1830 of 2213
Tried moving the amp and it has no effect. Hum is slightly stronger when I touch the pot but not much. With no input (jack not plugged in) there is no hum.

Setup is Macbook -> D10 (via optical) -> CTH (via line out). When I run directly from the Macbook to CTH via the headphone out there is no hum!!! If I touch the D10 the hum drops about 25%. If I turn off the D10 the hum gets very strong. What is going on?
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