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 21

post #301 of 2213
I could have sworn that there was info about his at Cavalli Audio at one point but maybe I was thinking of the SOHA II since I had previously thought about making it.

Why are some using a long version of the case? Is it to fit a Bantam Dac inside?
post #302 of 2213
Quote:
Originally Posted by m0b1liz3 View Post
SNIP
Why are some using a long version of the case? Is it to fit a Bantam Dac inside?
To be able to use RCAs and An RK27 or stepped attenuator.

EDIT: There's at least one amp in the works this weekend with such a configuration....
post #303 of 2213
It took a while for my board to arrive too (not as long as Ludo(sorry) but I'm only in Canada), and had some pressing school work I had to attend to, so I wasn't able to get started until yesterday. I'm about half way through populating my board, and want to put in some quality time tomorrow to get it done. I sold my work amp, and have been missing having music at work. With the complexity of the board (over 175 components) and tightness of the components, its critical to take a very methodical approach to building this little beauty.

Alex has made the CTH web pages available to the proto crew, but he probably wants to make sure that we help find all the "kinks", as well as adding any build details that we may have discovered. He'll likely wait until the proto phase is over before he releases the CTH web pages.
post #304 of 2213




It lives. I'm using a Context Engineering case, I need a 1/4" cardboard shim to keep the PCB from sliding front to back, but it still slides side to side about 1/16" (slots are 3" wide exactly). It's mounted in the 3rd from the top slot. Big caps are mounted under the PCB. The 24V reg is mounted underneath to the angle bracket show. I couldn't get the second screw (wiring difficulties mentioned below) in there so I used only the screw closest to the middle of the case.

I'm using a 120-ohm output resistor on each channel. I mounted it directly to the output jack instead of in the PCB slot.

Changes from the BOM:
- different jacks.
- different switches.
- different case plenty of room on the front panel for a decent sized knob.

Snags I hit...
1) Put C3P in reverse, promptly blew out Q1P and Q2P on power up. Reoriented C3P and replaced Q1P and Q2P and all was good.
2) Wiring the input jack in the back. PITA! The wire I used is too stiff (Kaptan shielded twisted pair), but would make a good whip. The amount of time to "stuff" the wires into the case was about 30 minutes, that's how much of a PITA it was. I needed extra length so I can pop the panels off as I bottom mounted the 24V reg onto an angle bracket.

Other than that, all is good. If I ever need to open this again, I'll need to find more flexible wiring for the input jack to pot.

It's pleasing so far using the EH 12AU7 tube, but too early to really comment. I may switch to RCA 5963 soon. It's still a bit too much gain for high sensitivity low-Z headphones, even with the 120-ohm output resistance. I dare not go over 120-ohm.








post #305 of 2213
^C3P-Oh!(I did that with R2D2 once)
Great looking case, I like the heatsink(big MacGyver fan).
Look forward to reading your listening impressions.
post #306 of 2213
Quote:
Originally Posted by holland View Post
It lives. I'm using a Context Engineering case, I need a 1/4" cardboard shim to keep the PCB from sliding front to back, but it still slides side to side about 1/16" (slots are 3" wide exactly).
< snip >
I'm using a 120-ohm output resistor on each channel. I mounted it directly to the output jack instead of in the PCB slot.
< snip >
It's pleasing so far using the EH 12AU7 tube, but too early to really comment. I may switch to RCA 5963 soon. It's still a bit too much gain for high sensitivity low-Z headphones, even with the 120-ohm output resistance. I dare not go over 120-ohm.
Hey, looks good & glad you got it going & like the sound so far...

Re: case - Yes the 75mm wide PCB is made for cases that take that size... Guess those made for 3" wide PCBs will have a little wiggle.

I lucked into a 2nd Proto PCB and will be building it in a similar case type, but larger 150mm x 105mm x 55mm (6" x 4.2" x 2.2") enclosure:
Aluminum Project Box Enclousure Case Electronic DIY-Mid - eBay (item 250343308549 end time Mar-14-09 21:01:18 PDT)
So Alps blue RK27 & all sorts of (internally switched) jacks & RCAs can fit. Will have to get creative w/stand-offs I think

Plan to bring both of these to the upcoming NYC Spring Meet..

Re: Gain/output resistor - Those must be some efficient low-Z cans. BTW, technically the output resistor is supposed to be in the OB loop & should be PCB mounted in R18 spots (I'd found it not that big a deal in POC)... And I think runeight has recommended a 150R max.

Re: tubes - There are a lot to explore... I've tried both an EH 12AU7 & RCA 5963 but so far really like a fleabay BIN Holland Amperex 6dj8 (search "amperex 6dj8 HOLLAND CODE") & the Siemens 63 ECC82 chrome I've talked about.
post #307 of 2213
Thread Starter 
Yes, let me suggest strongly that the series output resistors go on the board in the R18 slots so that they will be inside the output buffer servo loops.
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 #308 of 2213
Nice work Holland! I'vebeen raiding tubes fro my SOHA/SOHAII collection - The 5963 is nice, been giving some bugle boy 6dj8's a chance, and RCA Clear top. Still really like 12BH7s.

I tried some 12AT's but couldn't get the buffers to stabilize, not so fond of that tube anyhow...
post #309 of 2213
Quote:
Originally Posted by cfcubed View Post
but larger 150mm x 105mm x 55mm (6" x 4.2" x 2.2") enclosure:
Aluminum Project Box Enclousure Case Electronic DIY-Mid - eBay (item 250343308549 end time Mar-14-09 21:01:18 PDT)
So Alps blue RK27 & all sorts of (internally switched) jacks & RCAs can fit. Will have to get creative w/stand-offs I think
Thanks, cfcubed.

Interesting case. If you can measure the PCB slots (for potential future stuff), I would guess no more than 1/4" off the bottom.

There are some corner edge PCB slots out there that can be mounted the case.

Quote:
Originally Posted by cfcubed View Post
Re: Gain/output resistor - Those must be some efficient low-Z cans. BTW, technically the output resistor is supposed to be in the OB loop & should be PCB mounted in R18 spots (I'd found it not that big a deal in POC)... And I think runeight has recommended a 150R max.
I chose 120 for the supposed 120 ohm output resistance of some headphone jacks.

I tested with a DT440 that I have. My source is @ 2Vrms and the position of the pot is showing the limitations of the RK097 (imbalance) for quieter listening sessions. I suppose I can shunt the pot and drop another 6dB.

Edit: It's also possible I listen at a lower level?

Quote:
Originally Posted by cfcubed View Post
Re: tubes - There are a lot to explore... I've tried both an EH 12AU7 & RCA 5963 but so far really like a fleabay BIN Holland Amperex 6dj8 (search "amperex 6dj8 HOLLAND CODE") & the Siemens 63 ECC82 chrome I've talked about.
I switched in some RCA 5814s right now. Just looking for tubes I have that are odd man out right now.

Quote:
Originally Posted by runeight View Post
Yes, let me suggest strongly that the series output resistors go on the board in the R18 slots so that they will be inside the output buffer servo loops.
I'm not sure I understand this. Can you elaborate? If in series with the jack, it would be similar to using high-Z cans vs. low-Z cans. I don't understand the differentiation as to whether or not it is within the servo loop.

Edit:

One of the reasons I did this is because I've been building my amps with both 120ohm and 0ohm output jacks. Lately I've been using the 120ohm more frequently. I could've socketed R18, but it's in a harder spot to reach, and it seemed easier to put them on the jack for quick replacement.
post #310 of 2213
Quote:
Originally Posted by cfcubed View Post
I lucked into a 2nd Proto PCB and will be building it in a similar case type, but larger 150mm x 105mm x 55mm (6" x 4.2" x 2.2") enclosure:
Aluminum Project Box Enclousure Case Electronic DIY-Mid - eBay (item 250343308549 end time Mar-14-09 21:01:18 PDT)
I used the large case for my M^3 - basic and not bad cases. I was thinking about standoff mounted clips/clamps along the edge for the next one of these I might build ( The rumored balanced one. ).

If only there were room for three little mounting holes - that's just how tight this layout is!
post #311 of 2213
Quote:
Originally Posted by wiatrob View Post
Nice work Holland! I'vebeen raiding tubes fro my SOHA/SOHAII collection - The 5963 is nice, been giving some bugle boy 6dj8's a chance, and RCA Clear top. Still really like 12BH7s.

I tried some 12AT's but couldn't get the buffers to stabilize, not so fond of that tube anyhow...
Thanks wiatrob. I have a good size stash of tubes from the SOHA 2, so I'm just rummaging through them. It does sound different than the SOHA 2, so far. The sound seems a bit more dense.

I'm using some RCA 5814a tubes right now. It seems to sound better in this than I recall in my SOHA 2.
post #312 of 2213
I keep going back to my Bugle Boy. I dunno what it is, it just seems "smoother" then all the rest. My ears never get tired no matter what Im listening too. Maybe has has to do with the fact that I only have AKG's.....

Im glad these are getting pumped out! I cant wait for a production board so I can build one for my bro, hes an audio engineer so he should be easy to get into the scene.
post #313 of 2213
Holland, Who are you sourcing the Context case from?

I'm off to listen to my Compact Hybrid (thinking 8416), study up on cascode circuits, and drift off to sleep....
post #314 of 2213
Hey does anyone have a 1/4 inch insulated jack they could spare me? I wanted to get away from using a 1/4 to 1/8 adapter for the CTH and I discovered that there just isn't room for the locking 1/4 Neutrik that I had on hand on the panel after mounting the RCA's and the Blue Velvet. Of course, being the stubborn type and wanting the "all metal" look, I bought the Hammond version with the metal end panels.
post #315 of 2213
Quote:
Originally Posted by wiatrob View Post
Holland, Who are you sourcing the Context case from?

I'm off to listen to my Compact Hybrid (thinking 8416), study up on cascode circuits, and drift off to sleep....
Ah cool. I like the 8416 tube very much, but it depends on the headphones.

I bought the Context Engineering case from Fry's. They have a nicer feel than the Hammond cases, and I use Context Engineering quite a bit. I'm local to Fry's (and Context Engineering, but it's a hassle for them), but frys.com sells it and so does Circuit Specialists. The prices are the same for frys.com and in store. I'm not sure what the shipping to CO would be.
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