and now for something completely different part 3

[sorenb]

2 hours ago, jose said:

My amp module is ready. Now I'm working on a second Psu for the amp (dual-mono) and at the same time I work on the unbal/bal preamp (I have the PSU ready). I want to do a three module system.

Very nice build Jose con grat!

[MASantos]

Hey guys, starting to think about ordering the parts for this. How many of the output transistors should I get for matching? 

[Pars]

Because these are used in a Darlington configuration, the matching is a bit different on these. You can use either the MJE or MJF (the MJE tabs aren't isolated so you'll need pads and washers to insulate these from the heatsink). I would probably suggest 16 of each or so?

[MASantos]

1 hour ago, Pars said:

Because these are used in a Darlington configuration, the matching is a bit different on these. You can use either the MJE or MJF (the MJE tabs aren't isolated so you'll need pads and washers to insulate these from the heatsink). I would probably suggest 16 of each or so?

Could you elaborate on the matching process then? Shouldn't I just use 3 matched N and 3 matched P?

 

ps: check your inbox

[Pars]

These are really more matched as pairs, though having them all match if possible is always good. I did Q14/Q16, Q12/Q13 and Q5/Q17. Q21 is by itself, so no matching. For the front end, Q1/Q2/Q4/Q6, Q9/Q11, Q3/Q8, Q15/Q19, Q10/Q7 and Q27/Q28 if you can (SMT, but I was able to do some matching while still packaged by pushing resistor leads thru the covering.

[jose]

I bought 35 of each one for this proyect.  

I like to have reserve inventory.

Edited March 4, 2018 by jose

[navigator]

Hi All,

What do you think on running this amp on 4 SLA battery?

I know, not very practical, need decent batteries for hours of listening.

I'm really excited to build CFA 2 and supplied from GRLV, but I'm just thinking about battery also. Probably I would not stay with batteries, but I'm curious if you have tested. ?

Before, I had more effect from one PSU to another sometime than one amp to another. I have used to start the amps and do initial tests with a HP6624 PSU and strange, but I was never able to build one as good as this monster rack PSU.  .... but, not listened to the GRLV .... yet.

Thanks!

[Pars]

An SLA has more noise than a GRLV,  so I guess the question is why? Kevin had to use a screen room to measure the noise on a GRLV; something like 1 nV (it's in the GRLV thread).

[navigator]

5 hours ago, Pars said:

An SLA has more noise than a GRLV,  so I guess the question is why? Kevin had to use a screen room to measure the noise on a GRLV; something like 1 nV (it's in the GRLV thread).

Noise is just one parameter. Internal resistance, reaction time etc. is another - which is less important with class A amp, but still, I do not think that only noise counts. ... and, it is not straight forward that a better measured would sound better.

I'm almost sure I will stay with the GRLV, but I'm still curious. Long time ago, with preamps I did like the battery supply. That was NiCd. 

 

[navigator]

On 11/29/2017 at 11:57 PM, ti5002000 said:

Guys( the ones that already built the amp) ,what do you think in comparison with ss dynalo?

Hello,

I would have still the same question. I was reading the thread and I found a few bits of evaluations, but I would also appreciate if you guys would comment on how it really compares with ss dynalo. What are the positive and negative aspects with what source, what music and what headphone? How is it pairs with typical sennheisers "treble rich" sound? Is it emphasize it or compensate it? Neutral?

Thanks!

[jose]

I am very bad describing sounds and more when my language is not maternal.

IMHO CFA is very, very neutral I would say almost "surgical" with all headphones. My Dynalo SS too but it has a bass more warm and musical... if you like this term.

I think it would be more fair to compare the Dynahi SS with the CFA bal.

Obviously CFA is much more powerful than the Dynalo SS (Besides, my CFA is balanced and dual mono while the my Dynalo SS is "only" balanced), but with both you´ll have enough power to move things like the HD6X0, Akg, Beyer ... balanced or in SE, so I wouldn´t worry much about that except when you try to move the LCD or headphones with a miserable sensibility. Here, the CFA is the King but in exchange for losing that musicality that has the Dynalo SS.

 

[Pars]

My take: I’ve only listened to either of these with orthos (modded fostex t50rp). I always found the Senn hd6xx to be too syrupy for my taste. I’ve never listened to the HD800s (I know Kevin really likes the ss Dynalo with these).

This is comparing an SE CFP to a balanced SS Dynalo. First off, I don’t find the Dynalo to be more musical than the CFP. The CFP handles the orthos better, particularly in the bass. The CFP is neutral, though slightly darker than the Dynalo, which might just be a reflection on it being able to drive the orthos better with higher current capability. The CFP is using a single GRLV @+/-30V; the Dynalo also uses a single GRLV @+/-20V.

 

Edit: I didn’t mention that the Fostexes are wired balanced, so the SS Dynalo is SE in->bal out

 

Sent from my iPhone using Tapatalk

 

 

 

 

[navigator]

jose, Pars, I appreciate your posts. It is important for me because my first impression from reading the threads was that CFP is clearly above, now, I see the picture is not that simple (as always :-).

One more thing, jose, what headphone you use?

Thanks!

[jose]

Pars's point of view is very interesting. I only have two orthos (LCD2 and HE400I both balanced) and is true that with the CFA both has more bass and more "punch" but I think that which is due to the great power of the CFA. The rest of my headphones sound more neutral with the CFA than the Dynalo SS.

Notes: My Dynalo SS has Jfets (2SK170/2SJ74) on the input too and I guess this can also be a factor to consider but Pars has more experience with this. 

[jose]

43 minutes ago, jose said:

Notes: My Dynalo SS has Jfets (2SK170/2SJ74) on the input too and I guess this can also be a factor to consider but Pars has more experience with this. 

Thinking about this. Would it be possible to change in CFA Q9 and Q11 by Jfets as we did in the SuSis?

Edited April 5, 2018 by jose

[kevin gilmore]

I think it may screw up the first stage bias currents, but you can certainly try it.

[Pars]

Maybe the schematic is missing a connection point, but it appeared that Q9/Q11 are biased solely by the input?

At any rate Jose, it appears you are running a balanced CFP2? If so, if it were me, I would front-end this with a ubal->bal board, and use JFETs as the input stage for that. It will be a) transparent, and b ) give you flexibility on using SE sources as well as balanced. Well, transparent unless you are one who can hear a) plating on connectors, b ) teflon vs. cotton vs. air vs. any other form of dielectric known to man, or c ) some form of crystals within 1 mile of your listening environment, or d) grass growing.

Hate how the forum software turns a "b)" into a smiley

 

[jose]

No, noooooooooo... I assure you that my hearing skills are quite common.  

My idea is to test if the improvement is real using Jfets instead of Fets. Measurable things like the ones I saw on the Dynalo/hi Susi using Jfet vs Fet (or rather the That340. How I hate that integrated shit ). 

Probably you are right it´s a better idea to experiment on the unbal/bal or buffers instead of the amplifier. That by the way, I have to say that the un / bal works great. I have been using balanced and SE and it sounds nice, very nice.   I have also seen that the CFA works better with the unbal / bal with a 10k pot as preamp than with my Classé preamp. I´m not sure why

*About the buffers, these continue to give me real headaches,  I don´t get them to work.

 

[kevin gilmore]

the cfa input is a diamond buffer and is biased thru the base currents of the input pair.

[jose]

7 hours ago, kevin gilmore said:

the cfa input is a diamond buffer and is biased thru the base currents of the input pair.

Thanks Dr. Gilmore.  Silly question, what's the point of putting another buffer between unbal / bal boards and the CFA if it already has a buffer in its input? Just adapt the impedance?

I am using the unbal / bal directly connected to the CFA and the result is great. 

[kevin gilmore]

No reason for an extra buffer

[ti5002000]

Guys could use i use normal mpsw06 and 56 in place of the pzta06 and 56?Maybe soldering the colector leg only to the big pad?

I got many of the mpsw and the pzta are always off stock in mouser...

[Pars]

^Probably (respect any pinout differences). I think they are effectively the same transistor/die. The only thing that could potentially be a problem would be cooling. I know the pzta parts were put in because of that (power going beyond the BC capability and the MPSW being discontinued).

[ti5002000]

5 hours ago, Pars said:

^Probably (respect any pinout differences). I think they are effectively the same transistor/die. The only thing that could potentially be a problem would be cooling. I know the pzta parts were put in because of that (power going beyond the BC capability and the MPSW being discontinued).

Thanks Pars. 

I could maybe ,put some heatsink in it ,to avoid heat issues.

Another question ,if you guys can help. 

Can i use BC550/560 if i only go up to 22v in the power supply?

[lkong]

Got my Uberamp boards.

Here's my version of BOM if it helps anybody: https://docs.google.com/spreadsheets/d/1EIAvFJHqTJL5zzM43FIhz-wJhd_scJiClbLd24QNv9s/edit?usp=sharing

Here are a few questions:

1 Power rating of the big .47 resistors. The best option for 10W seems to be this: https://www.mouser.com/ProductDetail/Xicon/280-CR10-047-RC?qs=sGAEpiMZZMtbXrIkmrvidMioh4DscLtBmqbN3KPTLlY%3d Although the lead space is shorter than the length of the resistor. There are a lot more options at 5W.

2 What's the 5k trim pot for?

3 How to wire it for balanced setup (2 boards per channel)? Also what are +/- reg drvier for?