(AK) classA HA/Preamplifier.

[Deleted]

Feb 28, 2011 7:28:35 GMT XTRProf said:

Feb 10, 2011 20:05:51 GMT Will said:

Pin out of the LS devices

Just a quick check, which PTHs did you guys used for the LS devices? The outer or inner diameters? I'm going to put some "valve" sockets there so that I can easily swab between the test transistors and the LS devices after everything becomes stable. Also, I don't have to do any more solder work at those positions should the transistors kaput under use.

Hi Chong

how's it going?

i used the outer holes on mine with no problems

i know you are going to have this covered

but just to mention that i used Cardas Quatro solder for the HA boards. soldering those LS is pretty tight and the Cardas was just lovely to work with and made the job easier.

does it sound better?

I'm not sure but it flows better, seemed much more controllable and better for fine work than the normal stuff.

what kind of sockets have you in mind?

i hope you are enjoying the build

take care

[Deleted]

Also, becasue I'm going to "socket that area" I will need as much space as possble between pins for a better job done as well.

That's typical "wooly" thinking from a valve nut.
Fitting "valve sockets" is going to increase the capacitance between base and emitter, but more importantly between base and collector
of the devices.

[XTRProf]

Feb 28, 2011 10:48:08 GMT @sandyk said:

Also, becasue I'm going to "socket that area" I will need as much space as possble between pins for a better job done as well.

That's typical "wooly" thinking from a valve nut.
Fitting "valve sockets" is going to increase the capacitance between base and emitter, but more importantly between base and collector
of the devices.

Should not be much as the "sockets" are just pins without any "electrolye". Ideal will be to direct solder but then we will have a maintenance problem if and if the LS kaput as the PCB is just too thick to suck out the solder properly during desoldering. The degree of difficulty will be something like taking out a dip 8 IC and can destroy the pads during the desoldering process. Also, if we desolder too long, we can also destroy the LS devices if we choose to change to another device. Anyway, only "sockets" at the the LS place as the rest of the transistors are simply quite cheap even when destroyed during the desoldering process.

[XTRProf]

Feb 28, 2011 10:25:58 GMT @shaun said:

Hi Chong

how's it going?

i used the outer holes on mine with no problems

i know you are going to have this covered

but just to mention that i used Cardas Quatro solder for the HA boards. soldering those LS is pretty tight and the Cardas was just lovely to work with and made the job easier.

does it sound better?

I'm not sure but it flows better, seemed much more controllable and better for fine work than the normal stuff.

what kind of sockets have you in mind?

i hope you are enjoying the build

take care

Oh, just beginning to stuff some connectors, resistors that you and Will sent me, the diodes .......... Still doing now as my boss is away in the US for about 1.5 weeks and I can come home early.

The "sockets" are just improvised pins as used in the DIP8 sockets. Have thought about it for sometime yesterday and I think it's the best for those LS positions just in case the need for maintenance arises as the PCB is just too thick to suck free the solder during desoldering. That desoldering can destroy the pads if we are not careful. I will post what I mean when I have completed that operation. I have not started that yet and will continue to stuff some resistors after this and after eating dinner. I will post my "progress report" pictures later.

Yup, I like Cardas solder but I'm at present using Wonder solder which is lead free stuff and doesn't give you that shiny solder joint. I will change over to Cardas once I have used up the Wonder solder.

[Deleted]

I had a quick waz around for prices on the DACT CT2 stereo 50K, the best being on ebay;
here

this seller , (for when the product link dies).

At approx. £90 including post, compared to official distributors, eg in Uk at £132 plus post and Spain £145 plus post.

Anyone know better

[XTRProf]

Feb 28, 2011 15:23:00 GMT @cjarchez said:

I had a quick waz around for prices on the DACT CT2 stereo 50K, the best being on ebay;
here

this seller , (for when the product link dies).

At approx. £90 including post, compared to official distributors, eg in Uk at £132 plus post and Spain £145 plus post.

Anyone know better

Have you checked those ladder pots as well? Goldmine and Elma?

[Will]

Feb 27, 2011 22:21:18 GMT @sandyk said:

My hearing is not too good up at 100kHz ( ), but knowing that it's technically capable across a wide bandwidth is good, and shows the stability of the design.

Hi Will
Don't forget that it was square wave , not sine wave, which means that bandwidth is quite a bit higher than 100KHZ. This means that it is suitable for playback of 24/192 high resolution files.
I didn't check the -3dB point, as my function generator only goes to 300KHZ (in a fashion!)
Alex

Well, if you hadn't hit the -3db point by 300kHz, then this amp is spot on for the next must have resolution of 32/352-or-whatever-it-is! Nice to be future proof!!

[Will]

Regarding the two sets of pins for the LS devices, I went with this to make it easy to use either size of the device (we did not know what size we would get) In the end, we ended up with both the 352 and 313 in the smaller case, whereas we had the larger to78 case for one of the devices in the last GB for them.





In the end though, it seems much easier to fit the smaller device in the larger set of holes, as I did swearing when trying to fit the devices to the smaller holes. The future AK-Mods Class A power amp will have the larger hole set only.

[XTRProf]

Progress Report until today 1am (Singapore Time) ...........








That's all folks .......... Goodnight and nighty for me after bathing ..............

[XTRProf]

Feb 28, 2011 16:55:23 GMT Will said:

The future AK-Mods Class A power amp will have the larger hole set only.

Any Mk 3 AHA version with a thinner PCB, bigger pads and the offset adjustment for the op amp when using either AD744 or OPA134 to get close to 0 mV dc offset?

[Will]

Just out of interest how will you be powering the relays?

Hi Shaun,

I'll be using a 5v control circuit (posh for a small 6V traffo and LM7805 ), that'll be housed in the power supply, and feed in to the amp via it's own cable. As I want the amp to switch on when the input is selected, I've bought some mains rated relays that will switch the two main toroids on, when the front panel switch is turned on. This allows me to use a lower capacity signal switch to bring the mains in.

I'm glad you understand my idea for the signal switching, it proves that we are either both daft or I'm making sense, to some degree. The overall thing that I was aiming for is that when I'm doing my most critical listening (assessing a modification or upgrade, as opposed to relaxing and enjoying music) there are no energised relay coils near the signals. It just so happens this is the same state as just enjoying music.

Thanks for describing your bracketry. I bought my bracket, rod and bushing from ebay for £12, but the bracket is a flimsy and poorly pressed bit of metal. I think I have some angle in the shed, so will go with that, much sturdier I reckon. Do you think that 'shrinking the rod makes much difference?

[Will]

Any Mk 3 AHA version with a thinner PCB, bigger pads and the offset adjustment for the op amp when using either AD744 or OPA134 to get close to 0 mV dc offset?

Yes, Yes and maybe, but on the power amp

Mind you, those pads are still bigger than the ones I had with my pimeta and mini3. I reckon it's your eyes

Nice work, by the way

[Deleted]

Feb 28, 2011 15:23:00 GMT @cjarchez said:

I had a quick waz around for prices on the DACT CT2 stereo 50K, the best being on ebay;
here

this seller , (for when the product link dies).

At approx. £90 including post, compared to official distributors, eg in Uk at £132 plus post and Spain £145 plus post.

Anyone know better

Hi Chris

yes i ordered mine through ebay from him and he was the cheapest by a looooong way.

he seems reliable and mine arrived in the post after about a week.

I'm pretty happy with the one he sent me

my only complaint is that he did not send one of those nice big fat cigars with it

so good product, good price and efficient service.

so a BIG thumbs up from me

take care

[Will]

One thing I would point out, regarding the stepped attenuators.

I think originally that a bunch of us bought the the eBay steppers for our SCHA's, as they were similar price (back then) to the 'standard' Alps RK27 'blue velvet' pot , and offered an improvement SQ wise.

Don't feel that you need to fit a dact/elma/goldpoint to this amp to get the best out of it (even though it deserves it ), as the eBay stepped attenuators* will still offer better SQ than the typical pot based volume control, for the money, and get you going. The 'blue velvet' is also much cheaper these days.

Edit: Oh blimey! It may look it, but this post is not in reply to Shauns post up above!

* other volume control technologies are available

[Deleted]

I'm glad you understand my idea for the signal switching, it proves that we are either both daft or I'm making sense, to some degree. The overall thing that I was aiming for is that when I'm doing my most critical listening (assessing a modification or upgrade, as opposed to relaxing and enjoying music) there are no energised relay coils near the signals. It just so happens this is the same state as just enjoying music.Thanks for describing your bracketry. I bought my bracket, rod and bushing from ebay for £12, but the bracket is a flimsy and poorly pressed bit of metal. I think I have some angle in the shed, so will go with that, much sturdier I reckon. Do you think that 'shrinking the rod makes much difference?

Hi Will

I'll leave others to decide on our collective state of daftness

I've put shrink on the rod since building a Aikido pre and noticing a slight ringing when adjusting the volume. I've done it ever since and my thinking is that it won't make things worse.

if you would like a piece of that 3mm Ali i can get some to you. it's a long story as to it's acquisition but PM me if you'd like the full low down. believe me this is the top top top stuff.

let me know

take care

[Deleted]

Don't feel that you need to fit a dact/elma/goldpoint to this amp to get the best out of it (even though it deserves it ), as the eBay stepped attenuators* will still offer better SQ than the typical pot based volume control, for the money, and get you going. The 'blue velvet' is also much cheaper these days.

IMHO the Vlab out performs in terms of channel separation and bandwidth all of the tracked pots I've heard to date (and I've had a listen to most. one of the TDK ones i remember is pretty good but up there with the Dact price wise). IMHO the Alps Blue just don't get near to the Vlab SQ wise and i personally would not use one in the Class A.

horses for courses though and i may be wrong.

i loved my Class A with the Vlab and DACT so Will is spot on no super duper pot needed here to enjoy the Class A.

IMHO the DACT is a cherry among st cherries on a very good cake. i went with the DACT more for it's reliability over time not purely on SQ. although it is Better than the Vlab HF SQ wise i think i made the point that it's not a loooong way better over all.

take care

[Deleted]

Will,

Don't worry, I was only looking out of curiosity. I'll be starting off with the ebay smd jobby, if I get all excited I'll add the DACT later

Maybe I just have too much time to dream ahead before I actually build

Thinking from a preamp point of view, would it be possible to rig a mechanical LED switcher for input indication.
ie, have one rotary input selector to do the job of actual input selection. Maybe pop a D-shaft driven cog on it to drive the same type cog on another "slave" selector, this would then have the LED vdc running through it to switch the tell-tale LEDs?

I'm assuming the selector can handle low vdc.

just a nutty thought.......

Have you checked those ladder pots as well? Goldmine and Elma?

Chong, for me that would definitely be a step too far£££££££££££!

[Deleted]

Don't worry, I was only looking out of curiosity. I'll be starting off with the ebay smd jobby, if I get all excited I'll add the DACT later

Hi Chris

that's what i did and it worked for me

[Will]

Feb 28, 2011 18:03:24 GMT @cjarchez said:

Will,

Don't worry, I was only looking out of curiosity. I'll be starting off with the ebay smd jobby, if I get all excited I'll add the DACT later

Maybe I just have too much time to dream ahead before I actually build

Thinking from a preamp point of view, would it be possible to rig a mechanical LED switcher for input indication.
ie, have one rotary input selector to do the job of actual input selection. Maybe pop a D-shaft driven cog on it to drive the same type cog on another "slave" selector, this would then have the LED vdc running through it to switch the tell-tale LEDs?

I'm assuming the selector can handle low vdc.

just a nutty thought.......

Have you checked those ladder pots as well? Goldmine and Elma?

Chong, for me that would definitely be a step too far£££££££££££!

Hi Chris,

No problem on dreaming ahead, it's part of the fun I reckon, the audio diy version of being on a promise

As for the selector switch, I used this one uk.farnell.com/jsp/search/productdetail.jsp?sku=1123675&CMP=i-bf9f-00001000 which is lurking behind that new knob. It effectively has two 'separate' switches in one body, with 5 positions. You can use 'switch' for selection and the other led selection. I'll be using it to switch in relays, and power the led indicator from the dc going to the relay coil.

[Deleted]

Will,

you've got me baffled on that one! Your link was to a 2pole 5way switch, surely you'd need a 4pole? This I had thought of but wondered if passing signal and vdc so close together in the same switch may be counter productive.
Unless you can obtain two 2pole switches ganged on the same spindle?

Chris

[Will]

Hi Chris.

I think on this, it's different requirements that causing the confusion.
As I'm using relays to switch the signal and ground, I only need the one pole, and the 5 positions to meet my requirements. The other pole is unused (though I will most likely double up)

This switch could cope with signal (and associated GND) to 5 outputs , or 5 inputs to signal.

The led side of it would need another pole.

[Deleted]

Feb 28, 2011 17:16:13 GMT XTRProf said:

Feb 28, 2011 16:55:23 GMT Will said:

The future AK-Mods Class A power amp will have the larger hole set only.

Any Mk 3 AHA version with a thinner PCB, bigger pads and the offset adjustment for the op amp when using either AD744 or OPA134 to get close to 0 mV dc offset?

If you build it correctly using the LS devices you will not need any adjustment when using an OPA134 as recommended.
If you can't get close to 0mV at a normal listening level, then you have something wrong !
Even the bipolar input LME49710 which are not recommended in this application were able to do 7 mV.
The OPA134 are FET input with very low DC out. (check the data sheets.)

[Deleted]

Feb 28, 2011 20:22:47 GMT @sandyk said:

Feb 28, 2011 17:16:13 GMT XTRProf said:

Any Mk 3 AHA version with a thinner PCB, bigger pads and the offset adjustment for the op amp when using either AD744 or OPA134 to get close to 0 mV dc offset?

If you build it correctly using the LS devices you will not need any adjustment when using an OPA134 as recommended.
If you can't get close to 0mV at a normal listening level, then you have something wrong !
Even the bipolar input LME49710 which are not recommended in this application were able to do 7 mV.
The OPA134 are FET input with very low DC out. (check the data sheets.)

Hi Alex

I've used AD744 and OPA134 and they both get ridiculously close to 0mv offset.

Hi Chong

what's the point in complicating things on the board further for very little gain?

makes no sense to me

if it ain't broke
don't fix it.

take care

[leo]

Is the Dact ladder and the Valab shunt? if so I'd try replacing the series resistor on each channel of the valab with something like a Minimelf or other low noise low inductance type.

[Deleted]

Feb 28, 2011 20:59:30 GMT leo said:

Is the Dact ladder and the Valab shunt? if so I'd try replacing the series resistor on each channel of the valab with something like a Minimelf or other low noise low inductance type.

Hi Leo
The attached should answer your concerns.Attenuator design has improved .
Regards
Alex

The surface mounted resistors used on the standard Goldpoint Mini-Vs are 0.1% Nichrome THIN film with a thermal noise specification (TCR) of 25 PPM or 50 PPM. These are the best sounding resistors I have ever used (or ever heard). They have an essentially transparent sonic signature. This makes them better than Vishay S102, IRC RC55, or even Caddock MK32 resistor types, in our opinion, because they are not adding or subtracting any sound qualities to or from your musical signals - just precisely accurate level control.


Because of their precision, the standard Mini-Vs are also the best choice for recording studio and other Balanced Input applications. This precision means perfect channel-to-channel signal level tracking, so many audiophiles with regular (single-ended) stereo applications can skip the use of balance controls all together.
I highly recommend that you use our standard Mini-Vs unless you really need to build a custom value stepped attenuator with some other overall resistance value. For that situation you can use our Mini-V Custom (MVC) switches.
Goldpoint Level Controls used to offer Ladder and Shunt type stepped attenuators too. The fact is that with the very low noise, 0.1%, thin film resistors we are now using, we believe that there is no real advantage to Ladders and Shunts - and so have ceased offering them. The Mini-Vs sound that good! You get a more reliable level control - at a lower cost!
Goldpoint stepped attenuators, with their make-before-break, "low bounce", hard-gold switch contacts, do not create "clicks" or "pops" during use. (The Ladder and Shunt type attenuators of the past sometimes did.) They add only one switch contact per channel to the signal path. They make great potentiometer upgrades, are easy to install, and will last a lifetime under normal use.


www.goldpt.com/compare.html