Record-out buffer for Aleph1.7

[joho]

Hi Gents,

At the moment i'm working on a Aleph1.7 printboard design. My gool is a dual mono design compleet with dual supply,input relais,muting relais and the original shunt volume regulation.This all together on one dubble sided board (A4 format).
It's almost finisshed but there is a little space left for a record output buffer.
I want to use the original 60V supply because it's already avalable on the board.I did some research on the web and found two options and a variation on option 2. I build them like a "christmas tree" and did some measurement.They function well and the idle current for option 1 is 20mA and for option 2/3 5mA. I think option 1 is the best but a little overkill for a rec.out buffer so i concentrate on option 2 and 3. Also the space aspect on my printboard counts.
The problem with option 2 and 3 is the high supply voltage. Esspecialy the 2sj70(Uds 25v max) could be a problem. I try it with 60v supply voltage and it keeps working but i have a bat feeling about it. What to do ? use a pre-regulator ?(extra space on the board).

I few questions ;

Has it any sense to use the source resistors(10R)in option 3 ?

I can shift the working point by changing R11/R20 to 100k so that should be better for the 2sj70 but is it allowed for such a sourcefollower design ?

What is the output impedance of option 2/3 (5mA)?

Other idee's ?

Best regards,
Johan.

[joho]

Hmm. not much response for some serious questions. Maybe my Englisch is too bad.

O.k. here we go. I spoke to our local guru and he said don't use that drain resistor, it's bad for the output impedance so i use the pre-reg. to reduse the voltage to 30 volts.
See rec.out buffer rev1.
I implement this circuit on the main Aleph board and afterwards i had just enough space.

By the way , i found some image export possibility in Eagle so no screenshots anymore.

follow up.
Johan.

[joho]

Here is a complete Aleph 1.7 board. The most partnumbers refer to the original Pass design.The only difference is the relais supply,a unbalanced rec.out buffer and input relais on the main board.
At this moment i'm using one of the famous boards from Kristijan. The board sounds good and for a single-sided design the placing of the components is almost perfect.
Like the most bloody minded electronic-freaks, i wants to use my own choice of components and give a design my own signature. It's as the famous Dutch compagny said; Let's start(try) to make things better.
A few months ago there was also a 1.7 design made by a guy from Finland. That printboard gave me realy some serious inspiration and was the start for the final result. My gool was to make a complete all in one dual-mono board with star ground, as symetric as posible and short traces. I was thinking a long time about the use of 45 degrees curves. In the Pass designs it's usual to use only 90 degrees curves but that uses a lot of space. Maybe there was some discussion about that subject on the forum but a couldn't find it. Also the emc-suppression of my board is not optimal but this is such a specialism that i keep that for later times.

I didn't yet made this board for real so please give as much comment as possible before i turn on the etching machine.

Best regards,
Johan.

[Klaus]

Hi,

another idea, I did it this way in my P1.7. I have a "rec out on" switch on my front panel. It activates via one relay the connection of the passive rec out circuit w/o any buffer to the switched inputs. It can effect the sound of the P1.7 in a negitve way - but just when recording is running. Switch off means no influences at all. And for shure no buffer is affecting the quality of the rec out signal... A smart and simple solution

Of course I have to take care not to switch the same input as rec out destination. Bu I was not willing to create a own tape input szenario. Too seldom I do record.

regards

Klaus

[joho]

Hi Klaus,

I think we are on the same lime. When you look at my thirt posting there is a complete printdesign of the Aleph1.7. When you look good at the circuit around relais 19 and 20 you see the buffer circuit switched by ... I know, it's a bit a jigsaw and the partnummers of the little buffer schematics don't correspond with the printdesign. You know it's much easier(faster) to draw schematics on paper.
By the way, the first buffer i tried was a little variation on the design that you used at your D1 output.Thanks for that posting. It works very good but i didn't have enough space on my board.

What do you think of the pcb ?

Regards,
Johan.

[Klaus]

Hi Johan,

I talked about "no buffer" - I do not know why any buffer for this temporary rec out should be necessary. So I can not follow your ideas...

In principle I like your PCB - just the big coupling caps are IMHO not usefull. As written frequently before I prefer standard Panasonic FC electrolytic caps. They sound super and cost almost nothing... ANY big foil monster I compared against sounded tired. If interested in check again the other current treads about coupling caps.

Regards

Klaus

[joho]

Hi Klaus,

When you connect a record device direct on the input there is some influence. That's all clear.To use a record switch or relais makes the problem temporary. You can choose for that. Otherwise i had some small space left on the PCB and with a buffer i expect no influence and i can drive a longer cable without problems. That's the idea.

About the coupling capacitor story i spoke you before and in my actual 1.7 i use the FC's+1837's. It's much better than the standard wima 10uF mks.
I'm just like the most of us a little bloody-minded and want to have the possibility to use Mcaps.I never try them. Maybe i never use them but there is enough space and a FC always fit.

A total different question ;
I had a quick look in your personal data and found something interesting about impulse correct speakers. In Holland there is a impulse speaker factory but i have never seen a type "correct". Is it something special for the German market ?

Best regards,
Johan.

[Klaus]

Originally posted by joho
Hi Klaus,

A total different question ;
I had a quick look in your personal data and found something interesting about impulse correct speakers. In Holland there is a impulse speaker factory but i have never seen a type "correct". Is it something special for the German market ?

Best regards,
Johan.

Hi,

now I got you regarding caps... Regarding rec out buffer I hope that my source device buffer is capable to drive in between the P1.7 and the cable to the higher impedance rec in. When I see e.g. the NE5534 input buffer in my DAT recorder I do no longer think about losses of sound performance...

"Impulse correct" speakers means no brand. It means speakers designed to reproduce as well as possible a step response. Like electrostatic/-magnetic speakers or width range speakers are doing. Many guys and my ears tell me that those speakers sound so much more realistic. The company Audio Int´l in Germany created DIY kits with ESS AMT-speakers and 18´´ Excel Mg chassis which follow this ideal. Currently nothing is online about it because the main dealer reworks his homepage.

Regards

Klaus

[joho]

Hi Klaus,

Probably you're right. The most record devices are not really hi-end. Otherwise a good buffer does no harm.

The impulse correct story sounds very interesting , maybe you can start a threat at the speaker builder part of this forum.

Anyway, thanks for the info and the serious response.

Regards,
Johan.

[AuroraB]

Very nice PCB, Joho...............

Any files??