Kofi Annan in: "Cascodin' with Steve Bench's RIAA!"

[Sheldon]

You got it, except for one thing. I wouldn't reference the supply to ground, but lift it to about 50V.

Alternatively to the 12.6V supply, you can make a single 6.3V supply and simply connect the 6DJ8 in parallel.

Use 6.3 V on the 12AY7 by connecting one end to pin 9, the other end to pins 4 and 5. That way each half the AY7 filament sees 6.3V. Same heating as 12.6 across the entire filament. If you like, think of the 12AY7 filament as two 6.3V filaments in series. Steve Bench actually shows the pin connections for this.

With this approach, you can follow Salas' suggestion of using a single winding, but a separate voltage reg for each tube, if you like.

Sheldon

 

[Salas]

With this approach, you can follow Salas' suggestion of using a single winding, but a separate voltage reg for each tube, if you like.

Sheldon

Just one thing to remind. Having a 16V secondary, as Kofi ordered, will burn more power across the 317(s) if 6.3V will be used. A bigger heat sink is advisable.

 

[Kofi Annan]

Good. Glad to know there's an actual end to the learning curve.

I thought that the 12.6V connection would be preferrable to the 6.3v connection given the reduction in current, but maybe you could opine...

Kofi

 

[Salas]

The tubes certainly burn the same Wattage on their heaters, since the I*V on them totals the same in either case. Its better to burn less across the 317 I would prefer, since your secondary will be 16VAC. 12.6VDC is closer.

 

[Kofi Annan]

I guess I meant that the heater-induced noise would be greater with increased current on the heaters. I agree that the power dissipation would be the same, though...

Kofi

 

[Sheldon]

I guess I meant that the heater-induced noise would be greater with increased current on the heaters. I agree that the power dissipation would be the same, though...

Kofi

You could argue either case, with respect to noise. Probably a wash. If you regulate, you can burn off a little less overall with the higher voltage, as the dropout voltage of the regulators is the same with both cases, but the current is higher with 6.3V out.

Sheldon

 

[Kofi Annan]

OK-- I need some help with the heatsinks.

It looks like only the MOSFETS will require them, but I'm looking on Mouser and I think I'm out of luck there-- they appear to all be too small (36C @ 15W to about 76C @ 6W). I'm certainly no expert at this, but if Salas' recommendation was around 2.5K/W per sink, I'm screwed.

Any thoughts on proper heatsinking for these?

Kofi

 

[Salas]

Can you get this one? That is for the IRF840. For the IRFP9240 you only need a 2.5W one, like the larger ones for LM317T.

 

[Kofi Annan]

Got it! Thanks!

So, I'm working on my parts list and I'd like some recommendations:

For resistors, I've stayed with some metal fim jobs wherever possible-- mostly Vishay Dales. Any issues with this?

Also, I'm working on the capacitors and I was going to go with silver micas for the 5700pF / 6500pF jobs (although I'd consider -styrenes as the micas get expensive in these values), poly-somethings for the other caps with the exception of the lower section of the 12AY7 bypass caps, which is looking electrolytic to me. Oh yeah-- and maybe a nice Auricap for the .15uFs on the output.

Comments?

Kofi

 

[Salas]

Not bad. Better make that 6500pF in to an 6800pF. In case the 5700pF original turns out giving too much HF as in my case.

 

[Sheldon]

I'd consider -styrenes as the micas get expensive in these values), poly-somethings for the other caps with the exception of the lower section of the 12AY7 bypass caps, which is looking electrolytic to me.

Styrenes should be fine. Might be hard to get low enough tolerance, unless you have a way to measure them accurately.

Instead of the 2.8k bypassed resistor under the AY7, I used a green low current LED. Works just dandy, and SY Approved, to boot.

Sheldon

 

[Kofi Annan]

I'm guessing there'd be no need to bypass the LED given the constant current. Could I use a 1.7V greenie like in Salas' regulator?

 

[Sheldon]

I'm guessing there'd be no need to bypass the LED given the constant current. Could I use a 1.7V greenie like in Salas' regulator?

Yes, as in yes, no need to bypass the LED. Some use a small film cap for possible HF noise, but I can't hear any difference. If you look at my link, I fed a little extra current to the LED, but that's may be overkill here, given that resistor above. On the other hand, it's easy to do.

And, yes.

Sheldon

 

[Sheldon]

Something like this should be fine, even at low current:

http://mouser.com/Search/ProductDetail.aspx?qs=4kLU8WoGk0ufLkQmM3v%2bcg==

Sheldon

edit: wrong part first time

 

[Vlauga]

Dear Mr. Kofi Annan!
I developed this RIAApreamp specifically for beginners RIAApreampDIYer.
For the last three years this design was repeated by many people.
Including absolute humanists and humanities.
In respect of quality of sounding this design has only positive responses.
It is the scheme:

The first tube is any best sounding clone 6SL7, the second tube is 6SN7 (also any best sounding).

Here is possible to read detailed enough description for beginners how to make this design of improvised means (text language - one of official United Nations languages):

http://vlauga.livejournal.com/4812.html
or
http://audioportal.su/amplifiers/p2_articleid/27

BW, VU

 

[Salas]

Vlagua: Nice circuit.

Kofi: Today I had done a long tuning session on the Bench, measuring and listening against my other DIY and a very high dollar commercial phono. In case you will find the sound with original values questionable, keep in mind the values attached.

 

[Kofi Annan]

Vlauga,

This looks interesting, but I'll probably stick with the Bench RIAA for now as I have already ordered some parts.

Salas,

I'll order the original caps / RIAA resistor and the values you recommended as well. I can do a quick swap during listening tests to see which works better.

Thanks for all the input. I've got a parts list together, which I'll upload shortly for peer review.

Kofi

 

[Sheldon]

I have an inverse RIAA circuit that I used to check my pre with. Happy to send it to you if you want to contact me offline.

Sheldon

 

[sonata149]

Kofi,

Thanks to your posts I built the TL "El Cheaop" phono and linestage. It sounded very good (indeed the best of the handful of phono stages I built) but I have a problem with excessive hum. I'm rebuilding it in a larger case, paying attention to layout and wiring sheme.

The reason I'm writing is to encourage and ask you to post your building and listening experiences. Your posts can be very encouraging to newbies like me. Going by the favourable comments about the Steve Bench phono I am going to build one after I solve (I hope) the hum problem on my 'el cheapo' TL phono stage.

Thanks and best wishes for an happy new year to all members.

Joe A

 

[Salas]

Your hum problem is either PSU ripple or ground loop or both. Do you use a regulated PSU? Start from there if not.

Happy new year to you and to all members!