• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

AD797 Phono Stage Build and Help Desk Thread

Hi, As mentions before I found CORNELL DUBILIER 940C 8W2K 2.2 uF CAPACITOR sound way better than the normal Russian caps used, however there are currently not available on E/Bay. But there are quite a few 2.0 uF, so just to check, would these still be OK in this phono.

Cheers
 
tabarddn51 said:
Hi, As mentions before I found CORNELL DUBILIER 940C 8W2K 2.2 uF CAPACITOR sound way better than the normal Russian caps used, however there are currently not available on E/Bay. But there are quite a few 2.0 uF, so just to check, would these still be OK in this phono.

Cheers
Click to expand...
I bought 2/3 of the CD 940 caps that were left at Mouser. I am looking forward to trying them out. Going from the wima to the russian caps was already a huge + change so I am expecting amazing stuff. I boxed up the riaa board yesterday in a hammond cast box, I still have to make a small PS/transformer box. I will use an xlr connector to make an umbelical.
 
absolon said:
Here's a useful link for determining what you might want for coupling capacitor values.

Coupling Capacitor Calculator by V-Cap

Coupling capacitor calculator that calculates optimal coupling cap values based on the input impedence of load, and the desired low frequency response you desire
www.v-cap.com
Click to expand...
Here's a quote from that link:
"The real reason we don't select 20 Hz is because near the the -3db point, there may be some phase anomalies introduced into the signal, and therefore we want to operate with a buffer from this ragged edge."
It's total BS. Of course there's a phase shift - no "maybe" about it - and it can be calculated. As for the "ragged edge"... wtf? :dunno:
 
rothwellaudio said:
Here's a quote from that link:
"The real reason we don't select 20 Hz is because near the the -3db point, there may be some phase anomalies introduced into the signal, and therefore we want to operate with a buffer from this ragged edge."
It's total BS. Of course there's a phase shift - no "maybe" about it - and it can be calculated. As for the "ragged edge"... wtf? :dunno:
Click to expand...

It may be a layman's explanation of their own understanding, but the underlying idea of keeping the capacitor's value large enough that it isn't reactive at a frequency that would cause phase or other possible audible issues isn't total BS.
 
rothwellaudio said:
Here's a quote from that link:
"The real reason we don't select 20 Hz is because near the the -3db point, there may be some phase anomalies introduced into the signal, and therefore we want to operate with a buffer from this ragged edge."
It's total BS. Of course there's a phase shift - no "maybe" about it - and it can be calculated. As for the "ragged edge"... wtf? :dunno:
Click to expand...
Perhaps the tone in that site is a little preachy and not to be taken literally. Perhaps it sells more caps that way? LOL If one is serious about freq resp calcs, it's best to use a real sim program.
 
I put the CD 940 caps in service and I found that they let more high freq through and with wider sound stage vs the russian caps. I am not sure about the mids, maybe they thin out the balance in the male voice. Time will tell after break in. I have only tried one pickup, it's not new and I feel the need to try a different one, a new one and see what the diff that brings.
 
I found the toilet paper russian caps are much more balanced and musical so I switched back. the cornel dublier were very forward, all highs to the point I had to turn the autoformer of the horns down two notches to balance the freq response.
 
Hi, I have re-erected my AD797 phono amp as I have managed to get a Denon DL103M, which only outputs 1.2mv, which is very low. So I dusted it off & it's playing now we a couple new mods (new for me anyway)
- I have gone back o batteries to run if as I have found these available from Alli Express. USB rechargeable 9VDC, just plug them into your computer USB port & they take about 2 hours to charge. Play time from what I can see is about 15 to 18 hours.

- I have also replaced the AD797 with a are of these new composite op amps, again from A/E.
https://www.aliexpress.com/item/100....order_list.order_list_main.70.4c8d1802A6xVIw

Very impressed with the sound, a little more up front that the AD797's & bass just a shade deeper with more impact.
The other thing I found is that I can now play my Ort MC2000 (again with 1.2mv out) with the unit. Previously due to it's low impedance I could not play this cart with the AD797's.

Cheers
 
Is there any way to determin resistor values for a certain gain value? I dont like trim pots and stil have to order the resisitors for gain.
 
Duclasi said:
Is there any way to determin resistor values for a certain gain value? I dont like trim pots and stil have to order the resisitors for gain.
Click to expand...
First stage gain calc in db is below.

=20*((LOG(1+((R2)/47))))

Second stage gain is 35 db (55 - 20 for the RIAA eq loss).
 
Last week I started building mij First Hypno. Concerning the output caps I’m a bit confused. Based on the V-Cap calculator I have to take some 6.8uF caps. Input impedance of my amp is 11K, which is quite low. Any thoughts on this issue?


IMG_6493.jpeg

IMG_6498.jpegIMG_6499.jpeg
 
Hi, The output caps are there to protect a Pre from DC offset, But weather or not the spec'd 2.2uf caps can be changed, sorry I have no idea.
Perhaps ask a general question on the site, if this can be done & what could it effect.

Cheers
 
Hi Well done. I have found that it is (same for all phono amps) quieter if the P/S is separated with the trans in a seperate box, just a tip.
What op-amps are you using?

Cheers
 
I’ve used AD797ANZ and TI OPA 1611. Separate PSU depends on the final transformer I’ve ordered. I will use an EI core transformer, mainly to filter HF at mains input. In the current setup it’s remarkably quiet. There’s soms hissing, but no hum.
 
You must log in or register to reply here.
Back
Top Bottom