Search results

Yes, that's correct. Also, for this particular circuit, the plate voltage will be about 133V, so splitting the difference between the 100V and 250V values on the datasheet should put you in the ballpark.

Zo(unbypassed) = Ra || (ra + Rk + uRk)

FYI - I have updated the LTSipce plots I posted above to include the the impedance presented by the tone control circuit alone, as well as the output impedance of the driving stage. So, you're basically looking at about 41K output impedance over most of the frequency range, although it rises...

LTSpice model plots for the line stage circuit per schematic, pots at center. Plots show 20-20KHz response as well as the output impedance of the stage driving the tone controls. Note that the output impedance includes the reactance of the .05uF coupling capacitor, which becomes significant at...

Very creative and an excellent result. I will go this route. Thank you!

Nice work on the recreated PEC's. May I ask what was used to coat the boards? The end result looks quite authentic. I also have a restoration project for which I would like to reproduce the PEC's but have been stymied in finding a suitable coating that maintains a somewhat original appearance.

The resistor change is related to Dynaco's Derived Center Channel System. The original PAS 2/3 blend configuration was intended to alleviate the "hole in the middle" effect with wider speaker spacing. The later blend configuration is more aggressive and meant to better correct crosstalk created...

FYI the "MN" 750K balance pot used in the PAS (and SCA-35) does present a carbon track to the signal of about 10K when centered. Thus, the active channel will rise, although very slightly.

Since the knobs have been removed, in case you weren't aware, when reinstalling the tone control knobs be sure to follow the procedure indicated in the assembly manual. The flat response position does not correspond to the center of the mechanical rotation, there is an offset. Basically, you...

Unfortunately, his model contains numerous errors including both schematic and supply voltage, resulting in misleading conclusions. Furthermore it should be noted that there are significant variations in modeled response, particularly low end, among the various available 12AX7 subcircuit...

A lot of unwarranted criticism of the PAS has been propagated on various forums over the years, and especially in regard to the phono stage. A comprehensive technical review of the PAS is presented in these articles: http://www.audioregenesis.com/documents/PAS_Phono.pdf...

Keep in mind that a COUPLING capacitor is typically sized to pass all frequencies of interest equally. Where this is not the case, a FILTER function is being performed.

With a 200K load, a properly functioning PAS-2 should exhibit a slight reduction in bass response with the tone controls at 12 o'clock, perhaps -2 dB at 20Hz. Also note that, when the tone control knobs are installed as described in the manual, the 12 o'clock position does not correspond to the...

Nice! Some years ago I used a product called EZ ScreenPrint to restore missing lettering on PAS and SCA faceplates. Typically, single words using tiny sections of screen, most often for the On/Off switch. I recreated the font as well so the re-screened sections matched the existing lettering. A...

You might find this document useful in relating the selenium configuration to SS diode replacement. http://www.curcioaudio.com/PAS2-3X%20Fil%20Rect%20Replacement.pdf

Looking at the specs, it seems the line input impedance is either 44K or 60K relating to the fixed and variable inputs respectively. There will be loading issues with high impedance circuits. The instrument inputs are 1.5M but also much higher distortion, although more useful for response...

If your sound card input is not buffered, be aware that the input impedance may be rather low which could affect the readings.

Here is my latest line stage model and related response. The specs. as presented in post #115 state the response at the high level input as being within 1dB from 2Hz-100KHz, measured with a 1:1 probe and 100K load. Input and output levels not stated. This model reflects the load conditions...

Just using 1/8 is probably fine. The idea was basically just to confirm that cables and impedance aren't an issue. I suspect probably not.

Further to gadget's comment above, you may want to try running a response test that includes the power amp. and related interconnect cables. With the volume controls set to the position you usually listen, set your generator to a level that drives the PA to about 1W into suitable load...

More line stage modelling attempting to achieve the claimed 2Hz - 100KHz -1dB response. To keep things in the realm of reality, the model is driven with a 1VRMS line level signal and a 50K load added to the output. The model includes the 86pF measured input load capacitance. With the volume...

Line stage response 2Hz - 100KHz? I'll do some modelling to determine under what signal conditions that might possibly be achieved. The volume pot will be set way down, that's for sure.

I guess that depends on what YOU consider acceptable. One thing that I'd like to see is the actual specifications as printed by AI for that particular model. I haven't been able to find that online.

Ok, good. Using the 33KHz reading, that relates to 96.5pF total. Subtracting your probe results in 86pF load capacitance presented by the PCB, pot. wiring etc. That will be added to the Miller capacitance presented by the parallel tube combination. Going back to my line stage model, the response...

Further to my last response, I'm thinking I should have also included an explanation of why the model results, standing alone, make sense. Assuming the 6922 sub circuit model represents an ideal tube, based on the spec sheet, the modeled open loop gain of the phono stage is about 54dB at 1KHz...