PAS-2 to Z-PAS

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Andrew7DG
Posts: 3
Joined: Tue Dec 26, 2023 8:06 pm

PAS-2 to Z-PAS

Post by Andrew7DG »

I just wanted to share my experience with the Z-Boards from Erhard Audio

First the project was a PAS-2 with modifications done to it but most part keeping the stock boards in placed with replaced capacitors. I was going to go through the whole thing but it just seemed like it would be better effort installing new redesigned boards if I am going to go through all the effort.

I purchased the Combo kit #9: Z-PC5, Z-PC6 & Z-PSU - By keeping the Stock transformer 12x7 rectifier, this kept budget pretty reasonable IMO
Also installed
Selector switch
LED
PAS had upgraded RCA connectors on it already
100K Volume Pot
Tube purchased were JJ 12ax7 (preamp) and 12at7 (phono)
Balance Pot - Cleaned it with Deoxit and sprayed some preservative

Everything came with easy to read instructions. The boards were very well labeled with the component values so that there was little confusion.
Everything soldered really well.

Wiring was the most difficult part out of the whole project. What wire to use, how to twist the wires, where to route wires. It also took the most time. Of course if I had to do it again, it would go much quicker

To note I omitted the Tape out and replaced it with another input. I don't have any recording devices so it didn't make sense for me to keep that section.

Listening Impressions: Completely changed the way this tube preamp sounded. When I acquired the PAS-2, there were several questionable modifications done to it and it didn't sound very good to me. Sounded weak, muddy, and chanel separation was poor.
*My thought at first was the power supply and changed that first to see if there was an improvement. And there was... but still not up to my satisfaction

After the Z board installed, WOW it is a whole different preamp and it is the preamp I have been wanting.
-It is QUIET! I didn't think it was working at first
-Channel Separation- Soundstage is amazing. There is clear left and right channel. I am guessing tight tolerance parts contribute to this characteristic.
-Little Distortion - what may have been "Concert tube sound" now I understand was distortion of the preamp circuit. This could have been aging component, un educated modifications, bad ground but a lot of that is solved with the new circuits.
-No Tone Controls - I have never played with the tone controls on any of my pre amps or speakers and I don't think this pre amp needs them

My only critique is that there is a little of the high end that is missing. To be fair though, this could have been my A25 Speakers, or a characteristic of the JJ 12ax7 "Stable" (I have a set of RCA i will rotate in) or maybe the bigger power supply that Erhart offers will provide better power delivery
*But take this comment as nit picking as again this Preamp was a poor performer to Sounding Amazing.

Later going to pair this with a ST-70 with an AVA ultimate 70 board. I believe it will be a good pairing.

Pictures soon to come


*to note, from the instructions and from the website, these Z boards look like they have been re designed. I would like the circuit designer to hopefully give insight into the design of these boards and weigh in on why this circuit design works so much better than the original design.
Holger
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Re: PAS-2 to Z-PAS

Post by Holger »

glad to hear that you are enjoying the Z-series PAS upgrade kits.
Yes, they is no comparison to the original Dynaco circuits, like day and night. Not knocking the original Dynaco circuits, for the day and the quality of parts, compared to what is available these days, they were a very good performer.

Our Z circuits have been constantly tweaked over the years. However, it became apparent that some more serious time needed to be spent on them. There were some flaws, especially with the phono preamp. So last year they were given a much needed 'overhaul', again especially the phono preamps.
Main changes were in the RIAA, using the 12AT7 for the Z-PC6, adding the MOSFET output buffer and improving the RIAA on the Z-PH20. I think the results speak for themselves.
In hindsight, these improvements should have been done much earlier, I guess better late than never! ;)
A lot of credit for the circuit improvements goes to my partner in crime, Ray Waters. Rays knowledge in tube circuit far surpasses mine, thank you Ray.
Custom Handcrafted Tube Audio Gear
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Dynaco PAS upgrade kits, PAS upgrade kit forum
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Andrew7DG
Posts: 3
Joined: Tue Dec 26, 2023 8:06 pm

Re: PAS-2 to Z-PAS

Post by Andrew7DG »

Holger wrote: Wed Jan 17, 2024 8:58 am thank you Ray.
Thank you Ray!!

Final Product with twisted wires (So much cleaner looking)
FYI - Can cap is there just for looks. Doesn't actually function.
also all the power wires are routed underneath the chassis so that they are not near the signal wires. I can take pictures of those later to show how it is routed

Image

Boards installed
Image

Side by Side of Old Vs New
Image

Original PAS-2 with Power Supply Board (Selector Section already removed)
Image
Last edited by Andrew7DG on Wed Jan 17, 2024 11:15 am, edited 2 times in total.
Andrew7DG
Posts: 3
Joined: Tue Dec 26, 2023 8:06 pm

Re: PAS-2 to Z-PAS

Post by Andrew7DG »

Holger wrote: Wed Jan 17, 2024 8:58 am glad to hear that you are enjoying the Z-series PAS upgrade kits.
Yes, they is no comparison to the original Dynaco circuits, like day and night. Not knocking the original Dynaco circuits, for the day and the quality of parts, compared to what is available these days, they were a very good performer.

Our Z circuits have been constantly tweaked over the years. However, it became apparent that some more serious time needed to be spent on them. There were some flaws, especially with the phono preamp. So last year they were given a much needed 'overhaul', again especially the phono preamps.
Main changes were in the RIAA, using the 12AT7 for the Z-PC6, adding the MOSFET output buffer and improving the RIAA on the Z-PH20. I think the results speak for themselves.
In hindsight, these improvements should have been done much earlier, I guess better late than never! ;)
A lot of credit for the circuit improvements goes to my partner in crime, Ray Waters. Rays knowledge in tube circuit far surpasses mine, thank you Ray.
This was a budget build for me. I would like to visit the Z-PH20 someday as I am sure that circuit is much more refined. There are other weak spots in my system that I want to address before though.

I do have one question,
On the original RCA input section, there isn't a spot to ground the Turntable grounding wire. Where ideally should the turntable ground be? Should it just be connected to the chassis or should it be connected with all the wire shielding?
Holger
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Joined: Tue Oct 03, 2023 5:33 pm
Location: Ennis, MT
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Re: PAS-2 to Z-PAS

Post by Holger »

connect the turntable ground cable to the chassis. Try and find a suitable spot where you can use an existing chassis screw to connect that ground wire to.
Custom Handcrafted Tube Audio Gear
www.erhard-audio.com
Dynaco PAS upgrade kits, PAS upgrade kit forum
North American Lundahl Transformers Distributor
Audio Amp Auto Bias Modules Distributor
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