Soldano Astroverb Circuit Questions

[W5FH]

Hello-
   I have been studying the Soldano Astroverb schematic with interest. It appears to me there is only one version of this schematic that shows up in all of my searches. I am trying to understand the reasoning for a couple of things:
     1. Regarding the cathode follower stage V3-b a 1K cathode resistor is being used. This value seems pretty low compared to most 12AX7 cathode followers.
     2. Regarding the reverb recovery amplifier stage V4b I do not understand the reasoning of using a 10K plate load resistor and 100K cathode resistor.
Thanks all.

[sluckey]

All obvious mistakes. The 1K slope resistor in the tone stack is also a mistake.

[W5FH]

Thank you sluckey-
    I will look around for another schematic. Possibly someone here may have correct component values? I certainly do not trust this schematic now.

[nandrewjackson]

Have a search for some of the "333" Jet city amplifiers. I've heard that some of them are 1:1 foreign made clones of soldano amps, astroverb included.

[W5FH]

Thanks for the help guys -
     I believe I have arrived at, and put together, a correct schematic drawing after studying the incorrect version (that shows up under Astroverb searches) and studying the JCA 2112 in comparison. It appears there are errors on the JCA 2112 around the mixer stage. I also used the Atomic 16 as a reference.
     Something of great interest to me is the mixer stage coupled to a cathode follower in the Astroverb. V2-b and V3-a serve as a mixer with their plates tied together, sharing a common plate load resistor. Their cathodes are tied together and fairly hot biased with full bypassing. The common plate circuit of this mixer is coupled to V3-b as a cathode follower. I, not being a player just a builder for my son in who plays, would like to ask if anyone has comments on a circuit arrangement such as this. I have not noticed a mixer coupled to a cathode follower in other designs but am sure there are others out there that I have just not discovered yet. I bet this mixer/cathode follower combination has some unique sounds. I have studied operation of the mixer in Blencowe's book.
     I am putting together info for an Astroverb clone build that uses 6V6's and has vibrato. Not sure whether to use bias wiggle vibrato on 6V6's or do it in preamp at cathode of an early gain stage. If anyone has suggestions I am all ears.
Thank you all. 

[sluckey]

That active mixer combines the dry signal with the wet reverb signal and also provides gain. I like it. Most amps just use a simple passive resistor mixer with a gain stage to boost the combined wet and dry signal. Both methods accomplish the same. I don't know that there would be any sonic differences.

The bias wiggle vibrato on works fine on 6V6's. You may be interested in the Trem-O-Nator circuit. Quite a few people are using it and like the results better than other tremolo schemes.

[W5FH]

Thanks Sluckey-
    It is interesting to read about the operation of that mixer circuit in Blencowe's book. Being that both plates share the same plate load resistor as the grid is driven of one section it changes the operating conditions for the other tube section, and vice-versa. I would think that this would create some form of sonic effect, with both signals swinging around the operating lines for each other, what is your experience/opinion on this?

[PRR]

The two plates load each other. For small signals, it does not matter.

For large signals, plate mixing will distort slightly before separate plates and mix resistors.

See Radiotron Designers Handbook, 3rd edition, Chapter 12.

It really is a cheap trick, saves a few cents.

[W5FH]

Looking for advice in implementing the Sluckey "Trem-O-Nator" to this Astroverb preamp -
     Attached is my handwritten Astroverb preamp schematic. I used the Atomic 16 and the Jet City Astroverb clone as references; please review this for any errors if you are willing. The circuit stops at the treble pot wiper. I believe this schematic is correct but am not certain.
     I wish to implement the "Trem-O-Nator" to this preamp. In considering where to tie-in it is my inclination to do it ahead of reverb dry signal take-off point marked "D" on schematic. The reverb wet return signal is tied to point "C" which is one of the grids of the mixer triode pair V2-b and V3a. So my thinking is that I need to swing the dry signal ahead of reverb take-off point so that the vibrato swinging gets both dry signal and reverb equally.
     Again, thanks to all for the help and advice!

[sluckey]

The ideal place to tie in would be just before the PI input cap.

[W5FH]

OK sluckey-
      That would be between the master volume pot wiper and phase inverter coupling capacitor, per your suggestion. I will study how to accoplish this. Thanks!
  Say - Does the circuitry shown on schematic all look reasonable to you (if you don't mind critiquing it)?

[sluckey]

Lotta tubes! Lotta gain! But lotta voltage dividers between triodes. Layout will be critical. Could be a real squealer!