Best "Vintage" Stereo Pres that SoftClip and lotsa Harmonics

[billzoe]

hi all (newb here).

this is a research question BEFORE i build (my tech builds it) my next Tube Pre (12A_7 family or 6EU7 types) .

--what are some opinions on best vintage tube preamp ckts (1950s-60s, not modern) that give a lush, high in 2nd order harmonic sound (vs dull, or odd harmonics, or clean as in wont soft clip) that soft clips easily. this is for 2 channel preamp for audio (vs guitar, inst).

my tech and i have experimented w several CATHODDE FOLLOWER ckts. IMO , these are the opposite of the sound i want (not knocking it, but i want Thick, Rich and full of Soft Clip and Harmonix-these are relatively Clean !).

As well as NON- Feeback type units (similarly , not what i like).

Can someone point me as to what TYPE or specific ckt's are the opposite of the above and also opposite in behaviour (as noted above - thick, rich vs clean and wont soft clip) so i can know what to look for (what Type or What Schematic) to send my tech in right direction (hes a Great Tech , but has only been working w Tubes for 3-4 years).

Mostly this should be OLD, SIMPLE ckts (1-2 tubes) prob in White Papers or RCA Tube Manual from era noted above .

Example: Many "crappy" (ie: Silvertone-Sears, other Lo-End HiFi from then) Pre's ive heard from (late 1950s-1965) Stereo Consoles (tube) do this Sound well-but WHAT type (ckt) are they ?

I am pretty sure they are not Feedback and Cathode Follower types.

Thanks for any help - i need YOUR EXPERIENCED assistance as its getting Expensive to guess>build>then "no thats not it".
Again-THANKS !!!

 

[jerluwoo]

Perhaps this thread will give you good place to start.
http://www.diyaudio.com/forums/tubes-valves/171047-variable-harmonizer.html

As for what you hear in those old low-fi units, I would say its a combination of under rated, saggy power supplies and less than optimal working points of the amplifying tubes.

 

[Cassiel]

Maybe you're looking for a preamp with a high output impedance. That should be easy for your tech. Also your tech could install variable resistors at the plate and cathode of the tube, with a little bit of tweaking you should be able to find your sound.

 

[billzoe]

K - Thanks. Have tried the Plate Starving and get some results but not much. Could be not enough, the B+ is @ 285v and in my current unit the Plate , B+ is tied in w a pair of Line Lev Output transformers so the WHOLE B+ drops to drop the plate (only 30v). Maybe should be WAY more?

Will see about under doing the PS on the next unit - thats prob part of it.

What can i do so the Tubes are at "less than optimal " working points (or is that the same as Plate Starving) ?

Thanks!

Anymore ideas anyone ?

 

[Cassiel]

Well, I know you have tried cathode followers with no good results but you haven't tried messed up cathode followers. This schematic is a Jadis preamp, don't remember its name. I haven't listened to this circuit but have read some funny comments about it. I still remember one user's remark: sounds like a drunk Frenchman. Is that what you looking for? lol If you become desperate try the 12au7.

 

[morinix]

Goto Spice and the art of preamplifier design, Part 2 and build the LINE AMPLIFIER PURIST MOD. You can play around with a 500k pot wired as a rheostat in series with a 220uf cap to shunt audio signal to ground in parallel with C3C to vary the total gain. More gain, more rounded sound. Use carbon composition resistors and you will have a nice, complex, rich sounding unit. Change the output tube to a 12au7, lower R6C to 27k2w for more output drive if you want.

BTW this topology is based on the Merantz 7. Hovland used it on the HP100. I used it to make the GrooveTubes Ditto Box.

 

[billzoe]

Thanks... whats the "messed up" quality to the ckt ?

So, theres a Discussion somewhere on it ?

I have a 12Au7 Cathode Follower, but its super clean - what can be done to it?

Thanks !!!!!

 

[billzoe]

Goto Spice and the art of preamplifier design, Part 2 and build the LINE AMPLIFIER PURIST MOD. You can play around with a 500k pot wired as a rheostat in series with a 220uf cap to shunt audio signal to ground in parallel with C3C to vary the total gain. More gain, more rounded sound. Use carbon composition resistors and you will have a nice, complex, rich sounding unit. Change the output tube to a 12au7, lower R6C to 27k3w for more output drive if you want.

Wow - thanks for the details and tips !!!!

 

[morinix]

Wow - thanks for the details and tips !!!!

give me a bit and I will dig up the Groovetubes Ditto box schematics.

 

[billzoe]

give me a bit and I will dig up the Groovetubes Ditto box schematics.

Cool !

 

[morinix]

Here ya' go! Sorry it took sooooooo long I was really busy. This is the schematic to the GrooveTubes Ditto Box. When you turn the gain up it has a squishy sound like analog tape compression. There is a schematic floating around out there for "The Brick". That design was started by me but I left GT before it was finished. Mitch Margolis finished it and changed things to follow his design protocols. I never listened to a final production Brick so I can't comment on what his changes did to the sound.

btw, this unit will run fine with a pot in place of the output transformer.

 

[Cassiel]

Thanks... whats the "messed up" quality to the ckt ?

So, theres a Discussion somewhere on it ?

I don't know about messed up qualities* but I can tell you that the value of the cathode resistor is too low. Strange. Maybe the one who draw the schematic made a mistake -deliberate or not.

There's always some discussion on the net about almost anything. This one happened long ago so I don't remember the details.

Here ya' go!

Hey morinix thanks for the schematic.


*(On second thought I think I know a lot about messed up qualities)

 

[morinix]

Hey morinix thanks for the schematic.

My pleasure

The Ditto Box when run wide open has just shy of 30db gain with the output transformer so definitely an output level control is recommended if used without and output transformer. I have been slowly building a preamp based on this circuit with an 11hm7 as the output tube and tube regulation for the HV.