Best "Vintage" Stereo Pres that SoftClip and lotsa Harmonics - diyAudio
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Old 26th April 2012, 05:35 PM   #1
billzoe is offline billzoe  United States
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Default Best "Vintage" Stereo Pres that SoftClip and lotsa Harmonics

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 !!!
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Old 26th April 2012, 06:31 PM   #2
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Perhaps this thread will give you good place to start.
Variable Harmonizer

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.

Last edited by jerluwoo; 26th April 2012 at 06:34 PM.
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Old 26th April 2012, 07:45 PM   #3
Cassiel is offline Cassiel  Libya
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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.
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Old 26th April 2012, 10:30 PM   #4
billzoe is offline billzoe  United States
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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 ?
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Old 27th April 2012, 01:01 AM   #5
Cassiel is offline Cassiel  Libya
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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.
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Old 27th April 2012, 01:52 AM   #6
morinix is offline morinix  United States
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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.
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Last edited by morinix; 27th April 2012 at 02:08 AM.
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Old 27th April 2012, 01:55 AM   #7
billzoe is offline billzoe  United States
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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 !!!!!
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Old 27th April 2012, 02:04 AM   #8
billzoe is offline billzoe  United States
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Quote:
Originally Posted by morinix View Post
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 !!!!
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Old 27th April 2012, 02:23 AM   #9
morinix is offline morinix  United States
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Quote:
Originally Posted by billzoe View Post
Wow - thanks for the details and tips !!!!
give me a bit and I will dig up the Groovetubes Ditto box schematics.
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Old 27th April 2012, 05:13 PM   #10
billzoe is offline billzoe  United States
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Quote:
Originally Posted by morinix View Post
give me a bit and I will dig up the Groovetubes Ditto box schematics.

Cool !
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