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Old 11th December 2013, 01:07 AM   #11
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Hi,

One word of warning for the more technically inclined:

SRPP: SHUNT REGULATED PUSH-PULL is a monstruous mis-nomer.

To be kind, at best it's a circuit that can be of use for driving a lowish impedance source of say 10K or less (preferably less) fixed input impedance whilst sill pertaining some gain (mu/2) but not much else.

The worst part however is its extremely poor PSRR.

IOW, lest you understand the circuit and have a particular use for, avoid it. It's a bit akin to a hoax really....

Ciao,
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Old 11th December 2013, 09:52 AM   #12
DF96 is offline DF96  England
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Quote:
Originally Posted by fdegrove
The worst part however is its extremely poor PSRR.
In balanced form, yes. Most people run it unbalanced, with the lower cathode bypassed, and then the PSRR should be OK.
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Old 12th December 2013, 03:43 PM   #13
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Yes i understand that its not the best circuit around but to my ears it sounds not to bad. For those people here who know so much. What would you improve? This is my first pre amp diy.. But it's so fun and cheap

I was testing voltage and i have only 4,27v dc filament and 230v dc to plate. If now transformer should give 230v /6.3vac on secondary shouldn't it be higher after rectifier like 280?? I've been reading up on 7806 and see that i can not get 6,3v with this transformer, right? Is it better with a 1085?

Thinking to try with ac filament too. If i dont get hum maybe i'll go that way.
More costly is just to buy a 9v trafo only for filament. Should work better with L7806.

The 6n3 gets only fingerwarm actually as it is.. I know it's not good for tube with undervoltage but i have new russians on the way.
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Old 12th December 2013, 03:54 PM   #14
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I have not had time to update the schematic but they have implented (for one channel ) 1x 10k to earth after first cap 0,47 instead of the 100k and 1x 10k to earth before last cap 1,0uf .

In psu the first 100R is there but second (between caps) are 10k and then a bleeder over last cap of 100k.
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Old 14th December 2013, 10:33 PM   #15
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Quote:
Originally Posted by DF96 View Post
In balanced form, yes. Most people run it unbalanced, with the lower cathode bypassed, and then the PSRR should be OK.
Can you please explain more detailed? What Can i do to improve it to be an ok SRPP? Components i have alot of. I saw in datasheet that they use 240R instead of here 470R (for biasing?) Somebody wrote that a srpp goes in class A just beacause it's an SRPP. Also other tube pre amps i've seen the rather use 1M to bleed of maybe gain (?) after and before cap? thats what its for right?

I've been doing some modelling with Duncans psu designer and and pretty hard to say what's the best (maybe i'm to slow)
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Old 14th December 2013, 10:36 PM   #16
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Look here and see what you think:
Attached Images
File Type: jpg PSU original.JPG (117.1 KB, 833 views)
File Type: jpg PSU_new.JPG (111.6 KB, 739 views)
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Old 16th December 2013, 08:15 PM   #17
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Over 800 people checked this thread. I'm surprised not more people have commented.

I've tried to feed tubes with AC but got hum that i hear easy from listeing position. I will try to re-route the 6,3v line and feed directly instead of going through the pcb with a better twisted cable according to tip here on diyaudio forum and see if it helps. I couldn't hear any difference in SQ that someone mention in other threads.

But what really made a difference was to replace those old Nippon chemicon serie "CE" to BC 056/47uf para. with 2x10uf arcotronics MKPs. Holy mother! Smooth as silk with extreme big soundstage.
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Old 16th December 2013, 08:22 PM   #18
cjkpkg is offline cjkpkg  United States
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Is the heater voltage referenced to B+/4?
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Old 16th December 2013, 08:37 PM   #19
DF96 is offline DF96  England
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Quote:
Originally Posted by Max Martin
Over 800 people checked this thread. I'm surprised not more people have commented.
Difficult to comment on a moving target. Show us your current circuit.

Quote:
Can you please explain more detailed? What Can i do to improve it to be an ok SRPP?
As I said, the SRPP has too much gain. The unbalanced SRPP (with better PSRR) has even more gain. You can't improve the wrong circuit; you have to change the circuit.
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Old 18th December 2013, 07:34 PM   #20
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Quote:
Originally Posted by cjkpkg View Post
Is the heater voltage referenced to B+/4?
I'm not sure what you mean here.
I measured by the input of the board (near tubes) after regulator and caps. Checked again; 4,47 V here. B+ is now with new caps 225V. (before 230V) after rectifier and caps.

I've been going AC on the tubes and get about 6.3 V now and tubes little bit hotter. Little hum though... Used a screened cable and soldered directly and hum is there but much lower but I can't t live with it i think. Little bit annoying.

Also Russian tubes arrived today. 2x 6n3p-EB and one 6X4-R. From first note there was a big difference. All kinds of instruments sounds much more "true" and everything is so clear. Really impressed just after couple of hours compared to the chinese.
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