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Edited: Jun 02

Gain stage EAR 834 : resistors and tubes

Hi ! I'm testing for the first time my EAR 834 clone, following as close as possible the Skunkie's layout. I'm testing with cheap tubes : x2 12AX7 JJ and x1 Ruby 12AX7. Very satisfy with bass reponse, high, with all, wicked !!! but it's clipping RED on my vu-meter (I diy vu-meter on my ADC Sound Shaper EQ).

Could we talk about gain stage there ? Please, give me your science, advises, references etc. Just, I dont want volume pot ;)

I know tubes have differents gains. But resistors control the gain. Which value should I change for resistors ?

Thanks Everyone !

12 answers0 replies

12 Comments

Benzema Roy

Jul 04

Great info

Skunkie

Jun 07

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I'm really not understanding what you're trying to do cuz from you posts it appears like it sounds fine. You're just wanting to get some VU meters reading in the center or something?

Skunkie

Jun 07

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Replying to

You might be better off using a simple voltage divider on the output to drain off some of the gain. As I recall there is a 220k from the output to ground. Adding some resistance between the pre-out and this 220k to ground should work. Be careful as I've seen this sort of thing created a high pass filter when combined with the output coupling cap and ruin the bass response.

Tim Dat

Jun 07

Replying to

ok interesting, what is ruin the bass response ? pot or adding some resistance between the pre-out and this 220k, or both ? i dont see what you mean by voltage divider, i take a look on google. If i'm using this pot at 5% of his capacity, maybe it's fine for keeping safe sound quality ? I dont need more than 5-10% less gain, ok sometimes more maybe,.. That's working, but I want to choose cleanest method for signal... Here is a simple stereo pot.

Edited

Skunkie

Jun 08

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Replying to

If it sounds good, it is good :)

Tim Dat

Jun 06

Ok so i'm trying a 47k S.F.E.R pot with this RCA pannel, but i'm wondering about the output common ground, where is the best ground way on board ? on the chassis seems fine, nothing sound bad, as if pot was assembled on the chassis.

edit : this RCA pannel came from an EQ, and he provide a common ground as you can see in the photo. he going to the chassis (with those 10n ceramic caps), but thought the EQ board

Interesting fact : i don't need any EQ correction with this wonderful EAR 834 !

Edited

Tim Dat

Jun 04

@Skunkie ''Upstream'' , I mean ''in the preamp'', not after. Ok how to fix this mismatch impedance problem, do you know that? Is it the use of a buffer ? This preamp will be used, sometimes, on some mixer like this Pioneer.

Should i need a stereo potentiometer 2x3 pins ? what troubles me is that there are 9 holes for soldering on the clone pcb. I have to solder all ?

Edited

Skunkie

Jun 04

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Replying to

Simple, don't use any device below 50k impedance connected to the output of this pre-amp. I have no experience on using that 2X3 pad on the board or what type of pot it was designed for, or even how well it works. I honestly don't understand why this phono-stage isn't just being connected directly to an integrated amp. Why would you want to insert a "mixer" in the signal path and complicate your system in this way. Also I have found "remote" styles of volume controls universally sound worse than one integrated into an amp, or in the case of s system using power amps, the pre-amp controlling them. Adding components in the signal path invariably degrades the sound.

Tim Dat

Jun 04

Replying to

Ok no problem, I would like to use this preamp in a sound system context, outdoors, on high amplification powers. This preamp will necessarily fit into a mixer to be able to be used in this context. It will inevitably go into a line level input, and I think the problem will recur if I don't re-configure this output gain from RIAA correction to line level input. at first I thought I could keep the default gain without any thing more, any pot.., but I don't think that's possible, I need a potentiometer, or an RCA with integrated gain attenuator (yes it exists!), or a trimmer on each channel For my tests, now, is directly connected to my Rega integrated amplifier, for sure. But I have to test it on a mixer because we want tubes preamp on our turtables for our sound system project, and that one sound amazing as you said and as i can see ^^

Edited

Tim Dat

Jun 04

Ok so it's clipping red maybe doesnt mean EAR 834 is clipping, But I need less gain. Has anyone ever tried installing a stereo potentiometer?

I tried using a latest generation Pioneer DJM-450 mixer, to benefit from its gain potentiometers. But the sound is noticeably less good, surprisingly. Distortions are clearly audible. I don't think the Pioneer is to blame. I think you need to adjust the gain in the preamp, upstream. I think...

But I don't really understand why there are 9 pads to solder the potentiometer? I don't see a 50K potentiometer (VR) on the diagram.

Skunkie

Jun 04

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Replying to

Probably sounds bad because you are driving a low impedance mixer. Does the amp you are driving it with not have a volume control? and I have no idea why you would have a VU meter sound shaper EQ whatever in the signal path. And no you don't want to cut the signal strength upstream of the pre-amp, that is just asking for there to me more hum/hiss in the signal. Yes that board does have the capability of wiring a pot on the output, most people are sending the signal into a line level device with a volume control.