Lineamp

[merlin el mago]

How can get better perfomance of this lineamp based ECC88/6922 tube:

Rp 15K
Rk 100R
V 180V (it's after Rp, right?)

I don't use optional 80K & instead the 20Kpot I use 100K pot

An externally hosted image should be here but it was not working when we last tested it.

 

[Zen Mod]

I see just half of line stage preamp

other half is PSU

those halves are , obviously , equally important


say your needs and we can think is there better solution for you

 

[SY]

What gain and output impedance are you shooting for?

Taking the load directly off the voltage amplifier plate can compromise the performance unless the plate resistance is really low and there are minimal reactances in the load (e.g., very short, low capacitance cables). You also want to cathode bias to be considerably higher to avoid distortion from grid current. Why do you have an 80k resistor in series with the volume control?

It's easy to make the circuit nearly immune to power supply issues if you don't want to have to deal with overly elaborate regulation.

 

[merlin el mago]

I use Salas High Voltage shunt regulator

As heaters I use Rod Coleman

1. I want to know if I can use the reg directly to the anode but I measured only 40VDC after Rp 15K directly to anode

2. What's the difference objective & subjective to use or not to use optional input resistor 80K.

3. Other better way (less noise) as catode bias: led, active bias, etc.

Now the sound is full & rich I only need a little bit more definition.

 

[merlin el mago]

What gain and output impedance are you shooting for?

Taking the load directly off the voltage amplifier plate can compromise the performance unless the plate resistance is really low and there are minimal reactances in the load (e.g., very short, low capacitance cables). You also want to cathode bias to be considerably higher to avoid distortion from grid current. Why do you have an 80k resistor in series with the volume control?

It's easy to make the circuit nearly immune to power supply issues if you don't want to have to deal with overly elaborate regulation.

Well about gain the maximum without distorsion & the low output impedance possible

I use this schematic because it's easy to do but I'm open to other schematics using the same tubes 6922/ECC88 to have a better perfomance.

 

[SY]

The 80k resistor is just knocking your gain down without contributing anything except a little noise.

Taking your B+ directly to the plate eliminates distortion. It also eliminates signal. If it were me, I'd stick a green LED in the cathode circuit (getting rid of the RC that you have there), increase the grid stopper to 1k, use a CCS plate load, then buffer the output. This approach will sharply reduce distortion and greatly increase power supply rejection.

If your load is a high impedance and cables are short, you can get away without the buffer. Output Z will be 2k or so. With the buffer, output Z will be about 10 times lower.

 

[merlin el mago]

About 80k input resistor I suspected that so I don't used.

Wich voltage for B+ directly to the anode?

Can I use this Led: SLR-342MGT32 ROHM Semiconductor Standard LED - Through Hole

I'm using Salas High Voltage regulator as CCS.

I'm newbie, could you give me a schematic to buffer the output?

 

[SY]

You could go a lot cheaper on the LED. In fact, the cheapest ones are often the best for cathode biasing.

Remember what I said- if you run the B+ directly to the plate, you'll lose the signal!

 

[merlin el mago]

What about these other Led

VAOL-3HCE4 VCC Standard LED - Through Hole

I have both Leds on hand, wich is best suitable?

Any suggestion for the output buffer?

 

[merlin el mago]

Please help:

1. Wich values: voltage & current for Led?
2. I have other 6922/ECC88 any suggestion for ouput buffer?

 

[mastodon]

Please help:

1. Wich values: voltage & current for Led?

Something around 2V forward drop, so a green led as SIY suggests. Current doesn't matter; a normal 3 or 5mm led will do nicely. Don't over-think this one.

2. I have other 6922/ECC88 any suggestion for ouput buffer?

Look up what a 'cathode follower' is and how to design one.

 

[SY]

Cheapest 2V green LED you can find. I bought mine at Radio Shack.

The ECC88 works great for a buffer. With an LED bias and CCS plate load, it also makes a superbly linear voltage amplifier.

 

[Stixx]

Isn't an Rk of 100R rather small for ECC88?

 

[SY]

Yes- with that low of a value, grid current distortion is a near certainty.

 

[merlin el mago]

Something around 2V forward drop, so a green led as SIY suggests. Current doesn't matter; a normal 3 or 5mm led will do nicely. Don't over-think this one.


Look up what a 'cathode follower' is and how to design one.

Cheapest 2V green LED you can find. I bought mine at Radio Shack.

The ECC88 works great for a buffer. With an LED bias and CCS plate load, it also makes a superbly linear voltage amplifier.

Thanks, I'm newbie could you suggest me or link me to a good schematic of cathode follower?

 

[SY]

I would use as a good starting point the discussion in Morgan Jones's "Valve Amplifiers."

A much more complex and no-holds-barred CF design is on my website, but I'd definitely start with Morgan's treatment.

SYclotron Audio The Heretical Preamp

 

[merlin el mago]

What about this cathode follower schematic

 

[SY]

It's OK, could be better. You can improve linearity and PS noise rejection, as well as get rid of at least one LF rolloff.

 

[tmblack]

You could use both halves of the the 6922 and have half the output inpedance.
What is the advantage of the LED?
Would it not reduce the gain if using a plate resistor?

 

[merlin el mago]

How can improve linearity, PS noise rejection & get rid of at least one LF rollof?, I will use Rod Coleman heaters & Salas high voltage shunt regulation.