[Aljaheejus]

and how do you know if you need it?  There is a resistor change in the Piccolo instruction manual suggested for this, and I quote:

"For dc offset reduction, change R10 to 232 ohms."

Nearing build time...Thanks in advance.

[hagtech]

The JFETs are matched and will end up with close to zero dc offset voltage in this configuration - if the drain voltages are also equal.  However, due to a slight rise in transfer curves, the upper transistor has a slightly different Vgs at given current.  This resulted in a slight dc offset, which is never a really good thing to have when driving a high gain phono stage.  With a tube phono like the CORNET this is not a problem, as the circuit handles it with aplomb.  The problem may arise with a solid state phono or one that is dc coupled.  It such case, the 232 ohm provides a lower dc offset, on average.  There is variation in JFETs, so the ideal value is always a few ohms in either direction from this nominal.  Adding a trimpot for perfect nulling is possible (I did it), but turned out to be a clumsy change and I don't recommend it.

jh

[Aljaheejus]

Thanks.  Most of your reply is way over my head.  I have the Ripper as phono stage amplifier.  Bottlehead tube preamp, and ST-70 tube amp thereafter, FWIW.

I noticed the parts list has the 232 ohm resistor in this place for R10x, instead of the 220R shown in the schematic.   How can a common solder slinger, with Ripper and ears make this call?  Can the offset be measured with a DMM, for example?

[Aljaheejus]

.... The problem may arise with a solid state phono or one that is dc coupled. ....
jh

So, I guess your Ripper a candidate for this problem, being solid state.  I would appreciate some direction as to how to measure or approach this decision - 220 ohm or 232 ohm.
Thanks in advance.

[wdi]

So, I guess your Ripper a candidate for this problem, being solid state.

Aljaheejus,
I think that Jim is referring to a solid state phono stage that is downstream to the Ripper, not the Ripper itself. From my own experience, sending DC downstream to a SS amp that does not have coupling capacitors to filter out the DC is a recipe for disaster. I learned this the hard way when I blew a set of tweeters years ago while running a tube pre into a SS power amp that was direct coupled (no filter capacitors at the input of the amp). 

[Brinkman]

One shouldn't have a phono stage downstream from the Ripper, it would mess up the EQ.
A Piccolo --> Ripper combo is possible and I think this is what Jim was referring to. The Ripper has caps after the EQ and at the output.

Hey Aljaheejus, is your ST-70 stock or modified?

[wdi]

Good catch Brinkman, that is more likely what Jim meant; I was thinking Piccolo when the previous post clearly stated Ripper (and I even quoted it).

Not that it is relevant to this discussion, but in my situation I am running my Cornet2 ahead of a Ripper (when I use the Ripper) by bypassing the EQ of the Ripper. The EQ section of the Cornet2 is significantly better.

[poty]

...Can the offset be measured with a DMM, for example?
...
I would appreciate some direction as to how to ... approach this decision - 220 ohm or 232 ohm.

Yes, you can measure the DC voltage on the Piccolo's output. The DMM must have high internal resistance on low scale.
You goal is zero (or close to zero) DC from output. You can compare the voltage with 220 and 232 ohm and chose the value which produces lowest output DC.

So, I guess your Ripper a candidate for this problem, being solid state.

The problem is not «solid state», but non-capacitor input. And yes! the Ripper is sensitive for DC on its input.

... running a tube pre into a SS power amp that was direct coupled...

Do you have balanced tube pre? Because in the other case it's almost impossible to build tube amp without decoupling capacitors.
Meanwhile, the coupling capacitors can harm tweeters too at the moment of powering up..

...The Ripper has caps after the EQ and at the output...

The main problem is high gain DC-coupled first two stages (the gain is way more than a hundred for DC). The resulting output can overload the opamp and add excessive drain for the power supply. Both possibilities are bad.

[wdi]

Do you have balanced tube pre? Because in the other case it's almost impossible to build tube amp without decoupling capacitors

No I do not have a balanced pre, but the example I provided was caused by a lack of capacitors at both the output of the pre and the input of a solid state amp. I added caps to the input of the amp and replaced my blown tweeters, but have since replaced the solid state amp with a tube amp.

After re-reading the initial posts it appears that Brinkman has addressed the original poster's concern by pointing out that there are caps at the output of the Ripper.

[poty]

No I do not have a balanced pre, but the example I provided was caused by a lack of capacitors at both the output of the pre and the input of a solid state amp.

The single-ended tube amp always have high DC and so mustn't be used without output capacitors in tube or solid state following stages. It appears that you have wrong schematic.

After re-reading the initial posts it appears that Brinkman has addressed the original poster's concern by pointing out that there are caps at the output of the Ripper.

No, he hasn't. I explained why.

[Aljaheejus]

Hey Aljaheejus, is your ST-70 stock or modified?

First, thanks to all for all the input!   The problem for me may be combining the Piccolo output with the "input" circuitry of the Ripper.  Too bad JH is not commenting on that, but Poty seems to be familiar with this issue. 

My ST-70 is mostly stock.  Thanks for asking.  Original, restored, driver board and  7199 tubes still on that.  I recently replaced all board components with new, but used a few 1/4 watt where there should be 1/2 watt resistors.  Soon to be fixed with some PRP resistors.

I have modified the ST-70 inputs with the Van Alstine mod of capacitor filters, and I combined that modification in a voltage divider varying resistance to ground to lower the overall gain.  I have no idea whether this combination is of any merit, but it works, and VA insists the frequencies should be limited coming in....Maybe I'm learning something.

Now, is that the kind of capacitor filtering that needs to be downstream of the Piccolo?

Poty, can you explain how I can make those measurements of "offset".  What is "offset"?  Voltage difference between R and L channels?  Sorry but I need the basics in plain language.  Also, what is a "balanced pre"?  A pre-amp with balance control?  To reset the offset?

For some reason I was not getting notifications on this thread...I'll pay closer attention now.

BTW, the Piccolo is up and playing the last two days.  I worked some Elna cerafine electrolytic caps in for C12-C15 by laying them down and the little cubic MKP film caps allowed room for those by extending one lead and putting it at one end of the designated rectangle.

Sounds Nice with with my vintage Linn ASAK cartridge - certainly better than the high-gain Ripper experiment I tried which had a lot of hum & hiss.  Picking up a little hum but have not tried to troubleshoot it yet.

[poty]

The problem for me may be combining the Piccolo output with the "input" circuitry of the Ripper.

I don't think the problem will be definitely arise. With all the simplicity of the JH designs they are very good thought and in most configs they sound amazingly excellent.

Now, is that the kind of capacitor filtering that needs to be downstream of the Piccolo?

I'd not be in haste with this. You can easily start to use Piccolo-Ripper and then - if the problems arise - look into the ways of eliminating them (problems).

Poty, can you explain how I can make those measurements of "offset".  What is "offset"?  Voltage difference between R and L channels?  Sorry but I need the basics in plain language.  Also, what is a "balanced pre"?  A pre-amp with balance control?  To reset the offset?

Rather difficult to answer all your questions in one answer. I'll try...
"Balanced" design means that there are 2 symmetrical (in electrical way) parts in the circuit, representing two wires of incoming signal and "common ground". The parts are connected in such way, that if they have identical signals (relating to common ground) on its input, it is blocked (rejected) and do not appear in the output (usually it is acheved by connecting the parts in opposite phase). The design helps also eliminate DC from some auxiliary circuits (biases, offsets and so on) and (cleverly designed) to exclude coupling capacitors. The example of balanced design from JH is Trumpet http://hagtech.com/trumpet.html.
"Offset" is a deviation of something (for example - current, voltage and so on) from some point (value). For example, in the Piccolo there is curcuits, which compensates DC on the output (and in internal stages of course, but now we are speaking about output) by means of adding an equal opposite amount of DC voltage to the output. The resistor in your question defines this amount. JH said that as soon as there are some differences in specifications of transistors and working conditions in the circuit, it is impossible to define "universal" value for the resistor. The change in the value he made is just for optimal value suitable for more cases, then original value.
You can measure the Piccolo "DC offset" by connecting DC voltmeter to left output jack (one wire to the center, the second - to shell) and then - in another measurement - connect the voltmeter to the right output jack. You will have two values. Both voltages should be zero or very close to zero.
How Ripper cope with the DC in the input: you can measure the DC voltage between the leg 1 of the U4a and the ground wire for left channel and corresponding leg and ground for the right. It also should be zero or very close to zero.

BTW, the Piccolo is up and playing the last two days. Sounds Nice with with my vintage Linn ASAK cartridge - certainly better than the high-gain Ripper experiment I tried which had a lot of hum & hiss.

Good news! Welcome to JH design club!

[Aljaheejus]

....
You can measure the Piccolo "DC offset" by connecting DC voltmeter to left output jack (one wire to the center, the second - to shell) and then - in another measurement - connect the voltmeter to the right output jack. You will have two values. Both voltages should be zero or very close to zero.
....

Thanks!  I will try this and report back.  Can I assume the unit should be powered "on" and that there does not need to be a signal input?  Should the inputs be connected to the turntable, etc?

[poty]

The right questions!

Can I assume the unit should be powered "on"

Yes, it should!

and that there does not need to be a signal input?  Should the inputs be connected to the turntable, etc?

No, there does not. To ahieve clearer measurements you can short the input jacks.

[Aljaheejus]

Thank you, again.  I'm all clear and I can do that.

[Aljaheejus]

Powered with batteries, input jacks shorted yields:
L = 0.020 vdc
R = 0.032 vdc

Powered with "switched" AC adapter, input jacks shorted yields:
L = 0.021 vdc
R - 0.033 vdc

So, is this doing something detrimental in the Ripper?   Could it be creating the hum or hiss I hear?  There is an increase in these noises when the Piccolo is plugged into the Ripper preamplifier.  (The ripper preamp, with inputs shorted also makes hum and hiss.)

[poty]

Powered with batteries, input jacks shorted yields:
L = 0.020 vdc
R = 0.032 vdc

Powered with "switched" AC adapter, input jacks shorted yields:
L = 0.021 vdc
R - 0.033 vdc

In my opinion the values are safe.

So, is this doing something detrimental in the Ripper?

No, I don't think so. The first two stages of the Ripper (DC coupled) have total amplfication of around 147, so 0.033 gives us 4.86V on the right channel output (U4b). It is less than max voltage for given power supply voltage for the opamps. The voltage added around 3,5 mA for the second stage (R) and around 1 ma for the first stage (R) (for L channel it should be around 1.5 times less) - for two channels it could be around 7.5 mA. It may affect the weak power supply, but I think that problem is unfortunate.

Could it be creating the hum or hiss I hear?  There is an increase in these noises when the Piccolo is plugged into the Ripper preamplifier.  (The ripper preamp, with inputs shorted also makes hum and hiss.)

Some amount of hiss is normal with such small signals and big amplification. But if you have hiss with shorted inputs in Ripper - I'd investigate the source. I don't think the DC is the source of this hiss.
About hum... There can be probability, that the power suppy is overpowered by the DC, but as soon as the hum exists even with sorten inputs, I'd try to check everything that could be the source of it (nearby devices, bad shielding, maybe interconnects from outputs of the Ripper...).

[Brinkman]

My ST-70 is mostly stock.  Thanks for asking.  Original, restored, driver board and  7199 tubes still on that.  I recently replaced all board components with new, but used a few 1/4 watt where there should be 1/2 watt resistors.  Soon to be fixed with some PRP resistors.

In case you're curious, here's a thread I started at audiokarma in regard to all the replacement driver PCBs for the ST70.

FWIW, input filtering (aka bandwidth limiting) is only one method for improving an amplifier's performance. Some would say there's superior driver topologies that aren't so drastic.

I just updated the thread today; I hope it's useful!

[Aljaheejus]

Brinkman, thanks for the note.  I am very familiar with your thread, and thanks for that.  I did much research from that thread, and look forward to someday trying a new driver board.  For now I decided to repopulate the original board, and live with the two 7199s that came with it (new to me about a year and a half ago.)  It is interesting to hear that there are so many new offering from your most recent post!  I'd really rather find a new chassis to try something new on, and keep this one for comparison, for kicks, and to put music in another room....then again a new SET integrated amp kit from bottlehead (stereomour) would be another way to go.