Incompatibility between Aikido Pre and Tubelab SimpleSE - diyAudio
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Old 19th June 2015, 10:21 PM   #1
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Default Incompatibility between Aikido Pre and Tubelab SimpleSE

I built my 6SN7 years ago and remember having tons of problems with hum. In the end, after elevating the ground, adding many PSU caps, etc. I added a regulated PSU for the heaters and the hum disappeared.

I have been loving my Aikido paired with my AKSA 55N.

Just after completing the Aikido, I purchased a Simple SE board from George as well as board parts. I finished my SSE a couple of. On this ago and love the amp.

Could it be jealousy, but my Aikido and SSE aren't the best of friends. Together with a 30db voltage divider in front of the attenuator in the Aikido, I go great sound. My wife says it sounds warms and full (KT88 in the SSE, 6SN7 in the Aikido). BUT... every now and then, I'd get a dip in volume that I never had with my Aikido/AKSA. Of course I doubted the SSE, but I am now wondering otherwise.

I constructed a passive pre with volume control to run the SSE alone. No dips in volume. Then cleaned the signal wiring in my Aikido, removing the attenuator and source selector and refitting the RCA's. Again, my wife finds the sound warmer.

Then I switched a NOS Mullard 12AT7 and got a weird effect: I got a fluctuating up and down of the volume, not much and not fast. Back to my vintage Sylvania 12AT7 and no "volume vibrato." So, back to the SSE alone with the Mullard and great music.

OK..... So was I hearing the sound of oscillation?

If so, was it in the Aikido, or the SSE? I suspect the latter.

If this is the case, then the Aikido is obviously overdriving the SSE.

What solutions are there:

A. Add a voltage divider at the input in my SSE and use the SSE/Aikido all the time?

B. Reserve the Aikido for use with my AKSA only.

C. Modify option B and build an Aikido board bypass switch. Use the Aikido for source selection and volume, but use a bypass switch to bypass the Aikido circuitry, leaving the Aikido switched off.

D. Reconfigure the Aikido for lower gain, maybe using a 6bx7 or 6bl7 on the input and 6sn7 on output?

I'd appreciate any advise.

Charlie
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Old 20th June 2015, 06:38 PM   #2
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Any thoughts, guys?
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Old 21st June 2015, 08:42 AM   #3
AllenB is offline AllenB  Australia
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Power supply oscillation, motorboating?
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Old 21st June 2015, 01:59 PM   #4
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Motorboating in the SSE due to being overdriven by the input?

Charlie
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Old 21st June 2015, 03:43 PM   #5
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Lets see if I get this right - you had a 30dB attenuator in front of the Aikido gain stage to drive a KT88 amplifier (What is the SSE?) but replaced this with a passive volume control (assume max gain of 1) and had no problems with level changes but still had sufficient signal levels to drive the amp to okay volume, yes?

But you changed back to the Aikido for the sound quality but got the same problem of varying volume levels - what did you do about a volume control?

Then you changed a valve and got a worse problem - how are you fitting 9 pin 12AT7 valves into the 8 pin 6SN7 sockets? The 6BX7 are okay for the o/p buffer but not so good for the gain stage - they're also happier running at over 20mA - a 5965 (ECC81, etc) has a bit lower gain and a better candidate, IMO.

A question - why are you using a gain stage if you don't need one? The minimum gain in the 'standard' 6SN7 configuration is about 10 (about 18dB) and if you're using a 30 dB attenuator in front of this to get a reasonable volume out of the amplifier, then you don't really need to use the front gain stage of the Aikido at all, but just use the buffer o/p stage to get the 'colour' of the valves in the signal - I understand that there is a way to get lower gain from the gain stage of the Aikido (about 10dB) but have not seen it done in practice - maybe an email to Glassware will get you the information

There's a simple buffer project at Glassware Audio to follow but either way, it's all pretty straight forward as the o/p stage also has blocking capacitors, etc and only needs a simple wiring change or that switch.

This variation in volume could also be a ground problem - the Aikido is a pretty stable animal and it might be fighting off a ground loop problem, unusual as this may sound.

Can you reduce the gain on the amplifier?

Please excuse my mutterings if I've got all this wrong, and all the best ....
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Old 21st June 2015, 03:45 PM   #6
Sprags is offline Sprags  United States
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My plan is to use an ACF-2 tube buffer with my SSE rather than a pre with a lot of gain. Of course I'm still in the planning stages.
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Old 21st June 2015, 04:06 PM   #7
jgf is offline jgf  United States
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Option E. Reconfigure the Aikido as a cathode follower only (see the docs for that board on the tubecad site)

The aikido follower lets a lot of subsonics through, I found it enough to be apparent on the bias sense resistors on the power amp when the line voltage jumped. A series regulated B+ supply on the preamp solved that. I wonder if you are having a similar problem?

Last edited by jgf; 21st June 2015 at 04:07 PM. Reason: clarity
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Old 22nd June 2015, 12:18 AM   #8
wa2ise is offline wa2ise  United States
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Quote:
Originally Posted by cbutterworth View Post
Any thoughts, guys?
Maybe you need a grid stopper for each 12AT7 grid? A resistor value around 68K should do it. Mount this resistor with minimal lead length right at the grid terminal of the tube socket. What grid stoppers do is to create a low pass filter (using the stray and Miller capacitance of the tube) to kill any supersonic oscillations that can cause your trouble.
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Old 22nd June 2015, 01:30 AM   #9
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Quote:
Originally Posted by jameshillj View Post
Lets see if I get this right - you had a 30dB attenuator in front of the Aikido gain stage to drive a KT88 amplifier (What is the SSE?) but replaced this with a passive volume control (assume max gain of 1) and had no problems with level changes but still had sufficient signal levels to drive the amp to okay volume, yes?



But you changed back to the Aikido for the sound quality but got the same problem of varying volume levels - what did you do about a volume control?



Then you changed a valve and got a worse problem - how are you fitting 9 pin 12AT7 valves into the 8 pin 6SN7 sockets? The 6BX7 are okay for the o/p buffer but not so good for the gain stage - they're also happier running at over 20mA - a 5965 (ECC81, etc) has a bit lower gain and a better candidate, IMO.



A question - why are you using a gain stage if you don't need one? The minimum gain in the 'standard' 6SN7 configuration is about 10 (about 18dB) and if you're using a 30 dB attenuator in front of this to get a reasonable volume out of the amplifier, then you don't really need to use the front gain stage of the Aikido at all, but just use the buffer o/p stage to get the 'colour' of the valves in the signal - I understand that there is a way to get lower gain from the gain stage of the Aikido (about 10dB) but have not seen it done in practice - maybe an email to Glassware will get you the information



There's a simple buffer project at Glassware Audio to follow but either way, it's all pretty straight forward as the o/p stage also has blocking capacitors, etc and only needs a simple wiring change or that switch.



This variation in volume could also be a ground problem - the Aikido is a pretty stable animal and it might be fighting off a ground loop problem, unusual as this may sound.



Can you reduce the gain on the amplifier?



Please excuse my mutterings if I've got all this wrong, and all the best ....

James,

The SSE is Tubelab's SimpleSE amplifier. It uses a single 12AT7 driving two KT88's. It does not require a preamp, although it sounds fuller with my 6SN7 in front.

But, with the Aikido/SSE combo, I get the occasional volume drop, with a NOS Mullard in the SSE, I get the "motor boarding" effect.

I hope this clears any misunderstandings from my original post. As for volume, I do not need the Aikido in front of the SSE, but the fullness isn't quite there the same way. In comparison, with the KT88's and Aikido, the sound is more like my SSE alone, but with EL34's.

I'll look at the other options as posted by forum members, including my option E and the cathode follower from Broskie's website.

Thanks,
Charlie
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Old 22nd June 2015, 03:31 AM   #10
gabdx is offline gabdx  Canada
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The Aikido produces a lot of 2nd harmonics which is responsible for the 'fulness' effect.

Probably the SSE goes into clipping mode with the additional sub-sonics distortions of the Aikido. This clipping can produce a saturating effect and reduce the gain until capacitors and power supply recover.

If you want to keep the SSE you need to find which stage clips and possibly beef up that stage dealing with high level signals or beef up the power supply ( power transfo , rectifier)

It is great to learn that the SSE is a low distortion amplifier which lets you hear the effect of the Aikido. I would contact the designer of the SSE to see if he knows which part could reduce the recovery time or a simple upgrade.
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