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EDIT: Meant this in a good way about @ICBM - he told the truth about a circuit which Blackstar advertised 'optimistically'.
@ecc83 is actually 'the man' on this - he worked at Blackstar in the service department. He'll hopefully pop in, but in the mean time...
It could be the preamp valve (12AX7). If the valve has lost gain, that will have much more of an effect on the clean volume than the overdrive volume. The reason is that although the extra gain in the overdrive channel is indeed supplied by a 'Tube Screamer-like' circuit, it does almost only provide extra *gain*. Almost all the *distortion* comes from the valve, which is thus fairly self-limiting - so if its gain goes down, it will reduce the amount of distortion rather than volume. But on the clean channel, the same valve is being run clean so it will show a much greater drop in volume.
I could be wrong, but I would try changing the 12AX7 before doing anything else.
It's actually a very sensible way to use a mixture of valve and solid-state if you're trying to maximise the effect of the valves in the circuit by using them where they make most difference, while keeping the number to the minimum - and I think it's a shame Blackstar have chosen to hide this. It's really very little different from running a Tube Screamer set for minimum gain and full volume in front of a valve amp, in fact - the distortion still comes from the amp, you're just pushing it harder.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I will tell him to change that valve first and go from there.
Will let you know what happens
Mornin' all!
ICBM is quite correct, the circuit uses ICs for their very low noise (and low cost!) qualities but most of the gain (and dirt!) in the HT-5 pre amp comes from the valve.
I only have the mkll circuit to hand (have to dig deep for the earlier one) but I am sure the routing is much the same and in fact the clean channel is picked off from the first valve section so if you have the right OD gain the valve MUST be ok!
My guess would be either a FET not switching or not being switched. Should not be hard to trace armed with map and scope. Such faults are extremely rare but have happened, not, IIRC to the 5 but other chassis.
Best of,
Dave.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
The Vox Valvetronix claim to run a push-pull output stage using an ECC83, and my ancient desktop Tonelab even says A or AB depending on what type of output stage it's modelling. The Class A or AB thing is obviously BS though.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"it's not just the preamp, the HT5 is actually a miniature push-pull using the two halves of a double triode with a solid-state phase inverter (again not contributing to the distortion), which I think was the first time this was done."
Yes and the HT is very thought provoking 400V+! Just because it is a wee 5watter does not mean it can't kill!
The OP stage is also fixed biased (and has a balance control so PLEASE get it set properly if swapping the 12BH7) . This means that you can push the stage into higher power (with more distortion) and in fact the amp will kick out nearly 10watts if hardly pressed. It won't be clean but it will be impressively loud thru 4x V30.
OP stage configuration is done by listening tests. The HT-5 is "all" FB. The Artisans (15/30are CB.
The HT-1 is cathode biased push-pull using an ECC82 and the HT-20 uses CB and adjustable FB!
The PI as ICBM states is in most designs a pair of power MOSFETS and is capable of very big, very clean signal output. I was very miffed to read in an American forum some time ago a criticism of the stage as "Bipolar transistors well known for bad sounding distortion". Well, it ain't and it don't!
Dave.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Hi Bod,
"I've got a first gen HT5 and I love the OD channel, but the clean channel is just awful. "
I touched on getting the OP valve properly biased and balance?
Remember, we are talking just FIVE watts and if you have the Mk 1 combo that will be into a not top sensitivity ten incher. I won't get technical but a push-pull stage need to have the currents through the two valves |(or two sections here) the same otherwise distortion increases and it does not help the very wee output transformer none either!
But essentially if you want even moderately loud cleans you need another 15 watts at least!
The OD sound of the HT series is also a matter of some "Marmite" debate. My son has tried the 5 and I bought him a 20. He does not like the OD sound of either AT ALL! Oddly though he quite likes the OD sound of the HT Dual pedal! Oddly because the ECC83 is essentially doing the same job in all three circuits! What is different is the "voicing" and this is what makes valve guitar amps such fun and infuriating! How much and at what frequencies do you "distort"?
"Custom cannot stale their infinite variety!"
Dave.
So, i replace tubes.Nothing. I replace the output transformer, nothing again, the two PI driver MOSFETs and still nothing...... Is the HT5 combo with no reverb from 2009. Anyone, please? I appreciate anything that might help.
Tassos, PM me.
Dave.
Did not get any notification of the PM . Mods, have I got a setting wrong somewhere?
Dave.