Bill_P: I picked up yet another DH-101. This is an earlier model with the phono C1 capacitors and perhaps pre-106 upgrade. It also has the suicide capacitors in place. Can the suicide capacitors simply be removed, or are there other component/wiring changes to make up for their absence?
Hi Jack,
I'm dealing with this issue at the moment. I have replaced all of the resistors with mil spec film, and all of the electrolytics and transistors with 106 spec. parts.
I rebuilt the PS and was going to leave it at that. Then I started looking at the tantalums and the other existing film caps. I actually have another DH101 that I only replaced the electrolytics on (and I rebuilt the PS). That preamp sounds really good.
So I have a few questions that you might be able to help with hopefully.
1) in the diagram that shows a single capacitor (not two in series as is the case with both of my DH101's). The parts list indicates a value of 10Uf.
The parts list is part of the same manual that also shows only a single capacitor @ C2 and C11 locations. Since the amps were often built with two caps in series to achieve a bipolar result, wouldn't the single cap in the schematic be a 10Uf as listed in the parts list? And if so, wouldn't the two tantalums that you see installed back to back in series each be 5Uf?
The total wouldn't be 5Uf or would it be 10Uf regardless of using a single cap or two wired in series?
2) Is C11 not a critical cap in terms of sonics? I don't knw because I'm new to this. Just going by what I have read in other discussions. Some say by replacing this cap the sound improved. Is C11 a "coupling" cap?
3) I'm finding it next to impossible to find non metalized polypropylene caps at this point. Have manufacturers moved beyond non metalized and now focus on metalized? I know many are used for the automotive industry as well, etc.
Is it true that non metalized sounds better than metallized? How much will it make a difference in the DH101 if I replace the existing film caps such as C6, C16, C19, C7?
4) I have found some sources for polystyrenes that I can get for those locations. Would those be suitable?
Sorry for the long rant.
Better to use a true bipolar capacitor, like the Nichicon UES series. C11 is a coupling capacitor.
Foil capacitors are generally better than metallized types, but are larger, heavier, and more expensive.
They are best used where their advantages are actually necessary, such as for larger currents.
You can use any good quality, precision 1% film capacitor for the RIAA and tone circuits, if they fit.
Foil capacitors are generally better than metallized types, but are larger, heavier, and more expensive.
They are best used where their advantages are actually necessary, such as for larger currents.
You can use any good quality, precision 1% film capacitor for the RIAA and tone circuits, if they fit.
Same for the phono input loading capacitors, use precision 1% polypropylene or polystyrene.
Your preference for the dielectric type in all these small film types may vary depending on the circuit.
I prefer polypropylene to polystyrene myself in most cases, all other things being equal.
Some use ceramic COG/NPO dielectric capacitors, try some if you are interested. They will be different.
Your preference for the dielectric type in all these small film types may vary depending on the circuit.
I prefer polypropylene to polystyrene myself in most cases, all other things being equal.
Some use ceramic COG/NPO dielectric capacitors, try some if you are interested. They will be different.
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I have been doing some updates to my 101 and noticed something odd. I actually have built 2 (one for my brother back in 78 and then one for me in 79) and noticed that the output emitter resistor of the phono stage is 47 ohms on mine and 100 on the first one I built. I tracked down some discussion on this and in that discussion the reason for the change was changing Q1/Q2 to BC413/BC415. But that seems odd to me. The bias current in Q3/Q4 is now 21ma in the phono stage, up from the 10ma it was in the 1978 version. The final output Q9/Q10 uses 100ohms and uses the exact same transistors as the phono stage. It runs at 10ma. So I'm thinking either Hafler wanted more drive for the phono stage to drive the fairly low impedance negative feedback loop, or they thought that if the two record outs were loaded fairly heavily the phono stage could run out of gas. Thoughts? I'm tempted to bump it up to 100 or at least 75. Q3/4(phono output drivers) are running pretty hot and dissipating around 400mw.